Sox, JVo.
Essex Institute.
LIBRARY OF FRyVNCIS FEA.BOI3Y
PRESENTED BY
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Tlie Librarian shall have power by order of the Library Committee to call in any volume after it has been retained by a member for ten days.
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ELEMENTS
OF
SCIENCE AND ART.
VOL. II.
London : Printed by A, & R. Spottiswoode, New-Street-Square.
ELEMENTS
SCIENCE AND ART:
FAMILIAR INTRODUCTION
NATURAL PHILOSOPHY AND CHEMISTRY:
TOGETHER WITH
THEIR APPLICATION TO A VARIETY OF ELEGANT AND USEFUL ARTS.
By JOHN IMISON.
A NEW EDITION,
Considerably enlarged, and adapted to the improved State of Science,
By THOMAS WEBSTER, Sec. G. S.
IN TWO VOLUMES.
VOL. II. LONDON:
PRINTED FOR F. C. AND J. RIVINGTONJ J. SCATCHEBD ; J. NUNN; LONGMAN, HURST, REES, ORME AND BROWNJ T. CADELL; S. BAGSTER;
J. booth; J. booker; j. Murray; j. richardson; Baldwin,
CRADOCK AND JOY; BAYNES AND SON; J.HARDING; SHERWOOD,
NEELY AND JONES ; G. AND w. B. whittaker; t. tegg; j.bobinson;
AND E. EDWARDS.
1822.
CONTENTS
THE SECOND VOLUME.
CHEMISTRY.
Page
Simple substances 3
Operations and instruments in chemistry 4*
Pneumato-chemical apparatus 12
Of the nomenclature of chemistry 19
Caloric 22
Light 33
Electricity 35
Oxygen -. 36
Nitrogen 39
Combinations of oxygen and nitrogen 40
Nitrous acid 44-
Nitric acid 45
Atmospheric air 46
Hydrogen 49
Hydrogen and oxygen 54
Hydrogen and carbon 59
Sulphuretted hydrogen gas 61
Phosphuretted hydrogen gas 62
Chlorine 63
Iodine 66
Sulphur 67
Sulphuric acid 69
Carbon 70
Carbon and oxygen 71
Carbon and nitroffen 74
Phosphorus .,, , ,,,,, 74
VI CONTENTS.
Page
Phosphorus and oxygen 76
Boron 76
Fluorine » 77
Alkahes 78
Potash 79
Soda , 82
Lithia 84
Ammonia 85
Earths 86
Lime 87
Magnesia 89
Barytes 89
Strontia 90
Silica 90
Alumina 91
Yttria 92
Glucma 93
Zirconia 93
Thorina..... 93
Metals i 94
Platina 98
Gold 99
Silver 101
Mercury 103
Iron 104-
Copper 109
Tin Ill
Lead Ill
Zinc 114
Antimony 115
Bismuth 116
Arsenic 117
Nickel 117
Manganese 118
Cobalt 119
Molybdena 120
Tmlgsten 120
Osmium 121
Iridium 121
Pihodium 121
CONTENTS. vii
Page
Panadium 122
Cadmium • 122
Tellurium 122
Titanium 123
Chromium 123
Uranium 124?
Columbium 124*
Cerium 124<
Selenium 125
Vegetable substances , 125
Animal substances 137
Nomenclature of chemistry 142
MANUFACTURES'AND ARTS.
Making bread 147
Brewing , 153
Bleaching 160
Dyeing 178
Callico printing 198
Tanning 101
Currying i..., 211
Manufacture of soda 212
Manufacture of potash 214
Refining metals , 215
Pottery 228
Manufacture of glass 235
Varnishing 239
Japanning 248
Lacquering 258
Gilding 261
Silvering • 275
Tinning 281
Bronzing 282
Soldering 283
Moulding and casting 284
Cements 292
Lutes 304
Ink making 306
Removing stains 310
vm CONTENTS.
Staining wood 313
Staining ivory 316
Miscellaneous receipts 317
FINE ARTS.
Drawing -... 342
Geometry 348
Perspective 374-
Drawing the figure 388
Drawing landscapes 400
Mechanical drawing 403
Painting transparencies 407
Crayon painting 409
Colours 410
Of engraving 419
Etching 423
Mezzotinta scraping , 431
Aqua tinta , 432
Wood cutting 442
Etching on glass 442
Lithography , 445
ELEMENTS OF SCIENCE.
CHEMISTRY.
JHLiTHERTO we have considered the action of bodies on each other in masses, or what is called their mechanical actions ; and for this purpose it was not necessary to attend particularly to the difference in the many species or kinds of matter, which we distinguish more or less readily.
But if we present bodies of different kinds to each other in proper circumstances, a certain action takes place between the minute particles of one sort of substance upon those of another sort, by which, frequently, the individual or peculiar properties of eacli disappear, and a new substance is formed.
The study of this action of the minute or ulti- mate particles of different kinds of matter on each other is called chemistry^ and the powers thus ex- erted occasion chemical actions.
Independently of the enlargement of our views of nature, and the pleasure and entertainment de- rived from contemplating her operations, chemistry j^is essentially useful in many of the arts upan
VOL. IT. B
'■2 CHEMISTRY.
wliicli tlie comforts, and even the very existence, of civilized life, depend.
As exani])les, we may mention the arts of dyeing, bleaching, tanning, potting, glass-making, baking, brewing, distilling, working metals, &c. &c. which owe their present state of perfection to the science of chemistry In agriculture it is capable of affording great assistance, by explaining the nature of soils and manures; and in medicine its import- ance is invaluable, many of the most efficacious re- medies being entirely formed by chemical processes. In short, there is scarcely any art or trade which either does not altogether depend upon, or may be benefited by this science.
I3y chemical means we are enabled to reduce compound bodies to the constituent principles of which they are composed, and this operation is called analysis, or decomposition. When a substance cannot by any means be resolved into others, it is called a simple body j and it is now known that all that vast variety of substances which we see is composed of a few simple bodies, which hence are called elementary substances.
Formerly, air, earth, Jire, and icater, were sup- posed to be the elements of which all bodies were formed ; but modern chemistry has shown that this was an erroneous supposition. For the air, or at- mosphere, is compounded of several distinct kinds of aerial fluids or gases. Instead of one kind of earth, it is now known that there are several kinds. Water is no longer considered as an element, being, in fact, formed of two substances very different, viz. of oxygen and hydrogen. Fire is less understood, and is still retained as an element under the name of caloric.
From the improvements that are continually
CHEMISTRY.
s
making in the methods of analyzing bodies, or separating them into their component principles or elements, several other substances once supposed to be simple are now found to be compounds : and, as chemistry continues to advance, the list of simple substances may be reduced ; our inability to de- compose any body not proving it to be simple, but only, perhaps, that our methods of examination are still imperfect.
The substances which hitherto have resisted all the known methods of analysis, and which, in the present state oi' our knowledge, are considered as the elements of all bodies with which we are ac- quainted, are the following : —
Substances not metallic.
8. Iodine
9. Sulphur
10. Carbon
11. Phosphorus
12. Boron
13. Fluorine.
1. Light
2. Caloric
3. Electric fluid
4. Oxygen
5. Nitrogen
6. Hydrogen
7. Chlorine
Metallic substances.
14. Potassium
15. Sodium
16. Lithium
17. Calcium
18. Magnium
19. Barium
20. Strontium
21. Silicium
22. Aluminum
23. Yttrium
24. Glucinum
25. Zirconium
26. Thorinum
27. Platina
28. Gold
29. Silver Sa Mercury
31. Iron
32. Copper
33. Tin
34. Lead
35. Zmc
36. Antimony
37. Bismuth
38. Arsenic
39. Nickel
40. Manganese
41. Cobalt
42. Molybdena
43. Tungsten
44. Osmium
45. Iridium
46. Rhodium
47. Palladium
48. Cadmium
49. Tellurium
50. Titanium
51. Chromium
52. Uranium
53. Columbium
54. Cerium
55. Selenium.
4. OPERATIONS AND INSTRUMENTS
The utmost degree of mechanical division which we can effect in bodies, by pounding, grinding, and similar processes, can only reduce them to frag- ments so small that they can no longer be per- ceived by the sight ; but we cannot thus arrive at those ultimate atoms, molecules, or particles, of which the various s])ecies of matter are sup})osed to consist, and which arc, perhaps, incapable of subdivision.
Besides the attraction of gravitation possessed in common by all matter, these elementary sub- stances possess peculiar attractions for each other, whi-cli are called chemical attractmis. By these attractions, or affinities, as they are called, they combine together, and form com])oimd bodies.
OPERATIONS AND INSTRUMENTS USED IN CHEMISTRY.
The great principle of all chemical operations which enable us to decompose certain bodies, and to compound others, is, that every substance has a pecidiar affinity or attraction for other substances, but that it has different degrees of attraction for different substances. This is called elective affinity or attraction.
If some oil and some alkali be put together, they will unite and form soap. But if to this a little dilute sulphuric acid be added, the oil and alkali will be separated from each other again ; the alkali having a stronger attraction for the acid than it has for the oil, will leave the latter and join the acid.
Dissolve some magnesia in nitric acid, and the solution will be transparent. Also dissolve some lime in water by letting it remain for some hours: the solution of lime in water will also
USED IN CHEMISTRY. O
be transparent. Pour them together, and imme- diately a turbid appearance will be presented, and a white powder will fall to the bottom. This powder will be found to be magnesia. The ex- planation is this : the nitric acid has a greater attraction for lime than it has for magnesia ; there- fore, it lets fall the latter and takes up the former. The substance thus thrown down is called a pre- cipitate, and the process \'&c?i\\Qd. precipitation.
If all the bodies presented to each other are compounds, sometimes two new substances are formed. Thus, if solutions of nitrate of barytes and of sulphate of soda be mixed together, the former being composed of nitric acid and barytes, and the latter of sulphuric acid and soda, two new products will be obtained, viz. nitrate ot soda and sulphate of barytes. For the nitric acid will leave the barytes and join to tiie soda, and the sulphuric acid will give up the soda and seize the barytes. Tliis is called double elective affinity, as the former example was of single elective nffi^iity. When diiferent substances unite chemically, and form a compound, they always unite in the same proportion. Thus, water, which is composed of oxygen and hydrogen, always con- tains the same proportion of each ; that is, we do not find that in several specimens of water the pro- portions of oxygen and hydrogen vary. Also, if an acid and an alkali combine together, and thus form a certain salt, they always unite in the same proportion to form that salt ; however, they will sometimes combine in another proportion to form another salt j but when substances unite in more than one proportion, the second, third, &c. proportions are multiples or divisors of the first. This is one of the latest discoveries in chemistry,
B O
b OPERj^TlONS AND INSTRUMENTS
and has given rise to the doctrine of definite proportions.
Here it must be remarked that chemical com- bination and mechanical mixture are very different ; since, although bodies only combine in definite proportions, yet, they can be mixed together in all proportions.
in general, before substances can be made to act cliemically on each other, one of them, at least, must be in a fluid state ; and, that solids may be acted on more easily, they are generally mechanically divided into small pieces, or reduced to a powder.
By trituration^ pulverization, and levigation, is meant the reduction of solids into pov^ders of dif- ferent degrees of fineness. Brittle substances are reduced to powder by means of hammers, pestles and mortars, stones and mullers. Mortars and pestles are made either of metal, glass, porcelain, marble, agate, &c. according to the hardness and properties of the bodies to be pounded. Wedge- wood's ware affords a most excellent kind of mor- tar for most purposes, as it is very strong, and not liable to be acted upon by acids. Many bodies cannot be reduced to powder by the foregoing methods : such are fibrous substances, as wood, horns of animals, elastic gum, and mettles which flatten under tlie hammer ; for these, JileSy rasps, knives y and graters, are necessary.
The separation of the finer parts of bodies from the coarser which may want farther pulverization, is performed by means of sifting or "djashing.
A sieve for sifting generally consists of a cylin- drical band of thin wood, or metal, having silk, leather, hair, wire, &c. stretched across it. They are of diflerent degrees of fineness.
USED IN CHEMISTRY. 7
Washing is used for procuring powders of an uniform fineness, much more accurately than by means of the sieve ; but it can only be used for such substances as are not acted upon by the fluid which is used. The powdered substance is mixed ■with water, or other convenient fluid : the liquor is allowed to settle for a few moments, and is then decanted off; the coarsest powder remains at the bottom of the vessel, and the finer passes over with the liquor. By repeated decantations in this manner, various sediments are obtained, of different degrees of fineness : the last, or that which re- mains longest suspended in the liquor, being the finest.
Filtration is a finer species of sifting. It is sifting through the pores of paper, or flannel, or fine linen or sand, or pounded glass, or porous stones, and the like ; but it is used only for separ- ating fluids from solids, or gross particles that may happen to be suspended in them, and not chcr mically combined with the fluids. Thus salt water cannot be deprived of its salt by filtration j but muddy water will deposit its mud. No solid, even in the form of powder, will pass through the above- mentioned filtering substances : hence if water or other fluid, containing sand, insects, mud, &c. be placed in a bag or hollow vessel made of any of those substances, the sand, &c. will remain upon the filter, and the liquor will pass through, and may be received clear in a vessel under it. Unsized paper is a very convenient substance for making filters for chemical purposes. It is wrapped up in a conical form, and put into a glass funnel, which serves to strengthen the paper and support the weight of the fluid when poured into it.
Decantatioti.iS often substituted, instead of fil- B 4
8 OPERATIONS AND INSTRUMENTS
tration, for separating solid particles which are diffused through liquors. These are allowed to settle to the bottom, and the clear fluid is gently poured off. If the sediment be extremely light, and apt to mix again with the fluid, by the slightest motion, a syphon is used for drawing off the clear fluid.
Limviation is the separation by means of water, or other fluid, of such substances as are soluble in it, from other substances that are not soluble in it. Thus, if a certain mineral consists of salt and sand, or salt and clay, &c. the given body being broken to powder, is placed in water, which will dissolve the salt, and keep it suspended, whilst the earthy matter falls to the bottom of the vessel, and, by means of filtration, may be separated from the fluid.
Evaporation separates a fluid from a solid, or a more volatile fluid from another which is less volatile.
Simple evaporation is used when the more vola- tile or fluid substance is not to be preserved. Various degrees of heat are employed for this pur- pose, according to the nature of the substances, it is performed in vessels of wood, glass, metal, porcelain, &c. Basons made of Wedcewood*s ware are very convenient, as they are not apt to break by sudden changes of heat. Small flasks of thin glass also : these are placed either over the naked fire, or in a vessel filled with sand, which is then called a sand-bath. This affords a more re- gular degree of heat, and renders the vessels less liable to be broken.
When the fluid which is evaporated must be pre- served, then the operation is called distillation.
Distillation is evaporating in close vessels, when
USED IN CHEMISTRY. 9
we wish to separate two fluids of different degrees of volatility, and to preserve the most volatile, or both of them. The substance to be subjected to distillation is put into some vessel that will resist the action of heat, called a retort, an alembic, or a stilly having a beak or neck projecting from it, to which is attached another vessel, to receive the fluid that rises flrst, which is called the recipient, or receiver. The vessel that contains the liquor to be distilled is placed upon the fire, or in a sand- bath, or over a lamp : the heat causes the most volatile fluid to rise in the form of vapour, and to pass into the receiver, where it is again condensed by cold. This condensation is sometimes as- sisted by making the vapour pass through a tube which is immersed in a vessel containing cold water.
A (Plate 1. fig. 1.), represents a retort used for distillation. It is a vessel, either of glass or baked earth, for containing the liquid to be distilled. When it has a small neck, a, with a stopple fitted to it, for introducing the materials through, it is called a tubulated retort. B is the receiver for con- densing the vapour which is raised, and into which the neck of the retort is inserted. The joining, b, is made air-tight by means of some substance ap- plied to it, called a lute. Various methods are used for supporting both the retort and receiver, according to the degree of heat employed in the process, and several other circumstances.
When great heat is employed, earthen retorts are used, which are placed on or in the fire. When a less heat is wanted, glass retorts are generally employed, which must not not be placed imme- diately on the fire, unless they are coated over with a composition of clay and sand, which is
10 OPERATIONS AND INSTRUMENTS
sometimes done. Glass retorts are generally placed in a sand-bath, or suspended over a lamp, for which Argand's lamp is the best. The re- ceiver is placed upon some stand convenient for the purpose, with a ring made of hay under it, or some such contrivance, to keep it steady.
A (Fig. 2.), is a vessel called a mattrass, for the same purpose, having a vessel, B, called an alembic, fitted to the head. The liquid raised by heat into the state of vapour, is condensed in the alembic, and falls into a groove all round its inside, from whence it runs out by the spout, C, into the re- ceiver, D.
Fig. 3. are conical tubes that fit into another, for lengthening the necks of retorts, &c. to con- nect them with the receivers at any distance: they are called adopters.
Fig. 4. are phials with bent glass tubes fitted in them, for disengaging gases, and similar experi- ments : they were used by Priestley, and are hence called Priestleij^s bottles, and sometimes proofs : they are either tubulated or plain.
A (Fig. 5.), represents a common still. It is a large vessel of copper, into which the materials to be distilled are put. The still is built up in brick-work, which covers it up to the neck; the fire is applied underneath, and runs round it in a spiral manner. B is the Jiead of the still. This head is connected with the ivorm, which is a spiral tube, immersed in a vessel of cold water, called the refrigeratory, or cooling tube, C. The liquor be- ing condensed in its passage through the worm, runs out at the cock, D, into the vessel placed there to receive it.
This is the construction of the common still for distilling spirituous liquors ; but a very great im-
USED IN CHEMISTRY. 11
provement has been made upon this instrument, in Scotland, within these few years. This improved apparatus is known by the name of the Scotch still, a section of which is represented, Fig. 6. The principle of the improvement consists in exposing a great quantity of the surface of the fluid to the action of the fire, and affording a more ready means for the escape of the vapour or gas.
A, is the body of the still, made very shallow and concave at the bottom, in order that the fire may act better upon it ; bb^ are a number of tubes opening into the still, and communicating with the neck of the still B, in order to convey the vapour off as soon as it is formed ; cc, is a cover that shuts down over the pipes and top of tlie still, to keep it warm, by preventing the loss of heat which would be occasioned by the contact of the cold air. This is effected by the quantity of air that is confined between the cover and tlie top of the still ; for it is a fact which is now well known, that confined air is a non-conductor of heat. In general, the heads of stills are kept warm by laying blankets upon them, at least when this is attended to, as it ought always to be ; but this metallic covering, by sur- rounding the still with a quantity of confined air, answers the purpose still better.
When the materials which are evaporated con- crete in a solid form, within the neck of the dis- tilling vessels, then the distillation is more properly called sublimation.
By the above means, one fluid may be separated from other materials; but it often happens, that in distillation the substances which are subjected to this process have a chemical action upon each other ; new combinations take place, and perma-
IS PNEUMAT0-CHE31ICAL APPARATUS.
nently elastic fluids or gases are disengaged, which are required to be preserved and examined. For tliis purpose, a very useful apparatus is employed, called the
PNEUMATO-CHEMICAL APPARATUS.
Fig. 7, represents an improved pneumato-chemi- cal apparatus and lamp-furnace connected with it.
A, is a vessel filled with water. In this vessel a shelf is placed, so as to be a little under the surface of the fluid, having several holes bored through it, to which small funnels are attached underneath.
The glass air-jar, or receiver, B, which is to re- ceive and contain the gas, is filled with water, and being inverted wdth its mouth under water, it is raised up gently till its mouth is nearly out of the water, but not quite ; and it is then placed upon the shelf over one of the holes. The receiver will remain full of water, w^iich is kept up by the pressure of the atmosphere upon the principle of the barometer described under pneumatics.
The materials from w^iich the gas is to be dis- engaged, are now to be put into a glass retort, C, which is put through, and suspended in one of the rings of the lamp-furnace, D. An improved Ar- gand's lamp, £, having teo co7icentric wic/cs,* afl^brds a much greater degree of heat than the common Argand's lamp, wdiich has only a single circular Xiick; this is placed upon the shelf, F.
* This lamp with two concentric tvicks was first contrived by the editor some years ago, and is extremely useful m some chemical operations, as it gives a much greater heat than the common Argand's lump with one circular wick.
PNEUMATO-CHEMICAL APPARATUS. 13
The shelf, with the lamp and the ring having the retort in it, are now to be adjusted by moving them up or down, until the lamp is at a convenient height below the retort, the neck of whicli rests upon the edge of the cistern, and the end of its neck opens in the funnel under the jar standing upon the shelf. The lamp must now be lighted, and as soon as the substances in the retort act upon each other sufficiently, the gas will begin to be dis- engaged, and will ascend through the hole in the shelf into the vessel, B, and displace the water witli which it had been filled. When all the water is displaced, the receiver is full of the gas which was disengaged from the retort, and may be preserved in it by keeping its mouth always under the water in the cistern.
This gas may be transferred from the vessel, B, into any other vessel, in the following manner : fill the vessel into which the gas is to be transferred, with the fluid in the trough, and place it on the shelf as before directed, over one of the holes. -Then take the vessel, B, and keeping its mouth still under the fluid, bring it under the hole on which .the vessel is placed, then depressing its bottom, and elevating its mouth, so as to bring it more to a horizontal position, the gas in it will escape and rise up through the hole on which the other vessel has been placed, and will fill it by displacing the fluid. In this manner any gas may be formed, or transferred from one vessel to another.
The cistern for the water may be made of wood, in the manner of a tub, and hooped round, which may or may not be painted inside and out. But it will be much more elegant if made of sheet-iron, tinned, and japanned of a brown or chocolate co- lour. The ornaments, if any, may be of brass, or
14 PNEUMATO-CHEMICAL APPARATUS.
gilt. The best material for the lamp-furnace is brass lackered, and the lamp should be of tin ja- panned. The apparatus constructed in this man- ner has an extremely elegant appearance, and is found to answer perfectly well for a variety of che- mical operations.
When the gas to be procured is absorbable by water, quicksilver is used instead of water ; and, as it is very expensive, a smaller vessel is neces- sary, which must be made of some material not acted upon by quicksilver, as wood or stone ; and it must be sufficiently strong to resist the great weight and pressure of the quicksilver. It is usually cut out of a solid block of wood, or marble, or made very strong of mahogany, and varnished over, to make it perfectly tight.
A small glass vessel, capable of containing an ounce measure, is used for measuring gases ; for if this phial be successively filled, and inverted un- der a large jar, we may thereby throw into that jar any required quantity of an elastic fluid, or as many measures of one elastic fluid, and as many of ano- ther, as we please.
G (Fig. 7.), represents a tube for receiving a mixture of gases that are to be exploded by the electric spark. It is a very strong glass tube, closed at one end, and having a scale upon it, cut with a diamond. Near the closed end two wires pass through the glass, and almost touch each other, but not quite ; they are cemented in, so as to make the holes air-tight. When this graduated tube is filled with the fluid in the trough, and inverted upon the shelf, certain measures of the gases to be exploded are introduced in the usual way. If thus the interval between the two wires be made a part of the electric circuit, by fastening chains con-
PNEUMATO-CIIEMICAL APPARATUS. 15
nected with a Leyden phial to the rings of the wires, the spark will pass through the interrupted space between the two wires, and explode the gases. These instruments are called ea:ploding tubes.
In compound distillations, or when a decompo- sition of the materials subjected to this process takes place, and gases are formed, some of which are absorbable by water, some by alkalis, and others are not capable of being absorbed at all, it is often required to preserve separate the several new substances procured. The apparatus invented by Lavoisier for this purpose is the most con- venient.
A (Plate 2. fig. 1.), is a glass retort, the beak of which is adjusted to a double tubulated balloon, or receiver, B. To the upper tubulure of tliis re- ceiver is fitted a glass tube, C, the other extremity of which is conveyed into the Hquor contained in the glass vessel, D : with this vessel, D, which has three tubulures, are connected two or three other similar vessels, by means of glass tubes fitted into their tubulures, and to the last tubulure of the range of vessels is adapted a glass tube which is conveyed under a receiver placed upon the shelf of the pneumatic cistern. Water is put into the first of these vessels, caustic potash into the next, or such other substances as are necessary for ab- sorbing the gases, and the joinings are w^ell luted. Sometimes it will happen that a re-absorption of gas takes place; and in this case, that there may be no danger of the water in the pneumatic tub entering rapidly into the vessels through the tube, E, a capillary tube is adapted to the middle tubu- lure of each vessel, which goes into the liquid con-
l(i PNEUMATO-CHEMICAL APPARATUS.
tained in it. If absorption takes place, either in the retort or vessels, the external air enters through these tubes, to fill the vacuum which is occasioned by the absorption, and no water comes into the vessels.
Large vessels for containing air, and expelling any given quantity, are called gazometers. They are of various constructions ; one of the best is the following : AB (fig. 2.), is a cylindrical vessel of tin, japanned, nearly filled with water, and having a tube, C, in the middle, open at top, and branching, to communicate with the cock, D. Within this vessel there is another cylindrical vessel, generally of glass, of smaller size, F, open at bottom, which is inverted and suspended by the lines e e, whicli go over the pullies j^^^j^ and have weights^ o", attached to them, to balance the vessel, F. While the cock D remains shut, if the vessel F be pressed downwards, the air included within it will remain in the same situation, on the principle of the div- ing-bell ; but if the cock be opened, and the vessel, F, be pressed down, the air included within it will escape through the cock, and if a blow-pipe be at- tached to this cock, a stream of the gas may be thrown upon lighted charcoal, or any other body. By means of the graduated rod, //, also, the quan- tity thrown out is exactly ascertained : this rod is so divided as to express the contents of the inner vessel in cubic feet, &c. This instrument also an- swers for breathing any of the gases, by applying a mouth-piece to the cock. To render it more portable, the w^eights g gy are sometimes included in the uprights i i, which aie hollow, and wide enough to receive them. Sometimes, also, there is another branch from the bottom of the pipe, m
PNEUMATO CHEMICAL APPARATUS. 17
the middle, directed to the side of the outer cy- Hnder, and coming upwards by the side to the top, where there is another cock attached.
For soliitiony and dissoluiionSy and for crystal- lizing sails, vessels of glass or earthenware are used.
The melting, or causing any body to pass from the solid to the liquid state, by the action of fire, is caWed Jiisi on. The fusion of metallic substances requires vessels sufficiently strong to resist the fire. Those vessels are mostly, if not always, made of earthen-ware, or porcelain, or a mixture of clay and powder of black-lead. They are called cru- cibleSy and are generally of the forms represented Tig. 3. Sometimes these vessels have covers made of earthen-ware ; but sometimes the fused metal must be exposed to a current of air : in that case, the crucibles are broad and shallow, as at Fig. 4. these are called cupels, and they are formed of calcined bones, mixed with a small quantity of clay, or of a mixture of clay and black-lead pow- der. But the cupels must not be placed in a closed furnace, or be surrounded by coals ; for, in that case, the required current of air could not have access to the fused metal. They are, there- fore, placed under a sort of oven of earthen-ware, which is called a miiffle, as represented, Fig. 5, which, with the included cupel, is exposed to the heat of a furnace.
The various degrees of heat which are required for the performance of chemical operations render a variety of fire-places, ov furnaces, necessary for a chemist. Those furnaces are either open at top, or they are covered with what is called a dome, and have a chimney, or tube, to carry oft' the heated
VOL. 11, c
IS PNEUMATO CHEMICAL APPARATUS.
air, smoke, &c. They are sometimes supplied with air from the natural action of the fire, which rare- fies the air about the ignited fuel ; and the rarefied air becoming specifically ligliter, ascends into the chimney, whilst the colder, and consequently hea- vier air, is forced by the atmosphere to enter at the lower part of the furnace. Some furnaces are sup- plied with air by means of bellows ; and those are applied for forging iron, or for reducing metals from the ore, which is called smelting. Hence the furnaces derive their various names, and are called simple^ or open furnaces^ reverheratory furnaces, tvindy or air furnaces, blast furnaces, forges^ smelt' ing furnaces, <§t.
A very useful kind of furnace, for many pur- poses, is that invented by Dr. Black, of Edinburgh, represented in Fig. 6. It consists of a cylindrical or elliptical body of sheet-iron, coated within with a mixture of loam and clay. The aperture A at top is closed occasionally with an iron saucer full of sand, which forms a sand-bath ; B is the door of the fire-place, and C is the ash-pit register, which slides so as to admit more or less air. D is an iron tube which goes into the chimney of the room, to carry off the smoke.
Blow-pipes are used for directing the flame of a candle or lamp against any bit of ore or other sub- stance required to be examined. They ought to have a bulb upon the middle of their stem, to contain the moisture that is formed from the breath. See Fig. 7-
The blow-pipe contrived by Dr. Black, of a conical form, represented in Fig. 8., is very con- venient; a, is the nozzle.
When a solid substance, in powder or otherwise.
NOMENCLATURE OF CHEMISTRY. 19
is left for a certain time in a fluid, and the mixture - is kept exposed to a slow degree of heat, the pro* cess is called digestmi.
When one substance, which has an affinity to another, is mixed with as much of that other substance as its affinity will enable it to hold in combination, then the former substance is said to be saturated^ or the mixture to have attained the point of saturation. If the mixture contain a greater proportion of either substance, then that mixture is said to contain an excess of it, or to be surcharged. The same thing must be understood of the compounds of more than two substances.
The dry way of performing chemical operations is when strong degrees of lieat are used, and the humid way is when fluid solvents are used.
Combustion is when a body is burned with the assistance of respirable air.
Deflagration is when the combustion is attended with little explosions or cracklings.
Detonation is a pretty loud report.
OF THE NOMENCLATURE OF CHEMISTRY.
One of the chief improvements which have been made in modern chemistry has been the invention of names for the compound substances, which ex- , press the elements which enter into their compo- sition, as well as the proportions in which those elements are combined. By this the memory is much assisted, in recollecting the nature of the great variety of substances, and to which the an- cient chemists gave arbitrary and frequently unap- propriate appellations.
When the simple substances, oxygen, chlorine, and iodine, which are supporters of combustion^
c ^
20 NOMENCLATURE OF CHEMISTRY.
enter into combination with each other, or with the other elementary bodies, they form combinations that are divided into two classes. In one class the substances are ?iotacid, and their names have their termination in ide, as oa:ide of chlorine, oJ^ide of nitrogen, chloride of sulphur, iodide of iron, &c. \VTien these supporters of combustion enter into combination with a body in more than one propor- tion forming oxides, the terminations, ous and ic, are employed. Thus nitrogen, with the smallest proportion of oxygen, forms the 7iitroiis oxide ; and, with a large proportion, it makes the nitric oxide.
When the metals combine with oxygen in one proportion only, the compounds are called simply oxides of the metals. Formerly the compound of a metal with oxygen was called a caliv, as the calx of tin, now the oxide of tin; and the process of combining a metal with oxygen was called calcina- tiojiy now oaigenation.
Sometimes oxygen can enter into combination with a metal so as to form oxides in more than one proportion, and then a syllable is prefixed to the term oxide to denote that proportion ; the smallest quantity of oxygen forms the protoj:ide of the me- tal, the second quantity of oxygen makes the deutoaide, and the third, the tritodide ; antl, far- ther, the term peroxide is applied to that oxide of the metal that contains the greatest proportion of oxygen with which it is known to combine. The same syllables are prefixed to chlorides and io- dides.
An oxide combined with water is called a hydrat.
When an acid is formed by the union of a simple body with oxygen, it derives its name from that
NOMENCLATURE OF CHEMISTRY. SI
body ; as the sulphuric acid, which is formed of sulphur and oxygen ; the carbonic acid, which is formed of carbon and oxygen.
Sometimes oxygen will unite in several propor- tions with a simple body, so as to form different acids ; then the acid which is the most oxygen- ated, has its termination in ic ; and that which is the least oxygenated, in ous. Thus sulphur forms two acids ; when it unites to the least proportion of oxygen capable of making an acid, it forms the sulphureous acidf and with a larger proportion of oxygen it makes the sulphuric acid.
Hydrogen, like oxygen, combines with a certain number of simple substances, and with them forms compounds, some of which are acid, and others are not. To distinguish the acids Jbrmed hy hy- drogen, from those formed by oxygen, the former are designated by the word hydro^ as the hydro- chloric acid, hydro^uoric acid.
Products not acid, Jbrmed by hydrogen and a simple substance, if solid, are called hydruret : if gaseous, the name of the simple substance termin- ated in ed is prefixed to that of hydrogen gas ; as carburettedy or yhosphoretted hydrogen gas.
When chlorine, sulphur, phosphorus, and carbon, unite to each other, or to another simple body, the compound has also its termination in uret, as chloruret of phosphorus, and of iron, sulphuret of iodine, phosphuret of lime, carburet of iron, &c. Neutral salts, or substances produced by the union of acids and alkalis, are denominated from the names of the acids and alkalis of which they are composed. The salts produced by the acid whose names end in ous have their terminations in ite ; thus sulphurous acid and potash form sulphite of potash : salts produced by acids ending in ic have
c 3
^ CALORIC.
their termination in ate : thus sulphuric acid and potash form sulphate of potash, and so of all the rest.
The terms, bi-sulphuret, bi-phosphoret, bi-sul- phate, &c. denote that these compounds contain twice as much sulphur, phospliorus, sulphuric acid, &c. as the sulphuret, phosphoret, sulphate, &c.
CALORIC.
C4.L0RIC, or the matter of heat, is generally con- sidered as a peculiar elementary substance. It cannot be ascertained to have any weight, a body when heated not being heavier than before.
A distinction is made between caloy^ic, or the njiatter of heat, and the word heat when considered as a sensation. The sensation of heat, or sensible heati is the eifect produced upon our organs by the motion of caloric disengaged from the surrounding bodies. Whei> we touch a cold substance, the caloric^ which e?cists in unequal quantities in dif- ferent bodies, but which always tends to be in equi- librio in all bodies, passes out of the hand into the body, which feels cold, because at the time there w^s less free caloric in the substance than in the hand ; and as we have lost heat, we feel the sensa- tion of cold : cold being, not any thing positive, but merely the want of heat. The contrary happens "vyhen we touch a warm body j the caloric then in passing into the hand, gives the sensation of warmth. If the hand and the body touched be of the same temperature, or very nearly so, we re- ceive no impression either of heat or cold, because there is no motion of caloric.
l^yfree caloric, we mean that which is not com- bined with any other body. But, as caloric has a
CALORIC. ^S
very strong tendency to combination, we are not able to procure it in that state.
Combhied caloric is that which is fixed in bodies by affinity or elective attraction, so as to form part of their constitution. By the expression spe- cific caloric of bodies, we understand the respective quantities of caloric requisite for raising bodies of the same weight to an equal degree of temperature. This proportional quantity of caloric is thought to depend upon the distance between the consti- tuent particles of bodies, and their greater or less degrees of cohesion ; and this distance, or rather the space or void resulting from it, is called the ca- pacify of bodies for heat.
Heat has the property of expanding bodies, or increasing their bulk. This may be observed by fitting a piece of iron to an iron ring so as just to fill it : then if the iron be heated in the fire, it wdll be found that it has become too large to pass through the ring ; but when cooled, it contracts to the same size as before. Some metals will ex- pand more than others.
It is supposed that the caloric forces itself be- tween the particles of bodies so as to separate them. In acting thus, it is in direct opposition to the attraction of cohesion, which keeps them together.
Fluids also expand by heat. Put water into a very small glass tube with a bulb, and apply heat to the bulb ; the water will be seen to expand and fill more of the tube : as it cools, it will contract again.
Gases also increase in volume, by increase of temperature. Tie the neck of a bladder tight ; when it is almost empty, lay it before the fire ; the included air will expand, and the bladder will swell
c 4
24t . "- CALORIC.
and appear full, but will return to its former state by withdrawing it from the fire. From this pro- perty of matter in expanding by heat, the thermO" meter becomes a measure of the heat in bodies.
Every body, therefore, whether solid, liquid, or gaseous, is augmented in all its dimensions, by an increase of sensible heat : and on the contrary, all bodies contract by an abstraction of caloric. We are still very far from being able to produce the degree of absolute cold, or total deprivation of heat ; hence, we are incapable of causing the ulti- mate particles of bodies to touch each other.
It may be supposed, since the particles of bodies are thus constantly impelled by heat to separate from each other, that they would have no con- nexion between themselves ; and that, of conse- quence, there could be no solid body, unless the particles were held together by some power which tended to unite them ; this power is the attraction of cohesion. Thus, the particles of all bodies may be considered as subject to the action of two opposite powers, repulsion and attraction^ between which they remain in equilibrio. So long as the attractive force remains strongest, the body must continue in a state of solidity ; but if, on the con- trary, heat has so far removed these particles from each other, as to place them beyond the sphere of attraction, they lose the cohesion they had before with each other, and the body ceases to be solid.
Water gives us a regular and constant example of these facts. Whilst below 32° it remains solid, and is called ice. Above that degree of temper- ature, its particles being no longer held together by reciprocal attraction, it becomes liquid ; and when we raise its temperature above 212**, its particles giving way to repulsion caused by the heat, assume
\
CALORIC. 25
the state of vapour or gas^ and the water is changed into an aeriform fluid.
The same may be affirmed of all bodies in na- ture. They are either solid, or liquid, or in the state of elastic aeriform vapour, according to the proportion which takes place between the attrac- tive force inherent in their particles, and the re- pulsive power of heat acting on them ; or, what amounts to the same thing, in proportion to the degrees of heat to which they are exposed. But were there no other cause affecting the solidity of bodies except the powers of attraction and repul- sion, they would become liquid at an indivisible degree of the thermometer, and would almost in- stantaneously pass from the solid state of aggreg- ation to that of aeriform elasticity. Thus water, for instance, at the very instant when it ceases to be ice, would begin to boil, and would be trans- formed into an aeriform fluid, having its particles scattered indefinitely through the surrounding space. That this does not happen, must depend upon the action of some third power. The pres- sure of the atmosphere prevents this separation, and causes the water to remain in the liquid state until raised to the temperature indicated by SIS'^ ; the quantities of caloric, which it receives in the lower temperatures, being insufficient to overcome the pressure of the atmosphere.
Whence it appears, that, without this atmos- pheric pressure, we should not have any permanent liquid, and should only see bodies in that state in the very instant of melting ; for the smallest addi- tion of caloric would then instantly separate the particles, and dissipate them through the surround ing medium. Besides, without this atmospheric pressure, we should not even have any proper aeri-
96 CALORIC.
form fluids ; because the force of attraction would be overcome by the repulsive power of caloric ; and the particles of bodies would separate themselves indefinitely, having nothing to give limits to their expansion, unless their own gravity might collect them together so as to form an atmosphere.
It may be admitted, therefore, as a general prin- ciple, that almost every body in nature is suscep- tible of three several states of existence, soUd^ liquid, and aeriform ; and that these states depend upon the quantity of caloric combined with the body.
The elastic aeriform fluids are expressed by the generic name of gas ; and in each species of gas, a distinction is made between the caloric, which, in some measure, serves the purpose of a solvent, and the substance which, in combination with the caloric, forms the base of the gas. Thus water, united to a sufficient quantity of caloric, is called aqueous gas ; ammoniac saturated with caloric, is called ainmoniacal gas, he.
Caloric, when free, appears to move in the form of rays, and to be capable of being reflected in the same manner as light. The calorific part of the solar rays, or those which occasion heat, are con- densed by a lens, ora mirror, as well as those which produce light; and the rays of heat from any burn- ing body, or even of a body heated, although not in a state of combustion, are thrown off in a radiat- ing manner. If two polished metallic mirrors be placed opposite to each other, at several feet dis- tance, and if a pan of burning coals, or a heated piece of iron, be held in the focus of one of them, a thermometer placed in the focus of the opposite one, will be immediately affected as if it had been
CALORIC. %J
held close to the heated matter ; and this will be the case, even if the heated body is not luminous or incandescent, as hot water, for instance; so that the invisible rays of heat also are reflected like those of light. The chief part of the heat received from a common fire is in the form of radiant heat ; and whatever kind of construction will most promote the reflection of radiant heat into the room, will be the most advantageous form of the chimney. It is upon this principle that the grates introduced into common use by Count Rumford are so much pre- ferable to all others.
The effect of the solar rays upon bodies differs much according to their colour ; black and dark coloured bodies are more heated than white ones ; the latter throwing off" the rays, while the former absorb them. For this reason, black clothes are more heated by the sun than white ones. Polished surfaces, also, which reflect best, do not absorb so much heat as rough surfaces.
The boiling or ebullition of liquids is a phenome- non which depends upon the liquid being converted into vapour by a certain degree of temperature ; consequently, those liquids which assume the va- porous or aeriform state at the lowest temperature are most easily made to boil. The ebullition, or the noise and motion of the liquid in boiling, is occasioned by small quantities of vapour being formed at the bottom of the vessel, which rise by their lightness in a globular form, and break at the surface. The ebullition of liquids is easier in pro- portion as the pressure to which they are subjected is less ; thus water, which boils only at 212° Fahr. in the air, will boil with a much less degree of heat in an exhausted receiver of the air pump ; and it
28 CALORIC,
will also boil with much less heat on lofty moun- tains than in the valleys.
Bodies differ very much with respect to the fa- cility with which heat passes through them. Those which transmit caloric easily are called conductors of caloric ; and, according to the power of doing so, they are termed good or bad conductors. Those which do not transmit heat at all, or with great difficulty, are called non-conduct07^s. How- ever, it should be observed, that, perhaps, no substances are absolutely non-conductors ; but liquids and gases admit the passage of caloric through them with such great difficulty, that, for practical purposes, this division is found useful. Liquids carry heat chiefly by transportation ; the part of the liquid that is heated rises to the sur- face, and gives place to another which is warmed in its turn, and so on until the whole has been heated.
Many very important applications of this prin- ciple have been made by Count Rumford to oeco- nomical purposes. He showed that a stratum of confined air was one of the best modes of prevent- ing the escape of heat.
The best conductors of heat are metals, and the best non-conductors are fluids and porous sub- stances. Charcoal is an excellent non-conductor.
Heat may be excited by mere friction ; and this, probably, was the earliest mode of obtaining it to procure fire. It is still practised among uncivilized nations. For this purpose they take two pieces of dry wood, one about eight or nine inches long, and the other piece quite flat. They cut a blunt point upon the first, and, pressing it upon the other, they whirl it round very quickly, holding it
CALORIC. 29
oetween both their hands, as we do a chocolate mill. In a few minutes the wood takes fire. If the irons of the axle of a coach-wheel be left with- out grease or oil, they will become so hot as to set fire to the wheels j and accidents of this kind some- times happen.
It is no uncommon practice in the country, for a blacksmith to hammer a piece of iron till it be- comes red hot, as a substitute for a tinder-box. The heat excited by the boring of a cannon is suf- ficient to cause water to boil.
Heat is also produced by collision ; when a piece of hardened steel is struck with a flint, some particles of the metal are broken off, and so violent is the heat produced by the stroke, that they are rendered red hot, and melted. If the fragments of steel be caught upon a piece of white paper and examined with a microscope, they will be found to be spherules, and highly polished, showing that they had been fluid.
No heat seems to follow from the percussion of liquids in soft bodies.
The instruments for measuring heat by the ex- pansion of bodies are, thermometers for fluids, and pyrometers for solids.
A thermometer is a hollow tube of glass, her- metically sealed, and blown at one end into the shape of a hollow globe, or bulb. The bulb and part of the tube are filled with mercury, which is the only fluid that expands equally. AVhen we im- merse the bulb of the thermometer in a hot fluid, the mercury expands, and, of course, rises in the tube; but when we plunge it into a cold body, the mercury contracts, and, of course, falls in the tube. The rising of the mercury, therefore, indicates an increase of heat ; its falling, a diminution of heat.
30 cALonic.
To facilitate the observation, the tube is divided into a number of equal parts, called degrees, or there is a divided scale attached to it.
This scale is graduated in different manners by different nations : Fahrenheit's scale is that al- ways used in this country.
The standard points are obtained by freezing and boiling water, degrees of heat which are con- stantly the same in nature. The heat at which the mercury stands, when immersed in each, being marked, the distance between them is divided into 180 parts, and 32 parts of the same size are con- tinued downwards, so that 32° shows the heat of freezing water, and 212° that of boiling water. AVater cannot be made hotter than this in open ves- sels, because it then becomes converted into steamy or aqueous gas.
The mercurial thermometer, it is evident, cannot measure degrees of heat above that of boiling mer- cury, nor below that of freezing mercury ; the former is 600°, and the latter 40° below 0 of Fah- renheit's scale.
For greater degrees of cold, thermometers of spirits of wine, or essential oil, are used ; and to measure those higher degrees of heat to which the thermometer cannot be applied, pyrometers are em- ployed. An instrument of this kind was invented by the late Mr. Wedgewood. It consists of two pieces of brass, fixed so as to form an angle, having the legs divided into equal parts. Pieces of baked clay are prepared for this scale, so as to fit the brass at a certain place. If then the piece of clay be exposed to the heat required to be ex- amined, it will contract in its dimensions, and, when again applied to the brass scale, it will be seen how much it has contracted. By this the in-
CALORIC. 31
tensity of the heat is ascertained, for the clay of which these pieces are prepared, has the property of contracting regularly, according to the degree
of heat.
This is an exception to the general law of bodies expanding by heat ; the expansion of melted metal in the act of cooling is another, as likewise the ex- pansion of water in the act of freezing.
The greatest degrees of heat which can be raised have been produced by concentrating the solar rays with a mirror or lens, or by supplying a blow- pipe with oxygen gas ; or, what is still more power- ful, by a mixture of oxygen and hydrogen. This last method has been but lately employed, and pro- duces a far greater degree of heat than any other. The mixture is itself of an explosive nature, and, therefore, without proper precaution, exceedingly dangerous. The greatest degree of cold known to have been produced has been obtained by mixing snow with certain salts. The best salt for this purpose is muriat of lime. If this be mixed with dry light snow, and stirred well together, the cold produced will be so intense as to freeze mercury in a few minutes. Salt and snow also produce a great degree of cold.
Evaporation, likewise, produces cold. The me- thod of making ice artiiicialiy in the East Indies depends upon this principle. The ice-makers at Benares dig pits in large open plains, the bottom of which they strew with sugar-canes, or dried stems of maize, or Indian corn. Upon this bed they place a number of unglazed pans, made of so porous an earth that the water oozes through their substance. These pans are filled towards evening, in the winter season, with water v.'hich has been boiled, and are left in that situation till morning,
S^ CALORIC.
when more or less ice is found in them, according to the temperature of the air ; there being more formed in dry and warm weather than in cloudy weather, though it may be colder to the human body.
Every thing in this operation is calculated to produce cold by evaporation ; the beds on which the pans are placed suffer the air to have a free passage to their bottoms, and the pans, constantly oozing out water to their external surface, are cooled by the evaporation of it.
In Spain, they use a kind of earthen jars called buxaros, the earth of which is so porous, being only half baked, that the outside is kept moist by the water which filters through it ; and, though placed in the sun, the water in the jar becomes as cold as ice.
It is a common practice in China, to cool wine, or other liquors, by wrapping a wet cloth round the bottle, and lianging it up in the sun. The water in the cloth evaporates, and thus cold is pro- duced.
Ice may be produced, at any time, by the eva- poration of ether. Take a thin glass tube, four or five inches long, and about two or three eighths of an inch in diameter, and a two-ounce bottle of ether, having a tube drawn to a point, fitted to its neck. Pom- some water into the glass tube, and let a stream of ether fall upon that part of it containing the w^ater, which, by that means, will be converted into ice in a few minutes. If a thin spiral wire be introduced into the tube before the water is poured in, the ice will adhere to it, and may be drawn out.
33
LIGHT.
Under Optics, the mechanical properties of light were considered.
Light has considerable influence on chemical operations, but little is known of its real nature. Most generally it is considered as a certain simple substance, of which the chief source is the sun ; and it is also disengaged during the processes of combustion.
The most delicate experiments have been insti- tuted for the purpose of discovering whether it has weight, but without success ; on which account it is reckoned among the imponderable bodies. -
There appears to be an intimate connexion be- tween light and heat, and they are frequently given out together. But although they are both always found in the sun's rays, yet from them they may be obtained separately, the iusisible rays of heat being more refrangibible than those of light : see vol. i.
Light is capable of entering in union with many substances, and of being again separated from them. This is the case in the substance called pyrophorus, which is made by exposing to a red heat in a crucible for some time, a mixture of pounded oyster shells and sulphur. If this sub- stance be then carried into the light for a few seconds, it will imbibe so much that it will become luminous in the dark by again giving out this light.
Various kinds of meat, but particularly fish when they are beginning to putrefy, also rotten wood, sea-weeds, and some insects, as the glow- worm and lanthorn fly, have the property of shining in the dark.
VOL. II. D
34 LIGHT.
The effect of light upon vegetation is well known. Many flowers follow the course of the sun, and most flowers turn themselves more or less towards the light. Plants that grow in darkness are pale and without colour, and when this is the case they are said to be etiolated, or blanched. Gardeners avail themselves of this fact to render some vegetables, as celery and endive, white and tender. The more plants are exposed to the light, the more colour they acquire. Vegetables are not only indebted to light for their colour, but their taste and odour are derived from the same source. From this it happens, that hot climates are the native countries of perfumes, odori- ferous fruits, and aromatic resins. The action of light on the organs of vegetables causes them to pour out streams of oxygen gas from the surfaces of their leaves, while exposed to the sun, whereas, on the contrai'y, when in the dark, they emit air of a noxious quality.
Animal life seems also to be no less influenced by light. Birds that inhabit tropical countries have much brighter plumage than those of the north. Animals in general seem to droop when deprived of light ; and no doubt it is \Qry essential to the health of human beings.
The colour of metallic oxides is changed by the action of light : the yellow oxide of tungsten be- comes blue by exposure to hght ; the white salts of silver become black, and green precipitate of iron becomes red. Some oxides of metals lose w^eight by exposure to light, as the red oxide of mercury ; others lose their oxygen entirely, or become reduced, as the oxide of gold. Light, tlien, has the property of separating oxygen from several of the oxides.
ELECTRICITY. 35
Some substances when heated to a certain de- gree become luminous ; iron, for instance ; and this is what is called a red heat.
If bodies heated to redness be introduced into a gas, it does not become visible, and hence it has been concluded that gas is not capable of being made luminous : but it is now considered that flame is hydrogen gas in a luminous state.
Light is also produced by percussion ; as in the case of a flint and steel. The spark produced in this case is owing to the flint breaking off a small fragment of the steel, which is thus rendered red hot, and burns diu'ing its passage through the air. But two pieces of quartz struck smartly toge- ther also give out light, although here there can be no combustion.
Instruments for measuring the degree or inten- sity of light are called photometers,
ELECTRICITY.
Electricity and galvanism have been already treated of in the first volume. The electric fluid is now considered as a chemical agent of great importance, exciting a powerful influence in the decomposition of bodies. The connexion between electricity and chemical decomposition was first shown by Sir Humphry Davy, to whom the world is indebted for so many brilliant discoveries.
There is still, however, great uncertainty and various opinions with respect to the real nature of this influence, which is usually classed among the imponderable elementary bodies.
D 2
Si)
OXYGEN.
Oxygen is an elementary body that cannot be procured in a separate or free state, that is, it cannot be detached from tlie other bodies with which it is always combined.
Oxygen gas is so called from two Greek words, signifying the generator of acids, because it was considered by Lavoisier as the only acidifying principle. It has been called also piu^e or vital air.
About one fourth of the atmosphere consists of this gas, and it is essential to respiration and animal life. It is the most powerful and general supporter of combustion ; and by its union with other bodies^ it forms most of the acids. Oxygen gas may be easily procured by several processes.
1. It is obtained in the greatest purity from oxy-muriate of potash. Put some of this salt into a small glass retort, place the neck under the shelf of the pneumatic trough, and apply the heat of a lamp to the retort. The salts will soon melt and boil, when oxygen gas will come over in great abundance.
Q.. Black oxide of manganese is usually employed for furnishing this gas, as it affords it at a cheaper rate. Procure an iron retort made for the purpose, fill it with the oxide, fit a conducting tube to it, and place the retort between the bars of a grate which contains a good fire. Keep up the heat until the retort becomes red hot, and the gas will be received in the pneumatic apparatus. Or it may be made from oxide of manganese, put into a ^lass retort, with half its weight of strong sulphuric
OXYGEN. 37
acid. It may be likewise obtained in great quan- tity from nitrat of potass (salt petre) in an earthen retort exposed to a strong fire ; also from the red oxide of lead, heated with or without sulphuric acid. Having procured a sufficient quantity of this gas in separate vessels, its properties may be easily examined.
It will be found that water does not absorb it ; for if some of it be agitated in a small vial half filled with water, and again immersed into the trough, it will not be diminished in quantity ; nor will the water rise in an inverted vessel of this gas, if left on the shelf of the trough for a day.
Oxygen gas is eminently calculated to support the combustion of bodies. Plunge a lighted taper fixed to an iron wire, or a lighted splinter of wood, and the combustion will proceed with a splendour much encreased.
The flame of a lamp urged by a stream of oxygen gas, - instead of common air, excites a heat more intense than the hottest furnace.
Even the metals Which are not easily combustible in common air burn in oxygen gas with great readi- ness. Iron or steel wire burns in a very striking manner. It should be kindled by having a small bit of w^ood fastened to the point ; the combustion of this will communicate to the steel wire, which will continue to burn. The fused drops of iron that fall down, when examined, will be found to be no longer malleable, but brittle and converted into the oxide of iron. The same change will take place when the other metals are burnt in this gas. If a piece of charcoal, fixed to an iron wire, be lighted by a blow pipe, and put into ajar of oxygen gas, it will burn with a brilliant light, and throw
D 3
38 NITROGEN.
out numerous sparks, exhibiting a very beautiful appearance. Here the combustion pi'oduces a combination of" the oxygen with the carbon of the charcoal, and the result is carbonic acid.
A small bit of phosphorus, put into a copper spoon, burns in this gas with a light intensely bright. It is necessary to inform the young prac- titioner, that this experiment must be made with great caution. The phosphorus must be cut under water, and the piece employed must not exceed half the size of a small pea. The glass jar, in which the combustion is made, is not unfrequently broken by the heat. The result of this combustion is the phosphoric acid, from the combination of the phosphorus with the oxygen.
In all these cases, if the products of the com- bustions be carefully weighed, it will be found to ex- ceed that of the substances burned, and the oxygen will be diminished, which shows they have ab- sorbed a quantity of the oxygen employed. But this is still further proved, because the oxygen may be extracted from these newly-formed com- pounds, and the original bodies will be thus made to re-appear.
If the metal potassium, or sodium, be burned in oxygen, they form, by their union with it, the alka- lis, potass and soda ; so that oxygen is not only an acidifying^ but an alkalising principle.
Oxygen appears to be connected with the cause of the red colour in blood, for if dark coloured blood be put into a phial of oxygen gas and shaken, the blood will assume a bright red colour.
S9
NITROGEN.
Nitrogen gas is so called, because its base' forms nitric acid by its union with oxygen. It was by Lavoisier named azotic gas, and its base azote, from a Greek word signifying without life, because it is entirely destructive to animal life.
This, also, though a very abundant principle, cannot be exhibited in a free or uncombined state.
In the state of gas, it forms a considerable part of our atmosphere ; - in the solid state it enters into the composition of animal and vegetable bodies, nitric acid, and ammonia. It is incapable of sup- porting combustion or animal life. It is not ab- sorbed by water, and it has no acid properties.
It may be obtained by separating the oxygen from a portion of the atmospheric air ; the residue will be nitrogen. This is done by exposing a cer- tain quantity of atmospheric air to sulphuret of potass, which absorbs the oxygen, leaving the nitrogen free.
It may be also obtained by treating muscular flesh, (as lean veal) with nitrous acid in a retort ; the flesh is decomposed, and the nitrogen set at liberty.
That it does not maintain combustion, and is fatal to animal life, may be proved by plunging a lighted taper into a vessel filled with this gas, the taper will be immediately extinguished. If a small animal, as a mouse, or a bird, be immersed in it, it im- mediately dies.
D 4
40
COMBINATIONS OF OXYGEN AND NITROGEN.
Nitrogen and oxygen unite together in four different proportions :
1. Nitrous oxide, in which the oxygen is but half the vokime of the nitrogen.
2. Nitric oxide, in which the volumes of oxygen and nitrogen are equal.
3. Nitrous acid, in which the volume of oxygen is twice the volume of nitrogen.
4. Nitric acid, in which the oxygen is two and a half times the volume of nitrogen.
Nitrons oxide. This gaseous compound, called also the gaseous odide of nitrogen, or the gaseous oxide of azote, was first discovered by Dr. Priestley ; but it is to Sir Humphry Davy that we owe a tliorough knowledge of its properties.
Nitrous oxide is a permanent gas. A candle burns in it with a brilliant flame and crackling noise ; be- fore its extinction, the white inner flame becomes surrounded with a blue one. Phosphorus intro- duced into it, in a state of inflammation, burns with increased splendour, as in oxygen gas.
Sulphur, introduced into it when burning with a feeble blue flame, is extinguished ; but when in a state of vivid inflammation, it burns with a rose- coloured flame. Lighted charcoal burns in it more brilliantly than in atmospheric air.
Iron wire, v/ith a small piece of wood affixed to it, and introduced inflamed into a vessel filled with this gas, burns rapidly, and throws out bright scin- tillating sparks.
Nitrous oxide is rapidly absorbed by water that has been boiled, and a quantity of gas equal to rather more than half the bulk of the water may be thus
COMBINATIONS OF OXYGEN AND NITROGEN. 41
made to disappear ; the water acquires a sweetish taste, but its other properties do not differ per- ceptibly from common water. The whole gas may be expelled again by heat.
It does not change blue vegetable colours. It has a sweet taste, and a faint, but agreeable odour.
This gas explodes with hydrogen, when electric sparks are made to pass through the mixture. Animals, when confined wholly in this gas, give no signs of uneasiness at first; but they soon be- come restless, and then die.
When it is mingled with atmospheric air, and then received into the lungs, it generates highly pleasurable sensations. The effects it produces on the animal system are very extraordinary ; it ex- cites the body to action, and rouses the faculties of the mind, inducing a state of great exhilaration, an irresistible propensity to laughter, a rapid flow of ideas, and unusual vigour and fitness for muscu- lar exertions, in some respects resembling the sen- sations attendant on intoxication, without any lan- guor or depression of spirits, or disagreeable feelings afterwards ; but more generally followed by vigour and a disposition to exertion, which gradually subsides.
This gas is produced when substances having a strong affinity with oxygen are added to nitric acid, or to nitrous gas. It may, therefore, be obtained by various methods, in which nitrous gas or nitric acid is decomposed by bodies capable of attracting the greater part of their oxygen. The most commo- dious and expeditious, as well as cheapest mode of obtaining it, is by decomposing nitrate of ammo- nia by heat, in the following manner : put into a glass retort some pure nitrate, and apply to it an ArgaQd's lamp ; the salt will soon liquify, and
42 COMBINATIONS OF OXYGEN AND HYDROGEN.
when it begins to boil, gas vviJI be evolved. Increase the heat gradually, till the body and neck of the retort become filled with a milky white vapour. In this state, the temperature of the fused nitrate is between 340 and 480°. After decomposition has oroceeded for some minutes, so that the gas, when examined, quickly enlarges the flame of a taper, it may be collected over water. Care should be taken, during the whole process, never to suffer the tem- perature of the fused nitrate to rise above 500^ of Fahrenheit; which may be easily judged of from the density of the vapours in the retort, and from the quick ebullition of the fused nitrate ; for if the heat be increased beyond this point, the vapours in the retort acquire a reddish and more transparent appearance, and the fused nitrate begins to rise, and occupy twice the bulk it did before. The nitrous oxide, after its generation, should stand over water for several hours; it is then fit for respiration or other experiments.
The explanation of this process is as follows: Nitrate of ammonia consists of nitric acid and ammonia ; nitric acid is composed of nitrous gas and oxygen ; and ammonia consists of hydrogen and nitrogen. At a temperature of 480°, the attractions of hydrogen for the nitrogen in the ammonia, and that of nitrous gas for the oxygen of the nitric acid, are diminished; while, on the contrary, the attractions of the hydrogen of the ammonia for the oxygen of the nitric acid, and that of the remaining nitrogen of the ammo- nia for the nitrous gas of the nitric acid, are in- creased; hence all the former affinities are broken, and new ones produced; namely, the hydrogen of the ammonia attracts the oxygen of the nitric acid, the result of which is water. The nitrogen of the
NITRIC OXYDE. 43
ammonia now combines with the disengaged nitrous gas, and forms nitrous oxyd.
To experience its effects in breathing it, put about a gallon into a large bladder, or oiled silk bag, having a tube attached to it, of three-fourths of an inch in diameter. First, the common air must be expelled from the lungs, before the tube is received into the mouth, and the nostrils must be accurately closed with the hand. It must then be breathed backwards and forwards into the bag for a few minutes.
Nitric Oxyde is called also nitrous gas. This com- pound of oxygen and nitrogen cannotbe obtained by direct combination, but by abstracting from nitric acid a portion of its oxygen, leaving the remainder in such proportion as to constitute nitric oxide.
When pure, it is not acid, and is void of colour. It is incapable of supporting the combustion of most bodies; nevertheless, phosphorus and pyro- phorus burn in it. Nitrous gas is made by putting clippings or filings of copper into a retort with nitric acid, diluted with thrice as much water ; red fumes will be given out, if the gas is suffered to escape into the air ; but if collected in the pneu- matic apparatus, the gas is colourless. In this pro- cess, the metal attracts the oxygen from the nitric acid, and becomes oxydated ; the rest of the acid being deprived of a great portion of its oxygen, can no longer exist as acid ; it therefore expands, be- comes aeriform, and appears as nitrous gas.
When nitrous gas and oxygen gas are mixed to- gether in a glass vessel, previously exhausted of air, they instantly unite, and form a reddish coloured gas, which has but half the volume of the two gases, and which is highly acid. This new compound is called nitrous add gas.
44 NITROUS ACID.
Nitrous acid gas is very easily absorbed by water, rendering it a green, sour liquid.
When nitrous gas is mixed with atmospheric air, the same red fume appears, from the nitrous gas uniting to the oxygen of the atmosphere, leaving the nitrogen by itself. Hence this gas has been used for measuring the quantity of oxygen gas con- tained in air, and an instrument for this purpose has been called an Eudiometer. A tall glass tube, sealed at one end, is used for this purpose, filled with water, and inverted in the pneumatic apparatus. Send up a certain measure of the air to be examined into this tube, and mark the space which it occu- pies in the top of the tube. Then add to it a mea- sure of nitrous gas, and observe the degree of diminution. By comparing how much different specimens of air will be di"minished by the same quantity of nitrous gas, the relative quantities of oxygen in each may be estimated. This method of analysing atmosphere is not considered as very cor- rect, and other modes are sometimes used, where there are fewer sources of inaccuracy.
Nitrous Acid.
Considerable uncertainty prevails respecting this acid. The yellow coloured fuming acid, to which this name has been given, appears to be only nitric acid holding nitrous gas in solution. The nitrous gas may be expelled from it by the application of heat, and then the nitric acid is left colourless.
But if nitrous gas and oxygen gas be mixed together, without the access of water, by intro- ducing them into a vessel previously exhausted of air, an union takes place ; the two gases diminish to half the volume, and an acid gas is produced.
NITKIC ACID. 45
This is the nitrous acid in a gaseous form. This acid gas is extremely absorbable by water, which is at first rendered green : then, as the absorption goes on, it becomes blue, and, finally, of an orange colour : by adding more water, it may be brougTit back to the green colour.
If dry nitrate of lead be distilled, an orange- coloured liquid comes over; which is considered as nitrous acid nearly pure.
Nitric Acid.
This acid is one of those which have been longest known to chemists. It is so named from nitre, from which it was procured. The corrosive acid called aqua fortis is an impure and weak nitric acid: but it was long used before its analysis was known: this we owe to Cavendish.
NitrCi called also saltfetre^ consists of this acid united with potass, and the process for procuring the acid depends upon decomposing this salt. For this purpose, some substance is added to the nitre that has an attraction for the potass sufficiently strong to overcome that of the nitric acid, and, consequently, to allow it to be expelled by heat. Sulphuric acid is used for this purpose. During its expulsion, however, the nitric acid suffers a partial decompo- sition ; for though it is nitric acid that exists in the salt, it is nitrous acid that condenses in the receiver in the form of orange fumes. This is the common nitrous acid of commerce.
To convert this into nitric acid, another process is necessary. By distillation, nitrous acid gas is driven off, leaving the nitric acid colourless. Or,
40 ATMOSPHERIC AIR.
it is distilled on black oxide of manganese, which gives more oxygen to it.
Nitric acid is extremely caustic; that is, acts powerfully upon animal substances. It unites with the alkalis and earths ; it oxidates all the metals except gold and platina ; it thickens and blackens oils, converting them into a coal, or inflaming them, according to the nature of the oil, and the degree of the concentration of the acid.
The combinations of nitric acid with different bases are called nitrates.
When the nitrogen and oxygen gases are mingled together, they form a compound exactly resembling common or atmospheric air.
Atmospheric Air
Is, indeed, essentially composed of these two gases: and its analysis or decomposition has been one of the most interesting discoveries of modern che- mistry. It is curious that one of the ingredi- ents of this substance, so necessary to animal life, should, by itself, be highly deleterious.
It has been completely proved, that the air of the atmosphere is a compound body, formed by the mixture of oxygen gas and nitrogen gas. The first is the only one of them that supports combustion ; and when combustion takes place in common air, it is this part that unites to the burning body, form- ing either an oxide or an acid. If mercury be heated in a given quantity of atmospheric air for some time, it will become changed into a red pow- der, which will weigh more than the mercury ; the air will be found to be diminished in quantity, and
13
ATMOSPHERIC AIR. 4^
to be no longer capable of supporting combustion. The reason of this is, that the oxygenous part of the air has united to the metal, and converted it into an oxyde, leaving behind only the nitrogen.
This decomposition of the atmospheric air may be effected more easily by burning phosphorus in it. During the combustion of the phosphorus, it unites to the oxygen, and forms phosphoric acid j the remainder is nitrogen.
The proportion of oxygen gas contained in a given quantity of atmospheric air can be ascertain- ed by various processes. One method is, by in- verting a glass tube into a solution of sulphuret of potass. This substance will absorb the oxygen gas, but not the nitrogen ; hence the air in the tube will diminish in bulk, and what remains will show the proportion of nitrogen.
It was supposed by modern chemists, until lately, that oxygen was essential to combustion ; and that this process was, in all cases, the combination of oxygen with the combustible body; but it has been found, that there are some other substances, as chlorine and iodine, which have also this pro- perty of supporting combustioii : it is, however, the oxygen that acts in all the usual combustions in common air. The heat and light were supposed to be separated from oxygen, the base of the gas, which became fixed in the burned body. At pre- sent it is maintained by some, that combustion may be the consequence of intense chemical ac- tion, and need not depend upon any particular combination. This subject, however, remains very obscure.
Air, which has been breathed, is found to have lost its oxygen. This principle is retained in the
48 ATMOiSPHERIC AIR.
Jungs, and is absorbed into the blood: it appears essentially necessary to vitality.
An animal can only live for a limited time in a given portion of air. If a mouse or a bird be con- fined under a glass that is closed, they will soon die ; a candle, also, will burn only a short time. In crowded rooms, where there is not a free circula- tion of air, the oxygen is diminished by the respi- ration of so many persons, and the air is rendered unhealthy. The lights, also, are observed to burn dim, and contribute much to exhaust the oxygen. This points out the importance of ventilating all kinds of apartments, but particularly public places.
It has been found that in 100 parts by measure of atmospheric air, there are 21 parts of oxygen gas and 79 of nitrogen gas.
From the property of oxygen as being essential to respiration and animal life, it had been thought that the salubrity of air must depend upon the quantity of oxygen which it contained ; but, al- though the airs of various places have been ex- amined, as that of towns, prisons, the country, tops of hills, the ocean, &c., it appeared that the proportion of oxygen did not sensibly differ in them all. The healthiness of certain airs, therefore, must depend upon some other circumstances.
Although the great mass of the atmosphere is to be considered as consisting of oxygen and hydro- gen, yet it contains a small quantity of many other gases, and also water, and a variety of exhalations and substances dissolved in it. It always contains a portion of carbonic acid gas, perhaps 1 part in 1000,for alkaUes become effervescent when exposed to it, and lime water acquires a pellicle on being
HYDROGEN. 49
exposed a sufficient time to the action of the air, even upon the highest mountains.
Since the oxygen of the atmosphere is continu- ally abstracted from it by various decomposing processes, it would appear that nature must have some mode of renewing a principle so important. Vegetables have been supposed to perform this office, since they always exhale oxygen gas in the day, and particularly when the sun shines. This circumstance may be easily observed by putting some leaves into an inverted tumbler of water placed in the sun-shine. Minute globules of air will be seen rising from the leaves, which, col- lected at the top and examined, will be found to be oxygen.
HYDROGEN.
Hydrogen is so called from two Greek words signifying the genei^ator of water, because it is one of the constituent principles of this fluid. It is also one of the ingredients of bitumen, of oils, fat, ardent spirits, ether, and of all the proximate com- ponent parts of animal and vegetable bodies : it forms a constituent part of all animal and vegeta- ble acids : it is one of the elements of ammonia, and of various compound gases.
It possesses so great an affinity for caloric, that it is impossible to procure it in the concrete or liquid state, independent of combination. Hydro- gen united to caloric forms hydrogen gas.
Hydrogen gas is the lightest substance whose weight we are able to to estimate; when in its purest state it is about thirteen times lighter than atmospheric air. It is unfit for respiration j ani-
VOL. II. E
50 HYDROGEN.
mals, when obliged to breathe in it, die ahnost in- stantaneously. It has a peculiar and disagreeable smell.
It is decomposed by living vegetables, and its base is one of the constituents of oil, resin, &c. It is highly inflammable, and burns rapidly when kindled in contact with atmospheric air, or oxygen gas, by means of the electric spark, or by an in- flamed body, exhibiting a blue lambent flame. Water absorbs about one thirteenth of its bulk. It dissolves carbon, sulphur, phosphorus, arsenic, and many other bodies. When its basis combines with that of oxygen gas, water is formed, and with nitrogen it forms ammonia.
An easy method of obtaining hydrogen gas consists in subjecting water to the action of a substance which is capable of decomposing this fluid.
For this purpose, let sulphuric acid, diluted with four or five times its weight of water, be poured on iron filings or bits of zinc, in a small retort or glass bottle ; as soon as the diluted acid comes in contact with the metal, a violent effer- vescence takes place, and hydrogen gas escapes, without external heat being applied. It may be collected in the usual manner over water, taking care to let a certain portion escape, on account of the common air contained in the disengaging vessel.
Hydrogen gas is often found in great abundance in mines and coal-pits, where it is sometimes gene- rated, and becomes mixed with the atmospheric air of these subterraneous cavities. If a lighted can- dle be brought into this mixture, it explodes, and produces the most dreadful effects. It is called by miners the Jire damp. It generally forms a cloud
HYDROGEN. 51
in the upper part of the mine, on account of its lio-htness, but does not mix there with atmospheric air, unless some agitation takes place. The miners frequently set fire to it with a candle, laying, at the same time on their faces, to escape the violence of 'the shock. An easier and safer method of clearing the mine is, by leading a long tube through the shaft of it to the ash-pit of a furnace ; by this means the gas will be conducted to feed the fire.
Hydrogen gas, though itself inflammable, extin- guishes burning bodies, and is incapable of main- taining combustion. Bring an inverted jar filled with hydrogen gas over the flame of a candle, and depress the jar, so that the lighted wick may be wholly surrounded by the gas 5 the candle will be immediately extinguished.
Hydrogen gas is only inflammable when in con- tact with atmospheric air or oxygen gas. Fill a small phial with hydrogen gas, and take it from the pneumatic trough, placing the thumb on the mouth thereof, to prevent the gas from escaping ; if a lighted taper be applied to the mouth of the phial, the gas will take fire, and burn with a lam- bent flame. The gas will only burn where it is in contact with the atmospheric air ; the flame will descend gradually, till all the gas is consumed.
If the hydrogen gas be pure, the flame will be of a blue colour ; but if the gas holds any substance in solution, which is generally the case, the flame is tinged of different colours, according to the sub- stance. It is usually reddish, because the gas holds in solution a little charcoal.
On this principle i? constructed the philosophical candle, which cannot be easily blown out. Fill with hydrogen gas a bell glass, furnished with a
E 2
52 HYDROGEy.
capillary tube ; compress the gas, by making the bell descend below the surface of the water in the pneumatic trough ; then apply a lighted taper to the upper extremity of the tube ; the gas will take fire, and exhibit a candle, which will burn till all the gas is exhausted.
Artificial fire-works may be constructed by filling bladders with hydrogen gas, and connecting them with revolving jets, tubes, &c., bent in different directions, and formed into various figures pierced with holes of different sizes. The air which is forced through these holes by pressing the blad- ders, will, when inflamed, exhibit a curious fire- work, without either noise or smoke.
By the inflammable property of hydrogen gas, and the effects of electricity, a curious lamp has been invented by Volta, which, by turning a stop cock only, may instantly be lighted, and that many hundred times.
Hydrogen gas burns more readily in proportion as it is surrounded with a larger quantity of atmos- pheric air. Hydrogen gas and atmospheric air, or, what is better, oxygen gas, may be mixed together, so that every particle of each gas shall be contigu- ous to a particle of the other, in which case they will burn with great rapidity.
Into a strong bottle, capable of holding about four ounces of water, put one part of hydrogen gas and two of amospheric air. On applying a lighted taper, the mixture will explode with a loud report, and the inside of the bottle will become moist. It will be prudent to wrap a handkerchief round the bottle, to prevent it from doing any in- jury if it should burst.
The same experiment may be made with oxygen gas, instead of atmospheric air, changing the pro-
HYDROGEN. 53
portions, and mixing only one part of oxygen gas with two of hydrogen. The report will then be much louder than with common air.
This experiment may be made conveniently by means of an apparatus called the hiflammahle air pis- tol. To charge it, nothing more is necessary than to introduce its mouth inverted into a wide-mouthed bottle, filled with a mixture of oxygen and hydro- gen gas, leaving it in for a few seconds ; it is then to be stopped with a cork, and may be fired by the electrical spark taken from the prime conductor of the machine, or by a charged Ley den phial.
It has been, with great plausibility, conjectured, that the noise of thunder is the effect of the rapid combustion of hydrogen and oxygen gas, fired by the electric spark ; and that the rain which falls so copiously at the time of thunder-storms, is owing to a sudden formation of water by this means.
From its Hghtness, it has been employed for making air-balloons, which have been already de- scribed.
Soap-bubbles, filled with hydrogen gas, ascend in the air. To show this, fill a bladder with hydro- gen gas, and fasten it to a tobacco-pipe ; dip the bowl of the pipe into a lather of soap, squeeze the bladder gently, in order to form a bubble, and de- tach it in the usual manner. These bubbles will rise rapidly into the air : if a lighted taper be pre- sented to them, they catch fire and burn with a slight explosion.
If the bladder be filled with a mixture of hydro- gen and common air, the soap-bubbles will ascend, and when the taper is presented to them they will explode with a loud report. This experiment is more striking if oxygen gas be mixed with hydrogen. If the bladder be squeezed so as to
E 3
S4i HYDROGEN AND OXYGEN.
form a great many bubbles on the surface of the bason,'the report will be as loud as that of a cannon.
It has lately been discovered, that hydrogen, like oxygen, is an acidiJi,:hig prmciple. United to chlo- rine, it forms hydro -chloric acid, which is the same as muriatic acid. Combined with iodine, it forms hydriodic acid.
When hydrogen gas is united to sulphur, it forms sulphureted hydrogen, which has also the properties of an acid. Tellureted hydrogen has also acid properties.
Hydrogen and Oxygen.
It has been already mentioned, that these two elements, when combined, form "doater.
Till lately, water was considered as a simple sub- stance, or element ; no one had ever been able to decompose it ; and the decomposition of it, which is daily effected in natural processes, had escaped observation. We shall, however, give such evi- dent proofs of the decomposition and recompo- sition of water, as will clearly show that it is not a simple body.
Ea:periment I. — A tube of common glass E F (Plate 2. fig. 70j well annealed, and difficult to be fused, about ten or eleven lines diameter, was placed across a furnace C F E D, in a position somewhat inclined ; and to its upper extremity was adapted a glass retort A, containing a known quan- tity of distilled water, and resting on a furnace V V. To the lower extremity of the glass tube F was applied a worm S S, connected with the dou- ble-tubulated flask H, and to the other tubulure was adapted a bent glass tube K K, destined to con- vey the gas to an apparatus proper for determining
HYDROGEN AND OXYGEN. 55
the quality and quantity of it. When the whole was thus arranged, a fire was kindled in the fur- nace C F E D, and maintained in such a manner, as to bring the glass tube E F to a red heat, but without fiising it ; at the same time as much fire was maintained in tlie furnace V V X X, as to keep the water in the retort A in a continual state of ebullition,
In p]'oportion as the water in the retort A as- sumed the state of vapour by ebullition, it filled the interior part of the tube E F, and expelled the atmospheric air which was evacuated by the worm S S, and the tube K K. The steam of the water was afterwards condensed by cooling in the worm S S, and fell drop by drop, in the state of water, into the tubulated flask H. When the whole of the water in the retort A was evaporated, and the liquor in the vessels had been suffered to drain off completely, there was found in the flask H a quan- tity of water, exactly equal to that which was in the retort A, and there had been no disengage- ment of any gas ; so that this operation was merely a common distillation, which gave absolutely the same result as if the water had never been brought to a state of incandescence, in passing through the glass tube E F.
Ea:perime7it II. — Every thing being arranged as in the preceding experiment, twenty-eight grains of charcoal reduced to particles of a moderate size, and which had been previously exposed for a long time to a white heat in close vessels, were intro- duced into the glass tube E F. The operation was then conducted as before, and the water in the re- tort A kept in a continual state of ebullition, till it was totally evaporated.
The water in the retort A was distilled as in the E 4-
56 HYDROGEN AND OXYGEN.
preceding experiment, and being condensed in the worm S S, had fallen drop by drop into the flask H ; but at the same time there had been disen- gaged a considerable quantity of gas, which escaped through the tube K K, and was collected in a pro- per apparatus. When the operation was finished, there was found nothing in the tube E F but a few ashes, and the twenty-eight grains of charcoal had totally disappeared.
The gases disengaged were found to weigh alto- gether 113.7 grains. There were found two dif- ferent kinds of gas, viz. 114 cubic inches of carbonic acid gas, weighing 100 grains, and 380 cubic inches of a very light gas, weighing 13.7 grains. This last gas took fire, on being applied to a lighted body in contact with the air. In ex- amining afterwards the weight of the water whicli had passed into the flask, it was found less than that in the retort A by 85.7 grains. In this ex- periment, therefore, 85.7 grains of water and 28 grains of cliarcoal formed carbonic acid gas equal to 100 grains, and a peculiar gas susceptible of in- flammation, equal to 13.7 grains. To form 100 grains of carbonic acid gas, 72 grains of oxygen must be united to 28 grains of charcoal or carbon. The 28 grains of charcoal put into the glass-tube EF, took, therefore, from the water, 72 grains of oxygen, since there was formed carbonic acid equal to 100 grains. It appears, then, that 85-7 grains of water are composed of 72 grains of oxygen, and 13.7 grains of a substance forming the base of a gas susceptible of inflammation. The following is a proof of it.
The apparatus being arranged as above, instead of the 28 grains of charcoal, 274^ grains of thin -shavings of iron, rolled up in a spiral form, were
HYDROGEN AND OXYGEN. 57
introduced into the tube E F ; the tube was then brought to a red heat as before ; and, in the same manner, the whole of the water in the retort A was made to evaporate.
In this experiment there was disengaged only one kind of gas, which was inflammable ; there was obtained of it about 406 cubic inches, weighing 15 grains.
The 274 grains of iron put into the tube E F were found to weigh 85 grains above what they did when introduced ; and the water first employed was diminished 100 grains.
The volume of these iron shavings was found to be greatly enlarged. The iron was scarcely any longer susceptible of attraction by the magnet ; it dissolved without effervescence in acids ; in a word, it was in the state of a black oxyd, like that which has been burned in oxygen gas.
In this experiment there was a real oxydation of the iron by the water, entirely similar to that effected in the air by the aid of heat. 100 grains of water were decomposed ; and of these 100 grains, 85 united to the iron, to reduce it to the state of black oxyd ; these 85 grains, therefore, consisted of oxygen ; the remaining 15 grains, combined with caloric, formed inflammable gas. It thence follows, that water is composed of oxygen and the base inflammable gas, in the proportion of 85 to 15, or of I7 to 3.
If it be true, as we have endeavoured to prove, that water is composed of hydrogen combined with oxygen, it thence results, that, by re-uniting these principles, water ought to be produced. This, in- deed, is what takes place when, into a vessel filled with oxygen, a stream of hydrogen is introduced and set fire to.
58 HYDROGEN AND OXYGEN.
In proportion as the combustion proceeds, water is deposited in the internal surface of the vessel ; the quantity of this water gradually increases, and it unites itself intolarge drops, which run down the sides of the vessel, and are collected in the bottom of it.
In making this experiment, proper means were taken to ascertain the weight of the gases em- ployed. Before the experiment, the vessel v/as weighed ; and, by weighing it after the operation, the weight of the water that had been formed was obtained. Here, then, is a double proof; on the one hand, the weight of each of the gases em- ployed ; and, on the other, the weight of the water formed ; and these two quantities were found to be equal within a two hundredth part. It was thus found that 85 parts by weight of oxygen, and 15 parts also by weight of hydrogen, are required to compose 100 parts of water.
These phenomena of the decomposition and recomposition of water are continually effected be- fore our eyes, by the temperature of the atmos- phere, and the agency of compound affinities. It is this decomposition which gives rise, at least in a certain degree, to the phenomena of spirituous fer- mentation, to those of putrefaction, and to those of vegetation.
Pure water is perfectly transparent, and has no taste nor smell. It is not liable to change. It can absorb a variety of gases ; and when exposed to the atmosphere, it always contains a small quantity of common air, which may be separated by boiling, or by the air-pump. Rain-water is the purest which we see in nature ; but, for delicate chemical pro- cesses, it is distilled in glass vessels. Spring- water generally holds some salts in solution, which gives it various properties.
HYDROGEN AND CARBON. 59
Hydrogen gas combines with several simple bodies, constituting, with them, peculiar and dis- tinct gases.
Hydrogen and Carbon.
Hydrogen gas unites to carbon, and forms, with it, HydrO'Carhonate gas. Of this there are two kinds, according to the quantity of carbon which they contain.
Light Hyd?^o-Carbo?iate. — This is frequently seen rising from stagnant ponds, when stirred. It may also be procured by passing the vapour of water over red hot charcoal. It burns with a pale blue flame. It is also called Light carbureted Hy- drogen. It is contained very abundantly in many coal mines, where it is disengaged from fissures in the strata, often in great quantities; which are called by the miners blowers. When it has accumulated iu any part of the mine, it forms an explosive compound, by its admixture with the common air : and when the miners approach it with lighted candles or lamps, it inflames with a tre- mendous explosion, killing the workmen and de- stroying the works. Indeed, nothing can be more terrible than such accidents ; and there is reason to think that they have happened more frequently than is generally known. The body of miners are, therefore, infinitely indebted to Sir Humphry Davy for his invention of the Safety-lamp, an in- strument which they can carry lighted into an ex- plosive mixture, without any danger of setting fire to it. This gas is called the Fire-damp by the miners.
Bi'Carbureted Hydrogen. ■ — This gas contains
60 GAS ILLUMINATION.
twice as much carbon as the last. It is heavier than it, and is also called the Heavy hydro-car- bonate. It burns with a bright white flame, like that of the best wax candles. It has been called the olejiant gas, because, when mixed with chlo- rine in an exhausted vessel, or over water, a pe- culiar fluid was formed, resembling a thick oil, but which has been termed by Dr. Thomson, Chloric ether.
Bi-carbureted hydrogen may be procured by heating, in a retort, four parts of sulphuric and of one alkohol ; when the mixture boils the gas comes over.
Gas Illumination. — The carbureted hydrogen gases are now extensively employed for the pur- pose of giving light. When coal is put into an iron retort placed in a furnace, an inflammable gas is given out, which is a mixture of the two above- mentioned species of hydro-carbonate, together with small quantities of carbonic acid gas, car- bonic oxide, sulphureted hydrogen, tar, ammonia, and water. These last substances are separated by passing the gas through a mixture of quicklime and water; and the purified gas then passes into the gasometer^ from which it is distributed by means of pipes. The coal that has been thus acted upon, being deprived of its volatile principle, is con- verted into colce.
The kind of coal, fittest for the production of good gas, is that which contains most bitumen and least sulphur.
Messrs. J. and P. Taylor have lately taken out a patent for the production of carbureted hydrogen gas from oil. The oil is decomposed by suffering it to drop into a bent iron tube, laid through a furnace. The oil is separated into charcoal and
SULPHURETED HYDROGEN GAS. 6l
bi-carbureted hydrogen, the flame of which much exceeds in whiteness and brilliancy that of coal o-as, which is a mixture of the two species of hydro- carbonates. Another material advantage in the use of the oil gas is, that it is not mixed with the impu- rities of coal gas, many of which are highly inju- rious to health, and to the furniture of houses. From experiments it appears that the coal gas does not contain above 10 per cent, of bi-carbureted hydrogen ; while the oil gas consists almost entirely of it.
Sidphiir^efed Hydrogen Gas.
This is a combination of hydrogen gas with sul- phur. It has an extremely fetid odour. It is in- flammable. It cannot support life nor combustion : indeed, it is highly deleterious. Water can absorb it, and acquires its peculiar smell. The mineral waters of Harrowgate and Aix-la-Chapelle owe their properties chiefly to this gas.
Sulphureted hydrogen gas has the property of causing metallic oxides to re-approach the metallic state ; the hydrogen of the gas attracting the oxy- gen. If a piece of paper, dipped in a solution of acetite of lead, be exposed to this gas, it instantly becomes blackened. If letters be written with the solution of lead, they will be invisible when dry, but will become black on exposing them to sul- phureted hydrogen.
It has also acid properties. It unites with the alkalis and the earths, forming compounds called Hydro-sul'phurets.
This gas affords an exception to the doctrine of Lavoisier, that oxygen was the only acidifying prin- ciple ; for in it there is no oxygen, yet it performs
62 PHOSPHORATED HYDROGEN GAS.
the most important functions of an acid, reddening vegetable blues, and combining with alkalis. The hydro-sulphurets are formed by passing a stream of this gas through solutions of the alkalis.
Phosphorated Hydrogen Gas,
This gas consists of hydrogen and phosphorus. It is so combustible that it inflames by mere con- tact of atmospheric air. It has a very disagreeable smell, like that of putrid fish.
To procure it artificially, put one part of phos- phorus and ten of a concentrated solution of potass, into a glass retort, and apply a gentle heat. When the mixture boils, the gas will come over, and may be collected in the pneumatic apparatus.
In preparing this gas, the body of the retort should be filled as nearly as possible with the mix- ture, otherwise the first portion of the gas, finding atmospheric air in the retort, inflames, a vacuum is produced, and the water is forced up into the retort, endangering the bursting of it.
If the bubbles of air which are formed in the retort are suffered to escape into the atmosphere, they will inflame instantly with a slight explosion; at the same time a beautiful dense white circular ring of smoke rises, and gradually enlarges as it ascends.
This gas maybe made to burn under the surface of water. Put into a deep glass some phosphuret of lime, and half the quantity of oxy-muriate of potass : fill the vessel with water. Procure a long- necked glass funnel and plunge it into the vessel, putting it down to the bottom. Take some con-
CHLORINE. 63
centrated sulphuric acid and pour into the funnel. As soon as the decomposition of the water and that of the muriate takes place, flashes of fire will be seen to issue from the bottom of the vessel, having a screen colour.
If a ribbon be impregnated by a solution of gold, and hung in a jar containing this gas, the gold will be revived, and will gild the ribbon.
CHLORINE.
This gaseous body is now generally regarded as an elementary substance : but it was lately con- sidered as a combination of muriatic acid with oxy- gen, and was hence called oxygenated muriatic acid gas.
It is obtained by heating a mixture of muriatic acid and black oxide of manganese over a lamp : the chlorine will be evolved. In this process, ac- cording to the present theory respecting the ele- mentary nature of chlorine, the oxide of manganese and muriatic acid decompose each other : the oxy- gen of the oxide unites to the hydrogen of the muriatic acid to form water, leaving the other constituent of the acid, viz. the chlorine, disen- gaged.
Chlorine is rapidly dissolved by water, the so- lution being of a pale yellow colour : it has a nauseous taste, and an extremely suffocating smell. When the gas is perfectly free from moisture, it has no action on vegetable colours, but, dissolved in water, it destroys them entirely.
From this property, it is extensively employed in shortening the process of bleaching linen, and also paper; but it is said that it is apt to injure
64 CHLORINE.
the durability of the substances bleached, and no doubt, except due care is employed, this must be the case. Prints that have been stained by smoke and dust may also be whitened by it, as it does not act upon the printing ink.
Chlorine has likewise been found extremely effi- cacious in destroying the putrid effluviag in pri- sons, and hospitals, and preventing the infection of the small-pox. But when used for this purpose, a small quantity only is diffused through the air, for, when taken into the lungs by itself, it is fatal to animal life ; and, indeed, in preparing it, great precaution should be used not to inhale it, as it is extremely dangerous if not sufficiently diluted.
Notwithstanding its unfitness for respiration, it supports combustion in a remarkable degree. Some bodies, as phosphorus, and several of the metals, are spontaneously ignited when plunged into a vessel of chlorine ; on this account it is now reckoned one of the supporters of combustion, a property which was lately supposed to be only en- joyed by oxygen. In this view, combustion is re- garded only as the result of intense chemical action, and it is supposed that the compounds of chlorine have less capacity for caloric than their constituent principles, and, consequently, that ca- loric is evolved at the moment of their formation.
Chlorine is known to combine with oxygen in three different proportions, forming
1. Omde of Chlorine, or Euchloriney a gaseous body, not acid, having a smell less irritating than chlorine.
2. Ojnjchloric Acid, which does not exist inde- pendent of water or a base.
3. Chloric Acid. — Chloric acid cannot be ob- tained unmixed with water. It is colourless and
CHLORINE. C)5
sour ; acts on metals, and combines with alkalies, forming chlorates.
Chlorate of potash was formerly called oxymu- riat of potash. It is a soluble white salt. When heated it gives out oxygen, and the residue is chloride of potassium. It forms extremely explo- sive compounds with phosphorus, sulphur, and charcoal. A grain, with a minute portion of phos- phorus, laid upon an anvil, and struck with a hammer, makes a very loud report ; but this experiment should not be attempted by the i/owig student. From its detonating quahty, it had been imagined that it could be used advantageously in the manufacture of gunpowder, but it has not succeeded.
Chlorate of potash is made by causing a stream of chlorine to go through a solution of caustic potash.
The combinations of chlorine with other simple bodies, form chlorides, if they are not acids, as chloride of sulphur, &c.
Chlorine and hydrogen. This compound body, which, according to the present nomenclature, is called hydrochloric acid gas, was known by the name of muriatic acid gas. It is readily obtained by distilling a mixture of common sea salt and sul- phuric acid. The sulphuric acid combines with the soda, one of the constituents of salt ; and the other constituent, the muriatic acid gas, is set free. Mu- riatic acid gas cannot support life nor combustion. It has a «harp pungent odour, and occasions white fumes when it is mixed with moist atmospheric air. It reddens vegetable blues. It combines with the alkaline bases : with ammoniacal gas it forms mu- riate of ammonia.
VOL. II. F
60 IODINE.
It is decomposed by the electric spark into hy- drogen and chlorine.
It is readily absorbed by water, which then becomes very acid, and forms the liquid muriatic acid.
The muriatic acid, called also the mai^ine acid and the spirit of salt, is in very common use. It is obtained, as above-mentioned, by distilling sea salt and sulphuric acid. It exists in a state of combin- ation with alkalies and earths in the mineral kingdom in great quantity, chiefly with soda, lime, and magnesia. With soda it forms muriate of soda, common or sea salt, with which every part of the ocean is impregnated, and also some lakes. Mu- riate of soda also exists in the form of a rock in the earth, whence it is extracted : it is called rock salt. The most considerable mines of rock salt are in Poland ; extensive mines are also worked in Hun- gary, Spain, and Cheshire in England. Muriate of soda is obtained also from the sea water, by driving off the water by evaporation ; and this is done either by exposing salt water in shallow places, called saltpans, to be evaporated by the heat of the sun, or by boiling salt water in vessels, or by these methods combined. Muriate of soda, so procured, is always contaminated with muriate of magnesia and muriate of lime, from which the salt is puri- fied by different processes.
IODINE.
This substance, considered as a simple body, has been but lately discovered. It exists in certain marine plants, and is procured from kelp, which is
SULPHUR. ()7
made by burning them. It is obtained first in the form of fumes, of a violet color, which con- dense in small opaque crystals of a blackish grey color and metallic lustre, resembling plumbago. It appears to be an element that exists in small quan- tity. It is capable of producing acids by combin- ation with other substances. With oxygen, it forms iodic acid ; and, with hydrogen, it forms hy- driodic acid. It combines with phosphorus at the common temperature, giving out heat and light, and produces with it phosphuret of iodine. With sulphur, it makes sulphur et of iodine.
Iodine, also, unites with all the metals, forming with them iodurets.
SULPHUR.
Sulphur, known also by the name of brimstone^ is a mineral substance, frequently found pure in nature.
It is of a pale yellow colour, without taste and, also without smell, except when heated. It is chiefly a volcanic product, and a great deal of what is used in this country is brought from Italy and Sicily. It is found also in nature combined with most of the metals as ores : united to iron, it forms iron pyrites.
Sulphur is extracted from pyrites by exposing it to heat in tubes, by which the sulphur is driven out and received in vessels with water : when melted and poured into moulds, it constitutes the roll sul- phur in common use. A good deal of this is made in England. The sulphur thus obtained, however, is not quite pure. To purify it, it is sublimed by
F ^
(j8 sulphur.
a gentle heat in close rooms, and thus forms Jloxvei^s oj' sulphur.
If sulphur be exposed to heat it will soon fuse, and, by continuing the fusion for some time, it will become thick and tenacious. If worked between the fingers under water in this state, it acquires a consistency like wax, and may be employed for taking impressions from seals or gems. This change in the sulphur has been ascribed to oocijda- tion; but the same effect takes place if the sulphur be kept in fusion without access of air.
Sulphur becomes electric by friction, and then exhibits negative electricity. It is soluble in oils. It does not combine with charcoal, but unites to phosphorus by means of heat. Sulphur and iron have a great attraction for each other. If a bar of iron be heated to whiteness, and then touched with a roll of sulphur, the two bodies combine and drop down together in a fluid state, forming sulphuret of iron. Sulphur also unites to potash and to soda, by melting them together in a crucible : by this liver- brown substances are formed, called sulphurets of potash or of sodciy which are soluble in water.
Sulphur is a highly inflammable body, burning with a pale blue flame. Put some threads, dipped in sulphur, into a vessel floating in water. Set fire to them, and cover the whole with an inverted glass. The threads will continue to burn for some time, and the receiver will be filled with a dense white vapour. This vapour is the sulphurous acid, formed by the union of the sulphur and the oxy- gen during the combustion. It is absorbed by the water which will ascend in the receiver.
Let the whole then be left till the vessel is be- come again transparent. If the water be exam-
9
SULPHURIC ACID. Qg
ined, it will have a suftbcating odour and an acid taste.
Sulphurous acid, or the vapour of burning sul- phur, has been found very useful for destroying the infection of clothes and small uninhabited places, and for fumigating letters from contagious places. It is used in dyeing, and for whitening straw and silk.
Sulphuric Acid.
This acid is composed of sulphur and oxygen, and contains a greater proportion of oxygen than sulphurous acid.
This acid is the same with that commonly known by the name oi Oil of Vitriol. It was so called ori- ginally, because it was procured from green vitriol; now called sulphate of iron.
Common oil of vitriol has strong acid properties. It is of an oily consistence, and has usually a brown tinge, from impurities. It is inodorous, and about twice as heavy as water. It is highly corrosive, acting strongly on vegetable and animal substances. It attracts water very strongly, and cannot be entirely separated from it by any known process. When exposed to the air, it attracts the watery vapour in the atmosphere, so as to increase I'apidly in weight, which will be doubled in a month. If mixed with cold water, it suddenly becomes ex- tremely hot, even more so than boiling water; and on this account, when it is necessary to dilute it with water, this should be performed very gradually. Sulphuric acid is now made by burning sulphur mixed with nitre, in close chambers, entirely lined
F 3
70 CARBON.
with lead, on the floor of which a thin layer of water is put. The combustion of the nitre fur- nishes oxygen to the sulphur, and the sulphuric acid is condensed in the water. It is in this manner that the common oil of vitriol is made: but it then contains many impurities ; when freed from these, it is colourless.
If sulphuric acid be heated in contact with a combustible body, as charcoal or mercury, it loses part of its oxygen, and is then converted into sulphu- reous acid gas, which must be collected over mer- curv, as it is absorbable by water.
CARBON.
This elementary body is widely diffused through- out nature. Common charcoal consists of it, mixed with a small quantity of foreign matter. The purest variety of charcoal is lamp black.
Carbon exists as a constituent principle in all vegetable and animal matters, and remains fixed, after all the volatile parts have been carried off, during the process of combustion.
Charcoal is very nearly the same, from whatever it has been procured. It is always black and brittle, and exhibits the fibrous structure of the wood. It is not at all liable to change, and hence wood is some- times charred on the outside, when driven into the ground for piles, and similar uses.
The diamond, a substance so very dift'erent in appearance, has been found by experiment to be only crystallized carbon. Diamonds are found only in Asia and Brazil, and always in the alluvial soil. Diamond is the hardest body, and can only be cut
CARBON AND OXYGEN. 71
by its own powder. When found in the earth, they are crystalHzed, but are usually rough, having lost the angles of their crystals by attrition. They may be cleaved or split, and are then cut with facets for jewellery. They are of various colours. The diamond was long thought to be an incombustible body, but it is now known to be capable of being burnt ; and by its union with oxy- gen, it forms carbonic acid. But although we know that diamond is only carbon, no attempts to crys- tallize carbon, and thus to make diamonds, have succeeded. Art cannot always imitate the pro- cesses of nature, even when the materials she has used are known.
Carbon and Oxygen.
Carbon unites to oxygen in two proportions. We shall first consider the most common one :
Carbonic Acid. — If charcoal be burnt, it com- bines with the oxygen of the atmosphere, and thus forms an acid, which, however, cannot be condensed into the liquid form, but is always aerial. Carbonic acid exists in great abundance in nature, combined with mineral bodies, chiefly lime. All limestones are formed of carbonic acid in a fixed state, united to lime. Hence this gas was at first called jixed air, which name is still sometimes used.
It may be procured from limestone or marble, in the following manner : put a quantity of broken pieces of marble or chalk into a retort, and add to it some sulphuric acid, diluted with six times its weight of water: a brisk effervescence will ensuei,
F 4
7^ CARBONIC ACID.
and the carbonic acid gas will be disengaged, and maybe collected in the pneumatic apparatus. In this process the sulphuric acid severs the lime, leaving the carbonic acid free, which escapes in the gase- ous form.
Carbonic acid gas cannot support flame, as may- be seen by plunging a lighted taper into a vessel of it : it will be instantly extinguished.
It is fatal to animal life : a small animal confined in it would die in a few minutes.
Its taste is sour: and it is capable of being ab- sorbed by water. Water so impregnated has an acidulous taste, and reddens vegetable blues. Many mineral waters owe their qualities to this gas, which is contained in them, and they may be imi- tated by impregnating water with carbonic acid gas. Agitation and pressure promotes the absoi'ption ; and in this manner the artificial soda water is made.
During the process of fermentation, this gas is disengaged, and yeast is carbonic acid enveloped in a viscous substance. If a lighted candle be plunged into the upper part of a cask containing fermenting liquor, it will be extinguished, the apparently empty part of the vessel being filled with carbonic acid gas.
This gas is heavier than common air; hence, when disengaged, it occupies the lowest situation. It may be poured from one vessel into another, which makes a pretty experiment. Fill a vessel with this gas, and then, having placed a bit of lighted paper in the bottom of an empty tumbler, pour the gas into the tumbler upon the taper: the flame will be extinguished : here the gas will be invisible, but its presence is thus manifested.
CARBONIC OXIDE.- 7^
This gas is often found in the lower part of caverns, wells, mines, and other subterranean places. In mines it proves frequently fatal to the miners, who call it the choke damp. Wells, or similar places, which have been shut up for a long time, should never be entered without first putting down a lighted candle : if this is extinguished, it is not safe to go down. There are some caverns in which this gas is produced in so great a quantity, that it runs out at the opening, like a stream of water: this is particularly the case with the cele- brated Grotto del Cane. A dog is suffocated if it be held for a short time in the lower part of the cavern, but the upper part is free from this gas.
Charcoal should never be burnt in rooms that have no chimney, because the red hot charcoal unites with the oxygen of the atmosphere, and forms carbonic acid, which cannot escape. Some melancholy accidents have happened from this cause. This gas has also been called mephitic air, from its suffocating quality.
Carbonic acid combines with all the alkalies, and with the alkaline earths, lime, magnesia, barytes, and strontia. With these it forms a class of salts, called carbo7iates.
Carbon does not combine with any of the metals except iron. This combination is the carburet of iroiiy called also plumbago and black lead ; which, however, contains only five per cent, of iron. It is the substance used for making black lead pencils.
Carbonic Oiide. — This body is always gaseous. It contains only half as much oxygen as carbonic acid does. It is void of taste and smell, and fatal to animal life. It is inflammable, burning
74 CARBON AND NITROGEN.
with a blue lambent flame, but does not explode when mixed with atmospheric air. It is pro- cured by depriving carbonic acid of part of its oxygen. This is effected by exposing equal parts of chalk and filings of zinc to a gradual red heat, suftering the first product to escape, which is car- bonic acid gas. The zinc deprives the carbonic acid in the chalk of part of its oxygen.
Carbon and Nitrogen.
This combination is called cyanogen. It is a gas- eous body, having a penetrating and peculiar smell, and burning with a purple flame. It red- dens vegetable blues.
When cyanogen combines with hydrogen, it forms a triple compound, called hydrocyanic acid : this is also called Prussic acid. Prussic acid is a liquid having a very pungent odour, like that of bitter almonds. It is extremely acrid, and highly poisonous. It is called Prussic acid, because it forms one of the constituents of the well-known pigment Prussian blue, which is a combination of hydrocyanate of iron with alumine.
PHOSPHORUS.
This highly inflammable substance is not met with in nature uncombined ; but it exists combined with oxygen, forming phosphoric acid, in many animal and mineral substances.
Phosphorus is a yellowish semi-transparent mat- ter of the consistence of wax. It is luminous in
PHOSPHORUS. 75
the dark at the common temperature of the atmo- sphere.
To show this property in a striking manner, write with a stick of it upon black or purple paper, or any other smooth surface ; the writing will be luminous as if on fire. The fiery appearance dis- appears and appears again by blowing upon it. It is necessary, in making this experiment, to cut the phosphorus under water, and to put it into a quill, in order to defend the hands, lest it should take fire 5 and great care ought to be taken lest any particle should be left under the nails, or in any other place, for if this were afterwards to take fire it might occasion very serious accidents, as a burn by it is extremely severe.
Very slight friction is sufficient to inflame phos- phorus. Put a grain of it into brown paper and rub it with some hard body, and it will take fire and inflame the paper. It takes fire spontaneously, and burns rapidly in the open air at 122° Fahr., with a brilliant flame. On this account, it is alwavs kept under water ; and it should never be suffered to lie exposed to the air.
Phosphorus is obtained by decomposing the phosphoric acid by means of charcoal in a retort. The oxygen of the acid unites to the carbon, form- ing carbonic acid j and the phosphorus distils over into water. The phosphoric acid is obtained by decomposing calcined bones by sulphuric acid. Bones consist chiefly of phosphate of lime j and in this process the sulphuric acid joins to the lime, leaving the phosphoric acid free.
Phosphorus is soluble in oil in small quantity, which is thus rendered luminous. Sulphuric and nitric ether, and ardent spirit, dissolve it, though sparingly, in the cold.
70
Phosphorus and Oxygen*
Phosphorus unites with oxygen in two proper* tions, forming phosphorous acid, which contains the lowest proportion of oxygen ; and phosphoric acid, which contains the greatest proportion.
Phosphoric acid may be made by the rapid com- bustion of phosphorus in oxygen j but it is usually obtained from calcined bones, by decomposing them with sulphuric acid.
Phosphorus has the property of de-oxidizing se- veral metallic solutions, as those of gold, silver, copper, mercury, lead, tin. If a stick of phospho- rus be left in a concentrated solution of nitrate of copper, the copper wall be precipitated upon the phosphorus in a metallic state.
It also combines with lime, forming phosphu- ret of lime. When pieces of phosphuret of lime are dropt into water, flashes of fire are seen to rise out of the water, which is occasioned by the phosphuret decomposing the water, and part of the phosphorus uniting to the hydrogen gas, forming phosphuretted hydrogen gas, de- scribed before.
The phosphurets of barytes and strontia have similar properties.
J^hosphorus combines with chlorine and with io- dine j and also with sulphur and the metals. Its union with hydrogen has been already noticed as phosphuretted hydrogen gas.
BORAX.
This elementary substance is known only in the boracic acid, which consists of it united to oxygen.
FLUORINE. 77
Boracic acid is rarely found native, but is gener- ally procured from the salt called borax.
Borax is boracic acid united to soda, or a borate of soda. This is the //7zc«/ brought from Asia puri- fied. It is found at the bottom of certain lakes in Thibet, and in China. The boracic acid has been decomposed but lately, when it yielded to the ap- plication of galvanic electricity by Sir H. Davy. Borax is in the form of a powder of an olive colour. It is combustible.
Borax is much used as a flux in soldering metals, and also for such stones as cannot be brought into fusion by alkalies.
FLUORINE.
This name has been given, provisionally, to the supposed base of the fluoric acid, which is ima- gined to consist of fluorine and hydrogen.
The Jliwric acid has hitherto resisted all the en- deavours that have been made to decompose it completely ; and its real nature, therefore, con- tinues uncertain. According to the present no- menclature, it is now sometimes called hi/dro- Jluoric acid.
Fluoric acid is obtained by adding sulphuric acid to some pounded pure fluor spar, and ap- plying heat.
Fluor spar is that mineral well known by the name of Derbyshire spar, because very abundant in that county. It is employed for making vases and other ornamental works. It consists of fluoric acid and lime, or, perhaps, calcium, the metal of lime, and is hence called also fiuat of lime. The sulphuric acid, having a stronger attraction for lime
78 ALKALIES.
than fluoric acid has, expels the latter and unites itself to the lime.
It appears, that before the researches of Gay Lusac and Thenard, the pure fluoric acid had ne- ver been procured ; what had been considered as fluoric acid, being, in fact, a different acid, the siliceo-Jluorie acid. In their experiments, the leaden receiver was cooled by ice, and the fluoric acid condensed into a liquid form. In this state it is the most caustic substance known, corroding the skin instantly, and causing dangerous sores.
Fluoric acid combines with silica, and becomes with it a permanent acid gas, called the siUceo-fiu- oric acid. This was formerly called Jluoric acid gas. It has a pungent irritating odour, will not support combustion, and forms white vapours when it comes in contact with the air. It corrodes glass, and combines rapidly with water, forming the li- quid siliceo-fluoric acid. This acid, formerly called the Jiuoric, also acts on glass, and is very acid and corrosive. In the process for making it from fluor spar and sulphuric acid, a little silicious mat- ter generally existed in the spar, or glass vessels, that had been used ; and thus the siliceo-fluoric, and not the fluoric acid, had been obtained.
Fluoric acid forms Jluates with the alkalies and salifiable earths.
It also unites to borax, forming an acid called the Jluo-boric acid. This does not act on glass, and is not so corrosive as fluoric acid. It gives rise to JiuO'borates.
ALKALIES.
Alkalies are an important class of bodies. They have received this name because one of them,
POTASH. JO
soda^ was procured in great abundance from a plant called kali, by the Arabians.
Alkalies have peculiar properties. They change blue vegetable colours to green, and yellow to reddish brown. They unite to oil and fat, forming soap J thus rendering them miscible with water. They have an acrid and peculiar taste. They are caustic, or act powerfully upon animal substances. They combine with acids, forming with them a peculiar class of salts in which the properties of the acid and alkali disappear.
Until lately, only three alkalies were known, potash, soda, and ammonia. The two former were called the fixed, the latter the volatile alkali. Their number is now increased by the addition of lithia.
POTASH.
Potash had long been* known by the name of the vegetable alkali.
It is procured from the ashes of burnt vegetables in the following manner. Dried vegetables are burned in heaps ; the ashes are collected and lix- iviated with water. Thus the potash in the ashes is dissolved, while the rest of the ashes is insoluble. The solution is poured off from the sediment, and evaporated : what remains is the potash of com- merce, which is of a grayish colour, and contains some impurities: these are separated by being heated in a furnace. It is then white, and is called pearlash.
All xvood ashes have in them more or less of this alkali, and hence they are applied to the same purposes as potash, or pearlash.
so POTASH.
Potash and pearlash procured in this manner are combined with a certain proportion of carbonic acid, but not so much as to destroy completely its alkaline properties : hence it is a sub-car bonate of potash. To free the alkali from the carbonic acid, another process is necessary. Twice its weight of quicklime is added to the pearlash, and the whole mixed with water. The carbonic acid having a stronger affinity to the lime than to the alkali, quits the latter, and forms carbonate of lime, which, being insoluble, falls down, while the purer alkali is kept in solution by the water, and is afterwards separated by evaporation. Sometimes it is still farther purified, if necessary, by mixing the whole with alkohol, which dissolves the pure alkali alone. The alkoholic solution ascends to the top of the fluid, and is drawn off by decant- ation.
Potash, when thus prepared, is a solid white substance, and is called caustic potash, from its property of corroding the skin and flesh when it is applied to it : on this account it is frequently em- ployed by surgeons.
Caustic potash, when prepared by alkohol, is united to a portion of water, and is therefore a hydrate of potash. It may be obtained free from water by another process.
Potash may be made to combine with a greater proportion of carbonic acid than in the state of sub-carbonate, by causing a stream of carbonic acid gas to pass through a solution of the latter salt : when this solution is then evaporated, it af- fords crystals of bi-carbonate of potash. This salt is milder than the subcarbonate, and its crystals are not deliquescent.
POTASH. 81
Tlie fixed alkalies were, until lately, regarded as simple bodies, and one of the most brilliant disco- veries of modern chemistry has been that which showed them to be the oxides of peculiar metals.
The decomposition of the alkalies was effected by means of voltaic electricity. By acting upon a very small piece of caustic potash, the metallic base was liberated, and proved to be solid, malleable, and having a high metallic lustre resembling mercury. This new metal is called potassium. It differs considerably in its properties from all the metals previously known. It is lighter than water, and has so strong an attraction for oxygen, that it almost instantly attracts it from the atmosphere and re- turns to the state of oxide. If thrown into water, it produces a very singular phenomenon ; it decom- poses the water so rapidly that an explosion takes place, accompanied by a flame. The same effect is seen if a globule of the metal is placed upon a piece of ice. This metal can only be preserved by keeping it under naphtha, a liquid that does not contain oxygen as one of its constituents.
Potash combines with all the acids forming neu- tral salts.
Nitrate of potash, called also nitre, or saltpetre, is produced in considerable quantities naturally, particularly in Egypt. It has also been produced artificially by making beds of animal and vegetable substances, mixed with calcareous and other earths. In process of time, an efflorescence of nitrate of potash appears, and is separated by lixiviation. By the decomposition of these substances, nitrogen is disengaged, which, uniting to the oxygen of the atmosphere, forms nitric acid ; and this uniting to the alkali furnished by the vegetables and soil, pro- duces the nitre. Nitrate of potash has the property
VOL. II. G
8g SODA.
of detonating when inflamed witli charcoal or other easily inflammable bodies.
It is upon this property tlmt gunpowder is formed, which consists of five partsof nitrate of potash, one of charcoal, and one of sulphur. Chlorate of potash is formed by passing chlorine gas through a solu- tion of caustic potash. It is also called oxy-mu- riate of potash. This salt detonates violently when three parts of it mixed with one of sulphur are tri- turated in a mortar, or struck on an anvil. With phosphorus the effect is still greater. It makes a powerful gunpowder when employed as an ingre- dient.
If a small quantity of it be mixed with some sugar, and sulphuric acid be added, a sudden and vehement inflammation will be produced. These experiments require great caution.
SODA.
This has also been called the fossil or mineral alkali, because supposed peculiar to the mineral kingdom. It is obtained chiefly from the ashes of marine plants; all the fuci yield it in abundance ; when burnt, their ashes are called kelp, which con- tains a considerable proportion of this alkali. Ba~ rilla is the same, procured by burning a plant of that name in Spain. Soda is also found in large quantities in different parts of the earth, particu- larly Egypt ; and common sea-salt consists of it united to muriatic acid.
In all these cases, however, the soda is com- bined with carbonic acid. Of this there are two varieties, the carbonatey obtained by dissolving the soda of commerce and crystallizing it, and the bi-
SODA. Hfi
carhonate, obtained by passing a stream of" carbonic acid gas through a solution of the former.
Soda and potash considerably resemble each other, but the former does not deliquesce so as to liquefy, as potash does ; its crystals, however, efflo- resce or fall to powder. It is used in the manufac- ture of soap and of glass.
Soda, also, like potash, consists of a metallic base united t oxygen. The metal is called sodium. It resembles potassium in most of its properties. It unites with chlorine, forming chloride of potas- sium ; this is the common sea-salt so much used in food, and was, till lately, called muriate of soda.
Common salt exists in immense quantities in na- ture, both in the form of a rock, as rock-salt, which is dug out of the earth in a solid form, and also dissolved in the sea^ from which it is obtained by evaporation.
Common salt is decomposed by sulphuric acid. The sodium is converted into soda, by taking oxy- gen from the M^ater of the sulphuric acid, and the chlorine combines with the hydrogen of the water thus set free, and forms hydro-chloric acid gas^ which is the same with what has been called muri- atic acid gas. This gas, absorbed by water, forms muriatic acid. Hence, since muriatic acid was thus procured from sea-salt, it was supposed to exist in it, combined with soda, whence the name muriate of soda.
Soda unites with all the acids, forming neutral salts, the most remarkable of which are the fol- lowing : —
Sulphate ofsoda, called formerly Glauber's salts, is formed abundantly in the process for procuring the muriatic acid from common salt ; the sulphuric acid which is employed uniting to the soda.
G 2
84 LITHIA.
Borate ofsoda^ or borax, and
P/fOsphaie of soda, useful as a test.
The fixed alkalies readily combine with oils, and tluis form soap. Soap is soluble in water, and owes its detergent quality to the alkali contained in it. Alkali by itself would be too powerful, and would be apt to destroy the linen and other sub- stances to be cleaned.
Soap when in solution is decomposed by acids, which unite with the alkali ; hence if an acid is contained in water, the soap curdles. Neutral salts formed by acids with bases of the earths pro- duce the same effect. Hard waters are such as have earthy salts, and are unfit for washing ; soft water is that which is quite free from salts.
Hard soap is made from soda rendered caustic by lime, and olive-oil, or tallow. Soft soap is com- posed of potash and whale-oil.
LITHIA.
This alkali was lately discovered by M. Arfvred- son, a Swedish chemist. It is found to be a con- stituent of certain stones, and has been met with in the petalite, spodumen, and lepidolite. Jt is of the class of fixed alkalies ; is soluble in water, has an acrid taste, and changes vegetable blues to green. It forms neutral salts with the acids.
Lithia, like the other fixed alkalies, has been found by analysis to be the oxide of a peculiar metal, which has been called Lithium. Its decom- position has been effected by the voltaic pile, but the quantity of metal obtained has been extremely small.
85
AMMONIA.
This substance is known also by the name of the volatile alkali. It is composed of nitrogen and hydrogen. In its purest form it is in the gaseous state. It is then called ammoniacal gas.
Ammoniacal gas is procured by adding dry quicklime to muriate of ammonia, and exposing them in a retort to the heat of a lamp. The mu- riatic acid, having a stronger attraction for the lime than it has for the ammonia, leaves the latter, which is disengaged, in the state of gas. A pneumatic apparatus is necessary for this purpose, as this gas is rapidly absorbed by water. Ammoniacal gas has a strong pungent smell, and suffocates animals immersed in it. It changes vegetable blues to green. If water be introduced into the apparatus, in contact with the gas, it absorbs it entirely, and acquires its peculiar smell : this is a solution of ammonia in water, and is called liquid ammonia.
Ammonia exists as a constituent in animal bodies ; and it is obtained from bones, horns, &c.
It is a valuable material in manufactiu'es and medicine. Ammonia forms with the acids several valuable compounds.
With carbonic acid it forms carbonate and hi- carbonate of ammonia. The carbonate may be obtained by mixing ammoniacal gas with carbonic acid gas over mercury. The two gases inunedi- ately combine and form a solid white body, which still retains some of the pungent smell of the am- monia. This is the common smelBig salts. The bi-carbonate is procured by causing a current of carbonic acid gas to pass througli liquid ammonia. It has no smell.
G S
86 EARTHS.
Muriate of aynmonia wxi called sal ammoniac from its having been originally brought from the neighbourhood of the Temple of Jupiter Ammon. It is now abundantly prepared in this country by saturating carbonate of ammonia with sulphuric acid, which forms sulphate of ammonia : by de- composing this salt by muriate of soda, muriate of ammonia and sulphate of soda are obtained. Sal ammoniac is employed in many processes.
EARTHS.
At the first view it would seem, from the vast variety of soils on the surface of the globe, and the number of rocks and stony substances, that the different earths of which they are composed were innumerable : nevertheless, their number is very limited, and, by the mixture of these, the greatest part of mineral bodies is composed.
The earths were formerly considered as ele- mentary substances, but late discoveries have shown that most of them are, like the alkalies, me- tallic oxides. It is found, however, more conve- nient still to consider them as a separate class.
The earths are of two kinds :
1. Those which have some of the properties of alkalies and which are called alkaline earths.
2. Earths simply so called.
The alkaline earths are, lime, magnesia, barytes, and strontia. They unite with acids forming com- pound salts as alkalies do : like tliem they change vegetable blues to green ; they have a considerable degree of causticity and taste, and are soluble in water.
LIME. 87
The rest of the earths are insipid, and are scarce- ly at all soluble in water, and have no action on
vegetable colours.
I.IME.
Lime is one of the most abundant substances in nature. It is the chief constituent in vast moun- tains and rocks, and is very generally distributed, mixed with other earths. Chalk, marble, calcare- ous spar, and all those rocks called lim.e-stones, con- sist of it.
In these substances, however, the lime is not pure or uncombined. It exists in them united to carbonic acid, constituting carbonate of lime.
To obtain pure lime, these stones are exposed to a white heat, by which the carbonic acid is driven off in the gaseous state. This is called the huriiing of lime. The stone so treated is then called quicIiHme; or, in chemical language, properly lime.
Quicklime, or pure lime, is white ; has a hot acrid taste, and is caustic, or corrodes the skin. It changes vegetable blues to green.
Until the discovery of the bases of the alkalies by Sir Humphry Davy, lime, as well as all the other earths, was considered as an elementary substance ; but it has been ascertained to be the oxide of a metal to which the name of calcium has been given. From the extreme difficulty, however, in reducing lime to this state, the properties of calcium are but little known. It is white and solid, resembling silver, and soon returns to the state of oxide or lime by attracting oxygen from the air.
When water is thrown on quicklime just burnt, it swells, bursts, and falls to powder; giving out, at
G 4
88 LIME.
the same time, much steam and heat. This is called the slaking of lime. In this process, the water miites to the hme, and becomes soUd ; for slaked lime is quite dry. It is, therefore, called a hydrate of lime.
Lime is soluble in water : the solution has an acrid taste, and is called lime-watei\ When lime- water is exposed to the air, a stony film forms upon the surface, owing to the lime attracting carbonic acid, and returning to the state of carbonate, which is insoluble in water. This film breaks, falls down, and is succeeded by others in succession. Fresh quicklime has a strong tendency to attract mois- ture from the air, and also carbonic acid, so that it must be kept in closely-stopped vessels.
Quicklime is used for making mortar for build- ing, by mixing it with sand. This, by solidifying the water and attracting carbonic acid, becomes a very hard substance like stone. The lime should be newly burnt, and the sand silicious and free from impurities. It is also extremely valuable as a ma- nure when put upon the land.
Carbonate of lime is not caustic, nor soluble in water. It is decomposed by the stronger acids. Put chalk or marble into a vessel, and pour upon it diluted sulphuric or muriatic acid ; an efferves- cence will ensue, which is owing to the escape of the carbonic acid. Hence these acids are em- ployed to distinguish lime-stones.
Lime combines with phosphorus, forming j)hos- phuret of lime, to be afterwards described. With sulphur it forms siilphuret of lime.
It also combines with all the acids, forming a great number of neutral salts.
Sulphate of lime, called also gypsum, exists largely in a natural state. When burnt, it forms the sub.
MAGNESIA. BAKYTES. 89
stance called plaster of Paris, so much employed in making casts of statues, and in plastering rooms.
Filiate of lime, or lime united to the fluoric acid, is the substance so well known by the name of Der- byshire spar, and which is much used for vases and other ornaments.
Nitrate of lime is a very soluble salt ; its taste is acrid and bitter. It is often found efflorescing on old plaster walls.
MAGNESIA.
This earth, when pure, is white, nearly destitute of taste and has no smell. It is insoluble in water, but changes vegetable blues to green, and unites to the acids. It is conjectured to be composed of a me- tallic base, magnesiumy united to oxygen ; but the metal has not yet been distinctly obtained.
Native magnesia is a rare substance, but it en- ters as a constituent in many rocks, as serpentine, steatite, &c.
Carbonate of magnesia is extensively employed as a medicine. When a red heat is applied to it it loses its carbonic acid, and becomes calcined magnesia.
Sulphate of 7nagnesia is known by the name of Epsom salt, because formerly procured from the springs of Epsom, in Surrey.
BARYTES.
This earth was formerly called terra ponderosa, from its great specific gravity. It has strong alka- line properties, a caustic taste, and changes vege- table blues to green.
90 STRONTIA. SILICA.
It slakes in the air like lime, is soluble in water, and also in alkohol, the flame of which it causes to assume a yellow colour. It is a deadly poison. It is also found to consist of oxygen and a metallic base called barium.
Carbonate qfbarytes is found as a mineral, but it is not abundant.
Sulphate of barytes is found native more fre- quently. When calcined, it forms the Bolognian 2)hosphorus.
Barytes is used as a white paint under the name of permanent whiter not being liable to change its colour.
STRONTIA.
The name of this earth is derived from Strontian, in Argyllshire, in Scotland, where it was first dis- covered by Dr. Hope.
It is soluble in water, and changes vegetable blues to green.
It is also considered to be the oxide of a metal called str^ontium.
Strontia is not very abundant, and is always in nature found combined with the carbonic or sul- phuric acids.
The other salts of strontia are but little known. All the salts of Strontia have the property of tinge- ing the flame of alkohol red.
SILICA.
This earth, which forms a large portion of the surface of the earth, exists nearly pure in flint and rock-crystal : hence it has been called the earth of flints.
It may be obtained pure as follows : calcine
ALUMINA. 91
gun-flints tiil they become brittle, then pulverize them. Mix this powder with three or four times its weight of carbonate of potash, and fuse the mixture in a crucible, by a strong red heat. We shall thus obtain a compound of alkali and siliceous earth : dissolve it in water, and add to it diluted muriatic or sulphuric acid ; a precipitation will take place, which, when well washed, is pure silex.
Siliceous earth, when pure, is white and tasteless. It is infusible by itself, and insoluble in water. It has a harsh feel, and does not form a cohesive mass with water.
No acid can act upon it, except the hydro- fluoric, which dissolves it. When mixed with an equal weight of carbonate of potash, and fused in a strong furnace, it forms glass. With a larger pro- portion of alkali it forms a substance soluble in water, which has been called silicated alkali. The solution of this was called liquor ofjiints. The silex is precipitated from it in the state of a gelatinous hydrate by acids.
It is supposed that silica consists of oxygen united to a certain base, which has been assumed to be a metallic substance, and w^liich has been called Silicium : but its real nature has not been ascertained. It is imagined, however, that silicium forms an alloy with iron, and that the properties of some sorts of iron are owing to the addition of this substance.
ALUMINA.
This earth forms a part of all clays, and hence has been called argillaceous earth. It exists also in nu- merous rocks, particularly slate, and even consti- tutes some of the hardest gems and stones, as the sapphire, ruby, and corundum.
92 CLAY. — YTTRIA.
It rarely occurs in a pure unmixed state. But it has been found native, in small masses, at New- haven, in Sussex, and also in Hall, in Saxony.
Clay consists of this earth, joined to silex. For- celain clay proceeds from the decomposition of felspar ; it consists of silica, alumina, and some- times a little lime and potash. Pipe-day^ and 'potters' 'day are pure clays, but of variable com- position.
Alumina has no smell nor taste 5 is insoluble in water, but forms with it a ductile paste, and shrinks much when exposed to heat. It is dissolved by the liquid fixed alkalies, and unites chemically with barytes, strontia, lime, and magnesia. It is dis- solved by most of the acids.
The salt called alum^ which gives its name to this earth, is a sulphate of alumina and potash. Sulphate of alumina alone will not crystallize ; but when sulphate of potash is added, octahedral crystals of alum are produced. When alum is exposed to heat, it loses part of the acid and water of crystal- lization, becomes light and spongy, and is called humt alum. Alum is extensively employed in the arts of dyeing and calico printing, in consequence of the attraction which alumina has for colouring matter. Alumina also forms the basis upon which are precipitated certain colours used as pigments.
YTTRIA.
This rare earth, so called from Ytterby, in Swe- den, where it was discovered, is found only in a stone called gadolinite, so named from Professor Gadolin. It is insipid, and insoluble in water, but dissolves in carbonate of ammonia. It forms salts
Vd
GLUCINA. — ■ZIRCONIA.— ^THORINA. 9^
which have a sweetish taste. Its specific gravity is greater than that of any other earth. The base of yttria has been supposed to be a metaUic substance, which would receive the name of yttrium ; but it lias never been exhibited in a separate state. Yttria contains oxygen, and hence been inferred to be a metallic oxide.
GLUCINA.
Ghicina, or Glucinej is an earth which has been procured only from the beryl, the emerald, and the euclase.
It derives its name from its forming salts which have a sweetish taste. It has no taste nor smell, is infusible by heat, but dissolves in the acids, and pure alkalies. It is insoluble in water. It is also supposed to be a metallic oxide.
ZIRCONIA.
Zirconia is a very rare earth, found as yet only in the zircon or jargon of Ceylon, and the hyacinth. It is void of taste or smell ; is insoluble in water and pure alkalies ; but is soluble in alkaline car- bonates. Its base is supposed to be metallic.
THORINA.
This is another very rare earth, discovered by Berzelius, who extracted it from a species of gado- linite. It absorbs carbonic acid, and dissolves readily in acids. It is not soluble by the pure alkalies, but slightly so by the alkaline carbonates. It is supposed to be the oxide of a metal.
94,
METALS.
We come now to treat of the last division of the metaUic substances ; those which, remaining in the air in the metaUic state, have received the name particularly of metals.
Those metals whose combinations with oxygen form alkalies, as potassium, sodium, and lithium, as also those whose oxides form earths, as calcium, magnesium, barium, strontium, silicium, alumium, yttrium, glucinum, zirconium, and thorinum, have been already mentioned incidentally, in speaking of the alkalies and earths to which they give rise. But we shall now enumerate the general properties of this important class of bodies, including the above mentioned.
The metals are distinguished from all other sub- stances by certain properties, particularly a pecu- liar lustre ; and most of them have great weight, or specific gravity.
Several of them have been known to part of the world in ^ery ancient times, while some savages in the present day are totally unacquainted with their use : but a considerable number of the metallic sub- stances have been discovered only lately. The metals are so important in many mechanic arts, that mankind could never have attained their pre- sent state of civilisation without them.
Metals are, in general, solid bodies at the usual temperature : one only, mercury, is fluid.
They are opaque in the mass in its usual state ; but gold, when beat into very thin leaves, transmits a faint greenish light, when held between the eye and the direct rays of the sun.
METALS. Q5
Tlie lustre by which they are distinguished, called the metallic lustre, is not easily described, but may be exemplified in that of silver, steel, lead, tin, SiC, as distinguished from that of glass, diamond, &c. Mica has a lustre which approaches that called the metallic, but it loses this on being scratched, while the metals do not ; on the con- trary, they are more brilliant when fresh cut. This property of the metals renders them highly useful for ornamental purposes, and for reflecting light, as in mirrors.
Metals are the best conductors of heat, and also of electricity.
Some of the metals are capable of being extended under the blows of a hammer, which property is called malleahilityj and is peculiar to metals. Others, again, are brittle, on which account they were formerly called sejui-metals. The malleable metals are, gold, platina, silver, palladium, potas- sium, sodium, mercury in its frozen state, copper, iron, lead, tin, zinc, and nickel. These differ much in their degrees of malleability. Gold may be beat into the thinnest leaves, and zinc is very little malleable, except when heated. The malle- able metals are also ductile, or may be drawn out into wire. Gold and platina may be drawn into the finest wire.
One of the metals, iron, is capable of being made very elastic, which renders it fit for making springs.
Most of the metals are very fusible, or capable of being rendered fluid by the application of heat; on this account they may be cast into moulds, and formed into various utensils: some of the metals are volatile at a high degree of heat.
None of them are very hard naturally ; but some
96 METALS.
of them may be hardened by art: thus the moderns make cutting instruments of iron and steel, and the ancients made them of a combination of cop- per and tin.
All the metals are capable of combining with oxygen, and thus forming oxides ; but they differ very much in the readiness with which they com- bine with it, which occasions their division into several classes.
The oxides of metals have none of the metallic brilliancy, and no malleability : their appearance and nature are totally different from that of the metals themselves.
The oxides of some metals, as potassium and so- dium, are alcaline ; others are acid, constituting the metallic acids : the rest have neither acid nor alca- line properties, but are, as well as others, capable of being dissolved by the acids, thus forming salts.
Some of the metals attract oxygen so strongly, tliat they become oxidized almost immediately in the open air, and even take oxygen from all its combinations, so that they are, with great difficulty, preserved in the metallic state ; of this nature are metals that produce the alkalies and earths, which can only be kept in pure bitumen called naphtha, which has no oxygen in its composition.
Some of the metals do not experience any change on being kept in fusion by a strong heat with an access of air ; but others are by this means converted into oxides. The first have been called perfect metals, and comprehend gold, platina, sil- ver, and palladium. The rest differ very much in the degree of heat necessary to oxidize them. Arsenic, manganese, and the bases of the earths and alkalies become oxides at the usual temperature of the atmosphere, even when perfectly dry. Lead
METALS. 97
and copper are oxidized slowly by moist air. Iron, zinc, copper, tin, &e., require to be heated to red- ness. Although the perfect metals cannot be oxidized by any degree of ordinary heat, they may by the effect of electricity and galvanism. All the metals, that are converted into oxides by atmo- spheric air, undergo this change still more rapidly in oxygen gas, as was shown in the burning of iron wire in oxygen.
Metals are also converted into oxides by the ac- tion of acids, but in different manners. Some acids which contain oxygen loosely combined part with it to the metal ; while others, as the sulphuric and muriatic acids, do not act upon iron or zinc, except they are diluted with water, and then it is the wa- ter, and not the acid, which supplies the oxygen.
Metals cannot be made to combine with all pro- portions of oxygen, but are susceptible only of cer- tain degrees or stages of oxidation. Thus iron has only two oxides j the black oa:ide composed of 29.5 parts of oxygen, and 100 parts metal ; and the red oxide of 43.5 parts of oxygen, and 100 parts of metal : and there are no intermediate degrees of oxidation, nor will iron combine with a larger or smaller proportion of oxygen. Metals differ in the number of oxides which they form : thus some have two, some three, and others four oxides : and, according to the law of the atomic theory, the different oxides of the same metal contain oxy- gen in proportions that are simple multiples of each other.
The different oxides of the same metals have dif- ferent colours, which render them very valuable as pigments. They have also distinct chemical pro- perties, and combine, in different proportions, with the acids, forming distinct salts.
VOL. II. II
98 PLATINA.
All the metals are considered as simple bodies, none having been decomposed or resolved into other principles ; also, at one time, they were sup- posed to be formed of a peculiar basis and an ima- ginary inflammable principle called plilogisto7i. This theory was very favourable to the idea of forming metals, and transmuting or changing them into each other. The existence of phlogiston is no longer believed in, and the science of alchemy is only remembered as affording an instance of the dangers of false theories, and of the great credulity of persons in many respects well informed.
The oxide of a metal was formerly called a cal^r^ and its conversion was supposed to be owing to the loss of the phlogiston ; but it was observed that the metal gained instead of losing weight by this change ; in fact, it acquires just the weight of the oxygen it combines with. When the oxides of me- tals are made to part with their oxygen, hey are reduced to the metallic state, and upon this depends the art of reducing metals from their ores.
PLATINA.
This metal was unknown in Europe before 1748, and is still chiefly found in South America : it has been also found in Estremedura, in Old Spain.
In colour it is nearly as white as silver. It is very difficult of fusion, and can only be melted by the assistance of oxygen gas or by galvanic elec- tricity. From its refractory quality, it is employed for crucibles and other chemical utensils exposed to heat, for which it is admirably adapted.
It is also extremely ductile and malleable, and may be drawn into very thin wire, and hammered into thin plates.
GOLD. 99
Platina does not tarnish on exposure to the at- mosphere, and takes an excellent polish, on which account it is used in making specula for telescopes. It is also capable of being welded, a property only possessed by it and iron. It is the heaviest of the metals ; its specific gravity being nearly 22.
Platina is readily dissolved by the nitro-muri- atic acid and by chlorine, but is not acted upon by any other acid. It also combines with sulphur and phosphorus.
Platina is brought to Europe in small flattened grains, which, however, are not pure platina, but contain a mixture also of nine other metals. Four metals, osmium^ iridhmiy rhodhwiy and palladium, were unknown till they were discovered in these gi'ains.
GOLD.
Gold is found in nature in a metallic state. It is generally met with in grains called gold-dust, mixed with the sands of rivers, either b^ng carried away by them from the rocks which contain it, or having been deposited in ancient alluvium. It is chiefly found in Africa, also in Brazil and Peru. There are mines of it also in Hungary ; and it is met with in quantities too small to be worth work- ing, in the sands of many rivers of Europe.
Lately some was found in the county of Wick- low, in Ireland ; one grain weighed 22 ounces, and considerable expectations were formed ; but, not- withstanding, the works were abandoned as unpro- ductive.
Gold is the heaviest of the metals except platina. It is of a rich yellow colour, and not ^ ery hard when pure.
II 2
100 ' GOLD.
It melts at a bright red heat, but cannot be oxi- dated by any furnace, though it may by electricity and galvanism. It does not oxidate in the air ; hence it is so useful in gilding, its beautiful lustre remaining untarnished.
It is the most ductile and malleable of the me- tals, and may be drawn into the finest wire for gold- lace and other purposes, and may also be hammered into leaves of extreme thinness for gilding.
Gold is not acted on by any acid except the nitro-muriatic acid and chlorine. From this pro- perty the former was named aqua-regia^ gold being called by the alchemists the king of the metals.
The solution of gold, called muriate of gold, yields by evaporation crystals of a beautiful yellow co- lour, which, when dissolved in water and precipi- tated by a solution of tin, afford the beautiful pow- der called the purple precipitate qfcassiuSy much used in enamelling. This consists of oxide of gold mixed with oxide of tin.
If any substance, as a piece of ribband, be dipped into the muriate of gold, and then exposed to a stream of hydrogen gas, the gold will be revived, and the substance covered with it. Some com- bustible bodies attract the oxygen from the solu- tion of gold, and cause it re-appear in its metallic state. Thus, if a piece of charcoal be put into a glass-jar containing a diluted solution of gold, and exposed to the direct rays of the sun, it will soon appear gilt. When ammonia is added to a solution of gold, a yellow precipitate is formed, called ^ful- minating gold, because it has the property of ex- ploding when exposed to heat.
If to a solution of muriate of gold, sulphuric ether be added, the gold will combine with the ether,
15
leaving the acid, and wilt float on the surface of the fluid. If pohshed steel be dipped into this, it will be covered with a coating of metallic gold. This process is employed for gilding lancets, and other surgical instruments, to defend them from rust.
Gold easily alloys with mercury, which is, there- fore, much employed for extracting it from the substances with which it is mixed in its natural state. The mercury, being volatile, is driven off by heat, and the gold remains free.
Gold in its purest state is too soft to be used as coin ; it is, therefore, alloyed with n of copper. Jeweller's gold generally contains considerably more.
Gold seems to have been one of the earliest known of the metals. The ancients were lavish in its use, and it is still frequently used in orna- ments among savage tribes.
SILVER.
Silver is often found native, or in the metallic state, but it is most usually combined with other metals, or sulphur. In its native state it fre- quently assumes an arborescent form. The richest silver mines are in Mexico and Peru ; but others exist in many countries. Lead ore very frequently contains a quantity of silver, and sometimes it is worth extracting.
Silver is of a brilliant white colour. It is very ductile and malleable ; may be drawn into fine wire, and beaten into thin leaves ; but it is inferior to gold in these qualities.
Silver fuses when heated red hot, and may be cast into moulds, but is not thus converted into oxide
H 3
lOi . SILVER.
by any continuance of heat: it is oxidized by common and galvanic electricity.
It is not oxidized by the air ; but it is tarnished by exposure, because the sulphurous vapours form with the metal a sulphuret of silver.
Oxide of silver is of a dark olive colour, and is obtained by precipitating it from the nitrate of silver by lime-water, this metal being soluble in the nitric acid.
Nitric acid can dissolve more than half its weight of silver, the solution depositing crystals. When these are fused by a gentle heat, they may be poured into moulds, and form the substance called luna7' caustic^ used in surgery.
Nitrate of silver is used by chemists as a test for muriatic acid; for if it be dropped into any liquid containing muriatic acid, a white precipi- tate will appear, owing to the superior affinity of silver to muriatic acid, and to the insolubility of muriate of silver. Nitrate of silver is very caustic, staining animal and vegetable substances of a black colour, and hence it is employed as a ]ier- 7na7ient marking ink for linen, and also for staining hair ; though for this last purpose it should be used with great caution, and much diluted.
If a few drops of the nitrate of silver be put upon a piece of glass, and a copper wire be placed in it, a beautiful metallic precipitation of the silver will appear in an arborescent form.
When silver is precipitated from its solution in nitric acid by ammonia, it forms fulminating silver, M'hich is a dangerous preparation ; for it explodes by the slight contact of a body.
When mercury is added to the nitric solution of silver, a precipitation of metallic silver is Ibrmed
MERCURY. 103
resembling in appearance a vegetation, and called arbo7' Diance.
Silver is not soluble in the hydro-chloric acid (muriatic acid), yet, when this acid is added to a solution of nitrate of silver, it unites to the oxide, and a white curdy precipitate falls down, which is the muriate of silver^ or, in conformity with the new nomenclature, tlie chloride of silver. If this precipitate be fused by a gentle heat, a semi-trans- parent mass is formed, called formerly lima cornea^ or horn silvery the fused muriate of silver*
Silver is also dissolved by the sulphuric acid, and the sulphate of silver is used as a chemical test. Silver also unites to sulphur and phosphorus.
Silver, when employed for coin is alloyed with copper to increase its hardness. Our coin con- tains thirty-seven parts silver and three parts copper.
MERCURY.
This metal, called also quicksilver^ is always fluid when in the usual temperature of the atmosphere ; but when exposed to an intense degree of cold, it is frozen into a solid mass, and is then malleable. The temperature necessary for this purpose is 39*^. The cold is sometimes so great within the polar circle as to freeze the mercury in the thermometer ; but in this country that can only be effected by exposing it to a freezing mixture.
Mercury also boils at 655°, and then evaporates, and may be distilled from one vessel to another.
It is sometimes found in nature in a pure state, but usually it is united to sulphur, with which it
H 4
104 IRON.
forms the ore called finnabar. The greatest quan- tity of it is found in Spain and South America.
When acted on by heat and air for a long time, it absorbs oxygen, and is converted into a red oxide called formerly precipitate per se : and when the heat is increased, the oxygen is given out, and the mercury re-assumes its metallic appearance. When it is agitated long in air, it is converted into the black occidcy which contains a smaller propor- tion of oxygen than the red oxide. It is the black' oxide which is employed in mercurial ointment. Mercury is acted on by the acids, forming salts of mercury. It also unites to chlorine (oxymuriatic acid,) in two proportions, forming calomel and cor- rosive sublimate.
Mercury when triturated with sulphur, com- bines readily into a black compound called ethiops mineral ; when united to a larger proportion of sulphur, it forms the beautiful pigment called cinnabar.
Mercury combines with several of the metals, forming soft alloys called amalgams. The amal- gam with tin is used for mirrors : that with zinc is employed in electrical machines.
IRON.
ISIo metal is so universally diffused throughout nature as iron. It is never found in the earth in the metallic state, but is always procured from ores.
Iron is of a bluish-grey colour. It is very duc- tile, for it may be drawn into wire as fine as human hair. It is also very malleable, and pos-
IRON. 105
sesses the property of being welded; that is, of having two separate pieces united together by hammering when red hot. It is one of the most infusible of the metals, but may by intense heat be melted and run into moulds. It is in its pure state among the hardest of the metals, but may be made to exceed all the rest in hardness when converted into steel.
It possesses the magnetic property, the load' stone itself being an ore of iron.
Exposed to the action of the air and moisture, iron soon rusts or OTidates. It then attracts the oxygen and carbonic acid, and is changed into a reddish brown substance, which is a mixture of oxide of iron and carbonate of iron.
Iron unites to oxygen in two proportions. The protoxide of iron consists of one hundred parts of iron, and twenty-nine parts oxygen ; it is of a black colour ; hence it is called the black oxide of irony formerly martial ethiops. It is formed when iron is heated red hot ; scales form on the outside, which fly off when hammered. It is magnetic.
The peroxide is red, and consists of one hundred parts iron, and forty-three oxygen ; it is called the red oxide of iron. The red oxide is formed by keeping iron filings red hot in an open vessel, and agitating them constantly till they are converted into a dark red powder, formerly called saffron of Mars.
Iron is acted on by all the acids, and various salts of iron are formed : the most remarkable are the following : —
Sulphate of irony formerly called copperas or green vitriol.
Nitrate of iroUy and acetite of irdiiy used in dying.
106 IRON.
FerrO'prussiale qfirorij called prussian blue, used as a pigment.
Iron also combines with sulphur, phosphorus, carbon, chlorine, and iodine.
Sulphuret of iron, composed of sulphur and iron, is called also pyrites. Iron with carbon forms plum- hago, commonly called blach-lead, used for making pencils. Steel is another compound of iron with carbon.
The ores of iron consist either of the black ox- ide, which is called the magnetic iron oi^e, the red oxide or the i^ed iro7i ot^e, carbonate of iron, and clay ironstone.
The iron is separated from these ores by smelting in furnaces, where it is made to flow out into va- rious moulds made in a kind of loam. The first pro- duct is called cast iro7i. It contains some carbon and oxygen ; and, it is thought, also silicium, besides casual impurities. Of this, cannon, pipes, grates, and other articles of cast iron are made. It is of two kinds : "white cast-iron is very brittle ; grey cast iron is less brittle, though not malleable, but may be bored and turned in the lathe.
To render iron malleable it must be freed from those substances with which it is combined in the crude state. To effect this, it is kept in fusion in a furnace exposed to air and flame, and well stired. The oxygen combines with the carbon, and escapes in the form of carbonic acid gas ; and the earthy matter is vitrified, and rises to the surface as slag. It is then subjected to the action of large hammers and rollers, by which the remainder of the impuri- ties is forced out. It then constitutes bar iron, also called 'wrought iron, fit for manufacturing.
AVr.ought iron is of a fibrous structure, and is the metal in a pure slate. It is now extremely malle-
IRON. 107
able, soft, and easily filed, and also capable of being forged and welded. There are several va- rieties of iron in this state, arising from the ores from which they were procured, the process of smelting, or the intermixture of foreign substances.
One variety is called hot sJiort iron ; it is ex- tremely ductile when cold, and on this account is employed for making wire ; but when heated it is extremely brittle : it is also fusible. Cold short iron, on the contrary, is highly ductile when hot, but brittle when cold. The causes of these qualities are not precisely known, but it is said that the first is iron combined with arsenic, and that the latter contains phosphoric acid.
Iron is capable of being reduced to a third state, which is that of steel. It is converted into steel, by exposing it to heat in contact with carbonaceous substances, which unite themselves with it. Steel is, therefore, iron united to carbon, and is made by three processes.
Natural steel is made by keeping cast iron in a state of fusion in a furnace, its surface being all the while covered deep with scoriee ; part of the carbonic acid gas escapes, while another part com- bines with the iron. This steel is inferior to the other kinds.
Steel of cementatmi is made by placing bars of iron in charcoal powder, and exposing them to a strong heat in a furnace for six or eight days. The iron and the carbon thus combined constitute what is here called blistered steel. When this is rendered more malleable by the operation of the hammer, it is called sheer steel.
Cast steel is made by fusing bhstered steel with pounded glass and charcoal powder, in a close cru- cible. It is also made merely by fusing iron with
108 IRON.
carbonate of lime. This is the most useful of all the kinds of steel, and employed for razors, surgeons*" instruments, and similar purposes ; its grain is the most compact, and it takes the highest polish.
It is the particular property of steel to become extremely hard, if it be heated red hot, and then suddenly plunged into cold water ; but different instruments made of steel require to be of different degrees of hardness ; and they are, therefore, sub- jected to a process called tempering ^ which is heat- ing them again to a certain point after having been hardened. The tempering of steel, for some pur- poses, is a delicate process.
A polished bit of steel, when heated with access of air, acquires very beautiful colours. It first be- comes of a pale yellow, then of a deeper yellow, next reddish, then deep blue, and at last bright blue. At this period it becomes red hot, and the colours disappear: at the same time the metallic scales, or the black imperfect oxide of iron which is formed, incrusts its surface. All these different shades of colour indicate the different tempers the steel has acquired by the increase of heat. Artists have availed themselves of this property, to give to surgical and other instruments those degrees of temper which their various uses require. Iron may be alloyed with most of the metals, but these alloys are not much used.
Wootz is the name given to a kind of steel made in the East Indies, which is of a very superior quality for cutting-instruments.
109
COPPER.
Copper is sometimes found native, but in very small quantities. It is generally met with in the state of oxide, or united to sulphur, or to acids. In Cornwall there are very rich mines of copper.
Pure copper is of a red colour, very tenacious, ductile, and malleable. It melts at 27 of Wedge- wood's pyrometer, and burns with a green flame.
It is not oxided by water. When exposed to a red heat, it becomes covered with a crust of oxide of a blackish colour, this is the peroa:ide of copper. The fir»t, or protoxide^ is of a red colour when found native,but when formed artificially is orange.
The oxides of copper are reduced to the metal- lic state by heating with charcoal or oils.
The nitric acid disolves copper with efferves- cence, and the solution has a blue colour. The acid first oxidates the metal, a large quantity of nitric oxide (nitrous gas), is disengaged, and the oxide dissolves ; this forms the nitrate of copper.
The sulphuric acid does not dissolve copper un- less when concentrated, and in a boiling state. Fine blue crystals, which are the sulphate of copper, are the result. This is what is commonly called blue vitriol. This salt is decomposed by iron ; for if a piece of iron be immersed in a solution of sul- phate of copper, the copper will be precipitated upon the iron. This process is often employed for procuring the copper from the water ir copper mines, which has in it a large portion of sulphate of copper.
The muriatic acid does not act upon copper ex- cept in a state of ebullition, and then the muriate
110 COPPER.
of copper is formed, which is of a green colour, and of an astringent taste. A solution of it is used as a sympathetic ink ; for letters written with it will become yellow by warming, and will disappear again when cool.
The acetous acid in a sufficient degree of con- centration dissolves copper, but when not concen- trated, as in vinegar, it acts upon it very slowly, and forms common verdigris, which is an impure acetate of copper. This being dissolved in distilled vinegar, and subjected to evaporation, crystals are produced which constitute what is called distilled verdigris.
Copper is employed in making kitchen utensils ; but as these vessels are liable to be corroded by the acids and fatty substances used in culinary preparations, they often become dangerous, as all the salts of copper are poisonous. Culinary utensils of copper should always be well tinned, but those of iron tinned are safer, as iron has no poisonous quality. The alloys of copper with other metals are very useful.
Tombac is formed of copper, arsenic, and tin.
Prince's metal, or Pinchbeck, is made of copper and zinc.
Brass is also formed of another proportion of copper and zinc.
Bronze is made of copper and tin.
Bell-metal is also of copper and tin, but with more tin than the latter alloy.
A solder for silver is made of copper and silver.
Ill
TIN.
Tin is a metal of a colour approaching to that of silver, but somewhat duller. It is extremely malle- able. When hammered into leaves it constitutes tin-foil. It is not, however, very ductile. It is nearly as soft as lead, and may be easily bent, and then emits a crackling noise, which is peculiar to it.
Tin fuses more easily than any other metal : when it has been kept some time in a state of fiision, with access of air, its surface becomes wrinkled and covered with a grey pellicle, which is the Jirstj or grey oxide of tin. This oxide when mixed with melted glass forms white enamel.
The grey oxide, when exposed to a greater degree of heat, takes fire, acquires more oxygen, and becomes of a pure white ; the white oaide of tin.
Tin is not oxidized in the air at the common temperature ; on account of which property, it is used for covering iron plates, to prevent tlieir rusting.
Tin dissolves in the muriatic acid, forming muri- ate of tin, much used by dyers.
With nitric acid it forms nitrate of tin.
Tin united with sulphur forms the aurum mus- turn. Alloyed with lead, it forms plumber's solder.
The best pewter is composed of tin alloyed with antimony, copper, and bismuth.
Tin is not found native, and its ores are not much distributed. The richest mines are in Cornwall.
LEAD.
This metal is never found in a native state. The ore from which it is chiefly procured is galena^ which is lead united to sulphur, or a sulplntrel of lead.
112 ' LEAD.
Pure lead is of a greyish colour. When fresh cut it is bright, but it soon tarnishes in the air. It stains the fingers or paper when rubbed on them. It is easily cut with the knife; has little or no elas- ticity, and is very malleable, but not very ductile. Water does not act upon lead. It easily fuses ; and exposed to the air in a state of fusion, its surface becomes covered with a grey pellicle: if this be removed another succeeds, and in this manner the whole may be converted into a powdery substance. This pellicle is composed of oxide of lead mixed with a portion of metallic lead. If it be subjected to a strong heat, it is changed into a yellow powder, known by the name of massicot ; which is the Jirst, or yellow oxide of lead : it is used as a pigment.
If massicot be exposed to the flame of a furnace for some time, and kept stirred, it is converted into a beautiful pigment, called minium^ or red lead. This has been called the red oxide of lead ; but it is a mixture of the yellow oxide above mentioned, and another, the brown oxide of lead. This brown oxide may be procured by pouring nitric acid on red lead j when the yellow oxide in the red lead will be dissolved by the acid, and the brown oxide will remain, being insoluble.
If the oxides of lead be acted on by a strong- heat, they give up their oxygen, and metallic lead remains ; but they are more readily reduced by mixing them with combustible matter.
Lead, when procured from its ore, frequently contains so much silver, that the latter is wortli extracting. This process is called refining. Tlie lead is played upon by the flame of a furnace, by which the lead is oxidized, and the oxide is partly vitrified, and assumes a scaly form, called litharge. The silver then remains free.
LEAD. 113
The oxides of lead are easily changed into glass, and unite with all the metals except gold and silver; on this account they are employed for separating other metals from these. This process is called cupellation. The mixed metal is put into a dish called a cupel^ made of bone-ashes, and placed in a cupelling furnace ; the lead is oxidized and vitri- fied, and sinks into the bone-ash cupel, carrying with it all the baser metals.
White lead, so much used in painting, is a com- pound of the yellow oxide and carbonic acid ; or a carbonate of lead. It is made by exposing plates of pure lead to the warm vapour of vinegar. By this they are gradually corroded, and converted into a heavy white powder, which is white lead.
When the carbonate of lead is dissolved in dis- tilled vinegar, a salt is obtained, which crystallizes, and is called commonly sugar of lead; more pro- perly acetate of lead. All the salts of lead have a sweetish taste, and are of a poisonous quality.
The affinity of the muriatic acid (hydrochloric acid) for the oxides of lead is so great, that the latter decomposes all the combinations of this acid. They decompose the muriate of soda (common salt), and thus form muriate of lead, which, on fusion, affords minei^al oy patent yelloxv.
Sulphuric acid does not act on lead when cold; but dissolves it at a boiling heat, and forms sul- phate of lead, which is insoluble in water.
Chr ornate of lead , or chromic acid and lead, is a very beautiful yellow pigment. It is found native in small quantities, but is now prepared largely by art. Lead is one of the most useful metals. It is much employed in covering houses, when made into thin sheets by casting or by milling. It is used also for water-pipes and cisterns, and for a variety
VOL. II. I
Il4 ZINC.
of well-known purposes. Its oxides are used in the manufactures of glass, and the glazings of earthenware; also as pigments. Preparations of lead are also used as external applications in diseases. The alloys of lead with tin form solder, and other alloys are employed in various arts.
ZINC.
This metal is chiefly procured from calamine^ which is a liydy^ated oxide of zinc ; and from blende, a sulphuret of zinc.
Zinc is a whitish metal of the colour of tin. It is slightly malleable when cold ; but heated to between 200° and 300° it is very malleable, and has been manufactured into nails, drawn into wire, and made into sheets.
It is often known among workmen by the name of Spelter, It is easily fused, and is the most in- flammable of the metals; thin leaves of it will take fire with the flame of a taper.
It is scarcely oxidized in the air at common temperatures, but is rapidly converted into oxide when kept melted in an open vessel. Its surface then becomes covered with a grey pellicle, which is oxide of zinc. When zinc is made red hot in an open vessel, it takes fire and burns with a brilliant flame, sending off white flakes of oxide. These have been calledj^ower^ of zinc.
Zinc decomposes water very slowly when cold ; but with great rapidity when the vapour of water is brought into contact with it ignited.
Zinc dissolves very readily in diluted sulphuric acid; forming thus sulphate of zinc, or "white vitrioL During this solution, a great quantity of hydrogen
ANTIMONY. 115
gas is disengaged, and this is one of the best modes of procuring that gas.
The nitric and muriatic acids also act upon zinc. Zinc combines with phosphorus and sulphur.
It can be alloyed with most of the other metals. With copper, it forms brass,
ANTIMONY.
Antimony is rarely found native. It is procured from an ore called crude antimony, which is a sul- phuret of antimony.
Antimony is of a silvery white colour. It is so brittle, that it may be pulverised in a mortar ; and its interior texture appears to be scaly or lamellar. It requires 800° to fuse it. It does not change in the air, but when kept in fusion at a red heat, it emits white fumes, consisting of an oxide formerly called^oa;er5 of antimony.
There are two oxides of antimony. The protox- ide is procured by precipitating the muriate of antimony by potash. It is of a grey colour. The peroxide is formed by causing the nitric acid to act upon the metal, or by collecting the fumes already mentioned as the flowers of antimony. It is white. The oxidesof antimony are very valuable medicines. Tartrate of potash and antimony form emetic tartar, Jameses powder is composed of phosphate of lime and antimony. Kermes*s mineral is made from sul- phuret of antimony by potash.
Antimony is also used in printers' types ; and in specula for telescopes. The sulphuret has been used for staining hair black.
116 BISMUTH. — ARSENIC.
BISMUTH.
Bismuth is found native, and also combined with sulphur and arsenic.
It is of a reddish white colour, brittle, and easily fusible. It is not quite so hard as copper. It is not oxidated by water; it tarnishes in the air, but does not undergo any other change. Kept melted in an open vessel, its surface becomes covered with a dark grey pellicle, which is renewed till the whole is converted into oxide.
The oxide of bismuth is a yellow powder. When strongly heated it melts and becomes darker coloured.
Bismuth dissolved in the nitric acid, affords a white powder, if water be added to the solution. This is the magistry of bismuth^ ov pearl 'white, which has been used as a cosmetic, but very improperly, as it is apt to turn black by sulphuretted hydrogen.
Bismuth dissolved by the acetic acid forms a sympathetic ink. The characters written with it are invisible, until they are exposed to sulphuretted hydrogen, when they appear black.
Bismuth alloys with all the metals, and has the property of giving them great fusibility. If eight parts of bismuth, five of lead, and three of tin be fused together, they form what is called the fusible metal, which melts in boiling water. On this ac- count bismuth enters into the composition of some of the soft solders.
It has also the property of rendering gold ex- tremely brittle.
ARSENIC.
Arsenic, the poisonous effects of which are so well known, is a metallic substance, sometimes
NICKEL. 117
found native, but oftener combined with sulphur. The sulphuret of arsenic is called orpiment.
Arsenic is frequently mixed in metallic ores, and is driven off by heat. It is known by its pecu- liar smell, like garlic.
The colour of metallic arsenic is grey; it is very brittle. It soon loses its metallic lustre in the air, and becomes black. The oxides of arsenic have acid properties. There are two: the white oxide of arsenic is called arsenious acid. It is highly poisonous. It is soluble in water. It reddens vegetable blues. It is of a white colour, is semi- transparent, and brittle. Its taste is acrid, with a nauseous sweetness. The best way of getting rid of its action as a poison, when taken into the sto- mach, is to produce vomiting and purging.
Arsenic acid is a white deliquescent substance, of a sour taste, obtained by distilling nitric acid off metallic arsenic. It forms salts with several of the metals. Arseniate of iron crystallizes in cubes of a green colour. The arseniates of copper are among the most beautiful minerals. The alloys of arsenic with some of the metals are used for some purposes. It is mixed with lead to assist its granulation in making small shot. It is also used in making flint glass, and in calico-printing.
NICKEL.
Nickel is a rare metal. It is white, much resem- bling silver*, and possesses, like iron, the magnetic property. It is not easily fused, and it is malleable. It is rather softer than iron, and soon tarnishes in the air. It is found native, and combined with arsenic.
Nickel dissolves in the acids, and its salts are distinguished by their fine green colour.
I 3
us ivAnganese.
It forms two oxides, the black and the grey.
Nickel alloys with most of the metals, and it is found alloyed with iron in those masses that fall from the atmosphere, called meteoric stones. The origin of those lapideous masses that appear in so extraordinary a manner is entirely unknown: but the numerous well-authenticated accounts we have had of the fact put it now beyond dispute. They are first seen as large meteors, at a great height in the air, which suddenly burst with an explosion, and the fragments are seen to fall to the earth. It is very remarkable that their composition is always the same, although they have fallen at many difter- ent times, ,and in different places. They always contain native iron alloyed with nickel, in grains imbedded in a stony matter. The substance of these meteoric stones is not like any bodies which are found in the earth. In 1795, one weighing 56 lbs. fell in Yorkshire.
MANGANESE.
This metal is never found native. Indeed its attraction for oxygen is so powerful, that it is with difficulty preserved in the metalHc state. When pure, it is of a greyish colour, much like cast iron, and not malleable. It soon tarnishes, and at last becomes black. This change takes place more rapidly, if the metal be heated, or put into water.
There appear to be two oxides of this metal ; the protoxide^ which is of a greenish colour ; and the peroxide, which is steel black, and has a consi- derable lustre: the latter is found in abundance, particularly near Exeter, and is much used in bleaching, and also for procuring oxygen gas, as it parts with it simply by the application of heat. It
COBALT. 119
contains one-third of its weight of oxygen. This oxide is sometimes very beautifully crystallized. Manganese is also employed by glass-makers to destroy the greenish tint of glass, and for making violet-coloured glass.
Almost all the salts of manganese are soluble in water.
COBALT.
Cobalt is never found but in a state of combin- ation. It is met with united to sulphur, arsenic, and other metallic substances.
The ores of cobalt had been long used for giving a blue colour to glass, before its metallic nature was known.
The metal itself is not applied to any use. When pure, it is a reddish grey colour ; rather soft and brittle. Like iron, it is attracted by the magnet. It is not oxidized by the air nor by water. It is converted into a deep blue by exposure to heat and flame.
There are two oxides of cobalt. The 'protoxide may be formed by precipitating by potass, a solu- tion of cobalt in nitric acid. It is of a blue colour when first precipitated, but becomes black by absorbing oxygen. To recover the blue colour, it must be heated red hot, by which the oxygen is expelled. This oxide dissolves in acids. The mu- riate of cobalt is green, and forms a sympathetic ink. Letters written with it are invisible, until they are warmed, and then they appear of a fine green j when cold they disappear again.
The peroxide of cobalt is procured by drying in the air, with heat, the protoxide just precipitated; by this the protoxide absorbs oxygen, and becomes the peroxide. It is black.
I 4
120 MOLYBDENA. — TUNGSTEN.
Ores of cobalt are very valuable. Zaffre is a substance produced by roasting the ores of cobalt, by which the volatile matters (generally arsenic and sulphur,) are driven off; the remainder is then fused with sand or pounded flints. A blue glass is thus formed, which, when ground and washed, con- stitutes the pigment called smalt.
MOLYBDENA,
Molybdena is found in nature combined with sulphur; forming the sulphuret of molybdena, which resembles plumbago in some of its properties. This mineral is of a bluish colour, more brilliant than plumbago, and makes on paper a trace of a grey tint. The metal has only been procured in small grains, which do not differ much in their pro- perties from the sulphuret. It combines with oxygen, so as to form an acid called the molybdic acid. The molyhdate of lead is a beautiful yellow mineral.
The protoxide of molybdena is a tasteless pow- der of a brown colour. Molybdena alloys with the other metals,
TUNGSTEN.
A mineral called tungsten^ or ponderous stone, affords a peculiar metal. This metal is capable of being acidified, and when in this state it is joined to lime, it forms the tungstate of lime.
The metal when pure is much like steel, and is one of the hardest of the metals; a file can scarcely make any impression on, it : it is also the heaviest,
OSMIUM. — IRIDIUM.— RHODIUM, 121
except gold and platinum. It is not used for any purpose.
When heated in an open vessel it is oxidized, and there are two oxides of tungsten. The pro- toxide is of a brown colour, and when heated it burns, and is converted into the peroxide^ which is yellow, and has some of the properties of an acid, being capable of combining with salifiable bases.
The mineral called wolfram is composed of tungstic acid, manganese, iron, and tin.
OSMIUM.
This metal was discovered by Mr. Tennant, in the ore of platina. The metal is of a dark grey colour, and is oxidized when heated. Its oxide is volatile, and has a peculiar smell. It is little known, and has not been fused.
IRIDIUM.
This metal was also discovered by Mr. Tennant, in the ore of platina. It is of a wliitish colour. It is fusible, and malleable. It unites with oxygen, and alloys with the metals. Its combinations are little known.
RHODIUM.
Dr. WoUaston discovered this metal in the ore of platina. It is very infusible, and forms malleable alloys with the malleable metals. It unites to oxygen like all the other metals, but is very little known.
Igg PALI,AI)IUM.«- CADMIUM. -—TEJLiUmUM.
PALLADIUM.
This metal was discovered by Dr. WoUaston, who found it in the ore of platina. Its colour is of a duller white than platina ; it is malleable and ductile, and for fusion it requires a stronger heat than for gold. It is rather harder than iron.
It unites with sulphur, and is acted on by the acids, but most readily by the nitro-muriatic.
It forms alloys with other metals, that with gold has been usefully employed in astronomical instruments, as it is hard, and does not tarnish.
CADMIUM.
This metal was discovered by M. Stromeyer, in 1817> in ores of zinc, particularly in brown fibrous blende. It resembles tin, but is rather more fusi- ble. It does not tarnish in the air.
It readily disolves in acids, but its salts are lit- tle known. It is a rare metal, and not applied to any use.
TELLURIUM.
This metal was discovered by Muller in 1782. It is of a bluish w^hite colour, of considerable bril- liancy. It is extremely brittle ; melts in a heat a little greater than that required for lead. It is so volatile that it may be distilled like mercury.
Its oxide has acid properties. It is formed by burning the metal j a white smoke is disengaged, which is the oxide. It may be also obtained by
TJTANIUM.'— CHROMIUM. 123
dissolving the metal in nitromuriatic acid, and di- luting the solution with a large quantity of water.
Tellurium combines with hydrogen, and with it forms a gaseous substance, called telluretted hy- drogen.
This metal is scarce, and its combinations yet little known.
TITANIUM.
This metal is rare. It was discovered in a mineral, found in Cornwall, called menachanite. It was afterwards procured from another mineral, titanite, and some others. The metal when pure is brittle, very infusible, of a brass or copper co- lour, easily tarnishes in the air, and oxidizes by heat. There appear to be three oxides of titanium, the blue, the red, and the xvhite.
The ores of titanium are either pure crystallized oxide, or the oxide united to iron, or to silex.
CHROMIUM.
This substance, little known in the metallic state, is important on account of the fine pigments it affords. It is capable of being acidified, and the chromic acid forms salts. The beautiful mineral called red-lead of Siberia, is a chromate of lead. This is now artificially prepared, and is a very va- luable and beautiful yellow pigment. The chro- mic acid also unites to iron, the chromate of iron being found native ; and it is from this that the chromic acid is procured and united to lead, to form the chromate of lead. Chromate of iron is, therefore, much sought after, and is found in greatest abundance in America, from whence our colour-makers chiefly procure it.
124 URANIUM. —COLUMBIUM.— CERIUM,
The pure metal is of a tin colour ; it is very brittle, and is said to be magnetic. It is very in- fusible, and is not altered by the air, though when heated it is converted to an oxide.
Besides its acid, it seems to combine with oxy- gen in two other proportions, forming the green and hroTdon oxides.
URANIUM.
This metal was discovered by Werner, in a mi- neral called peclihlende, a blackish mineral re- sembling pitch.
Metallic uranium is brittle, and veiy infusible. It is of a grey colour. It is obtained with extreme difficulty, and little known.
Its oxide is greenish-yellow, and is found native, resembling green mica, and also in an earthy state.
COLUMBIUM.
This metal was discovered by Mr. Hatchet in analyzing an ore from North America. It has since been found in the minerals called tantalite and yttro-tantalite. The metal has been procured by Berzelius. It is of an iron colour, hard and brittle, and passes into an oxide at a red heat.
Its oxide is white. Its combinations are little known ; but it is one of the acidifiable metals.
CERIUM,
This metal was lately discovered by Berzelius, in a mineral which has been called cerite. The characters of the metal are imperfectly known, as
SELENIUM. — VEGETABLE SUBSTANCES. 125
it has been scarcely seen. The oxide of cerium (cerite) is found native. There appear to be two oxides, the white and the 7'ed.
SELENIUM.
Selenium is a metal lately discovered by Berze- lius in the sulphur of Fahhun, in Sweden. Its metallic lustre is considerable, and colour grey. It easily fuses and volatilizes before the blow-pipe, with a smell like horse-raddish. It alloys with the metals. It dissolves in nitric acid, and forms with it a substance which is considered as a new acid, selenic acidy which unites with alkalies, forming se^ leniates»
VEGETABLE SUBSTANCES.
Animals and vegetables differ essentially from minerals, in the two first possessing life and various organs fit for maintaining it, which is called organic structure. Through these organs, various juices and fluids circulate internally, and thus occasion the growth of the animal or plant. In mineral bo- dies this is pot the case j they increase in size only by successive portions of matter adhering to the outside^ nor is there any internal motion.
The principal ingredients of ail vegetables are, oxygen, hydrogen, and carbon : sometimes they contain also a little nitrogen, and other elementary substances ; and although these elements are few, yet, by many varieties in their proportions and modes of combinations, a great quantity of proxi- mate constituents are produced.
126 VEGETABLE SUBSTANCES.
Vegetable substances may be decomposed, or separated into their elementary principles by various means ; by heats, by acids, and by fermentation : some of these processes occasion not only decom- position, but also new combinations of the elements that did not exist in the living bodies.
The principal substances of which all vegetables consist are.
|
Mucilage, or gum, |
Woody fibre, |
|
Sugar, |
Colouring matter, |
|
Fecula, |
Tannin, |
|
Gluten, |
Wax, |
|
Fixed oil, |
Camphor, |
|
Volatile oil. |
Bitter principle, |
|
Resin, |
Narcotic principle. |
|
Caoutchouc, |
Vegetable acids. |
Mucilage^ or gum. — Various parts of vegetables impart to water, particularly if boiled with them, a certain viscous consistency : the substance so dissolved is called mucilage. Some trees suffer their mucilage to transude, either spontaneously or by incisions made in them. AVhen it has become concrete by drying in the air, it is called gum.
Gum is soluble in water, but not in oils or al- kohol, the latter of which precipitates it from its solution in water. It is insipid ; it does not un- dergo any change by exposure to the air when dry. The gums of different trees differ considerably in their properties. Gum arable may be considered as a very pure gum. Cherry-tree gum and gum tragacanth do not dissolve in cold water ; but dis- solve in boiling water, and, on cooling, assume the state of a jelly.
VEGETABLE SUBSTANCES. 127
Gum consists of carbon, oxygen, and hydrogen.
Sugar. — The sugar in common use is extracted from a cane that grows only in warm climates, called the sugar-cane ; but it may also be procured from all sweet vegetables. The American maple-tree affords a great deal of sugar, and this useful sub- stance has been made from the beet-root, car- rots, &c.
All sugars consist of carbon, oxygen, and hydro- gen ; but it appears that sugar from the cane contains more carbon than other sugars. That obtained from some vegetables will not crystallize. Sugar is first prepared in the countries where it is grown, by boiling the juice and evaporating ; one part of the juice crystallizes, and forms the raw or muscovado sugar ; the other part, the molasses or treacle, will not crystallize. The raw sugar when brought to this country is re-dissolved and crystal- lized again, which is called refining, by which the loaf-sugar is made. To whiten it completely, clay is put upon the tops of the conical pots in which the sugar has granulated, which allows water to percolate through, and thus drain off the last re- mains of the molasses. This is called claying the sugars.
Fecula, or starch. — This substance is contained in many seeds and roots. It is separated by bruising the vegetables containing it in water, and stirring them together. The fecula separates in the water, making it appear turbid. The white fluid is pour- ed off and suffered to settle ; the starch subsides to the bottom. Starch is made mostly from wheat; it is also made form potatoes. Starch is a white substance, insoluble in cold water, but soluble in warm. Its solution is gelatinous, and when solid it resembles gum : this, when dry, is a com-
128 VEGETABLE SUBSTANCES.
pound of starch and water. Starch is not soluble in alkohol.
In the process of converting grain into malty the starch or fecula is changed into sugar. It may also be converted into sugar by boiling it with diluted sulphuric acid.
Starch consists of carbon, oxygen, and hydrogen.
Gluten. — This principle is found in various vege- table juices, but most abundantly in wheat flour. It is separated from it by washing, with a stream of water, a paste made of flour and water, at the same time kneading it between the fingers. The water car- ries off the starch gradually, leaving the gluten be- hind. Gluten is insoluble in water, and is elastic like elastic gum. It has no taste, and, when dried, becomes hard and brittle. It considerably resem- bles animal gluten, furnishing ammonia by distil- lation.
Fixed oil. — This is obtained by pressure from certain seeds and fruits, as the olive, linseed, rape seed, almond, &c. The fixed oils differ much ; some being nearly solid, are called vegetable butters. When expressed, they are generally mixed with some mucilage, which occasions them to turn rancid. They may be deprived of their colour by charcoal. Fixed oils dissolve sulphur, and then form balsams. They also dissolve phosphorus.
Fixed oils are very combustible, and, when strongly heated, yield olifiant and carburetted hy- drogen gases.
They form soaps by being combined with alkali. The best soaps are made of olive oil and soda ; but common soaps are made with the animal oils and fat.
Transparent soap is made by dissolving soap in alkohol, and then concentrating the solution whicli
VEGETABLE SUBSTANCES. 129
is of a gelatinous consistence, by distilling off the alkohol.
Fixed oils are mucli used for painting, as they are of a drying nature : they are rendered still more drying by boiling them with the oxides of metals, as litharge.
Volatile oil. — This is also called essential oil. Many vegetables afford essential oil by expression, or by distillation, When dissolved in water they constitute perfumed essences and distilled waters. They have much odour and taste. They are in- flammable. They are volatilized by a gentle heat, and evaporate entirely when pure so as to leave no trace. The chief essential oils are, the oils of tur- pentine, spike, cloves, oranges, lemons, lavender, &c. Many of them bear a high price.
Resin. — The resins are an important class of vegetable substances from their application in the arts. They are very numerous, and often exude spontaneously from trees. Common resin is obtained from the^r ; a juice exudes from this tree, which is common turpentine: this consists of the oil of turpen- tine and resin. When the essential oil is separated by distillation, the resin remains. Mastich is a resin obtained from a tree that grows in Turkey. San- darach is the resin of a tree in Barbary. Copal is a resin from a tree that grows in America, and is a very valuable substance for varnishes. Lac is a resin made by an insect in the East Indies. It is very useful in varnishes, and in sealing-wax. Am- ber is a substance resembling in its properties the resins, but it is only found in the earth, or washed out and driven on the shores. All the resins are insoluble in water, but soluble in alkohol, especially when assisted by heat. The greater number are soluble in the essential oils, and some are so in the
VOL, II. K
ISO VEGETABLE S¥BSTANCES.
fixed oils. They are also dissolved by alkaline ]ys, and by the acids. Resins consist of oxygen, carbon, and hydrogen ; and they are supposed to be volatile oils saturated with oxygen.
Bitumen is a substance having some analogy witli oils and resins, although differing in its consti- tuents, and being also a mineral body. Pure bitu- men is called naphtha, which is transparent, highly inflammable, volatile, of a pungent odour ; it is found in certain wells, and there are springs of it in several parts of the world. When naphtha is exposed to the air, it thickens, and becomes dark coloured; it is then called j9e/ro/ez^w, which is procured in the same manner, and is used for burning in lamps. Maltha or mineral pitch is a still farther thickened bitumen, and when it has become solid it is called asphaltum. Caoutchouc. — This is the substance usually known by the name of Indian ri(hbcr, and- some- times elastic gum. It was first brought from South America. It exudes as a milky juice from a tree, which thickens and hardens by exposure to the air. The natives form it into bottles by coverina: balls of clay with this juice ; the clay is afterwards washed out after the caoutchouc is solid. When caoutchouc is pure, it is white, the black colour being owing to the smoke used in drying it. This substance is extremely elastic. It is perfectly inso- luble in water, but it may be softened by boihng, ; so that its edges may be united together. It is not ( soluble in alkohol : but it is soluble in ether j and when the ether is evaporated, the caoutchouc re- I mains unaltered in its properties : by this means tubes and other instruments might be made of it, \ but the method would be too expensive. It is so- luble in some of the fixed and essential oils, as in spermaceti and in oil of cajeput. if
I
I
VEGETABLE SUBSTANCES. 131
Woody fibre. — When a piece of wood has been boiled in water and in alkohol, until the soluble sub- stances have been extracted from it, what remains insoluble is the woody fibre, or lignin^ which is the basis oi wood, and consists of long fibres, having a considerable degree of transparency, without taste, and unalterable by the air. It is insoluble in water and alkohol. It is very inflammable ; and, when distilled in a close vessel, yields an acid sub- stance formerly thought to be a distinct acid called the pyro-ligneous, but now known to be the acetic acid with an empyreumatic oil. Pure acetic acid or vinegar is now made from wood by distillation. Wood consists of oxygen, carbon, and hydrogen j when burned, the carbon remains, constituting charcoal.
Colouring matter. — The colours of vegetables are owing to peculiar matters, which are extremely numerous, and but little known. Many of them are used as dyes and pigments. The extraction of colouring matters from vegetables, and fixing them on cloths, constitute the arts of dyeing and calico- printing (which see). The colouring matters sometimes are inherent in gums, sometimes in resins, sometimes in fecula ; consequently they require different chemical agents for their solution.
Tannin. — This principle is so called because it is employed in the art of tanning leather. It is also called the astringent principle. It is found abundantly in the barks of several trees, particu- larly the oak, and also in certahi seeds. The gall- nut and grape-seeds afford very pure tannin ; and a substance called catechu^ from India, consists chiefly of it. Tannin is distinguished by its forming a precipitate with glue, or isinglass. This precipitate is insoluble in water, and is that wliich
.132 VEGETABLE SUBSTANCES.
is formed when skins are tanned and made into leathe7\
Wax. — This substance appears to be formed by bees, by some animal process. It is also a vege- table substance, for the polish or varnish of leaves is owing to a coating of wax ; and in some vege- tables in Brazil wax exists in considerable quan- tity; Wax is insoluble in water, but sparingly dissolved by boiling alkohol. It is dissolved rea- dily by the fixed oils, and then forms cerates and ointments. Wax contains a large proportion of carbon, with hydrogen and oxygen.
Camphor. — This substance is brought chiefly from Japan, and is distilled from a species of laurel. It is white and semitransparent ; it is very inflam- mable, soluble in alkohol, and sparingly so in water. It is very volatile, and capable of converting into an acid, called the camphoric acid, which form ' neutral salts called camphorates. Camphor resem- bles essential oil in many of its properties.
Bitter principle. — It is supposed that this is a peculiar principle. It exists in many vegetables, particularly in quassia, gentian, hop, &c. When extracted, it is of a brownish yellow colour, and brittle when dry. Its taste is very bitter. It is soluble in water and alkohol. A variety of it is supposed to exist in unroasted coflfee.
Narcotic priiiciple. — This has lately been called morphine, and is found most abundantly in opium, which consists of this together with several of the principles which have been just described. It is a violent poison when taken internally. When pure it is white, without taste or smell. It is soluble in boiling alkahol, but is scarcely acted upon by water.
From the rapid progress of chemistry, many other vegetable substances are considered as pe-
VEGETABLE SUBSTANCE^. 133
culiar principles ; but it would exceed the bounds of this work to describe them all in detail. The chief amono- them are saber, or a peculiar substance found in cork j asparagin, found in asparagus ; medullinj from the pith of the sunflower ; fungin, the fleshy part of mushrooms, &c.
Vegetables also contain several acids ready formed. Vegetable and animal acids differ from the others essentially. They always contain car- bon and hydrogen : some of them contain azote, and generally, though perhaps not always, oxygen. They do not seem capable of combining with dif- ferent proportions of oxygen only, but whenever the quantity of this principle changes, that of the rest changes also.
Tartaric acid. — Tartar , or cream of tartar^ is a substance found in an impure state, incrusted^on the bottom and sides of wine casks : when purified by solution and filtration, it is sold for use. This salt, which is soluble in water, consists of tartaric acid and potash ; it is therefore tartrate of potash. Tartaric acid when crystallized is imperfectly trans- parent, white, and does not deliquesce in the aii« It is soluble in water. It combines with alcalies, earths, and metallic oxides, and forms tartrates.
Ojcalic acid, so called from being first obtained from oxalis acitosella, or wood-sorrell. It is also called the acid of sugar, because obtained from sugar by the nitric acid. It is proper that every one should know that oxalic acid is a deadly poison, and that many persons have lost their lives by mistaking it for Epsom salts, which it resembles. It IS much employed for cleaning boot-tops and leather, and also by the calico-printers.
Malic acid was first found in the juice of apples. It exists also in many other vegetables. This acid
K S
154 FERMENTATION.
is very sour, and does not crystallize ; it forms salts with many of the metallic oxides.
Gallic acid. — Tliis acid is found in gall-nuts. It crystallizes, and forms whitish crystals, of a sour taste and peculiar smell. When gallic acid is put into a solution containing iron, a black precipitate appears. The base of ink is iron thus precipi- tated. To produce good black ink, infuse one pound of powdered gall-nuts for four hours, without boiling, in common water, with six ounces of gum-arabic, and six ounces of sulphate of iron. With gold, gallic acid forms a brown precipitate j with silver, a grey ; with mercury, an orange; with copper, a brown ; and with lead, a wliite.
Citric acid is procured from the juice of lemons and other fruits. It is capable of crystallizing. Its crystals are soluble in water, and very sour. It forms citrates with the earths, alkalies, and metals. It is much used in calico-printing. It is also used for discharging spots of ink from linen.
Benzoic acid is obtained from gum-benzoin, or benjamin. It is a crystallizable acid. The com- pounds which it forms are called benzoates,
Kinic acid is found in Peruvian bark.
FERMENTATION.
If mucilagi-nous saccharine vegetable substances be subjected to the action of water and heat, (from 60 to 70 tleg. Fahr.) they experience, in a very short time, a very striking change. An internal commotion takes place, the mass grows turbid, a large quantity of air-bubbles, consisting of carbonic acid gas, are disengaged, which, on account of the viscidity of the matter in which they are inclosed, form a stratum on the surface of the fluid, known
FERMENTATION. 155
by the name of yeast. After a time these appear- ances cease, the fermented liquor becomes clear and transparent, and no more gas is discharged. The liquor now has lost its sweetness and viscidity, and has acquired the vinous taste and intoxicating quality. Sugar appears to be essential to this pro- cess J and all mucilaginous substances containing sugar are capable of this fermentation, which is called the vinous.
Wine is made in this manner from the juice of the grape ; if the fermentation be checked when at its height, by excluding the air, the wine begins to ferment anew, and effervesces when again ex- posed to the air. The sparkling wines, as Cham^ pagne, are prepared in this manner, and hence should be considered as imperfect wines.
To prepare vinous liquors from grain or corn, it must first be converted into maU^ by steeping it in water, and then exposing it to the air, turning it frequently over j by this process, the gluten of which the germ consists is separated, and the fecula is converted into sugar by the germination of the seed.
Beer is made by boiling the malt in water, which produces a sweet liquor called tvoi^t ; this is con- verted into beer by fermentation and the addition of hops, which furnish a bitter substance.
Wine, beer, and all fermented liquors, owe their intoxicating qualities to a peculiar substance which they contain, and which is the produce of fermen- tation alone. . This substance is a fluid called alko- hoi, or spirit of m7ie, and may be separated in a pure state by distillation. When first obtained it is mixed with a quantity of water, but if it be re- distilled, it is obtained very pure, and is then called rectified alkohol. Alkohol is of a strong heating
K 4
lS6 FERMENTATION*
taste, of a peculiar penetrating odour, and it is very inflammable and volatile. It dissolves resins, essential oils, camphor, sulphur, phosphorus, &c. It is composed of hydrogen, carbon, and a small quantity of oxygen.
Strong acids and alkoliol have a considerable action on each other, and this produces ether^ which is a fluid still more highly volatile, inflammable, and odorous. Nitric acid with alkohol produces nitric ether ^ and sulphuric acid in the same way produces sulphuric ether.
When wine, or any fermented or vinous liquor is exposed to a heat, from 75'^ to 85S Fahr., and access of air is permitted, the fluid becomes turbid, and a new change of principles takes place. It loses its taste and smell, it becomes sour, and is converted into vinegar, or acetous acid. Though vinegar is chiefly prepared from fluids which have undergone the vinous fermentation, yet this is not necessary to the production of vinegar, for simple mucilage is capable of passing into the state of acetous fermentation. When the saccharine prin- ciple predominates in any substance exposed to the necessary conditions of fermentation, alkohol is produced ; when mucilage is most abundant, vinegar or acetous acid is the product j and when gluten is predominant, ammonia will be discovered, and putrefaction will take place.
Common vinegar may be purified, or concen trated by distillation, and it is then called distilled vinegar. This, however, still consists of the acetic acid and water. To free the acid from the water, distilled vinegar is saturated with some metallic oxide, and an acetate is thus formed. The acetate is then heated red hot in a retort, by which it is decomposed, and the acetic acid passes over pure.
ANIMAL SUBSTANCES. 137
Acetate of copper or verdigris^ and likewise ace- tate of leady are used for this purpose. Acetic acid is very pungent and caustic. It is very vola- tile, and combines with the metals, earths, and alkalies.
This acid may also be obtained from wood, by subjecting it to distillation in a retort. In this state it is very impure, being combined with a quantity of empyreumatic oil. This was formerly called pi/- roligneous acid. When separated from impurities it is essentially the same with vinegar, and is now employed for the same purpose.
The last change, or final decomposition that vegetables undergo, is called the putrefactive fer- mentation^ OY putrefaction. Without moisture, heat, and a due access of air, this does not take place. By this vegetables are resolved into their consti- tuent principles, and ammonia is formed.
ANIMAL SUBSTANCES.
The elementary principles of animal substances are nearly the same with those of vegetables, but the former contain more nitrogen and phosphorus, and the latter more carbon and hydrogen.
The proximate constituent parts of animal sub- stances are the following :
Gelatine^ or animal jelly, is very generally dis- persed through all the parts of animals, even in bones, but exists in the greatest quantity in the tendons, membranes, and the skin. It is a viscid substance, very soluble in warm water, but not in alkohol ; insipid, and without smell ; when cold, it congeals into a cohesive, tremulous substance. It forms the basis of soups, broths, &c. and imparts to
138 ANIMAL SUBSTANCES,
them tlieir nutritious qualities. \VTien evaporated to dryness, it forms poi^table soup, size, ghie, &c. The union of this latter substance in the skin with tannin constitutes leather. Isinglass is gelatine procured from certain parts of several fish, particu- larly the sturgeon. The tendons and membranes of the body are chiefly gelatine.
Fibrin, or animal Jibre, forms the basis of the niusctdar, or fleshy parts of animals. It is there combined with albumen, and remains with it after all the soluble parts of the flesh have been separated by water. It may also be obtained from blood, by washing the clot or coagulum in water, till a white fibrous matter remains. Fibrin is not soluble in cold watei% but is very slightly so in boiling water. It is soluble in acids and alkalies, and by its union with the latter a soap is formed. Chaptal em- ployed this joroperty to make a soap from wool. It is very analogous to vegetable gluten.
Albinnen is the principal constituent of the serum of blood, and is also called coagidable lymijh. The white of eggs consists almost entirely of albumen. It is miscible with cold water, but is coagulated by heat, which forms the best test of its presence. It is also coagulated by acids and alkohol.
Mucus. — This substance in animals appears in- tended to lubricate or smooth certain parts of the body, and seems very analogous to a solution of gum. However, Dr. Bostock has shown that it diflfers from gelatine, as it cannot in cold water be brought to assume the gelatinous state. Tannin precipitates gelatine, but not mucus, whereas sub- acetate of lead, (extract of Goulard,) forms a preci- pitate with mucus, but not with gelatine. Mucus is found in saliva, tears, in the intestines, joints, &c.
ANIMAL SUBSTANCES. IS^
Oil.'— Animal oils are fat, tallow, butter, &c. They are mostly solid at the usual temperature. They may be rendered fluid by heat. Oil is ob- tained in great quantities from certain fish, parti- cularly the whale, seal, &c. and fish oil continues fluid. It is very similar to vegetable oil in its other properties. Spermaceti somewhat resembles wax, and is obtained from the head of a species of whale. Animal fibre may be converted into a substance like spermaceti by treatment with the nitric acid, or by exposing it to a current of running water for several months. This has been called adipoeire. It has been shown lately that fat is a compound body, consisting of a substance solid and much like wax, which has been called stearin^ and a fluid oil called elain.
Milk is a substance secreted by certain animals for the nourishment of their young. As is well known, milk on standing for a day throws up cream to the surface. Cream has mucli of the properties of an oil, and when agitated by churning, butter is separated from it. If milk stands until it becomes sour, it separates into a coagulum and a whey. This change may be more completely effected by adding to the milk a small quantity of certain sub- stances, as acids, or rennet^ procured by boiling in water the inner coat of the stomachy of a calf. The coagulum is thus made more solid, and when pressed and dried it forms cheese.
In animal bodies there are also found several pe-' culiar acids.
The lactic acid is found in sour whey. It com- bines with the earths and alkalies, forming salts called lactates. It resembles much the acetic acid.
The uric acid is found in urine. The substance voided with the urine called gravel, and also those
140 ANIMAL SUBSTANCES.
stones formed in the bladder called calculi, are almost entirely composed of nric acid. This acid, however, exists in urine even in its most healthy state.
The amniotic acid is found in the liquor of the amnios of a cow. It separates in white crystals.
The saccho-lactic acid is formed by acting on su- gar of milk, or on gum by the nitric acid. It forms salts called saccho-lactates.
The sehacic acid is procured from animal fat. It becomes solid, is of a white colour, with a taste slightly acid.
The Prussic acid has been described, p. under the name of the hydrocyanic acid.
The formic acid is an acid procured from ants.
Animal resins. — Peculiar tesins have been found in certain animal substances, as in the bile, amber- gris, &c.
Animal sugar is found in milk, also in the urine in certain diseases. It is similar to common sugar. " Blood, when suffered to rest, separates into two parts J the one a coagulum or clot, called the crassamentum ; the other, a fluid called the serum. The crassamentum consists of fibrin mixed with al- bumen and colouring matter. The colouring part of blood consists of extremely minute globules of a red colour, which float in the serum, and may be seen by the microscope. The red colour of blood has been supposed to be owing to iron which was oxy- dated by the air in the lungs, but this theory is now rendered questionable. The serum is com- posed of albumen, and also contains a small por- tion of alkali and other substances. It is coagu- lated by heat, the acids, and alkohol.
Bone is composed of gelatine, another substance which seems t5 be analogous to cartilage or coa-
ANIMAL SUBSTANCES. 141
gulated albumen, an oil, or marrow, and phosphate and carbonate of lime, besides other matters in minute portions.
Teeth are composed of similar ingredients.
Shells contain a greater proportion of carbonate of hme.
Horns, nails, hoofs, and quills are chiefly gelatine and albumen.
Besides the animal substances above enumerated, there are various matters secreted or formed by cer- tain organs in the body, as saliva, the gastric juice, the bile, thejluid ofi^erspiration, kc, the nature of which is not yet thoroughly known.
The examination of animal substances, called animal chemistry, is one of the most difficult, as well as one of the most important, branches of the science ; and a wide field is yet open for research.
When animal bodies are deprived of the vital principle, and are exposed to the air, they undergo a speedy decomposition called putrefaction. By this they are resolved partly into their elementary principles, and some of these form new compounds. The first change is observed by the bodies altering in their colour, losing their elasticity, and by their giving out a very fetid and noxious sm.ell. The greater part, in time, assumes a gaseous form, and nothing remahis but a small quantity of earths and salts.
One of the greatest improvements in chemistry has been that made in its nomenclature, which we owe chiefly to the French chemists. As the former names of many substances differ so entirely from those at present employed, that, without some assistance, many of the old writers on chemistry are not now" intelligible to those acquainted only with the modern nomenclature, a list is subjoined
142
NOMENCLATURE OFJ CHEMISTRY.
of the terms which most generally occur in old books on this subject, together with those which are now adopted instead of them.
}
Old Names arranged Alphabetically.
Acetous salts
Acid of vitriol, phlogisticated
— of alum
— of vitriol
— of vitriolic
— of sulphur
— of nitre, phlogisticated
— of nitre, dephlo-
gisticated
— of saltpetre
— of sea salt!
— marine - j"
— aerial - "]
— of chalk I
— cretaceous [>• -
— of charcoal |
— raephitic J
— of spar or fluor ")
— sparry - |
— of borax
— of arsenic
— of tungsten |
— of wolfram J'
— of molybdena
— of apples
— of sugar n
— saccharic J
— of lemons
— of tartar
— of benzoin
— of galls
— of amber
— of ants
— of phosphorus phio- ")
gisticated - j
— of phosphorus de- ")
phlogisticated J
New Names.
Acetates Sulphureous acid
Sulphuric acid
Nitrous acid Nitric acid
Muriatic acid
Carbonic acid
Fluoric acid
Boracic acid Arsenic acid
Tungstic acid
Molybdic acid Malic acid
Oxalic acid
Citric acid Tartareous acid Benzoic acid Gallic acid Succinic acid Formic acid
Phosphorus acid Phosphoric acid
NOMENCLATURE OF CHEMISTRY.
14.3
n
Old Names arranged Alphabetically,
Acid of fat \
— sedative /
— of lac -
— ofmilk
— of the sugar of milk Air -
— dephlogisticated'
— empyreal
— vital
— pure
— impure, or vitiated")
— burnt - - >
— phlogisticated J
— inflammable
— marine acid
— dephlogisticated)
— marine acid j
— hepatic - - 7
— fetid of sulphur 3 Air fixed - >
— sohd of Hales j
— alkaline Alkalies, fixed
■ volatile
— concrete volatile
caustic
effervescent, ae- \
rated, or mild J
vegetable
mineral or marine
Prussian -
Alum
Antimony, crude Aqua fortis -
regia -
ammonia pura
Argil, or argillaceous earth
Bezoar mineral
Black lead -
Borax
Butters of the metals
Calces, metallic
Ceruse
Nexv Names.
- Sebacic acid
- Laccic acid
- Lactic acid
- Saccho-lactic acid
- Gas
- Oxygen gas
- Nitrogen, azote, or azotic gas
- Hydrogen gas
- Muriatic acid gas
- Oxygenated muriatic acid gas,
or chlorine
- Sulphureted hydrogen
- Carbonic acid gas
- Ammoniacal gas
- Potash and soda
- Ammonia
- Carbonate of ammonia
- Pure alkalies
- Alkaline carbonates
- Potass
- Soda
- Prussiate of potash
- Sulphate of alumine and potash Svdphuret of antimony
- Nitric acid of commerce
- Nitro-muriatic acid Ammonia
- Alumine, or alumina
- Oxide of antimony
- Plumbago
- Borate of soda
- Muriates of the metals
- Metallic oxides
» Carbonate of lead
144<
NOMENCLATURE OF CHEMISTRY.
Old Names arranged Alphabetically. Ceruse of antimony - Charcoal, pure
Colcothar of vitriol -
Copper, acetated Copperas, green
• blue Cream of tartar Earth, calcareous
aluminous
siliceous
' ponderous
magnesian, or muriatic
Emetic tartar
Essences . - -
Ethiops, martial
• mineral
Flowers, metallic
of sulphur -
Fluors . - -
Hepars . - -
Heat, latent
Kermes mineral
Lapis infernalis Leys
Liquor sllicum 1 of flints J
Litharge
Liver of sulphur, alkaline
calcareous
Luna cornea
Magistery of bismuth
Magnesia alba ")
• aerated j
■ black
Masticot
Mephitis
Minium
Mother waters
Nitre, or saltpetre -
Neix Names.
White oxide of antimony
Carbon S Red oxide of iron by the sul- ( phuric acid
Acetate of copper
Sulphate of iron of copper
Acidulous tartrate of potash
Lime
Alumina, or alumina . Silex
Barytes
Magnesia
Antimoniated tartrate of potash
Volatile oils
Black oxide of iron J Black sulphureted oxide of \ mercury
Sublimated metallic oxides
Sublimated sulphur
Fluates
Sulphurets
Caloric f Red sulphureted oxide of an- \ timony
Fused nitrate of silver
Solutions of alkalies
Solution of siliceous potash
J Semivitreous oxide of lead or \ litharge
Sulphuret of potash of lime
Muriate of silver (Oxide of bismuth by the nitric I acid
Carbonate of magnesia '
Black oxide of manganese Yellow oxide of lead -
■ Nitrogen gas
• Red oxide of lead
• Saline residues
■ Nitrate of potass
NOMENCLATURE OF CHEMISTRY.
145
Old Names arranged Alphabetically. Nitres
Oils, fat - • etherial of tartar per deliquium
Phlogiston -
Phosphoric salts
Precipitate, red
■ per se
Principle, astringent
■ tanning -
— — acidifying
inflammable
Pyrites of copper
Pyrites martial
Realgar
Reguliis of the metals Rust of iron Saffron of Mars Sal ammoniac — polychrest Salt, common or sea
— febrifuge of Sylvius
— fusible of urine
— Glauber's
— Epsom -
— of sorrel
— of wormwood -
— vegetable Saltpetre Selinite
Spar, calcareous
fluor -
ponderous
Spirit, ardent "i
of wine 3
— — of nitre
of salt
Nex'o Names.
' Nitrates . Fixed oil ■ Essential oils
A solution of potash
f A principle imagined by Stalil,
\ but now not admitted . Phosphates
f Red oxide of mercury by the
\ nitric acid
- Red oxide of mercury by fire
- Gallic acid
- Tannin
- Oxygen
- See Phlogiston
- Copper pyrites
rlron pyrites, or sulphuret of "1 iron
("Red sulphuretted oxide of \ arsenic
- The metals in a pure state
- Oxide of iron
- Oxide of iron
- Muriate of ammonia
- Sulphate of potash
- Muriate of soda
- Muriate of potash
- Phosphate of soda
- Sulphate of soda
of magnesia
- Acidulous oxalate of potash
- Carbonate of potash
- Tartrite of potash
- Nitrate of potash
- Sulphate of lime
- Crystallized carbonate of lime
- Fluate of lime
- Sulphate of barytea
- Alkohol
- Nitric acid
- Nitrous acid
- Muriatic acid
VOL. II.
146
NOMENCLATURE OF CHEMISTRY.
Old Names arranged Alphabetically. Spirit of sal ammoniac
of vitriol
Spiritus rector Sublimate, corrosive Sugar of lead Tartar
emetic
vitriolated
Tartars
Tinctures, spirituous
Turbeth mineral
Vinegar, distilled")
radical j
Vitriols Vitriol, blue
green
— — white
Water acidulated "^ hepatic
Netu Names.
• Ammonia Sulphuric acid
• Aroma
- Muriate of mercury
■ Acetate of lead
■ Acidulous tartrite of potash Antimoniated tartrite of potash
■ Sulphate of potash
■ Tartrites
Resins dissolved in alkohol J Yellow oxide of mercury by the \ sulphuric acid
Acetic acid
■ Sulphates
. Sulphate of copper
of iron
of zinc
c Water impregnated with car- \ bonic acid gas
{Water impregnated with sul- phuretted hydrogen
147
MANUFACTURES AND ARTS.
The modern sciences, and particul-ajy cbemjstjy, have been of late successfully applied to the im- provement of several of the useful arts j and some, in consequence, have undergone almost an entire change. Of the principles of some of them we propose to give a brief description.
MAKING BREAD.
Scarcely any nation exists, in which the use of bread is entirely unknown, or something as a sub- stitute for it ; a dry food appearing to be neces- sary to promote the secretion of saliva, in the pro- cess of mastication.
In Lapland, where they have no corn, they make a kind of bread from dried fish, and of the inner rind of the bark of the pine. In some parts of xlmerica, they use, for this purpose, casava, the root of a plant which is poisonous till it is rendered whole- some by the extraction of its acrid juice. In the South Sea islands, the bread-fruit tree affords the natives a substance resembling bread.
From time immemorial, the farinaceous seeds have been employed as food, and they are the most nutritive of all the vegetables. Few of the alimen- tary substances are used by man in a raw ana crude state; almost all undergo some preparation, by which they are rendered more easy of diges- tion, or are more palatable. The application of
L ^
148 MAKING BREAD.
heat generally effects considerable changes in tlie different principles of which they are composed. Thus, bread from wheat is no longer capable of forming a paste with water, such as can be made with flour ; nor can starch, and gluten, elements existing in flour, be obtained from it after it has been baked in bread. The alteration in potatoes by the culinary process is even more considerable.
The farinaceous vegetables used for making bread, are chiefly wheat, barley, oats, rye, buck wheat, maize, beans, pease, rice, potatoes, &c. In times of scarcity, other substances have been used, as acorns, chesnuts, &c.
Of all these wheat is found to afford the best bread, and we shall begin by describing it. Wheat flour, when analysed, is found to consist of — 1. Gluten. 2. Fecula, or starch, 3. Saccharine matter, or mucilage.
The gluten is very elastic, of a greyish white colour, and when drawn out to its fullest extent, has the appearance of animal membrane. In this state, it adheres to many bodies, and forms a very tenacious glue, which has been used for mending broken porcelain. It is insoluble in water, alkohol, ether, or oil ; and, in many of its properties, it re- sembles animal substances.
The Jecula is a delicate white powder, soft to the touch, scarcely sensible to the taste, almost inso- luble in cold water, but soluble in warm water.
The saccharine part is a sugar similar to what is contained in other vegetables.
These three constituent principles are easily separated from each other in the following manner. Knead some flour with water, and let a stream of water constantly flow over it. The fecula, or starch, will be carried off' by the water, and will
MAKING BREAD. 149
fall to the bottom of the vessel where it is collected; the siiffar will be held in solution in the water em- ployed, and the gluten will remain alone.
There are three sorts of bread in general use, prepared from wheat flour : 1. Unleavened bread. 2. Leavened bread. S. Bread made with yeast.
Unleavened Bread.
When flour is kneaded with water, it forms a tough adhesive paste, containing the constituent principles of flour, with little or no alteration, and not easily digested by the stomach.
When formed into cakes, and baked by heat, the gluten, and probably the starch, undergo a con- siderable change, and the compound is rendered more easy of digestion.
Bread made in this manner, without any addition, is called unleavened bread. It is not porous, but solid and heavy.
This is, no doubt, the most ancient method of preparing bread, and it is still used in many coun- tries. The oat cakes, and barley bread, used in Scotland, and the north of England, are of this kind ; so are also biscuits of all kinds.
Unleavened bread is also used by the Jews during the Passover.
OfLeave7ied Bread.
When flour is kneaded with water, it is called dough ; and when this is kept in a warm place, it swells up, becomes spongy, and is filled with air- bubbles ; it disengages at length an acidulous and spiritous smell, tastes sour, and in this st3>t,e is called leaven, .7.: .
Here the saccharine part has been converted into ardent spirit, the mucilage tends to acidity,
L 3
||J0 MAKING BREAD.
and the gluten probably verges towards a state of putridity. By this incessant fermentation, the mass is rendered more digestible and light, that is, it becomes much more porous by the disengage- ment of elastic fluid, which separates its parts from each other, and much enlarges its bulk. The operation of baking puts a stop to this process, by evaporating a great part of the moisture, which favours the chemical attractions, and probably also by further changing the nature of the component parts. Bread, however, in this state, will not pos- sess the requisite uniformity. In order to promote an uniform fermentation, a small portion of leaven is intimately blended with a quantity of other dough, which, by the aid of heat, diffuses itself, and causes all the parts to ferment at the same time. As soon as the dough has acquired a suffi- cient bulk from the extrication of carbonic acid gas, it is considered as fit for the oven. It will be necessary here to consider more at large the nature of the fermentation^ which is so essential in the making of good bread.
When wheat-flour and water are mixed, the saccharine extract of the flour, in consequence of heat and moisture, has its constituent principles disunited ; the oxygen seizes the carbon, forming carbonic acid, which flies off in the form of gas, and occasions that internal motion and increase which appears. This process, if left to itself, is extremely slow, and is therefore accelerated by the addition of more dough and warm water. The gluten, being dispersed through every part of the mass, forms a membrane among the dougli, which suffers the carbonic acid gas to expand, but pre- vents its total escape, thus causing that porous reticulated appearance, which fermented bread
MAKING BREAD. 15|
always has. As soon as the dough begins to sink it is made up into the proper form, and put into the oven, where tlie heat converting the water into an elastic vapour, the loaf rises still more. The fer- mentation by means of leaven is thought to be of the acetous kind, because it is generally so managed that the bread has a sour taste.
Bread made mth Yeast.
Yeast is the froth formed upon the surface of beer, or ale, in a state of fermentation, and is com- posed of carbonic acid gas inclosed in bubbles of the mucilaginous liquor. When this is mixed with dough, it causes it to ferment, and rise better and more quickly than ordinary leaven ; and by this means the best bread, and that now most generally in use, is made.
Bread made with yeast is not only less compact, lighter, and of a much more agreeable taste than the preceding kinds ; but it is also more miscible in water, with which it does not form a viscous mass, a circumstance of the greatest importance in digestion.
Bread, if well baked, is materially different from flour and farinaceous cakes ; it no longer forms a tenacious dough with water, nor can starch or gluten be any more separated from it, : and hence most probably its good qualities result.
The method of making common family bread is as follows : to half a bushel of flour add six ounces of salt, a pint of yeast, and six quarts of water that has boiled ; in warm weather pour the water in nearly cold, but it winter let it be lukewarm. Put all these into a kneading-trough, and work them together till they are the proper consistence of dough. Cover up the dough warm that it may
L 4
152 MAKING BREAD.
ferment and rise. This is called setting the sponge. After letting it lie the proper time, an hour and a half, more or less, knead it well together, and let it lie some time longer covered up. The oven must in the mean time be heated : when this is done, and it is properly cleaned, make the bread into loaves, and place them in the oven to bake.
Household hread^ or brown bread, is baked in the same manner, only of flour that is made from the whole of the wheat, the bran as well as the flour being ground together ; whereas in the white bread, the coarser part of tlie bran is separated from the flour. In what is called French bread, the fermentation is carried on longer than in com- mon bread, by which it becomes more porous, and consequently lighter. Some bakers make a supe- rior kind of French bread, by putting together a peck and a half of the finest wheaten flour, called Hertfordshire white, a pint of milk, a quarter of a pound of salt, a pint and half of yeast, a quarter of a pound of butter, two eggs, and three quarts of water ; it is baked nearly in the same manner, only frequently turning the bread in the oven.
The process used by the bakers for making bread varies from what has been described, only in circumstances depending on the great quan- tity that is baked at a time. It is said that they are apt to adulterate the bread sometimes with alum, and also with chalk, and for this they are severely punishable ; and any one suspecting it may easily detect it by cutting a loaf in slices, and mixing it with water which will dissolve the alum : and it may then be obtained by evaporation.
Bread is made from the farinaceous grains ; but of these, barley, oats, and rye, are most generally used in Great Britain next to wheat. Wheat alone
MAKING BREAD, 153
possesses the gluten above described, which is so useful in making the bread porous and light ; on which account it is more difficult to make fer- mented bread from the other grains : but this dif- ficulty is obviated by adding to them a small quan- tity of wheat flour, and many of them afford bread nearly as nutritious, if not entirely so, as wheat. It appears to be the fecula, or starch, that is the the most nutritive part of the grain ; the potatoe, which contains a great proportion of this substance, forms the food of the most of peasantry in Ireland.
Ri/e h^ead is of a brownish colour, and has rather a sweetish taste. It is much used in the north of Europe, and also in some parts of this kingdom ; but it is more usually mixed with a quantity of wheaten flour.
Rye is also sometimes mixed with a fourth part of ground rice, and makes a good and economical household bread.
Bread has also been made by mixing turrdps and flour in equal quantities. This requires rather longer baking, and has at flrst a sweet taste, which it loses on being kept twenty-four hours.
RicCy though usually prepared for food by boil- ing, has been made into bread by mixing with it a little flour, or potatoes.
Potatoes have also been made into bread by mixing with them a quantity of wheaten flour,
BREWING.
The art of brewing, or of preparing a fermented liquor called heer^ from farinaceous seeds, is very ancient. It was known to the ancient Egyptians, Spaniards, Germans, Gauls, inhabitants of the British Isles, and of the north of Europe. The
l^l* BREWING.
liquor made by them, however, resembled more our sweet and mucilaginous ales, the use of hops being of modern invention.
Beer is made of an extract produced from malt and hops by boiling ; and this extract is after- wards fermented by adding yeast to it.
Malt is made from barley by a process which is called malting. Barley is a grain consisting of fecula, or starch, albumen, and a little gluten. By the process of malting, its fecula is converted into sugar, a substance essential to the production of ardent spirit or alkohol, w^hich is the substance that gives the intoxicating quality to every liquor. To prepare malt, the grain is put into a trough with water, to steep for about three days j it is then laid in heaps, to let the water drain from it, and afterwards turned over and laid in new heaps. In this state, the same process takes place as if the barley were sown in the ground; it begins to germinate, puts forth a shoot, and the fecula of the seed is converted into saccharine matter. When this is sufficiently accomplished, which is known by the length of the shoot, (about \ of the length of the grain) this process of germination must be stopped, otherwise the sugar would be lost, nature intending it for the nourishment of the young plant. The malt is, therefore, spread out upon a floor, and frequently turned over, which cools it, and dries up its moisture, without which the germination cannot proceed. When it is completely dried in this manner, it is called air- dried malt, and is very little altered in colour. But when it is dried in kilns, it acquires a brownish colour, which is deeper in proportion to the heat applied ; it is then called lUn-dried, This malt is then coarsely gi'ound in a mill.
BREWING. 155
The quality of the beer depends upon the way in which the malt has been prepared as well as the quantity. There are three kinds of malt generally used, pale, brown, and amber. Pale malt is dried by a slow fire, and only so much as just to check the future germination of the grain : it is dried sometimes upon hair or wire sieves, which are made to form the bottom of the kiln. Brown malt is dried with a quick fire, and the outside is in fact a little charred. Amber malt is intermediate be- tween these two.
Pale malt is used for fine ales and pale beer : brown malt is used for porter ; and amber is em- ployed for brown ale and beer, and also to mix with brown malt for porter, a practice which many prefer.
MasJiing is the next step in the process of brew- ing. This is performed in a large circular wooden vessel called the mash-tun, shallow in proportion to its extent, and furnished with a false bottom, pierced with small holes, and fixed a few inches above the real bottom. There are two side open- ings in the interval between the real and false bottom : to one is fixed a pipe, for the purpose of conveying water into the tun, and the other is for drawing the liquor out of it. The malt is to be strewed evenly over the false bottom of the same tun, and then, by means of the side pipe, a proper quantity of hot water is introduced from the upper copper. The water rises upwards through the malt, or, as it is called, the grist, and when the whole quantity is introduced, the mashing begins, the object of which is to efiect a perfect mixture of the malt with the water, so that the soluble parts may be extracted by it : for this purpose, the grist is sometimes incorporated with the water by iron rakes, and then the mass is beaten and agitated by
166 BREWING.
long flat wooden poles, resembling oars, which are either worked by the hand or by machinery.
When the mashing is completed, the tun is co- vered in, to prevent the escape of the heat, and the whole is suffered to remain still, in order that the insoluble parts may separate from the liquor : the side pipe is then opened, and the clear wort al- lowed to run off, slowly at first, but more rapidly as it becomes fine, into the lower or boiling copper.
The chief thing to be attended to in mashing is the temperature of the mash, which depends on the heat of the water, and the state of the malt. If the water was let in upon the grist boiling hot, the starch which it contains would be dissolved, and converted into a gelatinous substance, in which all the other parts of the malt, and most of the water, would be entangled beyond the possi- bility of being recovered by any after-process.
The most eligible temperature appears to be from 185° to 190^ Fahr. j for the first mashing, the heat of the water must be somewhat below this temperature, and lower in proportion to the dark colour of the malt made use of. For pale malt the water may be 180°, but for brown it ought not to be more than 170°.
The liquor, or wort, as it is called, of the first mashing, is always by much the richest in saccha- rine matter ; but to exhaust the malt, a second and third mashing is required, in which the water may be safely raised to 190°, or upwards.
The proportion of wort to be obtained from each bushel of malt depends entirely on the pro- posed strength of the liquor. It is said that twenty- five or thirty gallons of good table beer may be taken from each bushel of malt. For ale and porter of the superior kinds, only the produce of the
BREWING. 157
first mashing, or six or eight gallons, is to be em- ployed.
Brewers make use of an instrument called a sacchrometer, to ascertain the strength and good- ness of the wort. This instrument is a kind of hydrometer, and shows the specific gravity of the wort, rather than the exact quantity of saccharine matter which it contains.
The next process in brewing is boiling and hopping. The hop plant is well known : hops con- tain an aromatic and essential oil, having an agree- able bitter flavour. Hops are necessary to prevent the beer from passing into the acetic fermentation, which would take place after the vinous ferment- ation had ceased. They check the fermentation in a great degree, so as to occasion it to go on slowly, and thus to acquire strength ; and the quan- tity of hops depends upon the length of time the beer is intended to be kept. Hops are best when new, as they lose much of their flavour by keeping.
If only one kind of liquor is made, the produce of the three mashings is to be mixed together ; but, if ale and table beer are required, the wort of the first, or first and second mashings, is appropri- ated to the ale, and the remainder is set aside for the beer.
All the wort destined for the same liquor, after it has run from the tun, is transferred to the large lower copper, and mixed with a certain proportion of hops. The better the wort, the more hops are required. In private families a pound of hops is generally used to every bushel of malt ; but in public breweries, a much smaller proportion is deemed sufficient. When ale and table beer are brewed from the same malt, the usual practice is to put the whole quantity of hops in the ale wort, which.
158 BREWING.
liaving been boiled some time, are to be transferred to the beer- wort, and with it to be again boiled.
When the hops are mixed with the wort in the copper, the liquor is made to boil, and the best practice is to keep it boiling as fast as possible, till upon taking a little of the liquor out, it is found to be full of small flakes like that of curdled soap. The boiling copper is, in common breweries, unco- vered : but in many, on a large scale, it is fitted with a steam-tight cover, from the centre of which passes a pipe, that terminates by several branches in the upper, or mashing copper. The steam, therefore, produced by the boiling, instead of being wasted, is let into the cold water, and thus raises it very nearly to the temperature required for mashing, besides impregnating it very sensibly with the essential oil of the hops, in which the flavour resides.
Vv^hen the liquor is boiled, it is discharged into a number of coolers, or shallow tubs, in which it re- mains until it becomes sufficiently cool to be sub- mitted to fermentation. It is necessary that the process of cooling should be carried on as expedi- tiously as possible, particularly in hot weather ; and for this reason, the coolers in the brewhouses are very shallow. Liquor made from pale malt, and which is intended for immediate drinking, need not be cooled lower than 7-5 or 80 degrees ; of course this kind of beer may be brewed in the hottest weather ; but beer brewed from brown malt, and intended to be kept, must be cooled to 65° or 70*^ before it is put into a state of ferment- ation. Hence in the spring, the month of March, and in autumn, the month of October, have been deemed the most favourable for the manufacture of the best malt liquor.
BREWING. 159
From the coolers the wort is put into the "work- ing tun, in which it is mixed with yeast, in the proportion of a gallon to four barrels of wort, in order to excite the vinous fermentation. This process is called tunning. By this the beer obtains its strength and spirit ; the sugar extracted from the malt being con\^erted into alkohol. In four or five hours the fermentation begins. Its first appearance is by a white line on the surface of the liquor, next to the side of the vessel, which gradually advances to the middle, till the w^hole surface is covered with a scum, or froth, formed by innumerable minute bubbles of carbonic acid gas, which rise through the liquor. The temperature of the liquor increases, and the whole is much agitated. The froth on the surface accumulates, and constitutes the yeast. At this time the presence of carbonic acid gas may be easily perceived, by holding one's head over the barrel or tun ; and fatal accidents have happened through the accumulation of this gas in situations where persons have been exposed to it without being able to remove.
The vinous fermentation must be checked in time, otherwise the acetous fermentation would begin ; all the spirit would be lost, and the beer would become sour.
The fermentation requires from 18 or 20 to 48 hours J and the beer is then put into smaller barrels, called cleansing tuns. In them, the fermentation goes on again, and during a fev/ days, a copious discharge of yeast takes place from the bung-hole. Care must be taken that the barrels are filled every day with fresh liquor. This discharge gradually becomes less, and in about a week it ceases j when the bung-hole is closed.
The liquor is now suffered to stand for some
160 BLEACHING.
time tojine (or become transparent), by depositing the mucilage that was suspended in it. When there is time, the beer is allowed to fine itself; if not, a preparation of isinglass and sour beer, called Jinings, is put into it, to precipitate the mucilage.
A larger quantity of hops are used in porter than for ales. Although in porter the brown malts are necessary, it is bad economy to use them too highly dried for the deepening of the colour, since the consequence of drying too highly is a carbonization of part of the saccharine matter. A dark colour may be procured more economically by adding burnt sugar to the wort.
It is in Britain prohibited by law to use any sub- stance in brewing, as a substitute for hops.
BLEACHING.
Bleaching is the art of whitening cloths, made from vegetable or animal substances, by depriving them of their colouring matter. The art is of great antiquity; and mankind, in all ages, appear to have admired garments of a pure whiteness. The effects produced by the air and rain upon vegetable fibres exposed to them, must have led originally to the idea of producing this by artificial means. The ancients appear to have been acquainted with the uses of soap and leys ; and to have practised bleach- ing, nearly in the same manner as it existed among us until lately. But few manufactures have received so much benefit from modern chemistry, as that now under consideration ; so that since the year 1786, it has undergone a complete change.
Bleaching ofLineth
The processes of bleaching difl'er materially, according to the different materials of which cloths
BLEACHING. l6l
are composed: thus, linen, cotton, woollens, and silk, are whitened by different methods. lu order to understand the rationale of the bleaching pro- cesses, it is necessary to be acquainted with the nature of the materials.
Flax, from which linen is formed, is a vegetable consisting of several coats or layers. The external coat is a very thin bark ; under this is a green juice or sap; next lies a layer of fibres or filaments, which constitutes the part used for making linen ; and, lastly, in the centre, there is a woody part. To prepare flax for making cloth, the filaments or fibrous part must be separated from the rest. The filaments are held together by the sap, or succulent part. To detach them from this, the flax is steeped for several days in pools or ponds of soft stagnant water; by which the putrefactive fermentation takes place. But this fermentation must not be suffered to proceed too far; otherwise the fibres themselves would be aflR^cted by it, and their texture injured. The flax must be taken out while it is yet green, and while the wood breaks easily between the fingers. The putrefaction of the sap occasions the water in which the flax is steeped to be extremely offensive ; and it is even found that the fish are destroyed in any stream where this process is used.
In some places, instead of steeping the flax in water, it is simply exposed to the dew by laying it on the grass.
The time required for this part of the process is variable ; depending upon the state of ripeness of the flax, the quahty and temperature of the water, and other circumstances.
After steeping the flax, where the watering sys- tem is practised, it is spread very thin on the grass,
VOL. II. M
l6^ BLEACHING.
and occasionally turned, until it is found to be very brittlej so that on being rubbed between the hands, the woody part easily separates. It is then dried by the heat of the sun or of a kiln.
The flax is now ready to be beat or broke by a mill for the purpose, or by mallets on a sort of wooden anvil. The fibres of the flax are thus separated from the wood, which is reduced to frag- ments, most of which are cleared away by scutc7ii?ig.
To divide completely the fibres from each other, and to separate the remaining part of the wood, the process of hackling is employed. This consists in drawing the flax through piles or groups of sharp and polished iron spikes, placed close together, and fixed in wood. The Ifackles are of various degrees of fineness ; that is, the spikes are placed at different degrees of distance from each other. The coarsest, or most open hackles, are used first ; then a finer, and so on, till the process is completed.
The flax is now ready to be spun into thread or yarn, which is manufactured into cloth by the weaver.
The linen, as it comes from the loom, is of a brownish grey colour ; and it is then that the pro- cess of bleachiuff- be^'ins.
The linen is first steeped in cold water for 48 hours, to discharge from it the weaver's dressing ; which is a paste of flour and water, that had been brushed into the yarn to enable them to stretch it more easily.
The grey substance that colours the linen before it is bleached is of a resinous nature, and conse- quently it is insoluble in water. It is also intimately united with the fibres of the flax, and is of difficult separation. What appears to the eye to be a single fibre is, in fact, a bundle of minute filaments, agglu-
^I,E ACHING. 163
dilated t.ogethei' by this resiijoijs matter. To sepa- rate these filaments from eacli otlier, and to destroy entirely the resinous colouring matter, is ^a process of some difficulty. Solutions of alcalies rendered caustic *5 called alcaline leySy have the property of dissolving resins ; hence they have been used for this purpose in bleaching. The linen is boiied in water containing a quantity of ca'.:::;tic potash, which acts upon the resiil of the external filaments, and loosens them a little irom each Qther. The cloth is then spread upon the grass, and exposed to the action of the air, sun, and dew; and is also occasionally watered. It is then returned again into the bucking vat ; and the alkaline solution is poured over it : by this another layer of the fila- ments is opened, and the resin dissolved. It ds then carried again to the field, and ti'eated as before. In this manner, the ibucking and spreading on the grass are repeated alternately, for 15 oi' 16 times, according to the weather and other circum- stances, until the clotli is whitened. Were the alcaline ley go strong as to dissolve xill the resin at once, it would injure the texture of the fabric.
This alternate bucking and. exposing on the grass is the old manner of bleaching, and was universally used, till Scheele discovered the properties of the oxygenated muriatic acid in destroying vegetable colours. M. Bertholiet first applied this property to the purposes of bleaching, and he, with great liberality, communicated his observations to the public. For this purpose, he immersed the cloth into diluted oxygenated muriatic acid, between the operations of the alcaline leys, which produced .the
* Common potash is rendered sufficiently.c^usdcfor the pur- pose of bleaching, by adding to it quickhme, which nas a stronger affinity for the carbonic acid than potash.
M S
I64f BLEACHING.
same effect in whitening it, as by exposing it to the action of the air and light in the field.
The new method of bleaching was quickly and successfully introduced into the manufactories of France ; and almost as soon into those of Great Britain. It is now universally adopted. The advantages are, that the time required for bleach- ing is shortened in a surprising degree so that manufacturers experience a much quicker return of their capitals ; and that it may be carried on at all seasons of the year.
The first way in which the oxymuriatic acid was applied in bleaching was in the liquid state ; that is, when water is impregnated with the gas. The goods were immersed in this liquid according to the nature of the objects to be bleached. Skeins of thread were suspended on frames in the tub in- tended to receive them ; cloth was rolled upon reels. When every thing was thus disposed, the tubs were filled with oxygenated muriatic acid, by introducing a funnel that descended to the bottom of the tub in order to prevent the dispersion of the gas. The cloth, or thread, was made to pass through the liquid by turning the frames, until it was judged that the acid was exhausted by acting on the colouring matter.
But the volatility of this acid, and the suffocating nature of its vapours, which produced extremely noxious effects upon the health of the workmen, rendered its use very difficult, although very in- genious apparatus had been invented both by Ber- thollet and by Mr. Watts. It was also found diffi- cult to cause the acid to act upon all parts of the cloths equally, when they were stratified in the cis- terns with the acid.
A considerable improvement was made in the
BLEACHING. 16.5
apparatus by Mr. Rupp of Manchester, which is described in the Manchester Memoirs. Still it was found that the acid alone was apt to weaken the cloth, and that it injured the health of the workmen.
At length it was discovered by some manufac- turers at Javelle, near Paris, that the addition of an alkali to the liquor deprived it of its suffocating effects, without destroying its bleaching powers. Potash was the alcali they employed ; and this so- lution was called the Javelle liquor. The invent- ors came into this country, and established a bleaching-work. The process was then carried on in open vessels ; and the bleacher was able to work his pieces in the liquid, and expose every part to its action without inconvenience.
Although these advantages were unquestionably great, they were diminished by the heavy expense of the alcali, which was entirely lost. Also, the the potash, which added to the liquor, though it did not destroy its power of bleaching, diminished it; because a solution of the oxygenated muriate of potash, which differs from this bleaching-liquor in nothing but in the° proportion of alcali, will not bleach at all. This is a well-known fact; from which we might infer, that the oxygenated muri- atic acid will lose its power of destroying the co- louring-matter of vegetable substances, in propor- tion as it becomes neutralized.
Mr. Tennant discovered that lime might be substituted for the potash, the oxymuriatic acid combining with all the alcaline earths, and forming oxymuriates which were soluble in water, and had the property of bleaching. This is the substance nov/ employed. If the oxygenated muriatic acid be passed through lime-water, it will combine with
M 3
1©6 BLEACHING.
the lime, and form oxymuriate of lime ; but as the water can only retain a small portion of lime, this was not found of much use. To cause a larger quantity of lime to combine with the oxymuriatic acid gas, the lime is mechanically suspended by agitation in the water into which the gas is made to passj so as to present fresh matter to the gas. By this means, the oxymuriatic acid combines with the lime, forming a compound soluble in the water : this is used as a bleaching-liquor.
The oxygenated muriatic acid gas may also be combined with lime in a dry state. To effect this, the oxymuriatic acid gas is sent into a vessel contain- ing dry hydrate of lime (that is, lime slacked with water) : the powder is agitatedj and the gas com- bines with it to a certain amount, or till the hy- drate of hme becomes saturated. The compound is a soft white powder, possessing little smell. It is partially soluble in water, yielding a solution much the same as that obtained by the former process.
Although most salts that are soluble in Water are capable of being formed again by evaporating the water, either in crystals or in a dry Saline mass, this is not the case with oxymuriate of lime. When- ever a solution of it is evaporated, part of the acid escapes, and the rest is mostly converted into mii- riatic acid ; so that ins,te?A of oa^i/jrmriate of lime, muriate of lime is obtained. Hence the dry salt cannot be obtained from the liquid solution.
The dry oxymuriate of lime may be very Con- veniently transported without injury, an advantage not possessed by the acid alone, which cannot be transported without the loss of almost half its strength : but it must be observed that the dry salt is much imjiaired by being long kept.
BLEACHING. l67
*'We have hitherto used the old term of oxynuiri- atic acid, because it is best known by this name in the bleaching processes ; but it will be remem- bered that this substance is now considered as a simple body, and is known by the name of chlorine. What has just been called oxymuriate of lime is known among modern cliemists by the term cldorate of lime.
The oxymuriatic acid gas, or chlorine, may be procured by distilling muriatic acid in black oxide of manganese ; but to save the expense of first preparing the muriatic acid, the usual practice in bleaching is to mix three parts of black oxide of manganese with eight parts of muriate of soda or common salt, and five parts sulphuric acid, diluted with four parts water.
To ascertain the strength of the liquid for bleaching, a solution of indigo in the sulphuric acid is employed. The colour of this is destroyed by the oxygenated muriatic acid; and according to the quantity of it that can be discoloured by a given quantity of the liquor, its strength is known.
The linen is usually not immersed in the solution of oxymuriate of lime until after the fourth or fifth bucking ; because a great portion of the resin is removed cheaper by the alkaline leys, and washing in water.
Tlie last operation in bleaching is souring, or steeping the linen in some sour liquid of a blood heat. For this purpose, formerly sour milk was em- ployed : but now sulphuric acid is used. Of this as much is put into water as will give it the acidity of vinegar. The linens are generally steeped about twelve hours, and are tlien well washed. This souring is essential to the procuring of a good white, but the theory of its action is not well understood.
TNI 4
168 BLEACHING.
Nothing now remains, in order to complete them for the market, but rubbing them with a strong lather of soap, washing, and blueing them. The alcali is one of the chief articles of expense used in bleaching : and it is a great object with the bleacher to recover the pure alcali from the leys which have been used.
The sulphuret of lime, or the combination of sulphur and lime, which are both cheap articles, has been used in Ireland for bleaching, instead of potash. It was first proposed by Mr. Higgins, and it answers in some cases, particularly where the goods are intended for dying.
The sulphiu'et of Hme is prepared as follows: — sulpliur in powder, four pounds j lime, well slaked, twenty pounds ; and water, sixteen gallons ; are to be well mixed, and boiled for half an hour in an iron vessel, stirring them briskly from tim.e to time. Soon after the agitation of boiUng is over, the so- lution of the sulphuret clears, and may be drawn off free from the insohible matter, which is consider- able, and whicli rests upon the bottom of the boiler. The liquor in this state is pretty nearly of the colour of small beer, but not quite so transparent. Sixteen gallons of fresh water are afterwards to be poured upon the insoluble dregs in the boiler, in order to separate the whole of the sulphuret from them. When this clears (being previously well agitated) it is also to be drawn off and mixed with the first liquor ; to these again, thirty-three gallons more of water may be added, which will reduce the liquor to a proper standard for steeping the cloth. Here we have (an allowance being made for evaporation, and for the quantity re- tained ill the dregs) sixty gallons of liquor from four pounds of sulphur.
BLEACHING. IgQ
Althougli sulphur, by itself, is not in any sensible degree soluble in water, and lime but sparingly so, water dissolving only about one seven hundredth part of its weight of lime ; yet the sulphuret of lime 19 highly soluble.
After the paste used by the weaver has been re- moved, the linen is steeped in a solution of the sulphuret of lime, prepared as above, for about twelve or eighteen hours. It is then washed, and steeped in oxymuriate of lime. This process is repeated by six alternate immersions in each liquor. For the use of private families, where the linen is dirtied by perspiration or grease, it will be of great service towards rendering it white, to steep it for some time in a clear liquor, made by mixing one quart ofquick-Ume in ten gallons of water, letting the mixture stand for twenty-four hours, and then using the clean water drawn off from the lime. After the linen has been steeped in this liquor, it should be well washed as usual, but will require much less soap to be used.
It is of great consequence in bleaching with the oxygenated muriatic acid, that it may be employed of a proper strength ; as a test to ascertain its strength, a solution of indigo in sulphuric acid is used. A certain quantity is put into a glass tube, and Oxygenated muriatic acid is added until the colour of the indigo is destroyed : by the quantity of acid necessary to destroy the colour, its strength is estimated.
Steam has been employed in bleaching in France with great success. The process was brought from the Levant. Chaptal lirst made it known to the public. When an aicaline ley is boiled, a certain quau-tity of aicali always rises with ihe steam. The
170 BLEACHING.
cloth is first immersed in weak caustic alcaline liquor, and placed over a chamber constructed over a boiler, into which is put the alcaline ley which is to be raised into steam. After the fire has been lighted, and the cloth lias remained exposed to the action of the steam for a sufiicient length of time, it is taken out, and immersed in the oxygenated muriate of lime, and afterwards exposed for two or three days on the grass.
This operation, which is very expeditious, is suf- ficient for cotton ; but if linen-cloth should still retain a yellow tint, a second alcaline vapour-bath, and two or three days exposure on the grass, will be sufficient to give them the necessary degree of whiteness.
Bleaching of Cotton.
Cotton is a vegetable substance, and the pro- duction of a shrub that grows only in warm climates. It is a fine downy substance, in which the seeds of the plant are inclosed. Cotton, in its natural state, is generally of a dirty yellow, and opaque, being- covered with a colouring matter of an unctuous nature ; when this is removed, it is white and transparent.
Cotton is easier to bleach than linen. The colouring-matter is dissolved by the action of alca- line leys and washing. Sometimes the oxymuri- atic acid is also used to expedite the process. Steeping in diluted sulphuric acid, is also used to dissolve the earthy matter that always remains after the immersion in alcaline ley; and as cotton is not so easily injured by acids as flax, more use is made of the acid than in the bleaching of linen. The
BLEACHING. I7I
action of steam is very efficacious in bleaching cottons.
In bleaching cotton for calico-printing, a pure white is not so much sought for, as that the oil may be entirely extracted.
In applying the alcaline ley, great care must be taken that no lime remains in suspension in the liquor, as it might be fixed in the cloths ; and when the sulphuric acid is used, a sulphate of lime would be formed, which in fact is a mordant for the madder ; hence the latter could not be discharged from those parts intended to be white.
For the same reason, the oxy muriate of lime can- not be used, if madder is to be discharged from any part of the cloth. When this is the case, oxy- muriate of potash, or of soda, is substituted for oxymuriate of lime.
Bleaching of Wool.
The bleaching of animal substances is somewhat different from the processes employed for vegetable substances.
Wool is a sort of very fine hair which covers the bodies of some animals. Each hair is hollow, and contains an oily matter.
Wool is not easily acted upon by acids ; is unalter- able by water, cold or boiling; but may be entirely dissolved by strong alcaline leys. On this account, the latter must be used with great caution.
Wool is oiled before it is combed and spun, and the first operation is to free it from the oil which it has thus acquired. This is called scouring. Stale urine, which contains ammonia or the volatile ^Icali, is mixed with water ; and the wool is im-
17^ BLEACHING.
mersed in this for about twenty minutes, heated to 56° Fahr. It is then taken oat, drained, and rinsed in running water ; then put into the bath of urine, and washed again. This is sometimes re- peated a third time, and sometimes scouring with soap is used.
Fulling the cloth adds also to its whiteness. Fulling is a species of scouring with a particular kind of earth called J}dler's earth. It effectually removes all grease, from the chemical affinity existing between the alumina contained in the fuller's earth and the oil of the cloth ; and thus dis- poses the fibres to be entangled and matted toge- tiier in the subsequent process of milling, employed to thicken the cloth, and render it stronger and firmer.
Scouring entirely with soap is preferred when the articles are valuable.
Sulphureous acid is also used for giving the last degree of whiteness.
Sulphuring is performed in the following man- ner. The articles to be whitened are suspended iiopn poles across a chamber, constructed so as to be perfectly close. Into this chamber is pre- viously put a quantity of sulphur in dishes. When the cloth is in, the sulphur is set fire to, and the doors of t]ie chamber are accurately sliut, and all the interstices carefully stopt up, so as to exclude entirely the atmospheric air.
The combustion of the sulphur produces a va- pour which is the sulphureous acidj this destroys the colouring matter of the wool, whicli is conse- quently rendered white. The time necessary for this process varies from six to twenty-four hours. The cloth is left in the clianiber for some time after the combustion of the sulphur has ceased 4 it
BLEACHING. 173
is then taken out and rinsed, to remove the acid; and afterwards washed with soap, to give a degree of softness.
This mode of bleaching by the combustion of sulphur is also used for other substances, as straw in the manufacture of hats, &c.
A superior method of employing the sulphureous acid in bleaching is the following. Water is im- pregnated with the sulphureous acid, and tubs are filled with this; then the stuffs are drawn through it upon reels, till they are whitened. The sulphur- eous iicid is made by decomposing the sulphuric acid by the addition of any combustible matter capable of taking away a part of its oxygen. A cheap method of effecting this is by putting chopped straw, or saw-dust, into a nlattrass, and then pour- ing over it sulphuric acid, and afterwards applying heat. The sulphureous acid gas will be formed, but will be combined with the water in the vessel.
The stuffs are then taken out, and left to drain upon a bench covered with cloth; a precaution which is necessary, because the wood might be decomposed by the sulphuric acid, and would stain the goods. They are afterwards washed in clear water. It is generally necessary to sulphur them twice before the white is sufficiently bright. Some- times Spanish white is put into the water used for washing them; and they are also aziired or blued bv disolvino^ some Prussian blue in the water. Nothing then remains to be done but dryings stretching J and pressing.
Bleaching of Silk.
Silk is an animal substance, and is prepared by a caterpillar, usually called the silk-worm. This
174^ BLEACHING.
insect inhabits warm climates, and cannot be reared in this country without difficulty, nor in sufficient quantity for the purpose of procuring silk. The south of Europe and Asia are its proper countries.
The silk is spun by the silk-worm in the form of threads of a semi-transparent matter, which it winds up round itself when it passes into the crysalis state. The threads, when formed, are connected together by a viscous substance, from which they must be separated before they can be wound off, by putting them into hot water.
The silk itself is covered with a yellow varnish, which is soluble in alcaline leys ; and as this varnish conceals the lustre of the silk, it is necessary to detach it. Silk is itself soluble in strong alkaline leys ;| care must be taken, therefore, not to injure the silk in taking off the varnish. Water at a boil- ing heat has no action on silk ; but steam dissolves its varnish.
In France they proceed as follows. They fill a boiler with a very weak solution of caustic soda, and place in a chamber connected with tlie boiler, the skeins of raw silk, wound on frames ; then they close the door of the chamber, and make the solu- tion in the boiler boil. Having continued the ebullition for twelve hours, they slacken the fire, and open the door of the chamber. The steam, which is always above 250° Fahr., will have dis- solved the gum of the silk. The skeins are then washed in warm water, wrung, and boiled a second time ', then washed again several times with soap, till they have acquired the necessary whiteness and softness.
It is not possible, however, to give to silk all the necessary splendour by this process alone ; to com- plete it, the silk must be exposed to the action of
the sulphureous acid, either in the form of gas, or combined with water, as directed for wool.
Bleaching Prints and Frinted Books.
An application has been made of the new mode o^ bleaching to the whitening of books and prints that have been soiled by smoke and time.
Simple immersion in oxygenated muriatic acid, letting the article remain in it a longer or shorter space of time, according to the strength of the li- quid W'ill be sufficient to whiten an engraving.
If it be required to whiten the paper of a bound book, as it is necessary that all the leaves should be moistened by the acid, care must be taken to open the book well, and to make the boards rest upon the edge of the vessel in such a manner that the paper alone be dipped in the liquid : the leaves must be separated from each other, so that they may be equally moistened on both sides.
The liquor assumes a yellow tint, and the pa- per, becomes white in the same proportion j at the end of two or three hours the book may be taken from the acid liquor and plunged into pure water, with the same care and precaution as recommended in regard to the acid liquor, that the water may exactly touch the two surfaces of each leaf. The water must be renewed every hour, to extract the acid remaining in the paper, and to dissipate the disagreeable smell.
By following this process, there is some danger that the pages will not be all equally whitened, either because the leaves have not been sufficiently separated, or because the liquid has had more ac- tion on the front margins than on those near the
176 BLEACHING.
binding. On this account, the best way is to de- stroy the binding entirely, that each leaf may receive an equal and perfect immersion ; and this is the second process recommended by M. Chaptal.
" They begin," says he, " by unsewing the book, and separating it into leaves, which they place in cases formed in a leaden tub, with very thin slips of wood or glass ; so that the leaves, when laid flat, are separated from each other by intervals scarcely sensible. The acid is then poured in, making it fall on the sides of the tub, in order that the leaves may not be deranged by its motion. When the workmaa judges, by the whiteness of the paper, that is has been sufficiently acted upon by the acid, it is drawn off by a cock at the bottom of the tub; and its place is supplied by clear fresh water, w^hich weakens and carries off the remains of the acid, as well as the strong smell. The leaves are then to be dried, and, after being pressed, may be again bound up.
" The leaves may be placed also vertically in the tub ; and this position seems to possess some ad- vantage, as they will be less liable to be torn.
" With this view, I constructed a wooden frame, which I adjusted to the proper height, according to the size of the leaves I wished to whiten.
" This frame supported very thin slips of wood, leaving only the space of half a line between them. I placed two leaves in each of these intervals, and kept them fixed in their place by two small wooden wedges which I pushed in between the slips.
" When the paper was whitened, I lifted up the frame with leaves, and plunged them in cold water, to remove the remains of the acid as well as the smell ; this process I prefer to the other.
BLEACHING. 177
" By this operation, books are not only cleaned, but the paper acquires a degree of whiteness su- perior to what is possessed when first made.
" The use of this acid is attended also with the valuable advantage of destroying ink-spots. This liquor has no action upon spots of oil or animal grease ; but it has been long known that a weak solution of potash will effectually remove stains of that kind,
" When I had to repair prints so torn that they exhibited only scraps pasted upon other paper, I was afraid of losing these fragments in the liquid, be- cause the paste became dissolved. In such cases, I enclosed the prints in a cylindric glass vessel, which I inverted on the water in which I had put the mixture proper for extricating the oxygenated muriatic acid gas. This vapour, by filling the whole inside of the jar, acted upon the print, ex- tracted the grease as well as ink-spots, and the fragments remained pasted to the paper."
Bleaching of Paper.
The oxygenated muriatic acid has also been ap- plied to the bleaching of paper, which it has ren- dered considerably more expeditious.
Bleaching of old printed papers to he xvorked up again. — Boil the paper for an instant in a solution of soda, rendered caustic by potash. Steep it in soap water, and then wash it, after which tlie pa- per may be reduced to a pulp by the paper-mill.
Bleaching of old written papers to he worked again. — Steep the papers in a cold solution of sul- phuric acid in water, after which wash them before they are taken to the mill. If the acidulated wa- ter be heated, it will be the more effectual.
VOL. II. N
17^ DYEING,
Bleaching of printed papers "without destroying the texture qf^ the leaves. — Steep the leaves in a caustic solution of soda, and afterwards in one of soap. Arrange the sheets alternately between cloths in the same manner as paper-makers dispose their sheets of paper when delivered from the form. Put the leaves in a press, and they will be- come whiter, unless they were originally loaded with printers' ink or size. If this should not com- pletely effect the whitening of the leaves, repeat, the process a second, or even a third time.
Bleaching coloured rags to make ichite paper. — Soak or macerate the rags sufficiently ; put them into a solution of caustic alcali, and then into the oxygenated muriatic acid ; and, lastly, steep them into diluted sulphuric acid.
DYEING.
Dyeing is the art of extracting the colouring principle from different substances, and transfer- ring them to wool, silk, cotton, or linen. AVlien other matters are coloured, the process is called staifiing.
In dyeing, the colouring matter is not merely de- posited on the stuff, but is firmly attached to it by chemical combination depending on an affinity subsisting between them.
If the colouring matters were merely spread over the surface of the fibres of the cloth, the co- lours produced might be very bright, but they would not be permanent, since they would be rubbed off, and would disappear when the cloth Vvas washed, or even by exposure to the weather. Dye- ing is, therefore, a chemical process, consisting in combining a certain colouring matter with fibres of
cloth, 'the colouring matters are, for the most part, extracted from animal and vegetable sub- stances, and have usually the colour which they give to the cloth.
The particles of these colouring matters appear to be transparent, because the original colour of the cloth will appear through them. The colour of dyed cloth, therefore, does not depend upon the dye alone, but also upon the previous colour of the cloth. Thus, if the cloth be black it will not re- ceive a dye of any colour ; and hence it is neces- sary, that the cloth should be white, if we wish to dye it of a very bright colour.
The colouring matter, or dye-stuff, must be dis- solved in some liquid, that the particles may be precipitated upon the cloth ; and it is essential that its affinity for this solvent should not be so strong as for the cloth to be dyed.
Thus the facility with which cloth imbibes a dye depends upon two things ; namely, the affinity be- tween the cloth and the dye stuff, and that between the dye stuff and its solvent. Much of the accu- racy of dyeing depends upon preserving a due proportion between these two affinities. If the affinity between the dye-stuff and cloth, compared with that between the dye-stuff and the solvent be too great, the cloth will receive the dye tOb quickly, and the colour will be apt to be Unequal : and if the affinity between the dye-stuff and the solvent be greater than between the dye-stuff and the cloth, the latter will scarcely receive the dye, br, at least, very faintly.
JVool has the strongest affinity for colouring- matters ; silk the next strongest ; cotton lias much less affinity ; and linen has the least of all. Hence the dye-stuff for cotton or linen shotild be dissolvetl
N 9
180 DYEING.
ill substances which they have less affinity for, than when silk or wool are to be dyed. Thus iron dis- solved in the sulphuric acid may dye wool ; but when it is intended to dye cotton and linen by iron, the latter should be dissolved in the acetous acid.
There are few colouring substances that have, of themselves, so strong an affinity for cloth as to answer the purpose of dyeing so as to remain per- manent ; and, on this account, an intermediate substance is employed, that has a decided attraction for both the colouring matter and the cloth, thus serving as a bond of union between them. This substance is previously combined with the cloth, which is then dipped into the solution containing the dye-stuff. The dye-stuff combines with the in- termediate substance, which being firmly combined with the cloth, secures the permanence of the dye. Substances employed for this purpose are deno- minated mordants. Instead of this some prefer the term basis.
The most important part of dyeing consists in the proper choice, and the proper application of mordants; as upon them, the permanency of every dye depends. What has been said respecting the application of colouring matters applies equally to the application of mordants. They must be pre- viously dissolved in some liquid, which has a weaker affinity to them than the cloth has, to which they are to be applied ; and the cloth must be dipped, or even steeped in this solution, in order to saturate itself with the mordant. The mordants are earths, metallic oxides, tan, and oil.
Of the earths, alumine is the most useful. It is applied in the state of sulphate of alumine, or common alum j and in that of acetate of alumine.
DYEING. 181
When alum is used as a mordant, it is dissolved in water, and sometimes a quantity of tartar is added. The cloth is put into this solution, and kept till it has absorbed as much alumine as is ne- cessary. It is then taken out, and is washed and dried. A quantity of alumine has by this process combined with the fibres of the cloth, which is perceived by the latter weighing more than before. The addition of the tartar, or tartrate of potash, is made on two accounts ; the potash which it contains combines with the sulphuric acid of the alum, and thus prevents that very corrosive substance from injuring the texture of the cloth : the tartareous acid, on the other hand, combines with part of the alumine, and forms a tartrate of alumine, which is more easily decomposed by the cloth than alum.
Acetate of alumine is used as a mordant for cotton and linen, which have a much less affinity than wool for alumine. The alumine is retained less powerfully in a state of combination by the acetic than by the sulphuric acid ; and, therefore, cotton and linen are better able to separate it and attach it : also the acetic acid being volatile, gradually leaves the earthy basis, and allows the alumine to unite to the stuff*.
This mordant is now prepared by pouring acetate of lead into a solution of alum j on which a double decomposition takes place ; the sulphuric acid com- bines with the lead, and the sulphate of lead pre- cipitates in the form of an insoluble powder, while the alumine combines with acetous acid, and remains in the liquor.
This mordant gives a richer colour than alum.
Liine is also sometimes employed as a mordant : but it does not answer so well in general, not giving so good a colour. It is used either in the state
N 3
of limip v/at;er, or as sulphate of lime dissolved in water.
Although all the metallic oxides have an affinity for cloth, only two, the oxides of tin and of iron, are much used as mordants.
The oxide of tin is one of the most valuable mor- dants, and is the only one by which scarlet, the brightest of all colours, can be produced. It was first brought to London by Karsten, a German, in 1543, which period forms an epoch in the history of dyeing.
Prous^ 1]^S shown that tin has two oxides. The first, pr grey oxide, consists of seventy parts of tin, ai:id thirty oxygen : the second, or w^hite oxide, of sixty parts of tin, and forty oxygen. The first ox- ide absorbs oxygen rapidly from the air, andbecomes converted into the white oxide. It is, therefore, the white oxide alone that is the real mordant ; since if the first were applied to cloth, as it proba- bly often is, it must soon be converted info the white pxide by absorbing oxygen.
Tin is used as a mordant in three states ; dis- solved in nitro-muriatic acid, in acetous acid, and in a mixture of sulphuric and muriatic acids. That commonly used by the dyers, ^nd called by them sphit of tin, is the nitro-muriate. It is pre- pared by dissolving granulated tin in very dilute nitric acid, or what is called single aquafortis : and a quantity of muriate of soda, or muriate of am- monia, is added. These salts are decomposed by the nitric acid, and the muriatic acid is set free, sometimes to economize the nitric acid, a quan- tity of sulphuric acid is added, just sufficient to saturate the base of the muriate of soda.
When nitro-muriate of tin is used as a mordant, it is dissolved in a large quantity of water, and
tartar is added. The cloth is then put in and kept till it is saturated. A double decomposition takes place ; the nitro-muriatic acid combines with the potash of the tartar, Avhile tlie tartareous acid dis- solves the oxide of tin. When tartar is used, therefore, in any considerable quantity, the mor- dant is not a nitro-muriate, but a tartrate of tin.
The mur'iu-sidphate of tin, produced by dissolving tin in muriatic acid, combined with about one- fourth of its weight of oil of vitriol, is also a valuable mordant, and is preferable to the last for some pur- poses J it is also less expensive.
The oxide of iron is also a very useful mordant, and all kinds of cloth have a strong affinity for it. The permanency of the iron spots on linen and cotton is a sufficient proof of this. Iron, as a mor- dant, is used in different states. Wool is dyed generally by means of the sulphate of iron, which may also be used for cotton. Acetate of iron, pre- pared by dissolving iron in vinegar, sour beer, Sec, is preferable for some purposes. The pyro-lig- neous acid, which differs from the acetic only in having in combination a certain quantity of empy- reumatic oil, is at present preferred to the sulphuric, or acetic.
The astringent principle, or tannin, is also em- ployed as a mordant, and has a strong affinity for cloth, and also for colouring matters. An infusion of nut-galls, sumach, oak bark, or any other sub- stance containing tannin, is made in water, and the cloth is kept in it till it has absorbed a sufficient quantity oi tannin. Silk has so strong an affinity for tannin, that manufacturers sometimes employ this circumstance to increase the weight of their silk.
A compound mordant is sometimes produced by impregnating the cloth first with oil, then with the
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184 DYEING.
astringent principle, and, lastly, with the aluminous mordant. This is employed in dyeing the Adria- nople red.
Several other substances are used as mordants occasionally, either as principals, or to facilitate the combinations of others with the cloths ; such as ni- trate of bismuth, oxide of arsenic, corrosive sub- limate, acetate of lead, sulphate, or acetate of copper, &c.
The chief use of mordants is to render the dyes permanent, but they have also considerable in- fluence on the colour produced : thus, the same colouring matter will produce very different dyes, according to the mordant used to fix it. If the aluminous mordant be used for cochineal, the colour will be crimson ; but if the oxide of iron be used for the same colouring matter, black will be the result.
It is necessary, therefore, to choose such mor- dants and colouring matters as together shall pro- duce the desired colour. And this principle enables us also to produce various colours with the same dye-stuff, only by changing the mordant.
It is probable that the whole of the surface of the fibres of cloth are not covered by the colouring matters precipitated upon them ; but that the particles of colour are at some distance from each other. For cloth may be dyed different shades of the same colour; that is, it may be dyed deeper a second time than at first, by increasing the quan- tity of colouring matter, which could not be tlie case if the whole surface were covered. Another circumstance renders this opinion probable ; all those colours which dyers call compound are made by dyeing the cloth first one colour, and then another : thus, green is got by dyeing cloth first blue and then vellow.
DYEING. 185
In dyeing, the water employed should be as pure as possible, and the exact temperature in each process should be attended to. The dye-houses should be spacious, light, and airy, and cleanness is essentially necessary. The stuffs are supported in the cauldrons, or baths, by proper apparatus, and are drawn through them by a winch, or reel.
Of Dyeing Red,
The colouring matters employed for dyeing red are cochineal, kermes, madder, lac. Brazil-wood, logwood, and earth amus. Cochineal is a species of insect (the coccus cactiy Lin.) brought from America. The decoction of it affords a very bright crimson colour, inclining to violet. When alum is added to this decoction, it combines wdth its colouring matter, and forms a red precipitate. Muriate of tin gives a still more beautiful colour.
Kermes is also an insect found in several parts of Asia, and the south of Europe, which furnishes a red dye, by some thought not inferior to cochi- neal, but which has not been so much used since the introduction of the latter.
Madder is the root of a plant (rubia tinctoriuniy Lin.) The colouring matter of madder is extracted by water, either cold or hot, and precipitates of various shades of red may be obtained by alum, chalk, acetate of lead, and muriate of tin.
Lac is a colouring matter of animal origin, pro- duced in the East Indies, from tlie coccus lacca^ a small winged insect. This insect forms cells for its young, as regular as the honey-comb, but diffe- rently arranged ; and the lac is procured from the substance of which these cells are made. The whole matter of these cells is called stick lac ; when the
1 86 DYEING
"s >-
^?^
red colouring matter is extracted by water, what remains is a resinous substance called shell lac^ used for various purposes, as varnishes, sealing wax, &c. Water dissolves lac, and the decoction is of a deep crimson colour. The precipitate, with alum or nitro-muriate of tin, forms a fine red.
Brazil-wood is an article used in dyeing. It is the central part of a large tree, that grows in Brazil. It is heavier than water, and affords a decoction of a red colour with water. The precipitate, with alum and nitro-muriate of tin, is a fine red.
Peach-wood gives a colour inferior to Brazil, and also in smaller quantity.
Logwood affords a colouring matter extensively used in dyeing. It is very heavy, and sinks in water. Its decoction is yellow, but by alum be- comes violet or purple ; by sulphate of iron it becomes black.
Carthamus is the flower of a plant cultivated in Spain and the Levant. It contains two colouring matters ; a yellow, which is soluble in water ; and a red, which is insoluble in water, but soluble in alcaline carbon ats. The red colouring matter of carthamus, extracted by carbonate of soda, preci- pitated by lemon-juice, and ground with talc, con- stitutes the rouge employed as a cosmetic: the fineness of the talc, and the proportion of it mixed with the carthamus, occasion the difference between the cheaper and dearer kinds of rouge.
Wool is died scarlet, which is the most splendid of all reds, by cochineal. Alum will do as a mor- dant for fixing the red ; but nitro-muriate of tin, or what is still better, the murio-sulphate of tin, are now used as preferable mordants. To die wool scarlet, a bath is made by mixing pure tartar with a little cochineal and nitro-muriate of tin 5 but as
DYEINGf. 1P7
the red prodiiced by cochineal alone is rather a crimson than a scarlet; and as the colour of scarlet is, in flict, crimson and yellow, some yellow dye, or fustic, turmeric, or quercitron bark, is added to the cochineal in the first bath.
Into this the cloth is put, and boiled for two hours. It is then waslied, and afterwards put into a second bath of cochineal, which is called the red- dening. When crimson is the colour to be given to the cloth, the tin mordant is the best; but some- times the dyers use the alum for this purpose, and then a decoction of cochineal. The addition of archil and potash renders the crimson darker, and gives it more bloom, but this is very fugitive. For paler crimsons, some madder is substituted for a portion of the cochineal. Wool is dyed madder-red, by boiling it first two or three hours with alum and tartar, and then in a bath of madder.
Silk may be dyed crimson with cochineal or Brazil-wood, and sometimes carthamus is used. The nitro-muriate of tin is the best mordant, but alum may be also used. Madder does not give a colour sufficiently bright.
Poppy colour, cherry, rose, and flesh colour, are given to silk by carthamus or Brazil-wood. When the carthamus is employed, an alcaline solution is made, and as much lemon-juice as will give it a fine cherry-red is poured into it.
It is extremely difficult to give silk a scarlet, and it is scarcely possible to give it a full scarlet. The murio-sulphate of tin, as a mordant, is first used, then the bath of cochineal and quercitron, and lastly, the cochineal bath alone. A colour approach- ing to scarlet may also be given to silk, by dyeing- it first crimson, then dyeing it with carthamus, and lastly yellow, without heat.
188 DYEING.
Cotton and linen are dyed red with madder. Cochineal, which gives so fine a red to wool, by the nitro-muriate of tin, communicates only a dirty red to cotton and linen, by the same means.
Madder reds are of two kinds. 1. The common madder red, which is formed by impregnating the cotton or linen with galls, and afterwards alumed, and then putting them into the madder bath. 2. The Adrianople, or Turkey red. This process was brought from the East. It is more durable and more beautiful than the common red. The cloth is first impregnated with oil, then with galls, and lastly, with alum. It is then boiled for an hour, in a decoction of madder, which is commonly mixed with a quantity of blood. After the cloth is dyed, it is plunged into a soda ley, in order to brighten the colour. The chief difficulty is in the application of the mordant, which is the most complicated employed in the whole art of dyeing.
Cotton may be dyed scarlet by the murio-sul- phate of tin, cochineal, and quercitron bark j but the colour is extremely fugitive.
Of Dyeing Yellow.
The chief yellow dyes are M^eld, sumach, fustic, turmeric, and quercitron bark.
Weld is a vegetable that grows commonly in this country.
Sumach is a shrub growing naturally in the South of Europe.
Fustic is the wood of a tree wliich grows in the West Indies.
Querciti^on is the bark of a tree which is a native of North America.
DYEING. 189
It is not possible to give to cloth a permanent yellow colour without the use of mordants. Alum is the most usual mordant. TFool is dyed yellow by weld, by the use of alum and tartar. Quercitron bark gives nearly the same colour, but more abun- dantly, and it is rather cheaper than weld. The process is as follows : boil the cloth for an hour or more in a solution of alum, and then immerse it in a bath of quercitron bark. Next add a small quan- tity of clean powdered chalk, and continue the boiling for eight or ten minutes. The yellow thus given will be as good as that obtained from weld.
If very bright yellows are required, the tin mor- dant must be usedj and sometimes alum is added to the tin.
If an addition of tartar be made to the mordant, the yellow will have a slight tinge of green.
If an orange or an aurora be required, a small portion of cochineal must be added.
Silk used formerly to be always dyed yellow with weld, but quercitron bark is now found to answer equally well, and at less expense. The proportion should be from one to two parts of bark to twelve pounds of silk, according to the particular shade of colour wanted. The bark, powdered and tied up in a bag, should be put into the dyeing vessel whilst the water is cold, and as soon as it becomes blood warm, *the silk previously alumed should also be put in and dyed as usual, and when the shade is required to be deep, a little chalk or pearl-ashes may be added towards the end of the operation.
When very lively yellows are required, a little of the raurio-sulphate of tin may be employed as a mordant in addition to the alum. Annotto com-
1§0 byfitNG.
municates an aurora colour to silk, the colour of the annotto is extracted by means of alcali.
To dye cotton and linen yellow, proceed as fol- lows. Take a sufficient quantity of the acetate of alumine, formed by dissolving one pound of sugar of lead, aiid three pounds of alum, and the cotton or linen '.eing properly cleansed, immerse it in this mordant (which ought to be blood warm) for two hours, let it be then taken out and moderately pressed or squeezed over a proper vessel, to prevent the unnecessary waste of the mordant, dry it in a stove heat, and soak it again in the aluminous mor- dant; it is then taken out, and again pressed and squeezed as before ; after which, without being rinsed, it is thoroughly wetted in as much, and only as much, lime-water as will conveniently suf- fice for that purpose, and afterwards dried. The soaking in the acetate of alumine maybe again re- peated, and if the shade of yellow is required to be very bright and durable, the alternate wetting with lime water and soaking in the mordant may be re- peated three or four tim.es. Thus a sufficient quan- titv of alumine is combined with the cloth, and the combination is rendered more permanent by the addition of some lime. The dyeing both is pre- pared by putting 12 or 18 parts of quercitron bark, (according to the depth of the shade required,) tied up in a bag, into a sufficient quantity of cold water. Into this bath the cloth is to be put, and turned round in it for an hour, while its temperature is gradually raised to about 120*^, it is then to be brought to a boiling heat, and the cloth allowed to remain in it after that only a few minutes. If it be kept long at a boiling heat, the yellow ac- quires a shade of brown.
DYEING. 191
To dye nankeen yellow, boil the cotton in a so- lution of carbonate of potash, and then dip it in a solution of the red sulphate of iron.
Of Dyeing Blue.
There are but few substances capable of furnish- ing blue dyes. The only vegetable products are indigo and wood. Indigo is a rich blue colour procured from the fecula of a species of plant that is cultivated in America, and also in the East Indies. The colouring matter is extracted by water, and is at first green, but immediately absorbs oxygen, and then assumes a blue colour. It becomes at the same time insoluble in water, but is soluble in sulphuric acid.
As indigo has a very strong affinity for wool, silk, cotton, and linen, a mordant is unnecessary in dye- ing with it. The colour is very permanent, because the indigo being already saturated with oxygen, to which it owes its blue colour, is little liable to be decomposed. But it is essential that the indigo be applied in a state of solution in order to attach itself to the cloth.
A solution of indigo in the sulphuric acid is used for dyeing wool ; this is called ScLvon bluet and it gives a very beautiful colour. But it will not do for dying cotton or wool, because their affinity for indigo is not sufficiently great to enable them to decompose the sulphate of indigo.
To dye by the sulphate of indigo, dissolve oile })art of indigo in four parts of concentrated sul- phuric acid ; add to the solution one part of dry car- bonate of potash, and dilute the whole with eight times its weight of water. Boil the cloth for an
192 DYEING.
hour in a solution of five parts of alum, and three of tartar, for every thirty-two parts of cloth. The clotli is then to be put into a bath of sulphate of indigo, diluted according to the strength of shade required, and kept till it has acquired the desired colour. The use of the alum and tartar is not to act as mordants, but to facilitate the decomposition of the indigo. The alcaii is added to the sulphate for the same reason. Another use of these sub- stances is, that they protect the cloth from the action of the sulphuric acid, by neutralizing part of it, otherwise the texture of the cloth might be injured.
This, however, is not the most common method o[ dyeing by indigo. The usual method is to deprive the indigo of the oxygen which has been combined with the green fecula, and to which it owes its blue colour, and thus reduce to the green state again. It is then capable of being dissolved in water by means of the alcalies or alcaline earths, which act upon it very readily in that state,
To dye wool blue, indigo is mixed with wood, bran, and madder, vegetable substances which readily undergo fermentation ; and the whole is boiled together, stirring the mixture frequently. JBy this a fermentation takes place, and the oxy- gen is separated from the indigo. Quick lime or alcaii is then tlu'own in, which dissolves the green base of the indigo. The solution of indigo is apt to run into the putrid fermentation, which is known by the putrid vapours whicli it exhales ; the green colour then disappears, and, indeed, the colouring matter is decomposed. This danger is prevented by adding more lime to correct the putrescent tendency. Sometimes the fermentation does not proceed with sufficient activity, and then more bran
DYEING. 195
or wood is to be added. Wlien the wool or cloth is to be put into the indigo vat to be dyed, it should be wrung out of tepid water, and then in- troduced into the vat, where it should be kept for a longer or shorter time according to the strength of shade required. After being taken out, it is ex- posed to air, when the green colour which it had imbibed in the vat is changed to a blue by the absorption of the oxygen of the atmosphere. It is then to be carefully washed.
Woad itself contains a colouring matter exactly similar to indigo, and indigo may be extracted from it, but the quantity is small.
Cotton and linen are dyed blue by putting the indigo into a solution of some substance that has a stronger affinity for oxygen than the green bases of indigo. Green sulphate of iron, and metallic sulphurets answer this purpose, the green sulphate attracts the oxygen from the indigo, and reduces it to the green state, in which it is dissolved by lime added to the solution. The cloth is then put into the bath.
Silk is dyed blue by indigo fermented by bran and madder, and the indigo dissolved by potash. If the shade required be dark, it is dyed first with archill, which is called giving it a ground colour.n
Of dyeing Black.
The substance that produces the black dye is the ta nno'gallate oi'h'on. Decoctions of many vege- tables strike a black with a solution of the red oxide of iron. Of these nut-galls give the most copious precipitate.
Logwood is generally employed as an auxiliary, because it communicates lustre, and adds consider-
VOL. II. O
19*4 DYEING.
aljly to the fullness of the black. The decoction of logwood which is reddish becomes black by sulphate of iron.
To dye cloth or wool black, the first process generally is to dye it blue, which renders the black to be given more intense. If the cloth be coarse, and the blue dye too expensive, a brown dye may be given by means of walnut peels. It is then boiled for two hours in a decoction of nut galls, and then for two hours more in a bath composed of logwood and sulphate of iron, at a scalding heat, but not boiled. During the operation, it must be frequently exposed to the air. The common pro- portion are five parts of galls, five of sulphate of iron, and thirty of logwood, for every 100 of cloth. For coarse cloths the previous blue dye is omitted. The cloth is then washed and fulled.
Silk is dyed black as follows. After boiling it with soap, it is galled, and afterwards washed. It combines with a considerable portion of the astrin- gent principle, and increases in weight. It is then dipped into a bath of sulphate of iron and gum arable.
Cotton and I'men are first dyed blue, then steeped in a decoction of galls, and alder bark. It is then put into a batli of acetite of iron, taken out and exposed to the air. This operation is repeated several times.
Of dyeing Compotincl Colours.
Compound colours are produced either by mix- ing together two or more simple ones, or by dyeing cloth first one simple colour and afterwards another.
Greens are formed of blues and yellows. Wool is dyed green by dyeing it first blue of a depth of shade sufficient for the required kind of green. It is then washed and boiled in a bath of weld and tartar, or any of the processes used for dyeing blue and yellow may be used. Various shades will be given by different proportions of the dyeing ma- terials. The green called Saa:on gren? is obtained by solutions of indigo in sulphuric acid, sometimes quercitron bark is used. Another process for Saxon green is by the quercitron bark, and then a bath of the murio-sulphate of tin and alum with sulphate of indigo.
Purples, violets. Sec. — All the shades of these colours are formed of blue and red. Sometimes the cloth is dyed blue and then scarlet, and some- times cochineal is mixed with sulphate of indigo, and the purple dyed at once. Silk is dyed first by cochineal and afterwards by indigo. Cotton and linen are dyed blue, then galled, and boiled in loffwood. li ,, .,"
Orange colours are produced by mixtures of yellow and red. Wool is first dyed scarlet and then yellow.
Olive is blue combined with red and yellow.
Cinnamon colour is given to wool by dyeing it first with madder, then yellow. Silk is dyed the same colour by logwood. Brazil-wood, and fustic. Cotton and linen receive a cinnamon colour by weld and madder.
Brown is given to cloth by quercitron bark, or by walnut peels.
When walnut peels, or the green covering of the walnut, are first separated, they are white internally, but soon assume a brown or even a black colour on exposure to the air. They readily give up their
0 ^
196 CALICO PRINTING.
colouring matter to water. It is common to keep them in water for a year before they are used. Wool is dyed brown with them by steeping in a decoction for a length of time proportioned to the depth of colour required. The same colouring matter is found in the root of the walnut-tree, but in smaller quantity. Other trees, as the bark of the birch may be used for dyeing browns, and in these cases it is probable that the colouring matter is combined with the tanning principle, and this may be the reason why no mordant is necessary, both the cloth and colouring matter having a strong affinity for tannin.
Drab colours are dyed by combining brown oxide of iron with the cloth, and then the yellow of quercitron bark. The strength of shade will be more or less, by varying the quantity of the mor- dant, w^hen the proportion is small the colour in- clines to olive or yellow, on the contrary the drab may be deepened or saddened, as the dyers term it, by mixing a little sumach with the bark.
CALICO PRINTING.
Calico isa species of cotton cloth ornamented with coloured patterns. The name is derived from Cali- cut, a district of India, where it was first made, and from whence it was formerly imported. The art of making calicoes had been practised there from time immemorial, but it is scarcely, a hundred years since it was known in Europe; it has al- ready risen to such perfection as to equal if not exceed the manufactures of India, in the elegance of the patterns, the beauty and permanance of the colours, and the expedition with which the different operations are carried on.
CALICO PRINTING. 197
The process of calico-printing consists in impreg- nating those parts of the cloth which are to receive the coloured pattern with a mordant, and then dye- ing the cloth by the usual methods. The dye is firmly fixed to that part only where the mordant has been applied ; and, although the whole cloth has received the tint, yet the colour will be easily discharged from the unmordanted parts by washing, and exposing on the grass to the sun and air for some days with the wrong side uppermost. Thus, suppose a pattern had been applied to white cloth with a solution of acetite ofalumine, and that then the whole was dyed with madder ; when taken out of the dye-vat the whole cloth would be red ; but, by washing and bleaching, the madder will be dis- charged from every part of the cloth except where the acetite ofalumine had been applied ; and, con- sequently, the pattern alone will appear red. In the same manner the patterns may be applied of any other colour by varying the dye, as quercitron bark or weld for yellow, &c.
Two mordants are particularly employed in ca- lico-printing, acetite of alumine, and iron dissolved in some vegetable acid.
The acetite of alumine is made by a double de- composition of alum and sugar of lead. When iron is used as a mordant, it is dissolved in vinegar, soured beer, or pyroligneous acid ; and it is, there- fore, an acetite of iron mixed with a portion of tar- trite, gallate, and, perhaps, other salts of the metal.
When the colour of the required pattern varies in different places, this effect is produced on the cloth, by impregnating the several parts with vari- ous mordants. Thus, if one part is printed with acetite ofalumine, and another with acetite of iron,
o 3
1^ CALICO PRINTING.
and the whole cloth afterwards dyed with mad- der and bleached, tlie pattern will appear in red and brown.
The mordants are applied to the cloth either by a pencil, or by means of blocks on which the pat- tern is cnt. Care must be taken that the printing from the block does not spread, or that the impres- sions from the several blocks do not interfere with one another when more than one is apphed. For this purpose it is necessary, that the substance used as mordants should have a degree of consistence that may prevent them ft'om spreading. Flour paste, or starch, is mixed with the mordant when it is applied by blocks, and gum arable when it is but on by a pencil. This thickening reqiiires exact- ness : if too little is used, the pattern will spread ; and, if too much, the cotton will not receive a suf- ficient quantity of the mordant, and will take the dye imperfectly.
In order that the impression given by the blocks with the mordant may be seen easily before it is dyed, the mordant is tinged with some colouring matter that wdll not remain fixed. Decoction of Brazil-wood is used for this purpose.
Before printing, the cotton cloth is well bleached and calendered, and laid smooth on a table : the blocks are applied by hand, and struck with a mallet. The cotton is then dried well in a room with a stove, which not only fixes the mordant more securely, but drives off part of the acetous acid from its base, by which the mordant will com- bine in a greater proportion, and more intimately with the cloth.
To discharge the paste and gum used with the mordant, the cloth is next to be washed with warm
CALICO PRINTINe. 199
water and cow-dung ; this, also, discharges such parts of the mordant as are not properly fixed, enough being still left to fix the dye. The cloth is then rinsed in clear water. It is then dyed in the usual manner.
The principal dye-stuffs used by calico-printers are indigo, madder, quercitron bark, and weld.
After dyeing, the cloth is well washed, exposed on the grass, and bleached ; by which all the parts not touched by the mordant are restored to their original whiteness.
In this manner various colours may be given by one dyeing, merely by varying the mordant. Thus, if one pattern be printed with alum alone, a second with a mixture of alum and iron liquor, a third v.'ith iron liquor alone, and a fourth with iron li- quor and galls, and the piece be afterwards dyed with quercitron or weld, and the ground bleached in the usual manner ; the first pattern will be pure yellow, the second will be olive, the third of a dark drab colour, and the fourth nearly black, while the ground will be white.
As indigo does not require any mordant, it is applied at once, either by a pencil or by a block and paste. But, as has been mentioned under dye- ing, indigo will not combine with the cloth except in its disoxygenated or green state ; and, if applied thus by the pencil, it would return to the blue state before it had time to fix upon the stuff. The in- digo is, therefore, prepared by boiling with potash, made caustic by quicklime, to which is added orpiment for the disoxygenation of the indigo. This solution is thickened with gum. It must be excluded from the air, otherwise it would attract oxygen and return to the blue or insoluble state. Dr. Bancroft proposed substituting brown sugar
o 4 . .
500 CALICO PRINTING.
for orpiments, as it is equally efficacious in disoxy- genating the indigo, and will also serve instead of gum.
Some calicoes are printed only with one colour ; others have two ; others three, or more, even to the number of eight, ten, or twelve. The smaller the number of colours, the fewer are the processes. To give an example where six colours are used.
1. A nankeen yellow, of various shades down to a deep yellowish brown or drab, is given by acetite of iron put on with gum or paste, and afterwards plunged into the potash ley.
2. Yellow, by a mordant of acetite of alumine, the dyeing by quercitron bark and bleaching.
3. Red, by the last process, only madder is sub- stituted for the bark.
4. Light blue is given by making a block for all those parts that are to be white, and printing by it on the cloth a composition of which wax is the principal ingredient, or pipe- clay and paste. The cloth is then dyed in a cold indigo vat, and the wax removed by hot water.
5. Lilac flea-brown, and blackish brown, are given by acetite of iron, and dyeing afterwards with madder.
6. Dove-colour and drab, by acetite of iron and quercitron bark.
The same mordant will frequently do tor several colours. Thus, suppose one part of the cloth should be printed with acetite of alumine, another with acetite of iron, and a third with a mixture of these two mordants, and the whole afterwards dyed with quercitron bark ; then the following colours would appear, viz. yellow, drab, olive ; and various depths of shade will be given by varying the pro- portions ot" iron in the mordant.
TANNING, 201
If some parts of the yellow be covered over with the indigo liquor, applied with a pencil, it will be converted into green. By the indigo, also, any parts that are required to be blue may be pencilled.
If j instead of quercitron bark, the cloth printed with the three mordants just mentioned be dyed with madder, then the colours exhibited will be red, brown or black, and purple.
Other processes are still more complicated when a great number of colours are required. New mordants are applied to parts of the pattern alrea- dy printed, and the cloth again dyed, by which those parts only receive a new colour.
Sometimes the dye stuff and the mordant are mixed together in the first instance, and printed on the cloth, which is a great saving of time and ex- pense ; but the colours thus produced on the cloth are not permanent: washing, or even exposure to the air frequently destroys them.
TANNING.
Tanning is the art of converting the raw skins of animals into leather.
The skin is composed chiefly of two parts, a thin white elastic layer on the outside, which is called the epidermis, or cuticle ; and a much thicker layer, composed of a great many fibres, closely inter- woven, and disposed in different directions: this is called the cutisy or true skin.
The epidermis is that part of the skin which is raised in blisters. It is easily separated from the cutis by maceration in hot water. It possesses a very great degree of elasticity. It is totally inso- lubje in water and alcohol. Pure fixed alcalis dis- solve it completely, as does lime likewise though slowly.
S02
TANNING.
When a portion of cutis is macerated for some hours in water, with agitation and pressure, the blood, and all the extraneous matter with which it was loaded, are separated from it, but its texture remains unaltered. On evaporating the water em- ployed, a small quantity of gelatine may be ob- tained. No subsequent maceration in cold water has any farther effect ; the weight of the cutis is not diminished, and its texture is not altered ; but if it be boiled in a sufficient quantity of water, it may be completely dissolved, and the whole of it, by evaporating the water, obtained in the state of gelatine.
It was mentioned, when treating of chemistry, that gelatine wdth tannin^ or the tanning principle o^ vegetables, formed a combination, which is inso- luble in water. Upon this depends the art of making leather ; the gelatinous part of the skin combining with the tannin of the bark usually employed.
The process which has long been used in this country is as follows ; the leather tanned in Eng- land consists chiefly of three sorts, known by the name o^ butts or backs, hides, and skins. Butts are generally made from the stoutest and heaviest ox hides, and are managed as follows : after the horns are taken off, tlie hides are laid smooth in heaps for one or two days in the summer, and for five or six in the winter ; they are then hung on poles, in a close room called a smoke-house, in which is kept a smouldering fire of wet tan ; this occasions a small degree of putrefaction, by which means the hair is easily got offj by spreading the hide on a sort of wooden horse or beam, and scraping it with a crooked knife. The hair being taken off, the hide is thrown into a pit or pool of water, to
TANNING. 203
cleanse it from the dirt, &c. which being done, the hide is again spread on the wooden beam, and the grease, loose flesh, extraneous filth, &c. carefully scrubbed out or taken off; the hides are then put into a pit of strong liquor, called ooze^ prepared in pits kept for the purpose, by infusing ground bark in water ; this is termed colouring ; after which they are removed into another pit called a scower- ing, which consists of water strongly impregnated with vitriolic acid, or with a vegetable acid, prepared from rye or barley. This operation (which is called raising)^ by distending the pores of the hides, occa- sions them more readily to imbibe the ooze, the ef- fect of which is to combine with the gelatinous part of the skin, and form with \i leather. The hides are then taken out of the scowering, and spread smooth in ai pit commonly filled with water, called a binder, with a quantity of ground bark strewed between each. After laying a month or six weeks, they are taken up ; and the decayed bark and liquot being drawn out of the pit, it is filled again with strong ooze, when they are put in as before. With bark between each hide. They now lie two or thi^e months, at the expiration of which the saitie oper- ation is repeated ; they then remain four or five months, when they again undergo the same process, and after being three months in the last pit, aTe com- pletely tanned; unless the hides are so remarkably stout as to want an additional pit or layer. The whole process requires from eleven to eighteen months, and sometimes two years, according to the substance of the hide, and discretion of the tanner. When taken out of the pit to be dried, they are hung on poles, and after being compressed by a steel pin, and beat out smooth by wooden hammers, called hattSy the operation is complete ; and when
204 T4.NNING.
thoroughly dry, they are fit for sale. Butts are chiefly used for the soles of stout shoes.
The leather which goes under the denomination of hideSj is generally made of cow hides, or the lighter ox hides, which are thus managed. After the horns are taken off, and the hides washed, they are put into a pit of water, saturated with lime, where they remain a few days, when they are taken out, and the hair scraped off on a wooden beam, as before described ; they are then washed in a pit, or pool of water, and the loose flesh, &c. being taken off, they are removed into a pit of weak ooze, where they are taken up, and put down (which is technically termed handling') two or three times a-day, for the first week ; every second or third day they are shifted into a pit of fresh ooze, somewhat stronger than the former ; till at the end of a month or six weeks they are put into a strong ooze, in which they are handled once or twice a-week with fresh bark for two or three months. They are then removed into another pit, called a layer, in which they are laid smooth, with bark ground very fine, strewed between each bide. After remaining here two or three months, they are generally taken up, when the ooze is drawn out, and the hides put in again with fresh ooze and fresh bark, where, after lying two or three months more, they are completely tanned, except a few very stout hides, which may require an extra layer: they are then taken out, and hung on poles, and being hammered and smoothed by a steel pin, are, when dry, fit for sale. These hides are called crop hides ; they are from ten to eighteen months in tanning, and are used for the soles of shoes.
Skins is the general term for the skins of calves, seals, hogs, dogs, &c. These, after being
TANNING. 205
washed in water, are put into lime pits, as before mentioned, where they are taken up and put down every third or fourth day, for a fortnight or three weeks, in order to destroy the epidermis of the skin. The hair is then scraped off, and the excres- cences being removed, they are put into a pit of water impregnated with pigeon dung, called a grainer, forming an alcaline ley, which in a week or ten days soaking out the lime, grease, and sa- ponaceous matter (during which period they are several times scraped over with a crooked knife, to work out the dirt and filth), softens the skins, and prepares them for the reception of the ooze. They are then put into a pit of weak ooze, in the same manner as the hides, and being frequently handled, are by degrees removed into a stronger, and still stronger liquor, for a month or six weeks, when they are put into a very strong ooze, with fresh bark ground very fine, and at the end of two or three months, according to their substances, are sufficiently tanned : when they are taken out, hung on poles, dried, and are fit for sale. These skins are afterwards dressed and blacked by the curriers, and are used for the upper leathers of shoes, boots, &c.
The lighter sort of hides, called dressing hides, as well as horse hides, are managed nearly in the same manner as skins ; and are used for coach- work, harness work, &c. &c.
As the method of tanning above described, and all others in general use, are extremely tedious and expensive in their operation, various schemes at different times have been suggested to shorten the process, and lessen the expense.
Much hght has been thrown by modern che- mists upon the theory of tanning, and considerable
2015 TANNINE .
improvements have been made in the practice of this art. M. Seguin, in France, has particularly distinguished himself by his researches on thissu]b- ject, and mucli improved the art in his country.
In 179<5, Mr. William Desmond obtained a patent for practising Seguin's method in England. He obtained the tanning principle, by digesting oak bark, or other proper material in cold water, in an apparatus nearly similar to that used in the salt- petre works : that is to say, the water which has remained upon the powdered bark for a certain time, in one vessel, is drawn off by a cock, and poured upon fresh tan: this is again to be drawn off, and poured upon other fresh tan ; and in this way the process is to be continued to the fifth vessel. The liquor is tlien highly coloured, and and marks from six to eight degrees upon the hy- drometer for salts. This he calls the tanning lix- ivium.
The criterion for ascertaining its strength is the quantity of the solution of gelatine which a given quantity of it will precipitate. Isinglass is used for this purpose, being entirely composed of ge- latine. And liere it may be observed, that this is the mode of ascertaining the quantity of tanning principle in any vegetable substance, and, conse- quently, how far they may be used as a substitute for oak bark.
The hides, after being prepared in the usual way, are immersed for some hours in a weak tanning lix- ivium of only one or two degrees ; to obtain which, the latter portions of the infusions are set apart, or else some of that which has been partly exhausted by use in tanning. The hides are then to be put into a stronger lixivium, where, in a few days, they will be brought to the same degree of saturation
TANNING. 207
with the liquor in which they are immersed. The strength of the hquor will by this means be consi- derably diminished, and must, therefore, be renew- ed. When the hides are by this means completely saturated, that is to say, perfectly tanned, they are to be removed, and slowly dried in the shade.
It has been proposed to use the residuum of the tanning lixivium, or the exhausted ooze (which contains a portion of Gallic acid, this forming a constituent part of astringent vegetables), for the purpose of taking off the hair ; but tliis liquor seems to contain no substances capable of acting upon the epidermis, or of loosening the hair ; and when skin is taken off by being exposed to it, the effect must really be owing to incipient putre- faction.
The length of time necessary to tan leather completely, according to the old process, is cer- tainly a very great inconvenience ; and there is no doubt but that it may be much shortened by fol- lowing the new method. It has been found, how- ever, that the leather so tanned has not been so durable as that which has been formed by a slower process.
The public is much indebted to Sir Humphry Davy, for the attention which he has paid to this subject. From his excellent paper " On the Con- stituent Parts of Astringent Vegetables,'* in the Philosophical Transactions, we present the reader with the following extract.
" In considering the relation of the different facts that have been detailed, to the processes of tanning and of leather-making, it will appear suf- ficiently evident, that when skin is tanned in as- tringent infusions that contain, as well as tannin, extractive matters, portions of these matters enter,
208 TANNING.
with the tannin, into chemical combination with the skin. In no case is there any reason to beUeve that galUc acid is absorbed in this process ; and M. Seguin's ingenious theory of the agency of this substance, in producing the de-oxygenation of skin, seems supported by no proofs. Even in the formation of glue from skin, there is no evidence which ought to induce us to suppose that it loses a portion of oxygen ; and the effect appears to be owing merely to the separation of the gelatine, from the small quantity of albumen with which it was combined in the organized form, by the sol- vent powers of water.
*' The different qualities of leather made with the same kind of skin, seem to depend very much upon the different quantities of extractive matter it contains. The leather obtained by means of in- fusions of galls, is generally found harder, and more liable to crack, than the leather obtained from the infusion of barks ; and in all cases it contains a a much larger proportion of tannin, and a smaller proportion of extractive matter.
" When skin is very slowly tanned in weak so- lutions of the barks, or of catechu, it combines with a considerable proportion of extractive matter ; and in these cases, though the increase of weight of the skin is comparatively small, yet it is rendered per- fectly insoluble in water, and is found soft, and at the same time strong. The saturated astringent infusions of barks contain much less extractive matter, in proportion to their tannin, than the weak infusions; and when skin is quickly tanned in them, common experience shows that it produces leather less durable than the leather slowly formed.
** Besides, in the case of quick tanning by means of infusions of barks, a quantity of vegetable ex-
TANNING. 209
tractive matter is lost to the manufacturer, which might have been made to enter into the composi- tion of his leather. These observations show, that there is some foundation for the vulgar opinion of workmen, concerning what is technically called the feeding of leather in the slow method of tan- ning J and though the processes of the art may in some cases be protracted for an unnecessary length of time, yet, in general, they appear to have ar- rived, in consequence of repeated practical expe- riments, at a degree of perfection which cannot be very flir extended by means of any elucidations of theory that have as yet been known.'*
As a vast quantity of bark may easily be ob- tained in countries that are covered with natural forests, such as many parts of America, New Hol- land, &c. it has been suggested, as a method of lessening the expense of freight in bringing it over, to make an extract from the bark, which might be very easily transported, and which would serve the purpose of the tanner as well as the bark itself.
It was first suspected by Sir Joseph Banks, and afterwards confirmed by the experiments of Sir Humphry Davy, that a substance called catechu, or terra Japonica, brought from the East Indies, con- tained a vast quantity of tannin ; so much so, that it far excels every other known substance in this respect, Onepoun.-l of catecliu contains as much tannui as eight or ten pounds of common oak bark, and would consequently tan proportionately as much more leather. It is an extract made from the wood of a species of mimosa, by decoction and sub- sequent evaporation.
Oak bark being a very expensive article in the process of tanning, various substances have been proposed as substitutes for it. All the parts of ve-
VOL. ]I, p
210 TANNING.
getables which are of an astringent nature, contain tannin (which may be known by their giving preci- pitates with gelatine, insoluble in water), and will answer this purpose. The leaves, branches, fruit, flowers, of a vast number of plants; every part of the oak, as the leaves and acorns, oak saw-dust, and the barks of almost all trees, contain more or less tannin. Mr. Biggins made a great many experiments upon the quantity of tanning principle in various barks, from which he constructed the following table.
|
Tanning |
principle (in grains\ |
|
|
from half a pint of infusion |
||
|
and an ounce of solution of |
||
|
glue. |
^ |
|
|
Bark of elm, - |
- |
28 ' |
|
oak, cut in winter, |
- |
30 |
|
horse-chesnut, |
. |
30 |
|
beech. |
. |
31 |
|
willow (boughs) |
- |
31 1 |
|
elder. |
- |
41 * |
|
plum-tree, |
- |
58 |
|
willow (trunk). |
- |
52 |
|
sycamore. |
- |
53 |
|
birch, |
- |
54> |
|
cherry-tree. |
• |
59 |
|
saUow, |
- |
59 |
|
mountain-ash. |
- |
60 |
|
poplar. |
- |
76 |
|
hazel. |
- |
79 |
|
ash, - |
- |
82 |
|
Spanish chesnut. |
- |
98 |
|
smooth oak, - |
- |
104 |
|
oak, cut in spring. |
- |
108 |
|
Huntingdon, or Leices- |
. |
|
|
tershire willow. |
- |
109 |
|
sumach, |
- |
158 |
mi
CURRYING.
The art of currying consists in rendering tarinetl skins supple and of uniform density, and iiiipregr nating them with oil, so as to render them in a great degree impervious to water.
The stronger and thicker hides are usually em-? ployed for making the soles of boots r.nd shoes, and these are rendered fit for their several purposes by the shoemakers after they are tanned ; but suph skins as are intended for the upper leathers ^nd quarters of shoes, for the legs of boots, for coach find harness leather, saddles, and other things, must be subjected to the process of currying.
These skins after coming 'from the tanners, hav- ing many fleshy fibres on them, are well soaked in common water. They are then taken out aqcj stretched upon a very even wooden horse ; where with a paring knife all the superfluous flesh is scraped ofi\ and they are again put into soak. After the soaking is completed the currier takes them again out of the water, and having stretched them out, presses them with his feet, or a flat stone fixed in a handle, to make them more supple, and to press out all the filth that the leather may have acquired in tanning, and also the water it has absorbed in soaking.
The skins are next to be oiledf to render them pliant and impervious to wet. After they are half dried, they are laid upon tables, and first the grain side of the leather is rubbed over with a mixture of fish oil and tallow ; then the flesh side is im- pregnated with a large proportion of oil. After having been hung up a sufficient time to dry, they are taken down and rubbed, pressed, and folded in various directions, and then spread out, when th^Y
p 2
Sl^ MANUFACTURE OF SODA,
are rolled with considerable pressure upon both sides with a fluted board fastened to the operator's hand by a strap ; by this means, and by repeating the rolling, a grain is given to the leather.
After the skins are curried, it may be required to colour them. The colours usually given to them are black, white, red, green, yellow, &c.
If the skins are to be blacked, the process varies according: to the side of the skin to be coloured. Leather that is to be blacked on the flesh side, which is the case with most of the finer leather intended for shoes and boots, is coloured with a mixture of lamp black, oil, and tallow, rubbed into the leather. And what is to be coloured on the grain side is done over with chamber lye, and then with a solution of sulphate of iron, which turns it black.
MANUFACTURE OF SODA.
Soda, or the mineral alcali, (described above, under Chemistry) is sometimes found in a native state, as in the lakes of Natron in Egypt, which are dry in the summer season ; the water leaving after evaporation a bed of soda, or, as it is there called, natron, of two feet in thickness.
A marine plant, called the Salsola soda, whicli grows among the cliffs on the sea coast, seems to be endowed by nature with the property of decom- posing the salt water, that is, of separating the muriatic acid from the soda, which latter it absorbs. This plant is collected by the Spaniards with great care, and burnt for the manufacture of barilla, which is a carbonate of soda mixed with various impurities.
Soda is also procured in a still more impure state, by the burning of the sea weeds on our own
MANUFACTURE OF SODA. 213
shores, particularly in Scotland, from which is pro- j
duced a substance called help.
But the demand for a pure carbonate of soda having become very considerable of late years, from its great utility in many arts and processes, various means have been tried for procuring it by decom- posing the salts, in which it exists, combined with acids. Muriate of soda has been decomposed for this purpose. The following method is described in Nicholson's Journal.
Solutions of 500lbs. of sulphate of soda*, and 560lbs. of American potash, are made to boil, and are then mixed. As soon as the mixture boils, it is conveyed into a cistern of wood, lined with lead, half an inch thick, which is fixed in a cool place. Sticks of wood are then placed across the cistern, from which slips of sheet lead, two or three inches wide, are hung into the fluid, at four inches distance from each other. When all is cool, the fluid is let off, and the chrystallized salt is detached from the slips of lead, and the bottom of the trough. The salt is then washed, to free it from impurities, after which it is transferred again into the boiler, dis- solved in clear water, and evaporated by heat. As soon as a strong pellicle is formed, it is suffered to cool so far that the hand may be dipped into it without injury, and the heat is kept at that temper- ature as long as effectual pellicles continue to be formed over the whole surface of the boiler, and then fall to the bottom. When no more are formed, the fire is withdrawn, and the fluid ladled out into the cistern to crystallize. The sulphate of potash, &c. which had been deposited, is then taken out of
* Sulphate of soda is sold cheap by the bleachers, who save it as the residue in decomposing common salt by sulphuric acid with manganese.
p 3
2l4i MAKtl^ACTUilE of POTASH.
the boiler, and put aside. By this process from 136 to lo9lbs. of soda may be obtained from 1 OOlbs. Of sulphate of soda.
MANUFACTURE OF POTASH.
Potash, or the fixed vegetable alcali, exists as an ingredient, in very small quantity, in many mine- rals. It is also obtained from the tartar, or from lees of Wine, in which it is called salt of tartar.
But the great supply of this substance is procured from the ashes of burnt vegetables.
In many districts of England and Ireland they burfii the common fern to ashes, which they mould up with a little water, into balls of about three or foiir inches in diameter ; these are called ash balls, and are the rudest preparation of this alcali. . The potash of commerce, or Mack potash, i(s always procured from the combustion of wood, and can, therefore, only be made in those countries where wood is very plentiful^ as Poland, Russia, and Ger- manyw This country is chiefly supplied from Ame- rica. The ashes of burnt wood are put into a cistern with water^ and a strong lixivium is made. After a time, tlie water, holding the alcali in solu- tion, is drawn oflj leaving the impurities behind.
Potash is converted into a purer state by calcining it in a reverberatory furnace. It becomes then dry, poix)us, considerably caustic, extremely deliques- cent, and of a beautiful bluish colour, from which it is called pearl ash.
All these are carbonates of potash.
To obtain potash in a state of perfect purity, or uncombined with carbonic acid, the carbonate must be boiled with twice its weight of quicklime to de-
REFINING METALS. 515
prive it of the carbonic acid ; then to free it from other impurities, it must be dissolved in spirits of wine, (which dissolves alcalis and no other salt) and the solution evaporated to dryness. It is then pure and powerfully caustic.
REFINING METALS.
The term refining signifies the purification of some substance : but we mean to confine it at pre- sent to the separation of gold, silver, and copper from each other, and obtaining each of them in a pure state.
Cupellation.
Gold and silver being the only metals capable of withstanding the action of very strong heat, are therefore called perfect metals. All other metals are reduced to the state of oxides when exposed to a violent fire with access of air. Gold and silver may, therefore, be purified from all the baser metals by keeping them fused till the alloy be destroyed : but this process would be very expensive, from the great consumption of fuel, and would be exceed- ingly tedious. A shorter and more advantageous method of performing this operation has been dis- covered.
A certain quantity of lead is added to the alloy of gold and silver, and the whole is exposed to the action of the fire.
Lead is one of the metals which is most quickly converted by heat into an oxide, which is easily melted into a semi- vitrified, and powerful vitrifying matter, called litharge. By increasing the proportion of imperfect metals, it prevents them from being so
p 4
216 CUPELLATION.
well covered and protected by the perfect metals j and by uniting with these imperfect metals, it com- municates to them its property of being very easily oxidated. By its vitrifying and fusing property, which it exercises with all its force upon the cal- cined and naturally refractory parts of the other metals, it facilitates and accelerates the fusion, sco- rification, and separation of these metals. The lead, which in this operation is scorified, and scorifies along with it the imperfect metals, separates from the metallic mass with which it is then incapable of remaining united. It floats upon the surface of the melted mass, and becomes semi-vitrified. But the litharge so produced would soon cover the melted metal, and by preventing the access of air would prevent the oxidation of the remaining imperfect metals. To remedy this, such vessels are employed as are capable of imbibing and absorbing in, their pores, the melted litharge, and thus remove it out of the way ; or, for large quantities, vessels are so constructed, that the fused litharge, besides being soaked in, may also drain off, through a channel made in the corner of the vessel.
Experience has shown that for this purpose, ves- sels made of lixiviated wood or bone-ashes are most proper. These vessels are called cupels^ and this process is called cupellation. The cupels are flat and shallow. The furnace ought to be vaulted, that the heat may be reverberated upon the sur- face of the metal during the whole time of the operation. Upon this surface a crust or dark coloured pellicle is continually forming. In the instant when all the imperiect metal is destroyed, and, consequently, the scorification ceases, the sur- face of the perfect metal is seen, and appears clean and brilliant. This forms a kind of fulguration, or
i
REFINING METALS. 217
corruscation, called lightning. By this mark the metal is known to be refined.
Purification of gold by a7itimony.
When gold contains only a small quantity of alloy, it may be separated from them by melting it in a crucible that will hold twice its quantity at least, and throwing upon it, whilst in fusion, twice its weight of crude antimony (sulphuret of antimony). The crucible is then to be covered, and the whole is to be kept in a melting state for some minutes ; and when the surface sparkles, it is quickly to be poured into an inverted cone, which has been pre- viously heated and greased. By striking the cone on the ground, the metal will come out when cold. The compact mass consists of two substances ; the upper part is the sulphur of the crude antimony, united with the impure alloy ; and the lower part is the gold, united to some of the regulus of anti- mony, proportionable to the quantities of metals which have been separated from the gold, which are now united with the sulphur of the antimony. This regulus of gold may be separated from the regulus of antimony by simple exposure to less heat than will melt the gold, because antimony is volatile in such a heat, and is then dissipated. If the gold is not sufficiently purified by this first pro- cess (which is often the case,) it must be repeated a second, and even a third time. When a part is dissipated, more heat is required to keep the gold in fusion ; therefore, the fire must be increased to- wards the end of the operation. The purification is completed by means of a little nitre thrown into the crucible, which effectually calcines the remain- ing regulus of antimony. Sometimes, after these
218 PARTING.
operations, the gold is found to be deprived of much of its usual ductility ; this however is easily re- stored to it, by fusing it with nitre and borax. The first part of this process is founded on a pro- perty of sulphur, by which it is incapable of uniting with gold, and is strongly disposed to unite with all other metalUc substances, excepting pla- tina and zinc ; and also upon the property of sul- phur, that it has less affinity with regulus of anti- moiiy than with any metallic substance with which it can unite. Hence, when gold, alloyed with ^Iver, copper, iron, lead, &c. is fused together with sulphuret of antimony, these latter metals unite witli the sulphur of the antimony, while the regu- litm part, disengaged from them by its sulphur, unites with the gold.
The sulphur of the antimony, though it unites with the baser metals, does not destroy them, but forms with them a scoria, from which they may be separated by treatment as an ore.
Parting.
When the quantity of silver united to the gold is considerable, they may be separated by other processes. Nitric acid, muriatic acid, and sulphur, which cannot dissolve gold, attack silver very easily ; and, therefore, these three agents furnish methods of separating silver from gold, which operation is called parting.
Parting by nitric acid is the most convenient, and, therefore, most used ; and is even almost the only one employed by goldsmiths and coiners. Wherefore it is called simply, parting. That made with muriatic acid is only made by cementation, and is known by the name oi' concentrated parting.
PARTING. 219
Lastly, parting by sulphur is made by fusion, and is, therefore, called dry parting.
Parting gold from silver by iiitric acid or aqua j^Wf^.— Although parting by nitric acid be easy, it cannot succeed, or be very exact, unless we attend to some essential circumstances. The gold and silver must be in a proper proportion ; for if the gold be irl too great a quantity-, the silver would be covered and guarded by it from the action of the acid ; therefore, when assayers do not know the pro- portion of gold to silver in the mass, they rub the mass upon a touch-stone (which is usually composed of black basalt, though black pottery will do very weil^) so as to leave a maiiv upon it; they then make similar marks with the proof-needles, (which are needles composed of gold and silver alloyed together in graduated proportions,) and by comparing the colour of the several marks, they discover the probable sicaie of admiJiture.
If the trial shows that in any given mass the silver is not to the gold as three to one, this mass is improper for the operation of parting by aqua fortis. In this case, tiie quantity of silver neces- sary to make any alloy of that proportimi must be added. This operation is called quart<ition, be- cause it reduces the gold to a fourth of the whole mass. No inconvenience arises from too great quantity of silver, except a waste of aqua fortis. The nitric acid, or aqua fortis employed, must be very pure, and especially free from mixture of sul- phuric and muriatic acids. Its purity must, there- fore, be ascertained; and if this be found not suffi- cient, the acid must be purified by nitrate of silver. If the purity of the nitric acid W' ere not attended to, a quantity of silver proportionable to these two foi^eign acids, would be separated during the solu-
220 PARTING*
tion ; and this portion of silver converted by these acids to sulphate of silver, and to muriate of silver, would remain mingled with the gold.
When the metallic mass is properly alloyed, it is to be reduced to plates rolled up spirally, called cornetSy or to grains. These are to be put into a matrass, and upon them a quantity of aquafortis is to be poured, the weight of which is to that of the silver as three to two ; and as the nitric acid em- ployed for this operation is rather weak, the solu- tion is assisted, especially at first, by the heat of a sand-bath, in which the matrass is to be placed. When, notwithstanding the heat, no further mark of solution appears, the aqua fortis charged with silver is to be decanted. Fresh nitric acid is to be poured into the matrass, stronger than the former, and in less quantity, which must be boiled in the remaining mass, and decanted as the former. Aqua fortis must even be boiled a third timex)n the remaining gold, that all the silver be certainly dis- solved. The gold is then to be washed with boil- ing water. This gold is very pure, if the operation has been performed with due attention. It is called gold of parting.
The silver dissolved in the aqua fortis may be separated either by distillation — in which case all the aqua fortis is recovered very pure, and fit for another parting — or it may be precipitated by some substance which has a greater affinity than this metal with nitric acid. Copper is generally em- ployed for this purpose in the mint.
The solution of silver is put into copper vessels. The aqua fortis dissolves the copper, and the silver precipitates. When the silver is all precipitated, the new solution is decanted, which is then a solu- tion of copper. The precipitate is to be well
PARTING. 221
washed, and may be melted into an ingot. It is called parted silver. When this silver has been ob- tained from a mass which had been refined by lead, and when it has been well washed from the solution of copper, it is very pure. Or the silver may be separated from the nitric acid by adding to it mu- riatic acid, with which it forms muriate of silver. Muriate of silver may be decomposed by mixing it with soda, and exposing it to a sufficient heat in a crucible, whereby the soda unites to the muriatic acid, and sets the silver free.
The refiners frequently employ this solution of copper obtained in the process of parting, for making verditer ; which is prepared by adding quick lime to the solution ; a precipitate takes place, which is the blue pigment known by the name of verditer.
Parting gold from silver by cementatio7i. — This is also called parting by concentration, and is usually employed when the quantity of gold is so great to that of the silver, as to render it a difficult task by aqua fortis. The mixed metal to be cemented is to be reduced to plates, as thin as small pieces of money. At the bottom of the cru- cible, or melting-pot, is to be laid a stratum of cement, composed of four parts of bricks powdered and sifted, one part of green copperas (sulphate of iron) calcined to redness, and one part of common salt, about the thickness of a finger in depth. Upon this stratum a layer of plates of the metal is to be placed, and then another stratum of cement, and so on till the crucible is filled. It is now to be placed in a furnace, or oven (after a top has been luted on the crucible,) and exposed for twenty- four hours, till it is gradually made red hot, but by no means to be melted. The fire is now left to
2f22 REFINING MFTALS.
go out, and the metal is permitted to cool, that it may be separated from the cement, and boiled re- peatedly in large quantities of pure water. This gold is afterwards to be tried on a touch-stone ; and if it is not sufficiently purified, the process must be performed a second time. By the abov^e method, we see how powerfully silver is dissolved by muriatic acid, when it is in a state of subtile va- pour which is disengaged from the common salt of the cement. Instead of common salt, nitre may be used, as the nitrous acid readily dissolves silver ; but the mixture of common salt and nitre together is highly injudicious, because the joint acids are able to dissolve some of the gold with the silver. Whatever silver has been separated, will now re- main in the cement ; but it may be freed from this by lead, in the method described in cupellation.
Parting gold from silver in the dry *way, — This is also called jjarting by fusion^ and is performed by means of sulphur, which has the property of uniting easily with silver, while it does not attack gold. This dry parting is troublesome, and even expen- sive, and ought not to be undertaken but when the silver far exceeds the gold, because sulphur will not separate it so easily as aqua fortis, and will therefore require a further application to cupell- ation and solution.
Refining Silver by Nitre.
The principle upon which this operation is founded, consists in the property of nitre to oxy- date very powerfully all base metals; whereas, on the contrary, the noble metals are not at all affected by it. For as the metallic oxides and glasses do
REFINING METALS. 20,3
not remain united with reguline metals, and as these latter sink to the bottom when in fusion, on account of their greater specific gravity, they may be easily parted from the scoriae.
The silver to be purified by nitre is to be first granulated, and then mixed with a fourth part of its weight of dry nitre, an eighth part of potash, and a little common glass, all in powder. This mixture is to be put into a good crucible, two-thirds of which only must be full. This crucible is to be covered with a smaller crucible inverted, in the bottom of which a small hole has been made, and luted to the former. The crucibles, thus disposed, are to be placed in a furnace capable of drawing air sufficiently to make the fire intense enough only to melt the silver. Then charcoal is to be put into the furnace to such a height, that only the top of the inverted crucible shall be uncovered. The coal is then to be kindled, and the vessels to be made moderately red ; a hot coal ought to be put upon the small hole in the bottom of the inverted cruci- ble. If a shining light be observed round this coal, and a slight hissing noise at the same time heard, we may know that the operation proceeds well. The fire must be sustained at the same degree till these appearances cease, when it must be increased, so that the silver be well melted, and then the crucibles are to be taken out of the fur- nace. The larger crucible is to be broken when it is cold, and the silver will be found at the bottom covered with green alcaline scoriae. If the metal be not sufficiently ductile, the operation must be again repeated.
Some silver is apt to be lost in this operation, by the swelling and detonation of the nitre, which often forces it through the hole in the upper cru-
224 REFINING METALS.
cible, unless great care be used ; nevertheless, this method has its advantages, being much more expe- ditious than cupellation.
Separating Silver from Copper by Eliquation.
When it is desired to separate, in the large way, a small quantity of silver from much copper with which it is alloyed, the process called eliquation is resorted to. This operation is grounded on the nearer affinity of silver with lead than with copper ; in consequence of which it fuses, and combines with lead at a degree of heat in which copper continues imfused.
Whitening Silver hy Boiling.
Whitening of silver by boiling is one of the me- thods of parting copper from silver in the humid way. For this purpose, silver wrought in any shape is first ignitei.1 to redness, and afterwards boiled in a ley of muriate of soda, and acidulous tartrite of potash. By so doing, the copper is re- moved from the surface, and the silver receives a better appearance.
Precipitating Silver by Copper.
Copper has a much greater affinity v/ith oxygen than silver ; consequently, the silver is precipitated from its solutions as a fine silver dust, by metallic copper. This likewise affords a means to discover what portion of silver may be contained in an alloy of silver and copper. A quantity of the mixture determined by weight is dissolved in nitric acid j
REFINING METALS. 225
the solution is diluted with water, filtered, and a plate of copper hung in it, till no more precipitate falls down. Then the weight of the precipitate, when edulcorated, is compared v/ith that of the whole alloyed metal put to trial.
This silver dust well washed, and mixed with gum water, serves as a pigment in water painting.
Separating Silver from Copper hy an Alcaline Sulphuret.
The affinity of copper with sulphur is stronger than that of silver. Upon this ground, liver of sulphur (sulphuret of potash) has been proposed as an expedient to free silver from copper ; for if silver holding copper be fused with alcaline sul- phuret, the base metal combines with the latter, and is converted into scoriae floating on the silver,
Mr. Keir*s Mode of separating Silver from Copper*
Chemists have long been acquainted with the compound acid, called aqiia regia (nitro-muriatic acid), which has the exclusive property of dissolv- ing gold. The discovery of a compound acid, act- ing exclusively upon silver, is owing to Mr. Keir.
This compound acid is made by dissolving one pound of nitrate of potash (common nitre or salt- petre), in eight or ten pounds of sulphuric acid (oil of vitriol), or by mixing together sulphuric and nitric acids. This acid dissolves silver easily, while it will not attack copper, iron, lead, gold, or platina.
These properties have rendered it capable of a very useful application in the arts. Among the manufactures at Birmingham, that of making ves-
VOL. II. Q
%%^ REFINING METALS.
sels of silver, plated on copper, is a very consider- able one. On cutting out the rolled plated metal into pieces of the required form and sizes, there are many shreds, or scraps, as they are called, unfit for any purpose, but the recovery of the metals, by separating them from each other. The easiest and most e'conomical method of parting these two me- tals, so as not to lose either of them, is an object of some consequence to the manufacturers. For this purpose, two modes were practised ; one, by melting the whole of the mixed metals with lead, and separating them by eliquation and testing ; and the second, by dissolving both metals in sulphuric acid, with the help of heat, and by separating the sulphate of copper, by dissolving it in water, from the sulphate of silver, which is afterwards to be reduced and purified.
In the first of these methods, there is a consi- derable waste of lead and copper ; and in the se- cond, the quantity of sulphuric acid employed is very great, as much more is dissipated in the fonn of sulphureous acid than remains in the composi- tion of the two sulphates.
Some years ago, Mr. Keir communicated to an artist the method of effecting the separating of silver and copper, by means of the above-mentioned compound of sulphuric acid and nitre. It is now commonly practised by the manufacturers at Bir- mingham, and is much more economical, and much easier executed, that any of the above-mentioned methods ; for nothing more is necessary than to put the pieces of plated metal into a glazed earthen pan, to pour upon them some of the acid liquor, to stir them about, that the surfaces may be frequently exposed to fresh liquor, and to assist the action by a gentle heat, from 100« to 200'^ Fahr.
REFINING METALS. 2@7
When the liquor is nearly saturated, the silver is to be precipitated from it by common salt, which forms muriate of silver, or luna cornea, easily re- ducible to a metallic state, by melting in a cru- cible, with a sufficient quantity of potash ; and lastly, by refining the melted silver, if necessary, with a little nitre thrown upon it. In this manner, the silver will be obtained sufficiently pure, and the copper will remain unchanged. Otherwise, the silver may be precipitated in its metaUic state, by adding to the solution of silver a few of the pieces of copper, and a sufficient quantity of water to enable the liquor to act upon the copper.
Method of obtaining Gold in a pure State.
Perfectly pure gold may be obtained, by dis- solving the gold of commerce in nitro muriatic acid, and precipitating the metal, by adding a weak solution of sulphate of iron. The precipitate, after being well washed and dried, is pure gold.
Method of obtaining Silver in a pure State.
Dissolve the silver of commerce in nitric acid, and add to it some muriatic acid ; a white curdy precipitate will be formed, which is muriate of silver. To reduce muriate of silver to the metallic state, let one part of it be mixed with three of soda, and exposed to a white heat. When the mixture is well fused, suffer it to cool j then break the crucible, and separate the pure silvei' from the muriate of soda which has been formed.
Q 2
228 POTTERY.
Method of obtaiiiing pure Coppe?\
Let the copper of commerce be dissolved in mu- riatic acid, and precipitate it by a polished plate of iron ; the precipitate is pure copper.
Of making Brass, and other Alloys of Copper.
Brass is made by fusing together lapis calami- naris (which is an ore of zinc) and copper.
Tombac is formed by melting together twelve parts of copper with three of zinc.
Gun 7netal consists of nine parts of copper and one of tin.
Bell metal is copper alloyed with one sixth of tin. A smaller proportion of tin is used in making church bells than clock bells, and a little zinc is added for the bells of repeating-watches, and other small bells.
Cock metal is made with copper alloyed with zinc and lead.
The gold coins of this country are composed of eleven parts of gold and one of copper.
Standard silver contains fifteen parts of silver and one of copper.
POTTERY.
Pottery, or the art of making vessels of baked earth, is of the remotest antiquity. The ancient Greeks and Etruscans particularly excelled in it. Porcelain, the most perfect of species of pottery, has been made in China from time immemorial.
Alumine and silex are the two substances of which every kind of earthen-ware is made. Clay alone shrinks and cracks j the flint gives it solidity and strength.
POTTERY. 229
Common Pottery, such as coarse brown jugs, &c. are made of the ordinary clays, which are a mixture of sand and chiy, coloured by oxide of iron. The clay is well ground, or kneaded, and a lump of it is put upon the centre of a wheel which is kept in motion ; then, by means of the work- man's liand, or by proper tools, it is formed into the required shape. The pieces are then dried moderately, so as to bear being removed without danger ; they are then covered with a glaze, made from semi-vitreous oxide of lead, and put into a furnace, where they are baked. Some sorts are glazed by throwing sea-salt into the furnace among the different pieces of pottery. The salt is de- composed, and the vapours of it form a glazing upon the vessels ; but this, though a very simple and ingenious method, does not form a good glazing.
English stone-ware is made of tobacco pipe clay mixed with flints calcined and ground. This ma- nufacture owes its present state of perfection to that enlightened manufacturer the late Mr. Wedge- wood, who spared no pains or expense to improve the art of pottery. He first introduced a superior kind of which he called Queen's ware. The clay of which it is made comes chiefly from the neigh- bourhood of Corfe Castle in Dorsetshire. It burns extremely white. The pipe clay is much beat in water ; by this process tlie finer parts remain suspended in the water, while the coarser, sand, and other impurities, fall to the bottom. The thick liquid, consisting of water and the finer parts of the clay, is further purified by passing it through hair and lawn sieves, of different degrees of fineness. After this, the liquid is mixed (in various proportions for various wares) with another
Q 3
2M) POTTERY*
li^nofr of the same density, and consisting of flints calcined, ground, and suspended in water. The mixture is then dried in a kiln ; and being after- wards beaten to a proper temper, it becomes fit for being formed at the wheel into dishes, plates, bowls, &c. When this ware is to be put into the furnace to be baked, the several pieces of it are placed in cases made of clay, called seggars, which are piled one upon another in the dome of the furnace ; a fire is then lighted, and the ware is brought to a proper temper for glazing, and in this state it is called biscuit. Before the glazing takes place it is coloured or painted, Formerly the painting was done by the pencil by hand. It is now commonly effected by taken impressions on pdper from engraved copper plates, and transfer- ring them to the earthenware while the ink is wet. The ink is instantly absorbed by the biscuit, and the paper is washed oif. The ink for the blue and white ware is made from oxide of cobalt. It is then dipped into a glaze, made by mixing together in water, till it becomes as thick as cream, one hundred and twelve parts of white-lead, twenty- four parts of ground flint, and six parts of ground flint-glass. The ware, by being bakedj acquires a strong property of imbibing moisture, and when dipped into the glaze, therefore, it greedily attracts it into its pores, and presently becomes dry. It is then exposed a second time to the fire, by which means the glaze it has imbibed is melted, and a thin glassy coat is formed upon its surface. The colour of the coat is more or less yellow, according as a greater or less proportion of lead has been used. The lead is principally instrumental in pro- ducing the glaze, as well as in giving it the yellow colour} for lead, of all the substances hitherto
Lottery. 251
known, has the greatest power of promoting the vitrification of the substances with which it is mixed. TJie flint serves to give a consistency to the lead during the time of its vitrification, and to hinder it from becoming too fluid, and running down the sides of the ware, and thereby leaving them unglazed.
This glazing, made by means of lead, is liable to be attacked by acids, and is supposed to be pro- ductive of deleterious effects, when employed in jars used for pickling, &c.
The following composition has been recom- mended as a substitute.
To make this, white glass and soda, in equal portions, must be very finely pulverized, carefully sifted, and well mixed. The mixture is then ex- posed to a strong heat, till it is rendered very dry. It is afterwards put into vessels which have been already bilked; it is then melted, and the varnish is made. It may be applied in the same manner as that m common use.
The advantage of it is, that it is safe, and can have none of those poisonous effects which arise from the decomposition of the lead varnish.
A variety of ware has been of late manufactured which the potters call lustre. The glazing is formed with platina, or gold. For the first, the platina is dissolved in the nitro-muriatic acid with heat: by adding muriate of ammonia, a yellow precipitate falls down : wash and dry it, grind this powder with a small portion of enamel, in oil of turpentine, and spread it thinly over the glazed surface of the earthen-ware. The ware is now baked in a kiln with a red heat, and the platina will assume the metallic brilliancy.
The gold is managed in the same way. Q 4
23^ POTTERY-
The bla^k *ware owes its colour to the oxides of of iron and manganese. It has also less flint, and is more burned ; its compactness renders glazing unnecessary.
Porcelaifi, called also CImia, from being first brought from China, is the most beautiful and per- fect species of earthen-ware.
Genuine or true porcelain, is a semi-vitrified earthen-ware, intermediate between common ware and glass. It is infusible in the strongest fire ex- cited in furnaces ; it is hard, but not so brittle as glass : it is proof against sudden changes of heat and cold : it is fine grained, and dense without gloss in the fracture, and is translucent. The Chinese long excelled in the art of making porce- lain, but it is now made in various parts of Europe of an equally good quality and more ornamental. The Chinese porcelain is said to be composed of two ingredients, one of which is a hard stone called pehmtse, which is carefully ground to a very fine powder ; and the other, called kaoIi?i, is a white earthy substance which is intimately mixed with the ground stone.
Several compositions of mingled earths may yield a true porcelain, by being burnt; and the porcelain of various countries differ in their mix- tures. But the principal basis of any true porce- lain is that kind of clay M'hich becomes white by baking, and which, either by intermingled hetero- geneous earth, or by particular additions undergoes in the fire an incipient vitrificatior,, in which the true nature of porcelain consists. Feldspar and gypsum, if added, may give that property to in- fusible clay.
When porcelain is to be made, the clay is pro- perly selected, carefully washed from impurities,
POTTERY. 233
and again dried. It is then finely sifted, and most accurately mingled with quartz, ground very fine j to which, then, is added some burnt and finely pulverized gypsum. This mass is worked with water to a paste, and duly kneaded ; it is usually suffered to lie in this state for years. The vessels and other goods formed of this mass, are first moderately burnt in earthen pots, to receive a cer- tain degree of compactness, and to be ready for glazing. The glazing consists of an easily melted mixture of some species of earths, as the petrosilex or chert, fragments of porcelain and gypsum, which, when fused together, produce a crystalline, or vitreous mass, that, after cooling, is very finely ground, and suspended in a sufficient quantity of water. Into this fluid the rough ware is dipped, by which the glazing matter is deposited uniformly on every part of its surface. After drying, each article is thoroughly baked or burned in the violent heat of the porcelain furnace. It is usual to deco- rate porcelain by paintings, for which purpose, enamels or pastes, coloured by metallic oxydes, are used, so easy of fusion as to run in a heat less intense than that in which the glazing of the ware melts.
Delft-warCf so called because first made at Delft in Holland, is a kind of pottery made of sand and clay, and but slightly baked, so that it resists sud- den application of heat. Articles made of this are glazed with an enamel, composed of common salt, sand ground fine, oxyde of lead, and oxyde of tin. The use of the latter is to give opacity to the glaze.
Tobacco-pipes require a very fine tenacious, and refractory clay, which is either naturally of a per- fectly white colour, or, if it have somewhat of a grey
234 POTTERY.
cast will necessarily burn white. A clay of this kind must contain no calcareous or ferruginous earth, and must also be carefully deprived of any sand it may contain, by washing. It ought to possess, besides, the capital property of shrinking but little in the fire. If it should not prove suffi- ciently ductile, it may be meliorated by the ad- mixture of another sort. Last of all, it is beaten, kneaded, ground, washed, and sifted, till it acquires the requisite degree of fineness and ductility.
When, after this preparation, the clay has ob- tained a due degree of ductility, it is rolled out in small portions to the usual length of a pipe, per- forated with a wire, and put together wdth the wire, into a brass mould rubbed over with oil, to give it its external form ; after wdiich it is fixed into a vice, and the hollow part of the head formed with a stopper. The pipes, thus brought into form, are cleared of the redundant clay that adheres to the seams, a rim or border is made round the head, they are then miarked with an iron stamp upon the heel, and the surfaces smoothed and polished. When they are well dried, they are put into boxes and baked in a furnace.
In the Dutch manufactories, these boxes consist of conical pots made of clay, with conical lids, with a tube passing through the middle of them, by which the pipes are supported ; or else, they are long clay boxes, in which the pipes are laid horizontally, and stratified with fragments of pipes pounded small. Lastly, the pipes, when baked, are covered with a glazing or varnish, and afterwards rubbed with a cloth. This glazing consists of a quarter of a pound of soap, two ounces of white wax, and one ounce of gum arabic, or tragacanth, which are all
I
I
MANUFACTURE OF GLASS. ^35
boiled together in five pints of water, for the space of a few minutes.
MANUFACTURE OF GLASS.
This beautiful material is not of modern inven- tion ; it was known to the ancient Romans, but it was by no means common among them, and they do not appear to have had the method of forming it into vessels of various shapes as is practised at present.
Glass is made by fusing together silex and potash^ or soda, in proper proportions. Sea sand^ which consists almost entirely of quartz arid flints reduced to powder, is generally used for this pur- pose. The alcali is generally procured from the burning of sea weeds ; these are cut, dried, and burned in pits dug in the ground ; after a sufficient quantity of them have burned in the same pit, a melted or liquid mass is found in the bottom, which, after being well stirred, is suffered to cool ; it is then called kelp, and consists of a mixture of soda, potash, and parts of half burnt v/eeds, toge- ther with shells, sand, and other impurities.
When the ingredients of which glass is composed are perfectly fused, and have acquired a certain degree of heat, which is known by the fluidity of the mass, part of the melted matter is taken out at the end of a long hollov/ tube, which is dipped into it, and turned about, till a sufficient quantity is taken up ; the workmen then rolls it gently upon a piece of iron, to unite it more intimately. He then blows through the tube, till the melted mass at the extremity swells into a bubble, after
236 MANUFACTURE OP GLASS.
which he rolls it again on a smooth surface to polish it, and repeats the blowing, until the glass is brought as near the size and form of the vessel required as he thinks necessary.
If it be a common bottle, the melted glass at the end of the tube is put into a mould of the exact size and shape of its body, and the neck is formed on the outside, by drawing out the ductile glass.
If it be a vessel with a wide orifice, the glass in its melted state is opened and widened with an iron tool ; after which being again heated, it is whirled about with a circular motion, and by means of the centrifugal force thus produced, is extended to the size required. Should a handle, foot, or any thing else of the kind, be required, these are made separately, and stuck on in its melted state.
WindoxiD'glass is made in a similar manner, ex- cept that the liquid mass at the end of the tube is formed into a cylindrical shape, which being cut longitudinally by scissars or sheers, is gradually bent back until it becomes a flat plate.
Large plate glass, for looking-glasses, S^x, is made by suffering the mass in a state of complete fusion to flow upon a table, with iron ledges to confine the melted matter, and as it cools, a metal- lic roller is passed over it, to reduce it to an uniform thickness. There are various kinds of glass manu- factured for different purposes ; the principal of these are flint-glass, crown-glass, and bottle-glass.
Flint-glass is the densest, most transparent, colourless, and beautiful. It is sometimes called crystal. The best kind is said to be manufactured in London, from 120 parts of white siliceous sand, 40 parts of pearl-ash, 35 of red oxyde of lead, IS of nitrate of potash, and 25 of black oxyde of man- ganese. It is the most fusible glass. It is used
MANUFACTURE OF GLASS. 237
for bottles, and other utensils, intended to be cut and polished, and for various ornamental purposes.
Crown-glass differs from the last, in containing no lead. It is made of soda and fine sand. It is used for panes of windows, &c.
Bottle-glass is the coarsest sort of all. It is made from kelp and common sand. Its green colour is owing to iron. It is the least fusible.
Glass is sometimes coloured by mixing with it while in a fluid state, various metallic oxyds. It is coloured blue, by the oxyd of cobalt ; red, by the oxyd of gold ; green, by the oxyd of copper or iron ; yellow, by the oxyd of silver or anti- mony, and violet, by the oxyd of manganese.
The hardness of glass is very considerable ; its specific gravity varies from 2. 3 to 4, according to the quantity of metallic oxyd which enters into its composition. Though glass, when cold, is brittle, it is one of the most ductile bodies known. When liquid, if a thread of melted glass be drawn out, and fastened to a reel, the whole of the glass can be spun off; and by cutting the threads of a certain length, there is obtained a sort of feather of glass. A thread of glass may be thus drawn or spun so fine, as to be scarcely visible to the naked eye. Glass is almost perfectly elastic, and is one of the most sonorous bodies. Fluoric acid dis- solves it at common temperatures, and alcalis in a great degree of heat. These are the only sub- stances known wiiich act upon it.
Glass utensils require to be gradually cooled in an oven: this operation is called annealing, and is necessary to prevent their breaking by change of temperature, wiping, or slight accidental scratches.
238 MANUFACTURE OF GLA3S.
Two toys are made of imannealed glass, which, though commonly used for the amusement of chil- dren, exhibit phenomena which justly interest the curiosity of the philosopher; we mean Prince Rupert's drops, and the Bologna flask or philoso- phical phial.
Prince Riiperfs Drops are made by letting drops of melted glass fall into cold water : the drop as- sumes, by that means, an oval form, with a tail or neck resembling a retort. These drops are said to have been first invented by Prince Rupert, and are, therefore, called by his name. They possess this singular property, that if a small portion of the tail is broken off, the whole bursts into powder with an explosion; and a considerable shock is commu- nicated to the hand that grasps it.
The Bologna or philosophical phial, is a small vessel of glass, which has been suddenly cooled, open at the upper end, and rounded at the bottom. It is made so thick at the bottom, that it will bear a smart blow against a hard body, without break- ing ; but if a little pebble, or piece of flint, is let fall into it, it immediately cracks, and the bottom falls into pieces : but unless the pebble or flint is large and angular enough to scratch the surface of the glass, it will not break.
The most generally received explanation of these facts is founded on the assumption, that the dimen- sions of those bodies which are suddenly cooled, are larger than those which are more gradually cooled. The dimensions, therefore, of the smooth external surface of these glasses which are suddenly cooled, are supposed to be larger than is adapted to the accurate envelopement of the internal part, which is necessarily cooled in a more gradual man-
VARNISHING. 239
ner ; if, therefore, by a crack or scratch, a disjunc- tion of the cohesion takes place, in the internal sur- face, the hidden action of the parts which remained in a state of tension, to recover that of perfect co- hesion, is supposed to effect the destruction of the the mass.
VARNISHING.
By varnish is understood a clear limpid fluid, capable of hardening, without losing its transpa- rency ; used by painters, gilders, &c. to give a lustre to their works, and to preserve and defend them from the air and moisture.
A coat of varnish ought to possess the following properties: 1. It must exclude the action of the air : because wood and metals are varnished to de- fend them from decay and rust. 2. It must resist water j for otherwise the effect of the varnish could not be permanent. 3. It ought not to alter such colours as are intended to be preserved by this means. It is necessary, therefore, that a varnish should be easily extended or spread over the sur- face, without leaving pores or cavities, that it should not crack or scale, and that it should resist water. . Resins are the only bodies that possess these pro- perties, consequently they must form the basis of every varnish. For this purpose they must be dis- solved, as minutely divided as possible, and com- bined in such a manner, that the imperfections of those that might be disposed to scale, may be cor- rected by others.
Resins may be dissolved by three agents: 1. by fixed or fat oil; 2. by volatile, or essential oil; 3. by spirit of wine. Accordingly, we have three kinds of varnish : fat^ or oily varnish ; essential oil varnish ; and spirit varnish.
240 VARNISHING.
These agents are of such a nature as either to dry up and become hard, or to evaporate and fly off, leaving the resin fixed behind.
Varnishes should be carefully kept from dust, and in very clean vessels: they should be laid as thin and even as possible with a large flat brush, taking care to lay the strokes all one way. A warm room is best for varnishing in, as cold chills the varnish, and prevents it from laying even.
Varnishes are jiolisJied with pumice-stone and tripoli. The pumice-stone must be reduced to a very fine powder, and put upon a piece of serge moistened v»'ith vv^ater; witli this the varnished sub- stance is to be rubbed equally and lightly. The tripoli must also be reduced to a fine powder, and put upon a clean woollen cloth, moistened with olive-oil, with which the polishing is to be per- formed. The varnish is then to be wiped with soft linen, and, when quite dry, cleaned M'ith starch, or Spanish- white, and rubbed with the palm of the hand, or with a linen cloth.
Fat Oil Varnish.
Fixed or fat oil will not evaporate ; nor wifl it become dry of itself. To make it dry, it must be boiled with metallic calces or oxides. Litharge is generally used for this purpose. Oil so prepared is called drying-oil. To accelerate the drying of oil varnish, oil of turpentine is added.
Gum-copal, and amber, are the substances prin- cipally employed in oil varnishes ; the copal being whitest, is used for varnishing light, the amber for dark colours.
It is best to dissolve them before mixing them with the oil j because, by this means, they are in
VARNISHING. §41
less danger of being scorched, and at the same time the varnish is more beautiful. They should be melted in an iron pot over the fire : they are in a proper state for receiving the oil when they give no resistance to the iron spatula, and when they run off from it drop by drop.
To make oil varnish, pour lour, six, or eight ounces of drying-oil among sixteen ounces of melted copal, or amber, by little and little, con- stantly stirring tlie ingredients at the same time, with the spatula. When the oil is well mixed with the copal or amber, take it off the fire ; and when it is pretty cool, pour in sixteen ounces of the essence of Venice turpentine. After the varnish is made, it should be passed through a linen cloth.
Oil varnishes become thick by keeping; but when they are to be used, it is only necessary to pour in a little Venice turpentine, and to put them a little on the fire. Less turpentine is necessary in summer than in the winter : too much oil hinders the varnish from drying; but when too little is used, it cracks, and does not spread properly.
Black Varnish for Coaches and Iron- Work.
This varnish is composed of asphaltum, resin, and amber, melted separately, and afterwards mixed; the oil is then added, and afterwards the turpentine, as directed above. The usual propor- tions are, twelve ounces of amber, two of resin, two of asphaltum, six of oil, and twelve of turpentine.
A Varnish for rendering Silk Water and Air-ttghl.
To render the linseed-oil drying, boil it with two ounces of sugar of lead, and three ounces of
VOL. II. R
^42 VARNISHING. ,
litharge, for every pint of oil, till the oil has dis- solved them; then put a pound of bird-lime, and half a pint of the drying oil into a pot of iron or copper, holding about a gallon; and let it boil gently over a slow charcoal lire, till the bird-lime ceases to crackle; then pour upon it two pints and a half of drying-oil, and boil it for about an hour longer, stirring it often with an iron or wooden spatula. As the varnish in boiling swells much, the pot should be removed from the fire, and replaced when the varnish subsides. While it is boiling, it should be occasionally examined, in order to deter- mine whether it has boiled enough. For this pur- pose, take some of it upon the blade of a large knife, and after rubbing the blade of another knife upon it, separate the knives; and when, on their separation, the varnish begins to form threads be- tween the two knives, it has boiled enough, and should be removed from the fire. When it is almost cold, add about an equal quantity of spirits of tur- pentine; mix both well together, and let the mass rest till the next day; then having warmed it a little, strain and bottle it. If it is too thick, add spirits of turpentine. This varnish should be laid upon the stuff when perfectly dry, in a lukewarm state; a thin coat of it upon one side, and, about twelve hours after, two other coats should be laid on, one on each side ; and in twenty-four hours the silk may be used.
Mr. Blcmchard's Var7iishfor Air-balloons.
Dissolve elastic gum (Indian-rubber), cut small, in five times its'*weight of spirits of turpentine, by keeping them some days together ; then boil one ounce of this solution in eight ounces of drying
VARNISHING. g4S
linseed-oil for a few minutes, and strain it. Use it warm.
Essential Oil Varnish,
The essential varnishes consist of a solution of resin in oil of turpentine. This varnish being ap- plied, the turpentine evaporates, leaving the resin behind. They are commonly used for pictures.
To dissolve Gum Copal in Oil of Turpentine.
AVhatever quantity is to be dissolved should be put into a glass vessel capable of containing at least four times as much, and it should be high in proportion to its breadth.
Reduce two ounces of copal to small pieces, and put them into a proper vessel. Mix a pint of oil of turpentine with one-eighth part of spirit of sal ammoniac; shake them well together, put them to the copal; cork the glass, and tie it over with a string or wire, making a small hole through the cork. Set the glass in a sand heat, so regulated as to make the contents boil as quickly as possible, but so gently, that the bubbles may be counted as they rise from the bottom. The same heat must be kept up exactly till the solution is complete.
It requires the most accurate attention to suc- ceed in this operation. After the spirits are mixed, they should be put to the copal, and the necessary degree of heat be given as soon as possible. It should likewise be kept up with the utmost regu- larity. If the heat abates, or if the spirits boil quicker than is directed, the solution will immedi- ately stop, and it will afterwards be iu vain to pro- ceed with the same materials; but if properly
R 2
S44 VARNISHING.
managed, the spirit of sal ammoniac will be seen gradually to descend from the mixture, and attack the copal, which swells and dissolves, except a very small quantity which remains undissolved.'
It is of much consequence tliat the vessel should not be opened till some time after it has been per- fectly cold. It has happened, on uncorking the vessel, when it v/as not warm enough to affect the hand, that the whole of the contents were blown with violence against the ceiling. It is likewise important, that the spirit of turpentine should be of the best quality. The turpentine bought at the colour-shops seldom answers ; it should be had from Apothecaries' hall.
This varnish is of a rich deep colour, when viewed in the bottle, but seems to give no colour to the pictures it is laid on. If left in the damp, it remains tacky, as it is called, a long time ; but if kept in a warm room, or placed in the sun, it dries as well as any other turpentine varnish ; and when dry, it appears to be as durable as any other solution of copal.
Spirit Varnishes,
When resins are dissolved in alkohol, com- monly called spirits of wine, the varnish dries very speedily, but is subject to crack. This fault is corrected by adding a small quantity of oil of tur- pentine, which renders it brighter, and less brittle when dry.
To dissolve Gum Copal in Spirits of Wine.
Dissolve half an ounce of camphor in a pint of alkohol, or spirits of wine ', put it into a circulat-
VARNISHING. 245
ing glass, and add four ounces of copal, in small pieces ; set it in a sand-heat so regulated, that the bubbles may be counted as they rise from the bot- tom ; and continue the same heat till the solution is completed.
Camphor acts more powerfully upon copal than any other substance. If copal is finely powdered, and a small quantity of dry camphor rubbed with it in the mortar, the whole becomes in a few minutes a tough coherent mass. The process above described will dissolve more copal than the menstruum will retain when cold. The most economical method will, therefore, be,\to set the vessel which contains the solution by for a few days ; and when it is perfectly settled, pour off the clear varnish, and leave the residuum for a future operation.
This is a very bright solution of copal : it is an excellent varnish for pictures, and may, perhaps, be found to be an improvement in fine japan works, as the stoves used in drying those articles ,may drive ofi'the camphor entirely, and leave the copal pure and colourless upon the work.
N. B. Copal will dissolve in spirit of turpentine, by the addition of camphor, with the same facility, but not in the same quantity, as in alkohol.
A Varnish for Wainscot, Cane Chairs, ^c.
Dissolve in a quart of spirits of wine, eight ounces of gum sandarach, two ounces of seed-lac, and four ounces of resin ; then add six ounces of Venice turpentine. If the varnish is to produce a red colour, more of the lac and less of sandarach should be used, and a little dragon's blood should be added. This varnish is very strong.
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S^ VARNISHING.
A Variiishfor Toilet-Bocces, Cases, Fans, 8^c.
Dissolve two ounces of gum mastich, and eight ounces of gum sandarach, in a quart of alkohol j then add four ounces of Venice turpentine.
A Varnish for Violins^ and other Musical Instruments.
Put four ounces of gum sandarach, two ounces of lac, two ounces of gum m>astich, an ounce of gum elemi, into a quart of alkohol, and hang them over a slow fire till they are dissolved ; then add two ounces of turpentine.
Varnish for employing Vermilion for painting Equipages.
Dissolve in a quart of alkohol six ounces of sandarach, three ounces of gum lac, and four ounces of resin ; afterwards add six ounces of the cheapest kind of turpentine : mix it with a pro- per quantity of vermilion when it is to be used.
Seed-lac Varnish.
Take spirits of wine, one quart j put it in a wide mouthed bottle, add thereto eight ounces of seed-lac, that is large grained, briglit, and clear, free from dirt and sticks ; let it stand two days, or longer, in a warm place, often shaking it. Strain it through a flannel into another bottle, and it is fit for use.
VARNISHING. 24,7
Shell-lac Varnish.
Take one quart of spirits of wine, eight ounces of the thinnest and most transparent shell-lac, which, if melted in the flame of a candle, will draw out in the longest and finest hair ; mix and shake these together, and let them stand in a warm place for two days, and it is ready for use. This varnish is softer than that which is made from seed-lac, and, therefore, is not so useful ; but may be mixed with it for varnishing wood, &c.
White Varnish for Clock Faces, ^c.
Take of spirits of wine, highly rectified, one pint, which divide into four parts ; then mix one part with half an ounce of gum mastich, in a phial by itself J one part of spirits, and half an ounce of gum sandarach, in another phial ; one part of spirits, and half an ounce of the whitest parts of gum-benjamin. Then mix and temper them to your mind. It would not be amiss to add a little bit of white resin, or clear Venice turpentine, in the mastich bottle ; it will assist in giving a gloss. If your varnish prove too strong and thick, add spirits of wine only ; if too hard, some dissolved mastich ; if too soft, some sandarach or benjamin. No other rule can be given, unless the quality of the gums and the spirits could be ascertained. When you have brought it to a proper temper, warm the silvered plate before the fire, (if a clock face, taking care not to melt the wax,) and with a flat camel's-hair pencil, stroke it all over imtil no white streaks appear. This will preserve silver- ing many years.
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JAPANNING.
Japanning is properly the art of varnishing and painting ornaments on wood, in the same manner as is done by the natives of Japan in the East Indies.
The substances which admit of being japanned are ahnost all kinds that are dry and rigid, or not too flexible ; as wood, metals, leather, and paper prepared.
Wood and metals do not require any other pre- paration but to have their surfaces perfectly even and clean ; but leather should be securely strained, either on frames or on boards ; as its bending, or forming folds, would otherwise crack and force off the coats of varnish. Paper should be treated in the same manner, and have a previous strong coat of some kind of size ; but it is rarely made the subject of japanning till it is converted into papier mache, or wrought by other means into such form, that its original state, particularly with respect to flexibility, is changed.
One principal variation from the method for- merly used in japanning is, the omitting any prim- ing, or undercoat, on the work to be japanned. In the older practice, such a priming was always employed ; the use of it was to economize the varnish by filling up the inequalities in the surface. But there is a gieat inconvenience arising- from the use of it, that the japan coats are constantly liable to be cracked and peeled off by any vio- lence, and will not last near so long as the articles which are japanned without any such priming.
The French still retain the use of this under- coat, and their japanned goods are upon that
JAPANNING. 249
account less durable than those manufactured at Birmingham, where it is not used.
Of the Nature of Japan Grounds.
When a priming is used, the work should first be prepared by being well smoothed with fish-skin or glass-paper, and being made thoroughly clean, should be brushed over once or twice with hot size, diluted with two-thirds water, if it is of the common strength. The priming should then be laid on as even as possible, and should be formed of a size, of a consistency between the common kind and glue, mixed with as much whiting as will give it a sufficient body of colour to hide the surface of whatever it is laid upon, but not more. This must be repeated till the inequal- ities are completely filled up, and then the work must be cleaned off with Dutch rushes, and polished with a wet rag.
When wood or leather is to be japanned, and no priming is used, the best preparation is to lay two or three coats of coarse varnish, composed in the following manner.
Take of rectified spirits of wine one pint, and of coarse seed-lac and resin, each two ounces ; dis- solve the seed-lac and resin in the spirit, and then strain off the varnish.
This varnish, as well as all others formed of spirit of wine, must be laid on in a warm place ; and if it can be conveniently managed, the piece of work to be varnished should be made warm like- wise ; and for the same reason, all dampness should be avoided ; for either cold or moisture chills this kind of varnish, and prevents its taking proper hold of the substance on v/hich it is laid.
250 JAPANNING.
When the work is so prepared, or by the priming with the composition of size and whiting above described, the proper japan ground must be laid on, which is much the best formed of shell- lac varnish, and the colour desired, except white, which requires a peculiar treatment ; and if bright- ness be wanted, then also other means must be pursued.
The colours used with the shell-lac varnish may be any pigments Mdiatever which give the tint of the ground desired.
As metals never require to be imder-coated with whiting, they may be treated in the same manner as wood or leather.
White Japan Grounds,
The difficulty of forming a ground that shall be at the same time hard and white, arises from there being no substance that will form a very hard var- nish, and yet have no colour. The best is made as follows : Mix flake white, or white lead, with one- sixth of its v/eight of starch, and dry the mixture, and temper it v;ith mastich varnish. Lay this on the substance to be japanned, with or without the under coat of whiting; then varnish it with five or six coats of a varnish made by dissolving two ounces of picked lac, and three ounces of gum animi, in a a quart of spirit of wine, straining off the clear varnish.
A very good varnish, free from all brittleness, may be formed, by dissolving as much gum animi as the oil will take, in old nut, or poppy oil, boiled gently, when the gum is put into it. The ground of white colour may be laid on in this varnish, and then a coat or two may be put over the ground :
JAPANNING. 251
but it must be well diluted with oil of turpentine when it is used.
Blue Japan Grounds.
Blue japan grounds may be formed of bright Prussian-blue; or of verditer, glazed over by Prus- sian-blue, or smalt. The colour may be best mixed with shell-lac varnish, and brought to a polishing state by five or six coats of varnish of seed-lac; but the varnish, nevertheless, will somewhat injure the colour, by giving to a true blue a cast of green, and fouling in some degree a warm blue by the yellow it contains; where, therefore, a bright blue is, re- quired, and a less degree of hardness can be dis- pensed with, the method before directed in the case of white grounds must be pursued.
Red Japan Grounds.
For a scarlet japan ground, vermilion may be used; but the vermilion has a glaring effect, that renders it much less beautiful than the crimson produced by glazing it over with carmine or fine lake, or even with rose pink, which has a very good effect, used for this purpose. For a very bright crimson, nevertheless, instead of glazing with car- mine, the Indian lake should be used, dissolved in the spirit of which the varnish is compounded, which it readily admits of when good; and in this case, instead of glazing with the shell-lac varnish, the upper, or polishing coats need only be used, as they will equally receive and convey the tinge of the Indian lake, which may be actually dissolved by spirits of wine, and this will be found a much cheaper method than the using carmine. If^ liow- ever, the highest degree of brightness is required, the white varnish must be used.
S52 JAPANNING.
Yellow Japan Grounds.
For bright yellow grounds, king's yellow, or turpeth mineral should be employed, either alone or mixed with fine Dutch pink, and the effect may be still more heightened, by dissolving powdered turmeric root in the spirits of wine, of which the upper or polishing coat is made; which spirits of wine must be strained from off the dregs, before the seed-lac be added to it, to form the varnish.
The seed-lac varnish is not equally injurious here, and with greens, as is the case of other co- lours; because, being only tinged with a reddish yellow, it is little more than an addition to the force of the colours.
Yellow grounds may be likewise formed of Dutch pink only, which, when good, will not be wanting in brightness, though extremely cheap.
Green Japan Grounds.
Green grounds may be produced by mixing king's yellow and bright Prussian blue, or rather turpeth-mineral and Prussian blue. And a cheap, but fouler kind by verdigris, with a little of the above mentioned yellows, or Dutch pink. But where a very bright green is wanted, the crystals of verdigris, called distilled verdigris, should be employed; and to heighten the effect, they should be laid on a ground of leaf gold, which renders the colour extremely brilliant and pleasing.
Orange Japan Grounds,
Orange coloured japan grounds may be formed by mixing vermilion, or red lead, with king's yel-
JAPANNING. 253
low, or Dutch pink, or the orange lake, which will make a brighter orange ground than can be pro- duced by any mixture.
Purple Japan Grounds.
These may be produced by the mixture of lake and Prussian blue ; or of a darker kind, by Vermil- lion and Prussian blue. They may be treated as the rest, with respect to the varnish.
Black Japan Growids.
Black grounds may be formed without heat, by either ivory black or lamp black ; but the former is preferable where it is perfectly good. These may always be laid on v;ith shell-lac varnish; and have their upper, or polishing coats of common seed- lac varnish, as the tinge or foulness of the varnish can here be no injury.
Common black Japan grounds on iron or copper, produced by means of heat, are formed thus : the piece of work to be japanned must be painted over with drying oil, and a little lamp black ; and when it is of a moderate dryness, must be exposed to such a degree of heat, as will change the oil to black, without burning so as to destroy or weaken its tenacity. The stove should not be too hot when tire work is put into it, nor the heat increased too fast, either of which errors would make it blister ; but the slower the heat is augmented, and the longer it is continued, provided it be restrained within the due degree, the harder will be the coat of japan. This kind of varnish requires no polish, having received, when properly managed, a suffi- cient one from the heat.
254 JAPANNING.
Tortoise-shell Japan Ground.
The best kind is made by means of a varnish prepared in the following manner :
Take of good linseed-oil one gallon, and of umber half a pound ; boil them together till the oil become very brown and thick; strain it through a coarse cloth, and boil it in till it acquire the consistence of pitch.
Clean well the metal, or other pieces which are to be japanned, and lay vermilion tempered with shell-lac varnish, or with drying-oil diluted with oil of turpentine, very thinly, on the places intended to imitate the more transparent parts of the tortoise- shelL When the vermilion is dry, brush over the whole with the black varnish, tempered to a true consistence with oil of turpentine; and when it is set and firm, put the work into a stove, where it may undergo a very strong heat, which must be continued a considerable time ; if even three weeks or a month it will be the better.
This was given amongst other receipts by Kunckel ; but appears to have been neglected till it was revived with great success in the Birming- ham manufactures, where it was much used.
Method of painting Japan Work.
Japan w^ork ought properly to be pamted with colours in varnish; though, for the greater dis- patch, and in some very nice work in small, for the freer use of the pencil, the colours are sometimes tempered in oil ; which should previously have a fourth part of its weight of gum animi dissolved in it; or in default of that, gum sandarach, or gum mastich. When the oil is thus used, it should be
JAPANNING. 255
well diluted with oil of turpentine, that the colours may lay more evenly and thin ; by which means, fewer of the polishing or upper coats of varnish be- come necessary.
In some instances, water colours are laid on grounds of gold, in the manner of other paintings; and are best without any varnish over them. When they are to have the effect of embossed work, the colours for painting are prepared by means of isin- glass size, with some honey or sugar candy. The body of which the embossed woric is raised, need not, however, be tinged with the exterior colour, but may be formed of very strong gum water, thickened to a proper consistence by bole armoniac and whiting in equal parts; which being laid on the proper figure and repaired when dry, may be then painted with the proper colours, tempered with the isin- glass size, or, in the usual manner, with shell-lac varnish.
Manner of varnishing Japan I Fork,
The finishing of japan-work consists in laying on, and polishing, tiie outer coats of varnish. This is in general done best with common seed-lac varnish. But where brightness is the most material point, and a tinge of yellow will injure it, seed-lac must give way to the whiter gums ; where hardness, and a greater tenacity are most essential, it must be re- tained; and the mixed varnish mentioned above, under white japanned ground, made of the picked seed-lac, must be adopted.
With respect to making this varnish, it may be observed, that when the spirit of wine is very strong, it will dissolve a greater proportion of the seed-lac; but this quantity Vv'ill saturate the com- mon, which is seldom of a strength sufficient to
2.56 JAPANNING.
make varnishes in perfection. As the chilling, which is the most inconvenient accident attending varnishes of this kind, is prevented, or produced more frequently, according to the strength of the spirit ; we shall show a method by which weaker rectified spirits may be rendered of the first degree of strength.
Take a pint of the common rectified spirit of wine, and put it into a bottle, of which it vrill not fill above three parts ; add to it half an ounce of pearl-ashes, salt of tartar, or any other alcaline salt, heated red hot, and powdered as well as it can be vrithout much loss of its heat. Shake the mixture frequently for the space of half an hour ; before which time, a great part of the phlegm v/ill be separated from the spirit, and will appear, toge- ther with the undissolved part of the salts, in the bottom of the bottle. Let the spirit be poured off or freed from the phlegm and the salts, by means of a separating funnel -, and let half an ounce of the pearl-ashes, heated and powdered as before, be added to it, and the same treatment repeated. This may be done a third time, if the quantity of phlegm separated by the addition of the pearl- ashes appear considerable. An ounce of alum reduced to powder, and made hot, but not burnt, must then be put into the spirit, and sufiered to remain some hours, the bottle being frequently shaken ; after which the spirit being poured ofii* from it, v/ill be fit for use.
The addition of the alum is necessary to neu- tralize the remains of the alcaline salt, which would otherwise greatly deprave the spirit.
The manner of using the seed-lac, or white varnish, is the same, except with regard to the substance used in polishing ; v.hich, where a pure
JAPAN.VIXG. 257
\\hite of a great clearness of other colours is in question, should be itself white ; whereas the browner sorts of polishing-dust, as being cheaper, and doing their business with greater dispatch, may be used in otlier cases. The pieces of work to be varnished should be placed near a fire, or in a room w here there is a stove, and made perfectly dry ; and then the varnish may be rubbed over them by the proper brushes made for that pur- pose, beginning in the middle, and passing the brush to one end, and then with another stroke from the middle, passing it to the other. But no part should be crossed, or twice passed over, in forming one coat, where it can be possibly avoided. When one coat is dry, another must be laid over it ; ^nd this must be continued at least five or six times, or more, if, on trial, there be not sufficient thickness of varnish to bear the polish, without laying bare the painting or ground colour underneath.
When a sufficient number of coats is thus laid on, the work is fit to be polished ; which must be done, in common cases, by rubbing it w^th a rag, dipped in tripoli, or rotten-stone, finely powdered ; but, towards the end of the rubbing, a little oil of any kind should be used along with the powder ; and when the v/ork appears sufficiently bright and glossy, it should be well rubbed with the oil alone, to clean it from the powder, and give it a still brighter lustre.
In case of white grounds, instead of tripoli, or rotten-stone, fine putty, or whiting must be used ; both of which should be washed over, to prevent the danger of damaging the work, from any sand or gritty matter that may happen to be mixed with them.
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2.5S LACQUERING.
It is a great improvement in all kinds ofjapanned work, to harden the varnish by means of heat ; which in every degree that it can be appUed, short oi' what would burn or calcine the matter, tends to give it a more firm and strong texture.
Where metal forms the body, a very hot stove may be used ; and the pieces of work may be con- tinued in it a considerable time, especially if the heat be gradually increased ; but where wood is in question, heat must be sparingly used, as it would otherwise warp or shrink the body, so as to injure the general figure.
LACQUERING.
Lacquering is the laying either coloured or transparent varnishes on metals, in order to pro- duce the appearance of a different colour in the metal, or to preserve it from rust, or the injuries of the weather.
Lacquering is used where brass is to be made to have the appearance of being gilt ; where tin is wanted to have the resemblance of yellow metals ; and where brass locks or nails, or other such mat- ters, are to be defended from the corrosion of the air or moisture.
The principal substance used for the compo- sition of lacquers, is seed-lac ; but for coarser pur- poses, resin or turpentine is added, in order to make the lacquer cheaper.
A Lacquer for Brass^ to imitate Gilding.
Take of turmeric one ounce, and of saffron and Spanish annotto, each two drachms. Put them
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LACQUERING. 259
into a proper bottle, with a pint of highly rectified spirits of wine, and place them in a moderate heat, often shaking them for several days. A very strong yellow tincture will then be obtained, which must be strained off from the dregs through a coarse linen cloth ; and then, being put back into the bottle, three ounces of good seed-lac, powdered grossly, must be added, and the mixture placed again in a moderate heat and shaken till the seed-lac be dissolved, or at least such a part of it as may. The lacquer must then be strained, and must be put into a bottle well corked.
Where it is desired to have the lacquer warmer or redder than this composition, the proportion of the annotto must be increased ; and wdiere it is wanted cooler, or nearer to a true yellow, it must be diminished.
The above, properly managed, is an extremely good lacquer, and of moderate price ; but the following, which is cheaper, and may be made where the Spanish annotto cannot be procured good, is not greatly inferior to it.
Take of turmeric root, ground, one ounce, of the best dragon's blood half a drachm. Put them to a pint of spirits of wine, and proceed as above. By diminishing the proportion of dragon's blood, the varnish may be rendered of a redder or truer yellow cast.
Saffron is sometimes used to form the body of colour in this kind of lacquer, instead of the tur- meric ; but though it makes a warmer yellow, yet the dearness of it, and the advantage which tur- meric has in forming a much stronger tinge in spirits of wine, gives it the preference. Though being a true yellow, and consequently not suffi- ciently warm to overcome the greenish cast of
s 2
mo
LACQUERIXG.
brass, it requires the addition of some orange coloured tinge to make it a perfect lacquer.
Aloes and gamboge are also sometimes used in lacquers for brass ; but the aloes is not necessary where turmeric or saffron is used ; and the gam- boge, though a very strong milky juice in water, affords but a very weak tinge in spirit of wine.
A Lacquer for Tiny to imitate a Yellow Metal.
Take of turmeric root one ounce, of dragon's blood two drachms, and of spirits of wine one pint J add a sufficient quantity of seed-lac.
A Lacquer for Locks, S^-c.
Seed-lac varnish alone, or with a little dragon's blood : or a compound varnish of equal parts of seed-lac and resin, with or without the dragon's blood.
A Gold-coloured Lacquer for gilding Leather.
What is called gilt leather, and used for screens, borders for rooms, &c. is only leather covered with silver leaf, and lacquered with the following composition.
Take of fine white resin four pounds and a half, of common resin the same quantity, of gum san- darach two pounds and a halfj and of aloes two pounds ; mix them together, after having bruised those which are in great pieces, and put them into an earthen pot, over a good fire made of charcoal, or over any fire where there is no flame. Melt all
GILDING. Q6l
the ingredients in this manner, stirring them well witli a spatula, that tliey may be thoroughly mixed together, and be prevented also from sticking to the bottom of the pot. When they are perfectly melted and mixed, and gradually to them seven pints of linseed oil, and stir the whole well together with the spatula. Make the whole boil, stirring it all the time to prevent a kind of sediment that will form, from sticking to the bottom of the vessel. When the varnish is almost sufficiently boiled, add gradually half an ounce of litharge, or half an ounce of red-lead, and vhen they are dis- solved, pass the varnish through a linen cloth, or flannel bag.
The time of boiling this varnish should be about seven or eight hours. This, however, varies, ac- cording to circumstances. The way of knowing when it is sufficiently boiled, is by taking a little on some instrument, and if it draws out and is ropy, and sticks to the fingers, drying on them, it is done ; but if not, it must be boiled till it acquires these qualities.
GILDING.
Gilding is the application of gold to the surfaces of bodies: it is of two principal kinds, according to the method of applying the gold. i
Wood, leather, paper, and similar substances, are gilt by fastening on leaves of gold by means of some cement. But metals are gilt by a chemical application of the gold to the surface. This last is called icater gilding.
The gilding of wood, and similar substances, is
of three kinds ; oil gilding, burnished gilding, and
Japamiers* gilding, y^hichwe shall severally describe,
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'26^2 GILDING.
after noticing the materials and tools necessary for going to work.
OfGold-Leaf.
There are three kinds of gold-leaf in common use.
Pure gold'lecif, which is made by hammering gold between the leaves of a book made of skins, till they are sufficiently thin.
Pale leaf-gold, which has a greenish colour, and is made of gold alloyed with silver.
Dutch gold, which is brought from Holland, and is in fact only copper-leaf coloured by the fumes of zinc. It is much cheaper than true leaf-gold, and is very useful where large quantities of gilding are wanted, which can be defended from the weather, and where great nicety is not required ; but it changes its colour entirely when exposed to mois- ture ; and, indeed, in all cases, its beauty is soon impaired, unless well secured by varnish. It is therefore only a cheap substitute for true gold-leaf, which may be useful where durability is not an object.
Of the IfLStruments necessary Jbr Gilding.
The first instrument is the cushion, for receiving the leaves of gold from the books in which they are bought. It is made by covering a board of about eight inches square, with a double thickness of flannel, and over that, a piece of buff leather, and fastening it tight round the edges.
The hiife for cutting the leaves into the requisite sizes should be made like a pallet knife, and should not have its edge too sharp.
GILDING.
•263
The tip is a tool made by fastening the long hairs of a squirrel's tail between two cards, and is used for taking up the gold-leaf after it is cut, and applying it to the article to be gilded.
A^fitch pencil is used for the same purpose as the last, in taking up very small bits of gold-leaf. A ball of cotton is necessary for pressing down the leaf, after it is laid on. A large cameVs-hair brush is used lor dusting the work, and clearing away the superfluous gold.
Oil Gildings
Prime the work with boiled linseed-oil and white-lead ; and when that is dry, do it over with a thin coat of gold size, made of stone ochre ground in fat oil. When that is so dry as to feel clammy to the fingers, or to be, as the gilders call it, tacky ^ it is fit for gilding. Having spread your leaves upon the cushion, cut them into slips of the proper width for covering the work. Then breathe upon your tip, which, by moistening it, will cause it to take up the leaves from the cushion. Plaving ap- applied them by the tip on the proper parts of the work, press them down by the ball of cotton. Observe to repair, by putting small pieces of gold on any parts which you have omitted to cover. When all the work is sufficiently covered, let it dry, and clean it off with the brush.
This sort of gilding is the easiest, least expen- sive, and stands the weather best, and may be cleaned with a little water at any time ; but wants the lustre of burnished gilding.
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-04 GILDING.
Burnished Gilding.
This is the sort of gilding generally used for picture-frames, looking-glasses, &c.
The wood intended to be gilt in this manner should first be well sized, and then done over with seven or eight coats of size and whiting, so as to cover it with a body of considerable thickness. Having got a sufficient quantity of whiting upon the work, it must be carefully cleaned off, taking care to free all the cavities and hollows from the whiting that may have choked them up, and by proper moulds and tools restoring the sharpness of the mouldings intended to be shown.
It is then to receive a coat of size, whicli is made by boiling armeniac bole with parchment size. This must also remain till it is sufficiently dry for the gold. It must not be quite dry ; there- fore it would not be prudent to lay on more at a time, than can be gilt before it becomes too dry.
The work being thus prepared, place it a little declining from you, and having a cup of clean water ready and some hair pencils, moisten a part of the work, and then apply the gold by the tip to the moistened part. The gold will immediately adhere close to the work : proceed to wet the next part, and apply the gold as before, repeating this operation till the whole is completed ; taking care not to let any drops of water come upon any part of the gold already laid on. Care should therefore be taken, that no part be missed in going over it at first, as it is not so easily mended as the oil gilding.
The work being thus gilt, it is suffered to remain about twenty-four hours j when the parts that are
GILDING. ^2(j5
designed to be burnished are polished with a dog's tooth, or, wliat is better, with an agate burnisher. The gilding must not be quite dry when it is bur- nished; there is a state proper for the purpose, which is only to be known by experience.
Japanners^ Gilding,
The gilding of japanned work consists in draw- ing with a hair pencil, in gold size, the intended ornaments, and afterwards applying gold leaf or gold powder.
The gold size may be prepared in the following- manner: take of linseed-oil, and of gum animi, four ounces. Set the oil to boil in a proper vessel, and then add the gum animi gradually in powder, stirring each quantity about in the oil, till it appear to be dissolved, and then putting in another, till the whole be mixed with the oil. Let the mixture continue to boil, till, on taking a small quantity out, it appear of a thicker consistence than tar, and then strain the whole through a coarse cloth, and keep it for use ; but it must, when applied, be mixed with vermilion and oil of turpentine.
Having laid on the gold size, and suffered it to dry, the gold leaf is applied in the usual way, or if it is not wanted to shine so much, gold powder is applied, which is made by grinding gold leaf upon a stone with honey, and afterwards washing the honey away with water. If the gilding is to be varnished over, Dutch gold may be used, or aurum musivum may be used instead of real gold powder.
266 GILDING.
To write on Paper mth Letters of Gold.
Put some gum arabic into common wiiting ink, and write with it in the usual way. When tlie writing is dry, breathe on it ; the warmth and moisture softens the gum, and will cause it to fasten on the gold leaf, w^hich may be laid on in the usual way, and the superfluous ])art brushed off. Or instead of this,, any japanners' size may be used.
To lay Gold upon White Earthen-Ware, or Glass.
Procure some japanners' gold size, and with it draw your design upon the vessel to be gilt, moist- ening the gold size, as you find necessary, with oil of turpentine. Set your work in a clean place to dry, for about an hour, and then place it so near the fire that you could but just bear the heat of it with your hand for a few seconds. Let it remain there till it feels quite tacky or clammy, then, having procured a cushion, and some leaf gold, cut it into slips of the proper size, and lay it on with a little cotton wool. When the gold is all on, put the ware into an oven to be baked for two or three hours.
Glasses, &c. may also be gilt by drawing the figures with shell gold mixed with gum arabic and a little borax. Then apply sufficient heat to it ; and, lastly, burnish it.
Gilding on Glass or Porcelain, by Burning-in.
'Dissolve gold in aqua regia, and evaporate the acid by heat ; a gold powder will be obtained ; or
GILDING. ^7
precipitate the gold from the solution by pieces of copper. Lay this gold on with a strong solution of borax and gum water, and it will be ready for burning-in.
Gilding Metals.
One method of applying gold upon metals is by first cleaning the metal to be gilt ; then gold leaf is laid on it, which, by means of rubbing with a polished blood stone, and a certain degree of heat, are made to adhere. In this manner silver leaf is fixed and burnished upon brass, in the making of what is cdWed French plate ; and sometimes also gold leaf is burnished upon copper and iron.
Gilding hy Amalgamation is by previously forming the gold into a paste, or amalgam, with mercury.
In order to obtain an amalgam of gold and mercury, the gold is lirst to be reduced into thin plates or grains, which are heated red-hot, and thrown into mercury previously heated, till it be- gins to smoke. Upon stirring the mercury with an iron rod, the gold totally disappears. The pro- portion of mercury to gold is generally as six or eight to one.
The method of gilding by amalgamation is chiefly used for gilding copper, or an alloy of cop- per with a small portion of zinc, which more readily receives the amalgam, and is also prefer- able, on account of its colour, which more resem- bles that of gold than the colour of copper.
When the metal to be gilt is wrought or chased, it ought to be previously covered with quick-silver before the amalgam is applied, that this may be
'268 GILDING.
easier spread ; but when the siirtace of the metal is plain, the amalgam may be directly applied to it.
The metal required to be gilt is first rubbed over with a little aqua-fortis, by which the surface is cleaned from any rust or tarnish that might pre- vent the union of the two metals. The amalgam, being then equally spread over the surface by means of a brush, the mercury is evaporated by a heat just sufficient for that purpose; lor if it be too great, part of the gold may also be expelled, and part of it will run together, and leave some of the surface of the metal bare. While the mercury is evaporating, the piece is to be from time to time taken from the fire, that it may be examined ; that the amalgam may be spread more equally by means of a brush ; that any defective parts of it may be again covered, and that the heat may not be too suddenly applied to it. When the mercury is evaporated, which is known by the surface be- coming entirely of a dull yellow colour, the metal must then undergo other operations, by which the fine gold colour is given to it.
First, the gilded piece of metal is rubbed with a scratch-brush (which is a brush composed of brass-wire,) till its surface is made smooth ; tlien it is covered over with a composition called gilding 'waxj and is again exposed to the fire till the wax be burnt off. This wax is composed of bees-wax, sometimes mixed with some of the following sub- stances, red ochre, verdigris, copper scales, alum, vitriol, borax ; but according to Dr. Lewis, the saline substances are sufficient, without any wax.
By this operation the colour of the gilding is heightened ; and this effect seems to be produced by a perfect dissipation of some mercury remain- ing after the former operation.
GILDING. 269
The gilt surface is tiien covered over with a sahiie composition, consisting of nitre, alum, or other vitriohc salt, ground together, and mixed up into a paste with water or urine. The piece of metal thus covered is exposed to a certain de- gree of heat, and then quenched in water. By this method its colour is further improved, and brought nearer to that of gold. This effect seems to be produced by the acid of nitre (which is dis- engaged by the sulphuric acid of the ahim, during the exposure to heat) acting upon any particles of copper which may happen to lie upon the gilded surface.
Lastly, some artists tliink that they give an ad- ditional lustre to their gilt work, by dipping it in a liquor prepared by boiling some yellow materials, as sulphur, orpiment, or turmeric. The only ad- vantage of this operation is, that part of the yel- low matter remains in some of the hollows of the carved work, in which the gilding is apt to be more imperfect, and to w^iich it gives a rich and solid appearance.
It may here be noticed, that the use of the aqua- fortis or nitrous acid, mentioned in the beginning of the process, is not, as is generally supposed, confined merely to cleansing the surface of the metal to be gilt from rust or tarnish j but it also greatly facilitates the application of the amalgam to the surface of that metal, probably in the fol- lowing manner : It first dissolves part of the mer- cury of the amalgam ; and when this solution is applied to the copper, this latter metal having a stronger disposition to unite with the nitrous acid than the mercury has, precipitates the mercury upon its surface, in the same manner as a polished piece of iron precipitates upon its surface copper
270 GILDING.
from a solution of blue vitriol. When the metal to be gilt is thus covered over with a thin coat of precipitated mercury, it readily receives the amalgam.
On the subject of gilding by amalgamation, Dr. Lewis has the following remarks : " There are two principal inconveniencies in this business ; one, that the workmen are exposed to the fumes of the mercury, and generally, sooner or later, have their health greatly impaired by them : the other, the loss of the mercury ; for though part of it is said to be detained in the cavities made in the chimneys for that purpose, yet the greatest part of it is lost. From some trials I have made, it ap- peared that both these inconveniencies, particu- larly the first and most considerable one, might be in a good measure avoided, by means of a furnace of a due construction."
If the communication of a furnace with its chim- ney, instead of being over the fire, is made under the grate, the ash-pit door, or other apertures be- neath the grate, closed, and the mouth of the fur- nace left open, the current of air, which otherwise would have entered beneath, enters now at the top, and passing down through the grate to the chim- ney, carries with it completely both the vapour of the fuel, and tlie fumes of such matters as are placed upon it. The back part of the furnace should be raised a little higher above the fire than the fore part, and an iron plate laid over it, that the air may enter only at the front where the workman stands, who will be thus effectually se- cured from the fumes, and from being incom- moded by the heat, and at the same time have full liberty of introducing, inspecting, and removing the work.
GILDTNG, Oyi
If such a furnace is made of strong forged (not milled) iron plate, it will be sufficiently durable. The upper end of the chimney may reach above a foot and a half higher than the level of the fire ; over this is to be placed a larger tube, leaving an interval of an inch, or more, all round between it and the chimney, and reaching to the height of ten or twelve feet ; the higher the better. The exter- nal air, passing up between the chimney and the outer pipe, prevents the latter from being much heated, so that the mercurial fumes will condense against its sides into running quicksilver, which falling down to the bottom, is there catched in a hollow rim, formed by turning inwards a portion of the lower part, and conveyed by a pipe at one side into a proper receiver.
Gilding Iron or Steel, — In gilding iron or steel by means of an amalgam, as the metal has no affinity for the mercury, an agent must be em- ployed to dispose the surface to receive the gilding. For this purpose, a solution of mercury in nitrous acid (aqua fortis,) or what the workmen call quick- silver water, is applied to the parts intended to be gilded ; the acid, by a stronger affinity, seizes on a portion of the iron, and deposits in the place of it a thin coating of mercury, which will not refuse a union afterwards with the gold amalgam that may be applied ; but, by this process, the surface of the metal is injured by the nitrous acid, and the union of the mercury is very slight, so that a bright and durable gilding cannot be obtained.
Another method. — Sometimes a solution of blue vitriol is applied, with a cameFs hair pencil, to the parts of the steel intended to be gilt. By a che- mical action, exactly similar to what we have
f27!2 filLDIXG.
described as taking place wlien a solution of nitrate of mercury is employed, a thin coating of copper is precipitated on the metal. Copper having an affinity for mercury, a kind of union may by this means be effected between the amalgam and the iron or steel, as the case may be. In whichever of these ways the amalgam be brought into imion with the steel, the surface is injured by the action of the acid employed, and still a heat sufficient to volatilize the mercury, must be afterwards used.
Gilding of Iron by heat. — When the surface is polished bright, it must be heated till it becomes blue. Gold leaf is then applied to its surface, and burnished down. It is then heated again, and another layer of gold burnished on it. In this manner three or four coats are given, according to the strength of the gilding intended. This is a more laborious process than the two last, but it is not attended with so much risk.
An improved process for gilding Iron or Steel. — This process, which is less known among artists than it deserves to be, may prove useful to those who have occasion to gild iron or steel. The first part of the process consists in pouring over a solution of gold in nitro-muriatic acid (aqua regia) about twice as much ether, which must be done with caution, and in a large vessel. These liquids must then be shaken together ; as soon as the mixture is at rest, the ether will be seen to separate itself from the nitro-muriatic acid, and to float on the surface. The nitro-muriatic acid becomes more transparent, and the ether darker than they were before ; the reason of which is, that the ether has taken the gold from the acid. The whole mixture is then to be poured into a glass funnel, the lower aperture of which is small j but this
GILDING. 273
aperture must not be opened till the fluids have compleely separated themselves from each other. It is then to be opened ; by which means the liquid which has taken the lowest place by its greater gravity, viz. the nitro-muriatic acid will run off; after which, the aperture is to be shut, and tha funnel will then be found to contain nothing but ether mixed with the gold, which is to be put into well-closed bottles, and preserved for use. In order to gild iron or steel, the metal must first be well polished with the finest emery, or rather with the finest crocus martis, or colcothar of vitriol, and common brandy. The auriferous ether is then to be applied with a small brush ; the ether soon evaporates, and the gold remains on the surface of the metal. The metal may then be put into the fire, and afterwards polished. By means of this auriferous ether, all kinds of figures may be delineated on iron, by employing a pen, or fine brush. It is in this manner, probably, that the Sohlinger sabre blades are gilded.
Instead of ether, the essential oils may be used ; such as oil of turpentine, or oil of lavender, which will also take gold from its solution.
Cold Gilding of Silver. — Dissolve gold in the nitro-muriatic acid, and dip some linen rags in t!.e solution ; then burn them, and carefully preserve the ashes, which will be very black, and heavier than common. When any thing is to be gilded, it must be previously well burnished ; a piece of cork is then to be dipped, first into a solution of salt in water, and afterwards into the black powder ; and the piece, after being rubbed with it, must be burnished. This powder is frequently used for gilding delicate articles of silver.
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274 GILDING.
Gilding of Brass or Copper. — Fine instruments of brass, in order that their surface may be kept longer clean, may be gilded in the following manner.
Provide a saturated solution of gold, and having evaporated it to the consistence of oil, suffer it to shoot into crystals. These crystals must then be dissolved in pure water, and the articles to be gilded being immersed in it, are then to be washed in pure water, and afterwards burnished. This process may be repeated several times, till the arti- cles have been well gilt. A solution of gold crystals is preferred to a mere solution of gold j because, in the latter, there is always a portion of free acid, which will not fail to exercise more or less action on the surface of the brass or copper, and injure its polish.
Grecian Gilding. — Dissolve some mercury in muriatic acid (spirits of salts), which will give a muriate of mercury. Mix equal parts of this and sal ammoniac, and dissolve them in aqua fortis. Put some gold into this, and it will dissolve. When this is applied to silver, it becomes black ; but by heating, it assumes the appearance of gilding.
To make Shell-Gold.
Grind up gold-leaf with honey, in a mortar ; then wash away the honey with water, and mix the gold-powder with gum-water. This may be applied to any article with a camel's-hair pencil, in the same way as any other coloui'.
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SILVERING.
Wood, paper, &c. are silvered in the same manner as gilding is performed, using only silver instead of gold-leaf.
To Silver Copper or Brass.
Cleanse the metal with aqua fortis, by washing it lightly, and then throwing it into the water ; or by scouring it with salt and tartar with a wire-brush. Dissolve some silver in aqua fortis, and put pieces of copper into the solution ; this will throw down the silver in a state of metallic powder. Take fifteen or twenty grains of this silver powder, and mix with it two drachms of tartar, the same quan- tity of common salt, and half a drachm of alum ; rub the articles with this composition till they are perfectly white, then brush it off, and polish them with leather.
Anotfier method. — Precipitate silver from its so- lution in aqua fortis by copper, as before ; to half an ounce of this silver add common salt and sal ammoniac, of each two ounces, and one drachm oi corrosive sublimate ; rub them together, and make them into a paste with water. With this, copper utensils of every kind, that have been pre- viously boiled with tartar and alum, are rubbed ; after which they are made red hot and polished.
To Silver the Dial-plates of Clocks^ Scales of Ba- 7^omete7'S, S^x.
Take half an ounce of silver lace, add thereto an ounce of double refined aqua fortis ; put them into an earthen pet, and place them over a gentle
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276 SILVERING.
fire till all is dissolved, which will happen in about five minutes ; then take them off, and mix it in a pint of clear water; after which, pour it into another clean vessel, to free it from grit or sediment ; then add a spoonful of common salt, and the acid, which has now a green tinge, will immediately let go the silver particles, which form themselves into a white curd; pour off the acid, and mix the curd with two ounces of salt of tartar, half an ounce of whiting, and a large spoonful of salt, more or less, accord- ing as you find it for strength. Mix it well up to- gether, and it is ready for use.
Having well cleared the brass from scratches, rub it over with a piece of old hat and rotten-stone, to clear it from all greasiness, and then rub it with salt and water with your hand : take a little of the before-mentioned composition on your finger, and rub it over where the salt has touched, and it will adhere to the brass and completely silver it. After which, wash it well with water, to take ofi' what aqua fortis may remain in the composition ; when dry, rub it with clean rag, and give it one or two coats of varnish, prepared according to the direc- tions given under the article varnislies.
This silv^ering is not durable, but may be improved by heating the article, and repeating the operation till the covering seems sufficiently thick.
Silver Plating.
The coat of silver applied to the surface of the copper by the means mentioned above, is very thin, and is not durable. A more substantial method of doing it, is as follows : form small pieces of silver and copper, and tie them together with
SILVERING. 277
wire, putting a little borax between. The pro- portion of silver may be to that of the copper as one to twelve. Put them into a white heat, when the silver will be firmly fixed to the copper. Th;s whole is now made to pass between rollers, till it is of the required thickness for manufacturing various articles.
To make French Plate.
Heat the copper articles intended to be plated, and burnish silver-leaf on it, with a burnisher.
To make Shell Silver.
Grind up leaf-silver with gum-water or honey ; when you have ground it, wash away the gum or honey, and use the powder that remains with gum- water, or glaire of eggs. This is laid on with a hair-pencil.
To silver Looking Glasses.
The following apparatus must first be prepared.
1. A square marble slab, or smooth stone, well polished, and ground flat; the larger the better; with a frame round it, or a groove cut in its edges, to keep the superfluous mercury from running off.
2. Lead weights, covered with cloth, to keep them from scratching the glass; from one pound weight to twelve pounds each, according to the size of the glass which is laid down.
3. Rolls of tinfoil.
4. Quicksilver.
Cut the tinfoil a little larger than the glass every way, and lay it flat upon the stone; and with a straight piece of hard wood, about three inches
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278 SILVERING.
long, stroke it every way, that there be no crease or wrinkles in it; then drop a little mercury upon it, and with a piece of cotton, w^ool, or hair's foot, spread it all over the foil, so that every part may be touched with the mercur}-. Then, keeping the marble slab nearly level with the horizon, pour the mercury over the foil ; cover it with a fine paper ; and lay two weights very near its lowest end or side, to keep the glass steady, while you draw the paper from between the silvered foil and the glass, which must be laid upon the paper. As you draw the paper, you must take care that no air bubbles be left ; for they will always appear, if left in at the first. You must likewise be sure to make the glass as clean as possible on the side intended to be sil- vered, and have the paper also quite clean ; other- wise, when you have drawn the paper from under it, dull white streaks will appear, which are very disagreeable.
After the paper is drawn out, place as many weights upon the glass as you conveniently can, in order to press out the superfluous mercuiy, and make the foil adhere to the glass. When it has lain six or seven hours in this situation, raise the stone about two or three inches at its highest end, that as much of the mercury may run off as possi- ble ; let it remain two days before you venture to take it up» But before you take the weights offj gently brush the edges of the glass, that no mer- cury may adhere to them ; then take it up, and turn it directly over, wuth its face side downward ; but raise it by degrees, that the mercury may not drip off too suddenly : for if, when taken up, it is immediately set perpendicular, air will get in between the foil and the glass at the top, as the mercury descends to the bottom ; by which means.
SILVERING. 279
if you be not exceedingly careful, your labour will be lost.
Another method, is to slide the glass over the foil, without the assistance of paper.
To Silver Glass Globes,
Take half an ounce of clean lead, and melt it with an equal weight of pure tin; then immediately add half an ounce of bismuth, and carefully skim off the dross J remove the mixture from the fire, and, before it grows cold, add five ounces of mer- cury, and stir the whole well together ; then put the fluid amalgam into a clean glass, and it is fit for use.
When this amalgam is used for foiling or silver- ing, let it first be strained through a linen rag ; then gently pour some ounces of it into the globe intended to be foiled : the mixture should be poured into the globe, by means of a glass or paper- funnel, reaching almost to the bottom of the globe, to prevent its splashing to the sides; the globe should then be dexterously inclined every way, though very slowly, in order to fasten the silver- ing. When this is once done, let the globe rest some hours ; repeat the operation, till at length the fluid mass is spread even, and fixed over the whole internal surface, as it may be known to be, by viewing the globe against the light ; the super- fluous amalgam may then be poured out, and the outside of the globe cleared.
To Silver the Convex Side of Glasses for Mirrors.
Take an earthen plate, on which pour some pre- pared plaster of Paris, mixed with water, of a
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'2H0'
SILVERING*
proper consistence ; then immediately, before it grows too stiff, lay the glass, with its convex side downward, in the middle of the plate, and press it until it lies quite close to the plaster ; in which situation let it remain until the plaster be- comes quite dry. After which, work a groove with your fingei', round the outside of the glass, in order to let the superfluous mercury rest upon it ; then cut the tinfoil to a proper size, and press it with the glass into the plaster-mould, in order to make it lie close ; after which, cover it with the mercury, and, without a paper (as directed for sil- vering plain mirrors), slide it over the silvered foil ; then place a weight on it, and let it stand two or three days, rising it by degrees, that the mercury may drip off gradually.
Afler this method common window-glass, &c. may be silvered.
To la^ Paper Pi^ints on the Inside of Glass Globed,
First, cut off all the white part of your impres- sion, so that nothing appear but the print ; then prepare some strong gum arabic water, or size, with which you must brush over the face side ; after which put it into the globe, and with a long small stick, on which a camel*s-hair pencil is fixed, stick it even on ; and by this method you may put what number of prints you please into the globe. Let them dry about twelve hours; then pour some prepared plaster of Paris, either white or tinged, whatsoever colour you please, and turn the globe easily about, so that every part be covered; pour out the superfluous plaster, and it is finished.
28 1
TINNING.
Tinning is tlie art of covering any metal with a tliin coating of tin. Copper and iron are the me- tals most commonly tinned. The use of tinning these metals is to prevent them from being cor- roded by rust, as tin is not so easily acted upon by the air or water as iron and copper are.
What are commonly called tin-plates, or sheets, so much used for utensils of various kinds, are in fact iron-plates coated with tin.
The principal circumstance in the art of tinning, is to have tlie surfaces of the metal to be tinned perfectly clean and free from rust, and also that the melted tin be perfectly metallic, and not co- vered with any ashes or calx of tin.
Tinning of Iron.
When iron-plates are to be tinned, they are first scoured, and then put into what is called a pickle, which is oil of vitriol diluted with water ; this dis- solves the rust or oxyd that was left after scouring, and renders the surface perfectly clean. They are then again washed and scoured. They are now dipped into a vessel full of melted tin, the surface of which is covered with fat or oil, to defend it from the action of the air. By this means, the iron coming into contact with the melted tin in a perfectly metallic state, it comes out completely coated.
When a small quantity of iron only is to be tinned, it is heated, and the tin rubbed on with a piece of cloth, or some tow, having first sprinkled the iron with some powdered resin, the use of which is to reduce the tin that may be oxydated. Any
28'2 BRONZING.
inflammable substance, as oil, for instance, will have in some degree, the same effect j which is owing to their attraction for oxvffen.
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The Tinning of Copper.
Sheets of copper may be tinned in the same man- ner as iron. Copper boilers, saucepans, and other kitchen utensils, are tinned after they are made. They are first scoured ; then made hot ; and the tin rubbed on, as before, with resin. Nothing ought to be used for this purpose but pure grain-tin ; but lead is frequently mixed with the tin, both to adul- terate its quality, and make it lay on more easily; but it is a very pernicious practice, and ought to be severely reprobated.
To whiten Brass or Copper by boiling.
Put the brass or copper into a pipkin with some white tartar, alum, and grain-tin, and boil them to- fcether. The articles will soon become covered with a coating of tin, which, when well polished, will look like silver. It is in this manner that pins, and many sorts of buttons, are whitened.
BRONZING.
Bronzing is colouring plaster, or other busts and figures, with metallic powders, in order to make them appear as if made of copper or other metals. The powders used for this purpose are either fine copper-filings, aurum musivum, or copper precipi- tated from its solution in aqua fortis by iron. Having done over the substance to be bronzed with a dark green colour, the projecting parts are touched with either isinglass size, japanners' gold size, or, in some cases, with drying-oil, or oil-paint j the powders are 10
SOLDERING. 283
then rubbed on, taking care that the projecting parts receive more of the powder than the cavities, to imitate the brightness on those parts of bronze which are Hable to be rubbed.
SOLDERING.
Soldering is the art of joining two pieces of me- tal together, by heating them with a thin piece or plate of metal interposed between them. Thus tin is a solder for lead; brass, gold, or silver, are sol- ders for iron, &c.
To make Silver Solder.
Melt fine silver two parts, brass one part ; do not keep them long in fusion, lest the brass fly oft' in fumes.
Ayiotlierfor coarser Silver.
Melt four parts of fine silver, and three of brass; throw in a little borax, and pour it out as soon as it is melted.
A Solder for Gold.
Melt copper one part, fine silver one part, and gold two parts ; add a little borax when it is just melted, then pour it out immediately.
The Method of soldering Gold or Silver.
After the solder is cast into an ingot, it would be more ready for use if your were to draw it into small wire, or flat it between two rollers ; after that cut it into little bits ; then join your work together with fine soft iron-wire ; and with a camel's-hair per.cil, dipt in borax finely powdered and well mois- tened with water, touch the joint intended to be
'iS'i MOULDING AND CASTING.
soldered; })lacing a little solder upon the joint, apply it upon a large piece of charcoal, and, with a blow-pipe and lamp, blow upon it the flame until it melts the solder.
To cleanse Silver or Gold after it is soldered.
Make the silver red hot, and let it cool ; then boil it in alum-water, in an earthen vessel, and it will be as clean as when new. If gold, boil it in urine and sal ammoniac.
A Solder for Lead,
Put two parts lead to one part tin: its goodness is tried by melting it, and pouring the size of a crown-piece upon the table ; if it be good, there will arise little bright stars in it. Apply resin when you use this solder.
A Solder for Tin.
Take four parts of pewter, one of tin, and one of bismuth ; melt them together, and run them into narrow thin lengths. >
A Solder for Iron.
Nothing here is necessary, but good tough brass, with borax applied, mixed with water to the con- sistence of paste.
MOULDING AND CASTING.
The art of taking casts or impressions from pieces of sculpture, medals, &c. is of very great importance in the line arts.
MOULDING AND CASTING.; 285
In order to procure a copy or cast from any figure, bust, medal, &c. it is necessary to obtain a mould by pressing upon the thing to be moulded or copied, some substance which, when soft, is capable of being forced into all the cavities or hol- lows of the sculpture. When this mould is dry and hard, some substance is poured into it, which will fill all the cavities of the mould, and represent the form of the original from which the mould was taken.
The particular manner of moulding depends upon the form of the subject to be worked upon. When there are no projecting parts but such as form a right or a greater angle with the principal surface of the body, nothing more is required than to cover it over with the substance of which the mould is to be formed, taking care to press it well into all the cavities of the original, and to take it off clean, and without bending.
The substances used for moulding are various, according to the nature and situation of the sculp- ture. If it may be laid horizontally, and will bear to be oiled without injury, plaster of Paris maybe advan- tageously employed ; which may be poured over it to a convenient thickness, after oiling it, to prevent the plaster from sticking. A composition of bees- wax, resin, and pitch, may also be usedj which will be a very desirable mould, if many casts are to be taken from it. But if the situation of the sculpture be perpendicular, so that nothing can be poured upon it, then clay, or some similar substance, must be used. The best kind of clay for this purpose is that used by the sculptors for making their models with ; it must be worked to a due consistence, and having spread it out to a size sufficient to cover all the surface, it must be sprinkled over with whiting.
286 MOULDING AND CASTING.
to prevent it from adhering to the original. Bees- wax and dough, or the crumb of new bread, may also be used for moulding some small subjects.
When there are under cuttings in the bas relief, they must be first filled up before it can be mould- ed, otherwise the mould could not be got off. When the casts are taken afterwards, these places must be worked out with a proper tool.
When the model, or original subject, is of a round form, or projects so much that it cannot be moulded in this manner, the mould must be divided into several parts j and it is frequently necessary to cast several parts separately, and afterwards to join them togetl^er. In this case, the plaster must be tem- pered with water to such a consistence, that it may be worked like soft paste, and must be laid on with some convenient instrument, compressing it so as to make it adapt itself to all parts of the surface. When the model is so covered to a convenient thick- ness, the whole must be left at rest till the plaster is set and firm, so as to bear dividing without falling to pieces, or being liable to be put out of its form by any slight violence ; and it must then be divided into pieces, in order to its being taken off from the model, by cutting it with a knife with a very thin blade ; and being divided, must be cautiously taken off, and kept till dry: but it must be observed, be- fore the separation of the parts be made, to notch them across the joints, or lines of division, at pro- per distances, that they may with ease and certainty be properly put together again. The art of pro- perly dividing the moulds, in order to make them separate from the model, requires more dexterity and skill than any other thing in the art of casting, and does not admit of rules for the most advanta- geous conduct of it in every case. Where the sub-
MOULDING AND CASTING. 287
ject is of a round or spheroidal form, it is best to divide the mould into three parts, which will then easily come off from the model ; and the same will hold good of a cylinder, or any regular curve figure.
The mould being thus formed and dry, and the parts put together, it must be first oiled, and placed in such a position that the hollow may lie upwards, and then filled with plaster mixed with water; and when the cast is perfectly set and dry, it must be taken out of the mould, and repaired when neces- sary, which finishes the operation.
In larger masses, where there would otherwise be a great thickness of the plaster, a core may be put within the mould, in order to produce a hollow in the cast, which both saves the expense of the plaster, and renders the cast lighter.
In the same manner, figures, busts, &c. may be cast of lead, or any other metal in the moulds of plaster or clay ; taking care, however, that the moulds be perfectly dry ; for should there be any moisture, the sudden heat of the metal would convert it into vapour, which would produce an explosion by its expansion, and blow the melted metal about.
To take a Cast in Metal from any small Animaly Insect, or Vegetable.
Prepare a box of four boards, sufficiently large to hold the animal, in which it must be suspended by a string ; and the legs, wings, &c. of the animal, or the tendrils, leaves, &c. of the vegetable, must be separated, and adjusted in their right position by a pair of small pincers. A due quantity of
288 MOULDING AND CASTING.
plaster of Paris, mixed with talc, must be tempered to the proper consistence with water, and the sides of the box oiled. Also a straight piece of stick must be put to the principal part of the body, and pieces of wire to the extremities of the other parts, in order that they may form, when drawn out after the matter of the mould is set and firm, proper channels for pouring in the metal, and vents for the air ; which otherwise, by the rarefaction it would undero;o from the heat of the metals, would blow it out, or burst the mould. In a short time the plaster will set, and become hard j when the stick and wires may be drawn out, and the frame or coffin in which the mould was cast taken away ; and the mould must then be put, first, into a moderate heat, and, afterwards, when it is as dry as can be rendered by that de- gree, removed into a greater, which may be gra- dually increased, till the whole be red hot. The animal or vegetable inclosed in the mould will then be burnt to a coal ; and may be totally cal- cined to ashes, by blowing for some time into the charcoal and passages made for pouring in the metal, and giving vent to the air, which will at the same time that it destroys the remainder of the animal or vegetable matter, blow out the ashes. The mould must then be suffered to cool gently, and will be perfect ; the destruction of the sub- stance included in it having produced a corre- sponding hollow ; but it may nevertheless be pro- per to shake the mould, and turn it upside down, as also to blow "vvith the bellows into each of the air-vents, in order to free it wholly from any remainder of the ashes j or, where there may be an opportunity of filling the hollow with quick- silver, it will be found a very effectual method of
MOULDING AND CASTING. S89
clearing tlie cavity, as all dust, ashes, or small detached bodies, will necessarily rise to the surface of the quicksilver, and be poured out with it. The mould being thus prepared, it must be heated very hot when used, if the cast is to be made with copper or brass, but a less degree will serve for lead or tin. The metal, being poured into the mould, must be gently struck, and then suffered to rest till it be cold ; at which time it must be carefully taken from the cast, but without force ; for such parts of the matter as appear to adhere more strongly must be softened, by soaking in water till they be entirely loosened, that none of the more delicate parts of the cast may be broken off or bent.
When talc cannot be obtained, plaster alone may be used ; but it is apt to be calcined by the heat used in burning the animal or vegetable from whence the cast is taken, and to become of too incoherent and friable a texture. Stourbridge, or any other good clay, washed perfectly fine, and mixed wdth an equal part of fine sand, may be employed. Pounded pumice-stone, and plaster of Paris, in equal quantities, mixed with washed clay in the same proportion, is said to make excellent moulds.
Method of taking a Cast in Plaster' from a Fersoji's Face.
The person whose likeness is required in plaster must lie on his back, and the hair must be tied up so that none of it covers the face. Into each nostril convey a conical piece of stiff paper open at both ends, to allow of breathing. The
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290 MOULDING AND CASTING.
face is then lightly oiled over in every part with salad-oil, to prevent the plaster from sticking to the skin. Procure some fresh burnt plaster, and mix it with water to a proper consistence for pouring. Then pour it by spoonfuls quickly all over the face (taking care the eyes are shut), till it is entirely covered to the thickness of a quarter of an inch. This substance will grow sensibly hot, and in a few minutes will be hard. This being taken off will form a mould, in which a head of clay may be moulded, and therein the eyes may be opened, and such other additions and corrections may be made as are necessary. Then, this second face being anointed with oil, a second mould of plaster must be made upon it, consisting of two parts joined lengthwise along the ridge of the nose ; and in this a cast in plas- ter may be taken, which will be exactly like the original.
To take Casts from Medals,
In order to take copies of medals, a mould must first be made j this is generally either of plaster of Paris, or of melted sulphur.
After having oiled the surface of the medal with a little cotton, or a camePs hair pencil dip- ped in oil of olives, put a hoop of paper round it, standing up above the surface of the thickness you wish the mould to be. Then take some plaster of Paris, mix it with water to the consistence of cream, and with a brush rub it over the surface of the medal, to prevent air-holes from appearing; then immediately afterwards make it to a sufficient thickness, by pouring on more plaster. Let it
MOULDING AND CASTING. 291
stand about Iialf an hour, and it will in that time grow so hard, that you may safely take it ofFj then pare it smooth on the back and round the edges neatly. It should be dried, if in cold or damp weather, before a brisk fire. If you cover the face of the mould with fine plaster, a coarser sort will do for the back : but no more plaster should be mixed up at one time than can be used, as it will soon get hard, and cannot be softened without burning over again.
Sulphur must not be poured upon silver medals, as this will tarnish them.
To prepare this mould for casting sulphur or plaster of Paris in, take half a pint of boiled lin- seed oil, and oil of turpentine one ounce, and mix them together in a bottle ; when wanted, pour the mixture into a plate or saucer, and dip the surface of the mould into it; take the mould out again, and when it has sucked in the oil, dip it again. Repeat this till the oil begins to stagnate upon it ; then take a little cotton wool, hard rolled up, to prevent the oil from sticking to it, and wipe it carefully off. Lay it in a dry place for a, day or two (if longer the better,) and the mould will acquire a very hard surface from the effect of the oil.
To cast plaster of Paris in this mould, proceed with it in the same manner as above directed for obtaining the mould itself, first oiling the mould with olive oil. If sulphur casts are required, it must be melted in an iron ladle.
Another viethod with Ishmlass. — Dissolve isin- glass in water over the fire ; then, with a hair pencil, lay the melted isinglass over the medal : and when you have covered it properly, let it dry.
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292 CEMENTS.
When it is hard, raise the isinglass up with the point of a penknife, and it will fly off like horn, having a sharp impression of the medal.
The isinglass may be made of any colour by mix- ing the colour with it; or you may breathe on the concave side, and lay gold leaf on it, which, by shining through, will make it appear like a gold medal. But if you wish to imitate a copper medal, mix a little carmine with the isinglass, and lay gold leaf on as before.
CEMENTS.
Cements require to be of various compositions, according to the substances to which they are ap- plied, and whether they are to be exposed to heat and moisture.
Common Glue.
Common glue is formed by extracting by boil- ing the gelatinous part of cuttings or scraps of coarse leather, or the hides of beasts. It is then poured out in thin cakes and dried.
Isinglass Glue.
Isinglass glue is made by dissolving beaten isin- glass in water by boiling, and, having strained it through a coarse linen cloth, evaporating it again, o such a consistence, that being cold, the glue will be perfectly hard and dry.
This cement is improved by dissolving the isin- glass in any proof spirit by heat, or by adding to it when dissolved in water, an equal quantity of spirits of wine.
CEMENTS. 293
It is still further improved by adding to the isinglass, previous to its solution in spirits, one- third of its weight of gum ammoniac. Expose the mixture to a boiling heat, until the isinglass and gum are dissolved, and until a drop of the compo- sition become stiff instantly as it cools. It will at any future time melt with a degree of heat little exceeding that of the human body, and, in conse- quence of so soon becoming stiff on cooling, forms a very valuable cement for many purposes, particu- larly for the very nice and delicate one of fixing on the antennae, legs, &c. of insects in cabinets of na- tural history. The easy melting of this cement is no objection to its use in cases where the articles themselves may afterwards be exposed to moderate heat ; for it owes this property only to the presence of the spirit which evaporates soon after it has been applied. When used to join broken glass or china, the pieces to be joined should be previously warmed. Immersion in hot water will give them a sufficient degree of heat. Wipe off the water before applying the cement, which may be laid on with a pencil ; then press the pieces together, binding them with a string, or bit of soft wire, if necessary.
This isinglass glue is far preferable to common glue for nice purposes, being much stronger, and less hable to be softened either by heat or moisture.
Parchment Glue.
Take one pound of shreds of parchment, or vel- lum, and boil it in six quarts of water till the quan- tity be reduced to one quart ; strain off the fluid from the dregs, and then boil it again till it be of the consistence of glue.
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294 CEMENTS.
The same may be done with glovers* cuttings of leather, which are dressed with alum instead of being tanned ; this will make a colourless glue.
A good Glue for Sigii-BoardSy or any thing that must sta?id the Weather.
Melt common glue with water to a proper con- sistence ; then add one eighth of boiled linseed oil, dropping it into the glue gently, and stirring it all the time.
A very strong glue is made by adding some pow- dered chalk to common glue.
Another that will resist water is made by adding half a pound of common glue to two quarts of skimmed milk.
Preparation of Lip Ghwyfor cementing Taper ^ Silk, thin Leather, ^c.
Take of isinglass glue and parchment ghie, each one ounce ; of sugar-candy, and gum tragacanth, each two drachms ; add to them an ounce of water, and boil the whole togetlier, till the mixture ap- pears, when cold, of the proper consistence of glue. Then form it into small roils, or any other figure that may be most convenient.
This glue may be wet witli the tongue, and rubbed on the edges of the paper, silk, &c. that are to be cemented, which will, on their being laid to- gether, and suffered to dry, unite as firmly as any other part of the substance.
CEMENTS. '2D5
Lapland Glue.
The bows of the Laplanders are composed of two pieces of wood glued together ; one of them of birch, which is flexible, and the other of fir of the marshes, which is stiff, in order that the bow when bent may not break, and that when unbent it may not bend. When these two pieces of wood are bent, all the points of contact endeavour to disunite themselves, and to prevent this, the Lap- landers employ the following cement: they take tlie skins of the largest perches*, and having dried them, moisten them in cold water until they are so soft tliat they may be freed from the scales, which they throw away. They then put four or five of these skins into a rein-deer*s bladder, or they wrap them up in the soft bark of the birch-tree, in such a manner that water cannot touch them, and place them thus covered into a pot of boiling water, with a stone above them to keep them at the bottom. When they have boiled about an hour, they take them from the bladder or bark, and they are then found to be soft and viscous. In this state they employ them for glueing together the two pieces of their bows, which they strongly compress and tie up till the glue is well dried. These pieces never afterwards separate.
A Glue from Cheese.
Take skimmed-milk cheese, free it from the rind, cut it into slices, and boil it in water, stirring it
* It is lU'obable that ecl-skius would answer the same purpose.
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29Q CEMENTS.
Avitli a spoon until it be reduced to a strong glue, "which does not incorporate with water. Then throw away the hot water; pour cold water over the glue, and knead it afterward in warm water, sub- jecting it to the same process several times. Put the warm glue on a grinding-stone, and knead it with quick-lime until you have a good glue. When you wish to use this glue you must warm it ; if it be employed cold it is not so strong, but it may also be used in that manner. This glue is insoluble in water as soon as it is dry, and it becomes so in forty-eight hours after it has been applied. It may be used for glueing wood, and for cementing marble and broken stone and earthen-ware. Baits for catching fish may also be made of it. Fish are very fond of it, and it resists water.
Jewellers' Cement
In setting precious stones, pieces are sometimes broken off by accident. In such cases, they often join the pieces so correctly, that an inexperienced eye cannot discover the stone to have been broken. They employ for this purpose a small piece of gum mastich applied between the fragments, which are previously heated sufficiently to enable them to melt the interposed gum. They are then pressed together, to force out the redimdant quantity of gum.
Turkey Cement, Jbr jo hung Metals, Glass, ^c.
Dissolve five or six bits of mastich, as large as peas, in as much spirits of wine as will suffice to render it liquid ; in another vessel dissolve as much
CEMENTS. 297
isinglass (which has been previously soaked in water till it is swollen and soft,) in brandy or rum, as \vill make two ounces by measure of strong glue, and add two small bits of gum galbanum, or am- moniacum, which must be rubbed or ground till they are dissolved ; then mix the whole with a sufficient heat ; keep it in a phial stopt, and when it is to be used set it in hot water.
A Cement for broke?! China^ Glasses, S^c.
Take quick-lime and white of eggs, or old thick varnish ; grind and temper them well together.
Drying oil and white lead are also frequently used for cementing china and earthen-ware ; but this cement requires a long time to dry. Where it is not necessary the vessels should endure heat or moisture, isinglass glue, with a little tripoli, or chalk, is better. The juice of garlic also forms a strong cement, and the joining can scarcely be perceived.
A Cement for Chemical Glasses that "will bear the Fire.
Mix equal quantities of wheat flour, fine pow- dered Venice glass, pulverized chalk, with half the quantity of fine brick dust, and a little scraped lint in the whites of eggs : this mixture is to be spread upon a linen cloth, and applied to the crack of the glasses, and should be well dried before they are put into the fire.
A Cement useful for Turners.
Take resin, one pound ; pitch, four ounces : melt these together, and, while boiling hot, add
^yS CEMENTS.
brick-dust, until, by dropping u, little upon a stone, you perceive it hard enough ; then pour it into water, and immediately make it up in rolls, and it is tit for use.
Another^ finer. — Take resin, one ouuce; pitch, two ounces; add red ochre, finely powdered, until you perceive it strong enough. Sometimes a small quantity of tallow is used, according to the heat of the weather, more being necessary in winter than in summer.
Either of these cements is of excellent use for turners. By applying it to tlie side of a chuck, and making it warm before the fire, you may fasten any thin piece of w^ood, which will hold while you turn it ; when you want it off again, strike it on the top with your tool, and it will drop ofi' imme- diately.
A strong Cement f^r Electrical Purposes.
Melt one pound of resin in a pot or pan, over a slow fire ; add to it as much plaster of Paris, in fine powder, as will make it hard enough, then add a spoonful of linseed-oil, stirring it all the while, and try if it be hard and tough enough for your purpose ; if it is not sufficiently hard, add more plaster of Paris ; and if not tough enough, a little more linseed-oil.
This is a very good cement for fixing the necks of globes or cylinders of electrical machines, or any thing else that requires to be strongly fixed.
Another^ softer. — Take resin, one pound; bees- wax, one ounce ; add to it as much red-ochre as will make it of sufficient stiffness ; pour it into
10
CEMENTS. '2'fJ
water, and make it into rolls. This cement is useful for cementing hoops on glasses, or any other mounting of electrical apparatus.
A Cement for Glass-Grmders.
Take pitch, and boil it ; add to it sifted-vvood ashes, and keep stirring it all the while, until you have it of a proper temper : the addition of a little tallow may be added, as you find necessary.
Another, for small work. — To four ounces of resin add one- fourth of an ounce of bees-wax, and four ounces of whiting, made previously red hot and melt them together. The whiting should be put in while hot, that it may not have time to im- bibe moisture from the atmosphere.
Shell-lac is a very strong cement for holding metals, glass, or precious stones, while cutting, turning, or grinding them. The metal, &c. should be warmed, to melt it. For fastening ruby cylin- ders in watches, and similar delicate purposes, sheli- lac is excellent.
To solder or cement broken Glass.
Broken glass may be soldered or cemented in such a manner as to be as strong as ever, by inter- posing between the parts, glass ground up like a pigment, but of easier fusion than the pieces to be joined, and then exposing them to such a lieat as will fuse the cementing ingredient, and make the pieces agglutinate without being themselves fused.
A glass for the purpose of cementing broken pieces of fUnt glass, may be made by fusing some of the same kind of glass previously reduced to
300 CEMENTS.
powder, ulong with a little red-lead and borax, or with the borax only.
Cement for Derbyshire Spar and other Stones.
A cement for this purpose may be made with about seven or eight parts of resin and one of bees- wax, melted together with a small quantity of plaster of Paris. If it is wished to make the ce- ment fill up the place of any small chips that may have been lost, the quantity of plaster must be in- creased a little. When the ingredients are well mixed, and the whole is nearly cold, the mass should be well kneaded together. The pieces of spar that are to be joined must be heated until they will melt the cement, and then pressed together, some of the cement being previously interposed.
Melted sulphur applied to fragments of stones previously heated by placing them before a fire, to at least the melting point of sulphur, and then joined with the sulphur between, makes a pretty firm and durable joining.
Little deficiencies in the stone, as chips out of corners, &c. may also be filled up with melted sul})hur, in which some of the powder of the stone has been melted.
A Cement that will stand against boiling Watery and eve)i bear a considerable Pressure of Steam.
In joining the flanches of iron cylinders, and other parts of hydraulic and steam engines, great inconvenience is often experienced from the want of a durable cement.
CEMENTS. SOI
Boiled linseed-oil, litharge, red and white lead, mixed together to a proper consistence, and ap- plied on each side of a piece of flannel previously shaped to fit the joint, and then interposed be- tween the pieces before they are brought home (as the workmen term it) to their place by the screws or other fastenings employed, make a close and durable joint.
The quantities of the ingredients may be'varied without inconvenience, only taking care not to make the mass too thin with oil. It is difficult in many cases instantly to make a good fitting of large pieces of iron work, which renders it necessary sometimes to join and separate the pieces repeated- ly, before a proper adjustment is obtained. When this is expected, the white-lead ought to predomi- nate in the mixture, as it dries much slower than the red. A workman, knowing this fact, can be at little loss in exercising his own discretion in re- gulating the quantities. It is safest to err on the side of the white-lead, as the durability of the cement is no way injured thereby, only a longer time is required for it to dry and harden.
When the fittings w'ill not admit easily of so thick a substance as flannel being interposed, linen may be substituted, or even paper or thin pasteboard.
This cement answers well also for joining broken stones, however large. Cisterns built of square stones, put together with this cement, will never leak or want any repairs. In this case the stones need not be entirely bedded in it : an inch, or even less, of the edges that are to lie next the water, need only be so treated ; the rest of the joint may be filled with good lime.
302 CEMENTS.
Another Cement that will stand the Actio?! of Boiling Water and Steam.
This cement, which is preferable even to the former for steam-engines, is prepared as follows.
Take two ounces of sal ammoniac, one ounce of flowers of sulphur, and sixteen ounces of cast iron filings or borings. Mix all well together by rubbing them in a mortar, and keep the powder dry.
When the cement is wanted for use, take one part of the above powder and twenty parts of clean iron borings or filings, and blend them inti- mately by grinding them in a mortar. Wet the compound with water, and when brought to a con- venient consistence, apply it to the joints with a wooden or blunt iron spatula.
By a play of affinities, which those who are at all acquainted with chemistry will be at no loss io comprehend, a degree of action and re-action takes place among the ingredients, and between them and the iron surfaces, which at last causes the whole to unite as one mass. In fact, after a time, the mixture and the surfaces of the fianches become a species of pyrites, holding a very large proportion of iron, all the parts of which cohere strongly together.
Blood Cement.
A cement often used by copper-smiths to lay over the rivets and edges of the sheets of copper in large boilers, to serve as an additional security to the joinings, and to secure cocks, &c. from leaking, is made by mixing pounded quick-lime
CEMENTS. .303
witli ox's blood. It must be applied fresh made, as it soon gets hard.
\7e believe if the properties of this cement were duly investigated, it would be found useful for many purposes to which it has never yet been applied. It is extremely cheap, and very durable.
Flour Faste.
Flour paste for cementing is formed principally of wheaten flour boiled in water till it be of a glu- tinous or viscid consistence.
It may be prepared of these ingredients simply for common purposes, but when it is used by book- binders, or for paper hangings, it is usual to mix with the flour a flfth or sixth of its weight of powdered alum ; and where it is wanted still more tenacious, gum arable, or any kind of size, may be added.
Japanese Cement ^ or Rice Glue,
This elegant cement is made by mixing rice floiu' intimately with cold water, and then gently boiling it. It is beautifully white, and dries almost transparent. Papers pasted together by means of this cement will sooner separate in their own substance than at the joining, which makes it extremely useful in the preparation of curious paper articles, as tea trays, ladies' dressing boxes, and other articles which require layers of paper to be cemented together. It is in every respect preferable to common paste made with wheat flour, for almost every purpose to which that article is usually applied. It answers well in par- ticidar, for pasting into books the copies of writings
304 LUTES.
taken off by copying machines on unsized silver paper.
With this composition, made with a small quan- tity of water, that it may have a consistence simi- lar to plastic clay, models, busts, statues, basso relievos, and the like, may be formed. When dry, the articles made of it are susceptible of a high polish ; they are also very durable.
The Japanese make quadrille fish of this sub- stance, which so nearly resemble those made of mother of pearl, that the officers of our East India- men are often imposed upon.
Of Sizes.
Common size is manufactured in the same man- ner, and generally by the same people, as glue. It is indeed glue left in a moister state, by discon- tinuing the evaporation before it is brought to a dry consistence, and, therefore, further par- ticulars respecting the manufacture of it are needless here.
Isinglass size may also be prepared in the man- ner above directed for the glue, by increasing the proportion of the water for dissolving it. And the same holds good of parchment size.
I.UTES.
In many chemical operations the vessels must be covered with something to preserve them from the violence of the fire, from being broken or melted, and also to close exactly their joinings to each other, in order to retain the substances which they contain, when they are volatile and reduced to vapour.
LUTES. 805
The coating used for retorts, &c. to defend them from the action of the fire, is usually com- posed of nearly equal parts of coarse sand and re- fractory clay. These matters ought to be well mixed with water and a little hair, so as to form a liquid paste, with which the vessels are covered layer upon layer, till it is of the required thick- ness. The sand, mixed witii the clay, is necessary to prevent the cracks which are occasioned by the contracting of the clay during its drying, which it always does when pure. The hair serves also to bind the parts of the lute, and to keep it ap- plied to the vessel j for, notwithstanding the sand which is introduced into it, some cracks are al- ways formed, which would occasion pieces of it to fall off.
The lutes with which the joinings of vessels are closed are of different kinds, according to the nature of the operations to be made, and of the substances to be distilled in these vessels.
When vapours of watery liquors, and such as are not corrosive, are to be contained, it is sufficient to surround the joining of the receiver to the nose of the alembic, or of the retort, with slips of paper, or linen, covered with flour paste. In such cases, also, slips of wet bladder are very conveniently used.
When more penetrating and dissolving vapours are to be contained, a lute is to be employed of quick-lime slacked in air, and beaten into a liquid paste with whites of eggs. This paste is to be spread upon linen slips, which are to be applied exactly to the joining of the vessels. This lute is very convenient, easily dries, becomes solid, and sufficiently firm.
VOL. ir. X
306 INK-MAKING.
Lastly, when saline acids, and corrosive vapours are to be contained, we must then have recourse to the lute called fat lute. This lute is made by form- ing into a paste some dried clay, finely powdered, sifted through a silken search, and moistened with water; and then, by beating this paste well in a mortar, with boiled linseed oil, that is, oil which has been rendered dry by litharge dissolved in it, this lute easily takes and retains the form given to it. It is generally rolled into cylinders of a conve- nient size. These are to be applied, by flattening them to the joinings of the vessels, which ought to be perfectly dry; because the least moisture would prevent the lute from adhering. When the joinings are closed with this fat lute, the whole is to be covered with slips of linen, spread with lute of lime and whites of eggs. These slips are to be fastened with packthread. The second lute is ne- cessary to keep on the fat lute, because the latter remains soft, and does not become solid enough to stick on alone.
INK-MAKING,
Inks are fluid compounds, intended to form characters, or some other kinds of figures, on proper grounds of paper, parchment, or such other sub- stance as may be fit to receive them.
There are two principal kinds of ink, writing and printing ink.
Writing Ink.
When to an infusion of gall-nuts some solution of" sulphate of iron (green copperas) is added, a very
IMK-MAKING. SQJ
dark blue precipitate takes place. This precipitate is the gallic acid of* the galls united to the iron of the green vitriol, forming grdlat of iron, which is the basis of writing ink. If galls and sulphate of iron only were used, the precipitate would fall down, leaving the water colourless ; and, in order to keep it suspended in the water, forming a per- manently black, or rather very dark blue fluid, gum arable is added, which, by its viscid nature, pre- vents the precipitate from falling down.
Various receipts have been given for the compo- sition of writing ink, but very few have been founded upon a knowledge of its real nature. Though so important an article, it is but lately that it has been studied with any attention ; and even still, the principles and theory of its formation do not appear to be so thoroughly understood as might be wished. The receipt given by M. Ribancourt is as follows: Take eiglit ounces of Aleppo galls, in coarse powder; four ounces of logwood, in thin chips ; four ounces of sulphate of iron (green cop- peras); three ounces of gum arable, in powder; one ounce of sulphate of copper (blue vitriol) ; and one ounce of sugar-candy. Boil the galls and log- wood together in twelve pounds of water for one hour, or till half the liquid has been evaporated. Strain the decoction through a hair sieve, or linen cloth, and then add the other ingredients. Stir the mixture till the whole is dissolved, more especially the gum ; after whicii, leave it to subside for twenty-four hours. Then decant the ink, and pre- serve it in bottles of glass or stone-ware, well corked.
Red writing ink is made in the following manner : Take of the raspings of Brazil wood a quarter of a pound, and infuse them two or three days in vine- gar. Boil the infusion for an hour over a gentle
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308
INK-MAKING.
fire, and afterwards filter it while hot. Put it again over the fire, and dissolve in it, first, half an ounce of gum arabic, and afterwards of alum and white sugar, each half an ounce.
Printing Ink.
Printers' ink is a black paint composed of lamp- black and linseed or suet oil boiled, so as to acquire considerable consistence and tenacity. The art of preparing it is kept a secret ; but the obtaining good lamp-black appears to be the chief difficulty in making it.
The ink used by copper-plate printers, differs from the last only in the oil not being so much boiled, and the black which is used being Frank- fort black.
Sympathetic Inks.
Sympathetic inks are such as do not appear immediately after they are written with, but which may be made to appear at pleasure, by certain means. A variety of substances have been used for this purpose. We shall describe the best of them.
1. Dissolve some sugar of lead in water, and write with the solution. When dry, no writing ■will be visible. When you want to make it appear, wet the paper with a solution of alcaline sulphuret (liver of sulphur), and the letters will immediately appear of a brown colour. Even exposing the writing to the vapours of these solutions will render it apparent.
2. Write with a solution of gold in aqua regia, and let the paper dry gently in the shade. Nothing
INK-MAKING. 309
will be seen ; but draw a sponge over it, wetted with a solution of tin in aqua regia ; the writing will immediately appear of a purple colour.
3. Write with an infusion of galls, and when you wish the writing to appear, dip it into a solution of green vitriol ; the letters will be black.
4. Write with diluted sulphuric acid, and nothing will be visible. To render it so, hold it to the fire, and the letters will instantly appear black.
5. Juice of lemons, or onions, a solution of sal ammoniac, green vitriol, &c. will answer the same purpose, though not so easily, or with so little heat.
6. Green sympathetic ink. Dissolve cobalt in nitro muriatic acid, and write with the solution. The letters will be invisible till held to the fire, when they will appear green, and will disappear completely again when removed into the cold. In this manner they may be made to appear and dis- appear at pleasure.
A very pleasant experiment of this kind is to make a drawing representing a winter scene, in which the trees appear void of leaves, and to put the leaves on with this sympathetic ink; then, upon holding the drawing near to the fire, the leaves will begin to appear in all the verdure of spring, and will very much surprise those who are not in the secret.
7. Blue sympathetic ink. Dissolve cobalt in nitric acid ; precipitate the cobalt by potash ; dissolve this precipitated oxyd of cobalt in acetic acid, and add to the solution one-eighth of com- mon salt.
This will form a sympathetic ink, that, when cold, will be invisible, but will appear blue by heat.
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310
REMOVING STAINS.
To remove Ink Stai)i6.
The stains of ink on cloth, paper, or wood, may be removed by ahnost all acids; but those acids are to be preferred which are least likely to injure the texture of the stained substance. The muriatic acid, diluted with five or six times its weight of water, may be applied to the spot, and, after a minute or two, may be washed off, repeating the application as often as may be found necessary. But the vegetable acids are attended witii less risk, and are equally effectual. A solution of the oxalic, citric (acid of lemons), or tartareous acids, in water, maybe applied to the most delicate fabrics without any danger of injuring them; and the same solu- tions will discharge writing, but not printing ink. Hence they may be employed in cleaning books which have been defaced by writing on the margin, without impairing the text. Lemon-juice, and the juice of sorrels, will also remove ink stains, but notso easily as tiie concrete acid of lemons, or citric acid.
To remove Iron Stains.
These may be occasioned either by ink stains, v^hich, on the application of the soap, are clianged into iron stains, or by the direct contact of rusted iron. They may be removed by diluted muriatic acid, or by one of the vegetable acids, already men- tioned. When suffered to remain long on cloth, they become extremely difficult to take out, because the iron, by repeated moistening with water, and exposure to the air, acquires such an addition- of oxygen, as renders it insoluble in acid^. It luis
REMOVING STAINS. 311
been found, however, tliat even these spots may be discharged, by applying first a solution of an alca- line sulphuret, which must be well washed from the cloth, and afterwards a liquid acid. The sul- phuret, in this case, extracts part of the oxygen from the iron, and renders it soluble in diluted acids.
To 7'emove the Stains of Fruit mid Wine.
These are best removed by a watery solution of the oxygenated muriatic acid, or by that of oxygen- ated muriate of potash or lime, to which a little sulphuric acid has been added. The stained spots may be steeped in one of these solutions till it is discharged; but the solution can only be applied with safety to white goods, because the uncombined oxygenated acid discharges all printed and dyed colours. A convenient mode of applying the oxy- genated acid, easily practicable by persons who have not the apparatus for saturating water with the gas, is as follows: Put about a table-spoonful of muriatic acid (spirit of salt) into a tea-cup, and add to it about a tea-spoonful of powdered manganese; then set this cup in a larger one filled with hot water ; moisten the stained spot with water, and expose it to the fumes that arise from the tea-cup. If the exposure be continued a sufficient length of time, the stain will disappear.
To remove SjJOts of Grease Jrorn Cloth.
Spots of grease may be removed by a diluted solution of potash ; but this must be cautiously applied, to prevent injury to the cloth. Stains of white wax, which sometimes fall upon the
X 1
312 removix:g stains.
clothes from wax candles, are removable by spirits of turpentine, or sulphuric ether. The marks of white paint may also be discharged by the last- mentioned agents.
To take Spots of Grease out ofBookSy PiintSy or Paper.
After having gently warmed the paper that is stained with grease, wax, oil, or any other fat body, take out as much as possible of it by means of blotting paper ; then dip a small brush in the essential oil of turpentine, heated almost to ebul- lition (for when cold it acts only very weakly), and draw it gently over both sides of the paper, which must be carefully kept warm. This oper- ation must be repeated as many times as the quantity of the fat body imbibed by the paper, or the thickness of the paper, may render necessary. When the greasy substance is entirely removed, recourse may be had to the following method to restore the paper to its former whiteness, which is not completely restored by the first process. Dip another brush in highly rectified spirit of wine, and draw it in like manner over the place which was stained, and particularly round the edges, to remove the border that would still present a stain. By employing these means with proper caution,' the spot will totally disappear, the paper will re- sume its original whiteness, and if the process has been employed on a part written on with common ink, or printed with printer's ink, it will experience no alteration.
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313
OF STAINING WOOD.
To stain Wood Yellow,
Take any white wood, and brush it over several times with the tincture of turmeric root, made by putting an ounce of turmeric, ground to powder, to a pint of spirit, and after they have stood for some days, straining off the tincture. If the yel- low colour be desired to have a reddish cast, a little dragon's blood must be added.
A cheaper, but less strong and bright yellow, is, by the tincture of French berries made boiling hot.
Wood may also be stained yellow by means of aqua fortis, which will sometimes produce a very beautiful yellow colour, but at other times a browner. Care must be taken, however, that the aqua fortis' be not too strong, otherwise a blackish colour will be the result.
To stain Wood Red.
For a bright red stain for wood, make a strong infusion of Brazil wood in stale urine, or water impregnated with pearl-ashes, in the proportion of an ounce to a gallon ; to a gallon of either of which, the proportion of Brazil wood must be a pound, which being put to them, they must stand together for two or three days, often stirring the mixture. With this infusion strained, and made boihng hot, brush over the wood to be stained till it appear strongly coloured ; then, while yet
3[i' STAINING WOOD.
wet, bi'usli it over with alum-water made in the proportion of two ounces of alum to a quart of water.
For a less bright red, dissolve an ounce of dra- gon's blood in a pint of spirits of wine, and brush over the wood with the tincture till the stain appear to be as strong as is desired ; but this is, in fact, rather lacquering than staining.
For a pink or rose red, add to a gallon of the above infusion of Brazil wood two additional ounces of the pearl-ashes, and use it as was before directed : but it is necessary, in this case, to brush the wood over with the alum-water. By increasing the proportion of pearl-ashes, the red may be rendered yet paler ; but it is proper, when more than this quantity is added, to make the alum-water stronger.
To slam Wood Blue.
W-ood may be stained blue by means either of copper or indigo.
The method of staining blue with copper is as ibllows : Make a solution of copper in aqua fortis, and brush it w^iile hot several times over the wood ; then make a solution of pearl-ashes in the })ro])ortion of two ounces to a pint of water, and brush it hot over the wood stained with the solution of copper, till it be of a perfectly blue colour.
To slain Wood Green.
Dissolve verdigrease in vinegar, or crystals of verdigrease in water, and with the hot solution brusji over llie wood till il, ])c duly stained.
10
STAINING WOOD. 315
To Stain Wood Purple.
Brash the wood to be stained several times willi a strong decoction of logwood and Brazil, made in the proportion of one pound of the logwood and a quarter of a pound of the Brazil to a gallon of water, and boiled for an hour or more. When the wood has been brushed over till there be a sufficient body of colour, let it dry, and then be slightly passed over by a solution of one drachm of pearl-ashes in a quart of water. This solution must be carefully used, as it will gradually change the colour from a brown red, which it will be originally found to be, to a dark blue purple, and therefore its effect must be restrained to the due point for producing the colour desired.
To stain Jf^ood a Mahoganij Colour.
The substances used for staining mahogany colour are madder, Brazil wood, and logwood ; each of which produce reddish brown stains, and they must be mixed together in such proportions as will produce the tint required.
To stain Wood Black.
Brush the wood several times over with a hot decoction of logwood. Then having prepared an infusion of galls by putting a quarter of a pound of }iowdered galls to two quarts of water, and setting them in the simshine, or any other gentle heat, for three or fx)ur days, brush the wood over three or four times with it, and it will be of a beautiful black. It may be polished with a hard brush and shoemakers' black wax.
316
STAINING IVORY.
To stain Ivory Green.
Dissolve some copper or verdigrease in nitrous acid, and soak the ivory in it.
To stain Ivory Yellow.
Put a quarter of a pound of alum in a pint of water, boil the ivory in the solution ; then boil it in a decoction of turmeric.
To stain Ivory Blue.
Boil it in the sulphate of indigo, and after- wards in a solution of three ounces of white tar- tar in a quart of water. Or it may be first stained green, and then dipped into a solution of pearl- ashes, made strong and boiling hot.
To stain Ivory Purple.
Put into nitrous acid one fourth of its weight of sal ammoniac J soak the ivory in it.
MISCELLANEOUS.
To make Phosphorus.
Phosphorus was formerly prepared from urine, and was therefore called phosphorus of urine ; but it is exactly the same substance, from whatever materials it is procured. The following is a pro- cess for procuring it from bones, which consist chiefly of Jime, combined with the phosphoric acid.
MISCELLANEOUS. Sl'J
Take a quantity of bones ; burn them to white- ness in an open fire, and reduce them to a fine powder. Upon three pounds of this powder, after having been put into a matrass, pour two pounds of concentrated sulphuric acid of commerce ; four or five pounds of water must be afterwards added by degrees, to assist the action of the acid. During the process, the operator must place himself and the vessel so that the fumes of the mixture may be blown from him. The whole is then to be left in a sand-bath for about twelve hours, or more, taking care to supply the loss of water which happens by evaporation. The next day, a large quantity of water must be added; the clear hquor must be decanted, and the rest strained through a cloth or sieve. The residuary matter is to be washed by repeated aflfusions of hot water till it passes tasteless. The water which has been used to wash out the adhering acid is mixed with the decanted or strained liquor, and the whole fluid is gradually evaporated in a flat earthen bason to the consistence of a syrup. It is then mixed with an equal weight of charcoal powder, and submitted to distillation in an iron or earthen retort. Instead of using a receiver, the neck of the retort may be immersed in a bason of water, to a small depth, and the phosphorus, as it comes over, will fall in drops to the bottom.
Phosphorus made in this manner is blackish and dirty ; it is purified by a second distillation. It may also be prepared from urine by the following method.
Dissolve as much lead in the nitric acid as it will act upon, and the solution will be nitrate of lead. Pour this into a quantity of urine, and a precipitate will be formed. When no more pre-
318 MISCELLA\^EOUS.
cipitate falls clown by the addition of the solution, suffer the whole to stand undisturbed till it has all subsided, and then pour off the clear fluid. Make this precipitate into a paste with charcoal finely pounded, and dry it in an earthen pan gra- dually. Then put the mass into an iron or earthen retort, and distil it. The phosphorus will come over, and may be collected under water.
To make Canton\s Phosphortts.
Take some oyster-shells ; calcine them, by keeping them in a good fire for about an hour. Select out of the calcined shells the purest and whitest parts, and pound and sift them. To three parts of this lime add one of flowers of sulphur ; mix tliem well together, and put them, well pressed, into a crucible. Place it in a good fire, where it must be kept red hot for an hour at least ; it may then be taken out to cool. AVhen it is cold, break the mass to pieces, and select out of it the brightest part, which will shine in the dark.
A beautiful representation of the telescopic appearance of one of the planets may be made by means of this. Cut out in paper the shape of the planet, such as a half moon, Saturn and his ring, &c., and cover it over with strong gum water; then strew some of this phosphorus, finely pow- dered, over the surface. When you Y/ant to exhibit it in the dark, you must previously expose it for a few minutes to the light of an Argand's lamp ; or, what is better, make the flash from the discharge of a large electrical jar, or battery, pass over its surface, and it immediately becomes
MISCELLANEOUS. 319
Juminous, and exhibits a very exact resemblanc^e of the planet.
To make Fhosiihor'ic Oil,
Put one part of pliosphonis into six of olive-oil, and digest tiiem over a sand heat. The phosphorus will dissolve. It must be kept v.ell corked.
This oil has the property of being very luminous in the dark, and yet it has not sufficient heat to burn any thing. If rubbed on the face and hands, taking care to shut the eyes, the appearance is most hideously frightful j all the parts with which it has been rubbed appear to be covered with a very luminous lambent flame of a bluish colour, and the mouth and eyes appear in it as black spots. There is no danger attending this experiment. The light of it is sufficient to show the hour of the night on. a watch, by holding it close to the bottle when it is unstopped.
To make Phosphorated Lime,
Put a few grains of phosphorus into t!ie bottom of a Florence flask, and fill it up with quick-hme. Place it over a lamp till the phosphorus has sub- limed, and is thoroughly mixed with the lime. If any of this lime be thrown out in the dark, it has the appearance of a shower of fire, but cannot burn any thing, as the quantity of phosphorus is too small to produce any sensible heat.
To make a Phosphoric Fii^e Bottle.
Take a very small phial, and put into it a bit of phosphorus as large as a pea, and fill up the
S20 MISCELLANEOUS.
bottle with lime. Fix an iron vessel, as a shovel, for instance, with common sand, and put it over the fire. Set the phial in this sand, having loosely stopped it with a cork. Stir about the ingredients with a wire, and mix them together ; taking care that the phosphorus does not catch fire by too great an access of air. Keep the bottle in the sand till the phosphorus is thoroughly incorpor- ated with the lime, when it will be of a reddish yellow.
This bottle is extremely convenient for pro- curing an instantaneous light in the dark. For this purpose, nothing more is necessary than to uncork the bottle, and to introduce a brimstone match, stirring it about a little, by which it will catch fire and light.
The bottle must be always kept carefully cork- ed, and opened as seldom as possible.
A more durable kind may be made by uniting together one part of sulphur with eight of phos- phorus. When this is used, a match is introduced into it, and then rubbed upon a bit of cork.
To make Phosphuret of Lime.
Put half an ounce of phosphorus, cut into small bits, into a glass tube about a foot long, and half an inch in diameter, closed at one end. Fill up with quick-lime grossly powdered, and stop the mouth of the tube loosely. Heat that part of the tube which contains the lime over a chafing-dish, till it be red hot; and then apply the heat of a lamp to the part containing the phosphorus, which will sublime, and mix with the
MISCELLANEOUS. S^l
lime. When cooled, the mixture will be a reddish mass.
If phosphuret of lime be dropped into water, air bubbles will be disengaged, which, on bursting at the top, will inflame with small explosions. They consist of phosphorated hydrogen gas.
To make Fulminating Powder.
Triturate in a warm mortar three parts, by weight, of nitre, two of mild vegetable alkali (car- bonate of potash), and one of flowers of sulphur. A few grains of this laid upon a knife, and held over the candle, first fuses, and then explodes with a loud report. A drachm of it put into a shovel, and held over the fire, makes a noise as loud as a cannon, and indents the shovel as if it had received a violent blow.
To make Fulminating Mercury,
Dissolve 100 grains of mercury with heat, in a measured ounce and a half of nitric acid. This solution being poured cold upon two measured ounces of alkohol, previously introduced into any convenient glass vessel, a moderate heat is to be applied till effervescence is excited. A white fume then begins to undulate on the surface of the liquor, and the powder will be gradually precipi- tated on the cessation of action. The precipitate is to be immediately collected on a filtre, well washed with distilled water, and cautiously dried in a heat not exceeding that of a water bath. The immediate washing of the powder is material,
VOL. II. Y
322 MISCELLANEOUS.
because it is lialfle to the re-action of the nitric acid ; and while any of the acid adheres to it, it is very subject to the action of light. From 100 grains of mercury, about 120 or ISO of tlie powder are obtained.
This powder, struck on an anvil with a hammer, explodes with a stunning disagreeable report j and with such force as to indent both the hammer and the anvil. Three or four grains are as much as ought to be used for such experiments.
To make the Arbor Diance^ or Tree of Diana.
Take half an ounce of fine silver, and two drachms of mercury, and dissolve them separately in a quantity of aqua fortis. When the solutions are perfectly made, mix them together, and pour them into a pint of common water, and stir it about, that the whole may be well mixed. Keep this preparation in a bottle well corked. In a glass globe, or other vessel, put the quantity of a small nut of the amalgam of silver with mercury, and pour three or four ounces of the above liquor over it. After some hours there will arise from the little globular amalgam small branches, which, by increasing, will form a beautiful kind of shrub or tree of silver.
To make a Tree of Silver 07i Glass.
Put a few drops of the solution of silver in aqua fortis on a piece of glass, and having formed a bit of copper or brass-wire to represent a tree with its
s
:\irSCELLANF.OUS. 323
branches, but flat so as to lie upon the glass, lay it in the liquid, and let it remain for an hour or two. A beautiful vegetation will be perceived all round the wire, which will nearly be covered by it. This may be preserved by washing it very carefully with water, and putting another glass over it.
To produce a Tree of Lead.
Dissolve an ounce of sugar of lead in a quart of clear water, and put it into a glass decanter or globe. Then suspend in the solution, near the top, a small piece of zinc of an irregular shape. Let it stand undisturbed for a day, and it will begin to shoot out into leaves, and apparently to vegetate. If left undisturbed for a few days, it will become extremely beautiful j but it must be moved with great caution.
It may appear to those unacquainted with che- mistry, that the piece of zinc actually puts out leaves ; but this is a mistake, for if the zinc be ex- amined, it will be found nearly unaltered. This phenomenon is owing to the zinc having a greater attraction for oxygen than the lead has ; conse- quently, it takes it from the oxyde of lead, which re-appears in its metallic state.
Arbor Mar^tiSy or Tree of Mars.
Dissolve iron filings in aqua fortis moderately concentrated, till the acid is saturated ; then add to it gradually a solution of fixed alcali, formerly called oil of tartar per deliquium. A strong ef- fervescence will ensue, and the iron, instead of falling to the bottom of the vessel, will afterwards
Y 2
SM MISCELLANEOUS.
rise, so as to cover the sides, forming a multitude of ramifications heaped one upon the other, which will sometimes pass over the edge of the vessel, and extend themselves on the outside with all the appearance of a plant.
To change Iron apparently into Copper,
Dissolve some blue vitriol (sulphate of copper) in v/ater, and dip into the solution a piece of bright iron or steel ; in a few seconds it may be taken out, when it will be apparently turned to copper. This is a deception ; the iron is not changed into copper ; it is only encrusted over with that metal, as may be easily seen by removing the copper by a file. The iron having a stronger attraction for sulphuric acid than copper, it takes the acid from the latter, which is consequently precipitated. This process is used for obtaining the copper from waters near mines that contain a great quantity of that metal. Iron plates are put into them, which become incrusted with copper, which is scraped off.
To prepare the Precipitate ofCassius.
This beautiful purple colour is extremely useful to enamellers and glass stainers. To make it, pro- ceed as follows.
Dissolve some gold in aqua regia (nitro-muriatic acid), and also dissolve some pure tin in diluted aqua regia, and pour it into the solution of gold. A purple powder will be precipitated, which must be collected and washed in distilled water.
MISCELLANEOUS. S25
A Method q/^ Silvering Ivory,
Take a slip of ivory, immerse it in a weak solu- tion of nitrate of silver, and let it remain in it till the ivory has acquired a bright yellow colour ; then take it out of the solution, and immerse it in a tumbler of pure water, and expose it in the water to the rays of a very bright sun. After the ivory has been exposed to the sun's rays for about two or three hours, it becomes black ; but on rubbing it a little, the black surface will become changed into one of silver. Although this coating of silver is extremely thin, yet if the ivory be well impreg- nated with the nitrate of silver, the solution will penetrate to a considerable depth; and as fast as the silver wears off from the surface of the ivory, the nitrate below being exposed to the light, is con- verted into silver, and the ivory retains its metallic appearance.
To cover Ribbons with Gold by a Chemical Process.
Let ether stand over phosphorus for some weeks, and some of the phosphorus will be dissolved. Dissolve also some gold in aqua regia (nitro-mu- riatic acid). Dip the ribbon, first, into the nitro- muriatic solution, and then into the phosphorated ether, and it will be covered with a firm coating of gold.
The same efi'ect may be produced by exposing the ribbon, after having dipped it into the solution of gold, to a current of phosphorated hydrogen gas for some days.
To prepare Aurum Musivum.
Aurum musivum is used by japanners, and for many varnished works, as snuff-boxes, coaches, &c.
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326
MISCELLANEOUS.
When well managed, it has all the beautiful ap- pearance of gold in powder.
To make it, amalgamate twelve parts of the purest tin with three parts of mercury. The amal- gam must then be triturated in a stone mortar with seven parts of flowers of sulphur, and three parts of sal ammoniac. The mixture is then put into a matrass, and the whole is exposed to a gentle sand heat, until no more white fumes arise. When, upon this, the heat is somewhat raised, cinnabar sublimes, together with some oxygenated muriate of tin ; while, at the same time, the remaining tin unites with the remaining sulphur, and forms the aurum musivum, exhibiting a golden yellow and flakey or scaley matter, of a metallic lustre.
The main point in this process is the proper re- gulation of the fire : when this is too strong, the operation does not succeed j and instead of aurum musivum, common sulphuret of tin is obtained.
To make an Artificial Volcano,
For this curious experiment, which in some re- spects resembles the effect of volcanoes, we are indebted to Lemery.
Mix equal parts of pounded sulphur and iron- filings, and having formed the whole into a paste with water, bury a quantity of it, forty or fifty pounds, for example, at about the depth of a foot below the surface of the earth. In ten or twelve hours afterwards, if the weather be warm, the earth will swell up and burst, and flames will issue out, which will enlarge the aperture, scattering around a yellow and blackish dust.
It is not impossible, that what is here seen in miniature, takes place on a grand scale in volca-
MISCELLANEOUS. 327
noes ; as it is well known that they always furnish abundance of sulphur, and also metallic substances
To produce Artificial Lightning,
Provide a tin tube, that is much larger on one side than the other, and in which there are se- veral holes. Fill this tube with resin, in powder, and when it is shook over the flame of a torch, it will prqduce a sudden corruscation that strongly represents a flash of lightning. This is the manner in which lightning is produced at the theatres : it is not the flame itself that is to be seen, but its reflection only, as happens for the most part in nature.
In this manner also the flambeaux of the furies on the stage are constructed, except that, at the end of each of them, there is a match dipped in spirits of wine ; by means of which it is only necessary to shake them, and they will produce a sudden and very considerable flame.
Method of cutting GlasSy by means of Heat,
Take a common wine-glass, or any vessel you want cut, and having heated a poker in the fire till it is almost red hot, but not quite, apply it to the part where you wish the crack to begin ; having held it upon the part for about a minute, remove the poker, and wet the place: the glass will imme- diately crack. Having now begun the crack, you may lead it in any direction, by merely drawing the hot poker in the direction you want. This is ex- tremely useful in many chemical experiments, where you are in want of proper apparatus.
Glass tubes may be easily cut with a file. Y 4
3*i8 MISCELLANEOUS.
A Method ofjorming Pictures by Nitrate of Silver.
It is well known that light has a powerful effect upon many of the metallic oxydes, causing them to turn black.
Mr. J. Wedgewood has availed himself of this property, for copying paintings on glass, and making profiles of figures, by means of nitrate of silver.
Cover white paper, or leather, with a solution of nitrate of silver, and place it behind a painting on glass, which is exposed to the rays of the sun. The rays which come through will blacken the paper; but the shades will be more or less deep, in propor- tion to the quantities of light transmitted through the different parts of the glass. Where the glass is transparent, and all the light comes through, the paper will be made quite black ; where the glass is quite opaque, and does not transmit any light, tlie paper will be quite white, and there will be degrees of intensity of the shadow of every variety between these.
This picture is not sensibly affected by the light of candles or lamps; bat the day-light destroys it very soon, causing all the paper to become black ; nor have any means, hitherto tried for preventing this, been successful.
Besides the application of this property of nitrate of silver to copying the light and shadow of paint- ings on glass, it may be applied to some others. By means of it delineations may be made of all such objects as are partly opaque and partly transparent. The fibres of leaves, and the wings of insects, may- be pretty accurately represented by it, by only making the solar rays pasvS through them, upon prepared leather or paper.
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Sir Humplirey Davy found, that the images of small objects produced by means of the solar mi- croscope, may be copied without difficulty on prepared paper : the best proportion was one part of nitrate to about ten of water. This is sufficient to enable the paper to become tinged, without hurting its texture.
Artificial Fire- Works.
Artificial fire-works are of two kinds — those made of gunpowder, nitre, and other inflammable substances and filings of the metals, camphor, &c.; and those produced by hydrogen or inflammable air.
Those made with gunpowder are well known, and are called rockets, fire-wheels, tourbillons, &c.
Of these, the most usual are rockets. They are made by ramming into strong cylindrical paper cases put into wooden moulds, like small hollow columns, powdered gunpowder, or the ingredients of which it is composed ; viz. saltpetre, sulphur, and charcoal, very dry.
If you would represent a fiery rain falling from the rocket, mix among your charge a composition of powdered glass, filings of iron, and saw dust ; this shower is called the peacock's tail, on account of the various colours that appear in it. Camphor mixed with the charge produces white or pale fire; resin a reddish colour; sulphur a blue ; sal ammoniac a green ; antimony a reddish yellow ; ivory shavings a silvery white, pitch a deep or dark coloured fire, and steel filings beautiful corruscations and sparks.
Sticks are fastened to the rockets by which they are projected into the air, after they have been lighted ; the charge, burning with great intensity at one end, acts upon the air, which, in its turn,
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330 MISCELLANEOUS.
re-acts upon the rocket, and causes it to ascend, on the same principle as a boat is put off by a man in it who pushes against the shore with a boat-hook.
Fire-works by means of infiammahle air are the most elegant ; and being free from smell or smoke, may be exhibited in a room without any disagree- able effect.
By referring to what has been already said when treating on hydrogen gas, the principle of these fire- works will easily be understood. Small copper or tin tubes must be provided, of about a quarter of an inch in diameter ; these tubes must be formed into the shapes required, and pierced with very small holes where a flame is wanted to appear; to these pieces must be attached large bladders, or air-tight bags, filled with hydrogen gas. There must also be a stop-cock between the tubes and the bladders, to open or close the communication. Having prepared every thing properly, open the stop-cock, and press the bladders; the hydrogen will be forced out through the holes in the tubes, and by means of a taper may be inflamed. A con- stant stream of fire may be kept up as long as there is any air in the bladders.
Upon this principle were constructed the beau- tiful fire-works exhibited in London by Mr. Cart- wright.
The philosophical candle, formed by hydrogen, has been already described under chemistry.
Of Artificial Gi^ottos and Shell-Work.
The idea of artificial grottos is often wrongly conceived. They are usually intended as imita- tions of nature; yet natural grottos are never seen
MISCELLANEOUS. 33i
ornamented within with shells, corals, pieces of looking-glass, &c., disposed in a regular manner. Sometimes, indeed, a more sober species of grotto is attempted, composed of rough masses of stone, representing natural rocks, and covered with moss, and various plants. The difficLdties, however, in this art, considered as an imitation of nature, are much greater than most persons suppose. To suc- ceed, the knowledge of the painter and the archi- tect are necessary ; and only those who have been accustomed to study nature with great attention, are sufficiently acquainted with natural forms. The chief aim should be to dispose the parts so that one may forget that the arrangement is artificial.
There is another idea, however, that may be en- tertained with regard to artificial grottos ; which is, that they need not represent natural caverns; but the supposed productions of enchantment or magic. In this light, most of the incongruities will disappear, and every possible license may be given for the display of imagination and taste. Nothing is supposed to be impossible to magical power : therefore every species of natural or artifi- cial productions may be combined together, and every thing introduced that may excite astonish- ment and surprise. Here there is no necessity for imitating the appearance of natural grottos, but every species of regularity and irregularity may be licensed. The sciences of architecture and me- chanics may thus lend their aid in the construction of places, where mere nature is not the object of imitation, but where every thing may be employed that can have a powerful eft'ect upon the imagination.
Shell-work, corals, statues, fountains, streams of water, paintings, curious musical pieces of mechan- ism J in short, every thing extraordinary, may be
3S'i MISCELLANEOUS.
introduced with great success ; and in this art there is an ample field for the display of taste.
The external of a grotto is the part where the least attempt at ornament should be made. It is best made to resemble some hermitage constructed of roots of trees, or some similar kind of structure ; but no attempt should be made to imitate a natural cavern, except the situation should be peculiarly happy for this purpose.
A cement for fixing large shell-work and stones may be prepared as follows : Melt together a quantity of resin, pitch, and bees-wax, and add to it powdered marble or freestone, and a little sulphur. Any of the finer cements, mentioned under the article cements^ may be used for delicate purposes.
To make Artificial Coral for Grottos.
To two drachms of fine vermilion add one ounce of clear resin, and melt them together. Having your branches or twigs peeled and dried, paint them over with this mixture while hot. The black thorn is the best branch for it. Hold them over a gentle fire, turning them round till they are perfectly covered and smooth. You may make white coral with white lead, and black with lamp-black.
To take Impressions from Leaves.
Take green leaves of trees or flowers, and lay them between the leaves of a book till they are dry. Then mix up some lamp-black with drying oil, and make a small dabber of some cotton wrapped up in a piece of soft leather. Put your colour upon a
MISCELLANEOUS. 333
tile, and take some on your dabber. Laying the dried leaf flat upon a table, dab it very gently with the oil colour, till the veins of the leaf are covered ; but you must be careful not to dab it so hard as to force the colour between the veins. Moisten a piece of paper, or rather have a piece laying between several sheets of moistened paper for several hours, and lay this over the leaf which has been blackened. Press it gently down, and then subject it to the action of a press, or lay a heavy weight on it, and press it down very hard. By this means you obtain a very beautiful impression of the leaf and all the veins ; even the minutest will be represented in a more perfect manner than they could be drawn with the greatest care. These impressions may also be coloured in the same manner as prints.
A Method of making Pictures of Birds, hy means of their own Feather's.
Get a thin board or pannel of deal, or wainscot, well seasoned, that it may not warp. Paste w^hite paper over it, and let it dry. Take any bird that you would wish to represent, and draw its outline on the paper, in the attitude you desire, and of the full size, adding what landscape, back ground, &c. you wish. This outline, so drawn, is afterwards to be filled up with the feathers from the bird, placing each feather in that part of the drawing corresponding to the part of the bird it was taken from.
To do this, cover the representation with several coats of strong gum water, letting it dry between each coat, till it is of the thickness of a shilling-.
334) MISCELLANEOUS.
When your ground is thus prepared, take the feathers off from the bird, beginning at the tail or the points of the wings, as you must work upwards towards the head. These feathers must be pre- pared by cutting off all the downy part ; and the larger feathers must have the insides of their shafts pared off, to make them lie flat. To lay them on, make use of a pair of small pliers to hold them by; and moistening the gummed ground with water, place each feather in its natural and proper situ- ation. Keep each feather down, by putting a small leaden weight upon it, till you have another prepared to lay on. You must be careful not to let the gum come through the feathers, as it smears them, and sticking to the bottoms of the weights, will be apt to pull the feathers off. When you have put on all the feathers, you must cut a piece of round paper, and colour it like the. eye, which you may stick in its place j but the best way is to get small eyes made of glass. The bill, legs, and feet must be drawn and coloured from Nature. When it is finished and adjusted to your mind, lay a sheet of paper upon it, and upon that a heavy weight to press itj which must remain till the whole is quite dry.
To take the Impressmi of any Butterfly in ail its Colours.
Having taken a butterfly, kill it wdthout spoiling its wings, which contrive to spread out as regularly as possible in a flying position ; then, with a small brush or pencil, take a piece of white paper; wash part of it with gum water, a little thicker than ordinary, so that it may easily dry ; afterwards,
MISCELLANEOUS. 33.5
laying your butterfly on the paper, cut off tlie body close to the wings, and throwing it away, lay the paper on a smooth board, with the fly upwards ; and laying another paper over that, put the whole preparation into a screw press, and screw it down very hard, or otherwise press it, letting it remain under that pressure for half an hour. Afterwards take off the wings of the butterfly, and you will find a perfect impression of them, with all their various colours marked distinctly, remaining on the paper. When this is done, draw between the wings of your impression the body of the butterfly, and colour it after the insect itself.
' To lay Mezzo t into Prints upon Glass.
Take what mezzotinto print you please ; cut off the margin, and lay it flat in a dish of clear hot water ; let it remain on the surface till it sinks. When you take it out, be careful not to break it, and press it betwixt clean cloths or papers, so that no water may appear on the surface, but the print be quite damp : then lay it, face uppermost, on a flat table ; have ready a plate of pure crown glass, free from all spots or scratches ; lay some Venice turpentine all over one side of it with a soft brush, and hold it to the fire a little, to make it run quite equal and thin ; then let it fall gently on the print. Press it down, that the turpentine may stick to the print ; and also press the print with your fingers, from the middle to the edges of the glass, so that no blisters may remain. Wet your print now with a soft cloth, and rub it gently with your finger, and the paper will peel off, leaving only the impression
3S6 MISCELLANEOUS.
npon the glass. When it is dry, wet it ever with oil of turpentine till it is transparent, and set it by to dry, when it will be fit for painting. The colours used for painting in this manner are the usual oil colours, and there is nothing in the pro- cess particular.
To make Artificial Pearls.
Take the blai/ or bleak Jishy which is very com- mon in the rivers near London, and scrape off the fine silvery scales from the belly. Wash and rub these in water. Then suffer this water to settle, and a sediment will be found of an oily consistence. A little of this is to be dropped into a hollow glass bead of a bluish tint, and shaken about, so as to cover all the internal surface. After this, the bead is filled up with melted white wax, to give it solidity and weight.
To prepare the Nuremberg Powder of variegated Colour,
Mix together clean filings of copper, brass, iron, steel, and other metals. Put each of them sepa- rately into an iron vessel, and heat them till they change colour. The degree of heat can only be regulated by trial. Take these to a good flatting- mill, furnished with a funnel at top, and pass these filings through it, and you will procure a most beautiful sparkling powder of all sorts of lively colours.
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To make very beautiful Artificial Petrifactions.
Put into a retort a quantity of pounded fluor spar and a few bits of broken glass, and pour upon them some sulphuric acid ; fluoric acid gas will be disengaged, holding silex in solution. The substances to be made to resemble petrifactions, as lizards, frogs, branches of trees, birds nests, &c. must now be moistened with water, and placed in a vessel connected with the neck of the retort. The fluoric acid gas will be absorbed by the moisture adhering to the substances, and the silex will be precipitated upon them like a sort of hoar- frost, which will have a very beautiful appearance, and is very durable.
A Method of making Cast Steel.
This method has been invented in France. It is as follows : Take small pieces of iron, and place them in a crucible, with a mixture of chalk or lime-stone and the earth of Hessian crucibles. Six parts of chalk and six of this earth must be employed for twenty parts of the iron. The mat- ters are to be so disposed, that, after fusion, the iron must be completely covered by them, to pre- vent it from coming into contact with the external air. The mixture is then to be gradually heated, and at last exposed to a heat capable of melting iron. If the fire be well kept up, an hour will generally be sufficient to convert two pounds of iron into excellent and exceedingly hard steel, capable of being forged ; an advantage not possessed by steel made in the usual manner.
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388
MISCELLANEOUS.
Method of distinguishing Iron from Steel.
Drop a little weak aqua-fortis on the metal ; let it remain for a few minutes, and then wash it off with water. If it is steel, the spot will be black, but if iron, the spot will be whitish grey.
A Test for discovering the presence of Lead ^ Copper, 8^c, in Wines.
Lead and copper being sometimes used to amend the taste of wines, and these metals being of a very poisonous quality, a test that shall detect this is of great value. The following test is the discovery of Mr. Hanhemann.
Equal parts of oyster shells and crude sulphur are to be kept in a white heat for a quarter of an hour, and, when cold, this is to be mixed with an equal quantity of acidulous tartrite of potash, and put into a strong bottle with common water for an hour, and then decanted into bottles holding an ounce each, with twenty drops of muriatic acid in each.
This liquor precipitates the least quantities of lead, copper, &c. from wines, in a very sensible black precipitate.
To make Pearl White.
Put some good aqua-fortis into a Florence flask, and gradually add to it bismuth broken into small pieces, till no more dissolves ; tlien let the solution remain till it is transparent. Add to this some
MISCELLANEOUS. 339
water, and a white precipitate will be formed, ■which is to be washed and dried. This is white oxyde of bismuth, commonly termed magistery of hismuthy or pearl-xvhite.
This is used as a cosmetic, and is sold by the perfumers ; but it very much impairs the skin, blackening it by degrees, so that once used, it itnist be continued ; and it is also to be feared, that it has, besides, deleterious effects upon the constitution.
To procure Anhnakiilce for the Mia^oscope.
The surface of infused liquors is generally covered with a thin pellicle, which is easily broken, but acquires thickness by standing ; the greatest number of animalculas are generally to be found in this superficial film.
To malce mi infusion of pepper. — Cover the bot- tom of an open jar, about half an inch thick, with common black pepper, bruised ; pour as much soft water in the vessel as will rise about an inch above the pepper. The pepper and water are then to be well shaken together ; after which they must not be stirred, but be left exposed to the air for a few days, when a thin pellicle will be formed on the surface of the water, containing miUions of animal culae.
To procure the eels in paste. — Boil a little flour and water till it becomes of a moderate consistence ; expose it to the air in an open vessel, and beat it together from time to time, to prevent the surface from growing hard or mouldy : after a few days, especially in summer time, it will turn sour ; then, if it be examined with attention, you will find myriads of eels on the surface. Apply them to
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,340 MISCELLANEOUS.
the microscope on a slip of flat glass, first putting on it a drop of water, taken up by the head of a pin, for them to swim in.
A very usqful Method of breaking up Logs of Wood,
The usual way of breaking up logs of wood for the purposes of fuel, is by axes, and driving wedges in. This, particularly in roots of trees, is very laborious. It is also sometimes done by gun- powder, in tlie same way as stones and rocks are blasted j but this is very troublesome, as the plug is often driven out. A better method of perform- ing this operation has lately been invented. A hole is bored with an augre, and a charge of pow- der introduced. An iron screw, with a good thread, having a hole bored through its axis, is then introduced into the hole, and turned till it come near to the powder. While the screw is putting in, a wire is kept in the hole through its axis, but it is afterwards drawn out, and a piece of twine dipped in a solution of nitre is put into its place. This quick match is set fire to, and by its slow burning, affords time for the operator to retire be- fore it sets fire to the gunpowder.
By this means, any roots or old stumps of trees may be easily broken up.
A P?'Ocessfor purifying Fish Oil.
Take a gallon of crude stinking oil, and put to it a pint of water poured off from two ounces of lime slacked in the air; stir the mixture up several times for the first twenty-four hours ; then let it stand a day, and the lime water will sink
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below the oil, which must be carefully separated from it.
Another Method for purifying it more completely.
Take a gallon of crude stinking oil, and mix with it a quarter of an ounce of powdered chalk, a quarter of an ounce of lime slacked in the air, and half a pint of water; stir them together; and when they have stood some hours, add a pint of water, and two ounces of pearl-ashes, and place the mix- ture over a fire that will just keep it simmering, till the oil appears of a light amber colour, and has lost all smell, except a hot, greasy, soap-like scent. Then superadd half a pint of water, in which one ounce of salt has been dissolved, and having boiled it half an hour, pour the mixture into a proper ves- sel, and let it stand for some days, till the oil and water separate.
If this operation be repeated several times, di- minishing each time the quantity of ingredients one-half, the oil may be brought to a very light colour, and rendered equally sweet with the com- mon spermaceti oil.
Oil purified in this manner is found to burn much better, and to answer better the purposes of the woollen manufacture. If an oil be wanted thicker and more unctuous, this may be rendered so by the addition of tallow or fat.
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142
FINE ARTS.
Under the name of Fine or Polite Arts, have been generally comprehended, painting, sculpture, architecture, poetry, and music: but in the com- mon acceptation of words, the term line arts is usu- ally confined to the three first; and the professors of them are called, by way of eminence, artists.
It would exceed the limits to wliich we are con- fined in this work, to descant on the value and im- portance of the fine arts ; and it is the less neces- sary, as this subject is beginning to be generally understood, since drawing ha5 become a necessary branch of education.
To treat fully and professionally on the fine arts, would require a separate and extended work. What is here proposed, is to consider that part which enters into our system of usual school education.
Draining strictly means the delineation of the contours or outlines of objects: and in this sense the term is used by painters, who distinguish between drawing and colouring : but the meaning of the word drawing is not sufficiently restricted, since, in common language, it has been applied to all such paintings as are executed with water colours on paper; the title of paintings having been rather given to those executed with oil colours on canvass.
Since this difference of the materials only afforded a very bad ground of distinction on which to found two species, the term paintings in tcater colours has very properly been lately introduced.
DRAWING. ~ 343
Still, however, in common language, the name of drawings is given to all works in water-colours, whether in outline only, in black and white, or in colours ; and the term paintings to those in oil.
Painting in oil is capable of the greatest degree of perfection, but is also the most difficult, and is seldom attempted but by professional artists: whereas, the use of water-colours is comparatively easier, and better adapted for common use.
The first step in the arts is to learn to draw the outlines of objects: next to express the light and shadow: and, lastly, to add the colour.
But before we proceed, it will be necessary to describe the implements and colours made use of.
Im'plemeyits for Dramng.
DroTdiing-boards are for jSxing the paper upon, so that it may not shift, and also for straining it, to prevent the colours, when laid wet upon the paper, from causing it to swell up, so as to be uneven. The simplest sort is made of a deal board framed square, with a strong piece across each end, to prevent warping. Upon this the paper may be fixed down with pins, wafers, or sealing-wax, or it may be strained with paste or glue, as follows : having wetted the paper well with a sponge, lay it upon the board, and turning up the edges about half an inch, run a little good paste or glue all round on the under side, and press the paper down upon the board with a cloth; then set it by to dry : the paper, which had expanded and blistered up much when wet, will contract in drying, while the edges, being fixed immoveably, will strain quite flat and tight, and will be much better for drawing upon than when loose.
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344 IMPLEMENTS FOR DRAWING.
The best kind of drawing-boards, however, are made with a frame and a moveable pannel, upon which the paper is simply put wet, and then forced into the frame, where it is confined by wedges at the back. This strains equally well without the trouble of pasting, so that you may dry it at the fire ; and it also looks much neater. These drawing-boards may be bought at most colour-shops. It is necessary to mention, that all the angles of drawing-boards should be exactly square.
Parallel rulers are for drawing parallel lines readily : they are made of two pieces of ebony fas- tened together by brass bars, so as always to move parallel to each other. They may be bought of different kinds and prices, at the mathematical instrument makers.
Tee-squares are rulers made in the form of the letter T, which are used with the drawing-boards ; the short end, called the stock, being apphed to the edge of the board, so as to slide forwards and backwards ; while the long part, called the blade, is used for drawing lines by. These are more con- venient than parallel rulers, wlien a drawing-board is used, as by them you draw lines at right angles to each other at once, without using the compasses.
Dividing compasses are instruments of brass and steel, for dividing lines, and laying down measures from scales, &c. : they are generally sold in cases, containing also a steel pen for drawing lines cleaner than can be done by a common pen, which is very useful where neatness is required ; and points with a black lead pencil, for putting into the compasses, when circles are to be described. These cases also contain scales of equal parts, and protractors
IMPLEMENTS FOR DRAWrNG. 34f5
for laying down angles. All these may be had at the instrument makers.
Black lead pencils are made of plumbago sawed into slips, and fitted into sticks of cedar. They are of various qualities. The best are fine, without any grit, not too soft, and that cut easily without break- ing. An inferior kind is made by mixing up the dust of plumbago with gum or glue, and thus form- ing a composition, which is fitted into sticks in the same manner as the best : these are always gritty, and do not answer so well for most drawings ; yet, being cheaper, they may be used upon many occa- sions. It is necessary to examine pencils before any quantity is bought, by cutting one of them, because the composition pencils, having the same outward appearance, are often sold for the best.
Indian rubber, or elastic gum, as it is also called, is a substance much like leather, which has the curious and useful property of erasing or defacing lines drawn with black lead ; it is, therefore, much used for this purpose. It is brought chiefly from South America, in the form of small bottles, which are cut up into slips. It is originally the juice of a tree that grows very abundantly in Surinam, and is like milk when exuded from the tree, but soon becomes solid when exposed to the air. The na- tives form balls of clay, which they smear over with this milk : when this coating is almost dry, they apply another, and so on, till it is of the re- quired thickness ; they then moisten the clay with water, which does not dissolve the Indian rubber, and wash it out. These bottles are used by the natives for containing water, or other liquors. It is a production common to the East Indies also, from whence it is imported in various forms.
34() IMPLEMENTS FOR DRAWING.
more convenient for use than the bottles above- mentioned.
Indian Ink. — This very useful substance comes from China, where it is used for common writing, which is there performed with a brush instead of a pen. It is a solid substance, of a brownish black colour. When ground up with water upon a clean tile or earthenware plate, it may be made either lighter or darker, as required, by adding to it more or less water. The best Indian ink is always stamped with Chinese characters, breaks with a glossy fracture, and feels smooth, and not gritty, when rubbed against the teeth. The composition is not accurately known. An inferior kind is made in this country ; but it may be easily distinguished by its grittiness. This is made of lamp black or ivory black, ground up with gum.
Hair pencils are made of camel's hair, put into a goose or swan's quill. To choose these, moisten them a little, and if they come to a point without splitting, they are good ; if they do not, they are not fit for drawing with.
Charcoal is used for slightly sketching in the outlines of figures, in order to get the proportions, previous to making a drawing in chalk. The best charcoal for this purpose is that of the willow ; it is cut into slips, and the strokes made with it may easily be rubbed out with a feather of goose's or duck's wing.
Black chalk is a fossil substance resembling slaty coal, which is cut into slips for drawing, it is generally used in an instrument called a port crayon, which is made either of steel or brass. It is much employed for drawing figui'es, and is the best substance i'or this purpose, in making drawings
IMPLEMENTS FOR DRAWING. 347
from plaster, or after the life. It is more gritty than black lead, but is of a deeper black, and has not the glossiness of the former. It is of two kinds, French and Italian ; the former is soft, the latter hard.
For mellowing and softening the shadows into each other when black chalk is used,
Stumps are necessary. They are pieces of soft shamoy leather, or blue paper, rolled up quite tight, and cut to a point.
White chalk is used together with black, for laying on the lights. This is different from com- mon chalk, being much harder. Tobacco-pipe clay will do very well instead of it.
Red chalk is a fossil substance of a red ochrey colour, which is sometimes used for drawing, but not so much now as it formerly was, the black being preferred ; however, the red being cheaper, will do very well for some purposes.
Drawing 'pape7\ — Any paper that will do for writing will do for drawing ; but as the wire-marks in common writing paper are injurious, paper made without any wire-marks, called wove paper, is generally used for this purpose. It is made of various sizes and thickness.
Middle tint papier is paper of a brownish or of a grey colour, which is used for drawing upon \\\t\\ black and white chalk. Being of a dark colour, the strokes of the white chalk are distinctly seen ; and it saves a great deal of time in making draw- ings, as the tint of the paper answers for the half shadow, so that all that is necessary to be done, is to lay in the dark shadows and the lights.
348
GEOMETRY.
Various are the opinions upon the best modes of beginning to learn to draw : and it is by no means easy to decide upon this point, as so much must always depend upon the genius, turn of mind, and opportunities of the student. But, for general purposes, and when circumstances will admit of it, we have no hesitation in recommending to begin by the study of geometry and perspective.
The' first forms the best introduction to a know- ledge of form, by giving accurate ideas respecting the most simple forms, of which all the others may be considered as compounds : and the last is abso- lutely necessary, not only to enable us to draw the representations of regular objects, but even to see them correctly : and it is certain that no one unacquainted with its rules can ever attain the power of drawing, without making the grossest mistakes.
Geometry is a branch of mathematics which treats of the description and properties of magni- tudes in general.
Definitions or Ej^planations of Terms.
1. A point has neither length, breadth, nor thickness. From this definition it may easily be understood that a mathematical point cannot be seen nor felt ; it can only be imagined. What is commonly called a point, as a small dot made with a pencil or pen, or the point of a needle, is not in reahty a mathematical point ; for however small such a dot may be, yet, if it be examined with a magnifying glass, it will be found to be an irregular
GEOMETRY. 349
spot, of a very sensible length and breadth ; and our not being able to measure its dimensions with the naked eye, arises only from its smallness. The same reasoning may be applied to every thi:ig that is usually called a point ; even the point of the finest needle appears like that of a poker when examined with the microscope.
2. A li?ie is length, without breadth or thick- ness. What was said above of a point, is also ap- plicable to the definition of a line. What is drawn upon paper with a pencil or pen, is not, in fact, a line, but the representation of a line. For how- ever fine you may make tliese representations, they will still have some breadth. But by the defini- tion, a line has no breadth whatever ; yet it is im- possible to draw any thing so fine as to have no breadth. A line, therefore, can only be imagined. The ends of a line are points.
o. Parallel lines are such as always keep at the same distance from each other, and which, if pro- longed ever so far, would never meet. PI. 3.
Fig. 1.
4. A right line is what is commonly called a straight line, or that tends every where the same way.
5. A curve is a line which continually changes its direction between its extreme points.
6. An angle is the inclination or opening of two lines meeting in a point. Fig. 2.
7. The lines A B, and B C, which form the an- gle, are called the legs or sides ; and the point B where they meet, is called the vertex of the angle, or the aiigular point. An angle is some- times expressed by a letter placed at the vertex, as the angle B, Fig. 2 : but most commonly by three letters, observing to place in the middle the
350 GEOMETRY. •
letter at the vertex, and the other two at the end of each leg, as the angle ABC.
8. When one line stands upon another, so as not to lean more to one side than to another, both the angles which it makes with the other are called right-angles^ as the angles ABC and A B D, Fig. 3, and all right-angles are equal to each other, being all equal to 90° ; and the line A B is said to he per- pendicular to C D.
Beginners are very apt to confound the terms perpe?idiculary SLXid plumb or vertical line. A line is vertical when it is at right-angles to the plane of the horizon, or level surface of the earth, or to the surface of water, which is always level. The sides of a house are vertical. But a line may be per- pendicular to another, whether it stands upright or inclines to the ground, or even if it lies flat upon it, provided only that it makes the two angles formed by meeting with the other line equal to each other ; as for instance, if the angles ABC, and A B D be equal, the line AB is perpendicular to CD, what- ever may be its position in other respects.
9. When one line, BE (Fig. 3), stands upon another, C D, so as to incline, the angle E B C, which is greater than a right-angle, is called an obtuse angle ; and that which is less than a right- angle, is called an acute angle, as the angle E B D.
10. Two angles which have one leg in common, as the angles ABC, and ABE, are called co/i/i- guous angles, or adjoining angles j those which are produced by the crossing of two lines, as the angles E B D and CBF, formed by C D and E F, crossing each other, are called opposite or vertical angles.
11. A^^'?^r^ is a bounded space, and is either a surface or a solid.
GEOMETRY. 351
IS. A superficies, or surface, has length and breadth only. The extremities of a superlicies are lines.
A plane, or plane surface, is that which is every where perfectly flat and even, or which will touch every part of a straight line, in whatever direction it may be laid upon it. The top of a marble slab, for instance, is an example of this, which a straight edge will touch in everv point, so that you cannot see light any where between.
A curved surface is that which will not coincide with a straight line in any part. Curved surfaces may be either convex or concave.
A convex surface is when the surface rises up in the middle, as, for instance, a part of the outside of a globe.
A concave surface is when it sinks in the middle, or is hollow, and is the contrary to convex.
A surface may be bounded either by straight lines, curved lines, or both these.
13. Every surface bounded by straight lines only, is called a rectilinear fgure.
14. Three is the fewest number of sides that a rectilinear figure can have ; and it is then called a triangle.
15. Triajigles are of different kinds, according to the lengths of their sides.
An equilateral triangle has all its sides equal, as A B C, Fig. 4.
An isosceles triangle has two equal sides, as D E F, Fig. 5.
A scalene triangle has all its sides unequal, as G H I, Fig. 6.
16. Triangles are also denominated according to the angles they contain.
352 GEOMETRY.
A inght-angled triangle is one that has in it a right-angle, as A B C, Fig. 7.
A triangle cannot have more than one right-an- gle. The side opposite to the right-angle B, as AC, is called the h^pothenusef and is always the longest side.
An obtuse-angled triangle has one obtuse angle, as Fig. 8.
An acute-angled triangle has all its angles acute, as Fig. 4.
An isosceles, or a scalene triangle, may be either right-angled, obtuse, or acute.
Any side of a triangle is said to subtend the angle opposite to it : thus A B (Fig. 7), subtends the angle A C B.
If the side of a triangle be drawn out beyond the figure, as A D (Fig. 8), the angle A, or CAB, is called an internal angle, and the angle CAD, or that without the figure, an external 2ing\e.
17. A figure with four sides is called a quadri- lateral %ure. They are of various denominations, as their sides are equal or unequal, or as all their angles are right angles or not.
18. Every four-sided figure whose opposite sides are parallel, is called a parallelogram. Provided that the sides opposite to each other be parallel, it is immaterial whether the angles are right or not. Fig. 9, 10, 11, and 12, are all parallelograms.
When the angles of a parallelogram are all right angles, it is called a rectangular parallel- ogram, or a rectangle y as Fig. 11 and 12.
19. A rectangle may have all its sides equal, or only the opposite sides equal. When all its sides are equal, it is called a square^ as Fig. 12.
20. When the opposite sides are parallel, and all the sides equal to each other, but the angles not
GEOMETRY. 8.53
riglit angles, the parallelogram is called a rhomhiiSy as Fig. 10.
21. A parallelogram liaving all its angles oblique, and only its opposite equal, is called a rhomboid^ as Fig. 9.
22. When a quadrilateral or four-sided figure has none of its sides parallel, it is called a traj)e- zhim, as Fig. 13. ; consequently every quadrangle, or quadrilateral which is not a parallelogram, is a trapezium.
23. A trapezoid has only one pair of its sides parallel, as Fig. 14.
24. A diagonal is a right line drawn between any two angles that are opposite in a quadrangle, as I K, Fig. 15. In parallelograms the diagonal is sometimes called the diameter^ because it passes through the centre of the figure.
25. Co7nplements of a parallelogram. If any point, as E (Fig. 15.), be taken in the diagonal of a parallelogram, and through that point two lines are drawn parallel to the sides, as A B, C D, it will be divided into four parallelograms, D D, L, F, G G. The two divisions, L, F, through which the diame- ter does not pass, are called the complements.
26. Figures having more than four sides are called polygons. If the sides are all equal, they are called regidar polygons: if they are unequal, they are called irregular polygons.
A pentagon is a polygon of five sides.
A hexagon has six sides.
A heptagon seven sides.
An octagon eight sides.
A nonagon nine sides.
An undecagon eleven sides.
A duodecagon twelve sides.
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354 GEOMETRY.
When they have a greater number of sides, they are called polygons of 13 sides, of 14 sides, and so on.
27. Base of a figure is the side on which it is supposed to stand erect, as A B and C D. (Fig. 16.)
28. Altitude of a figure is its perpendicular height from the base to the highest part, as E F. (Fig. 16.)
29. Area of a plane figure, or other surface, means the quantity of space contained within its boundaries, expressed in square feet, yards, or any other superficial measure.
30. Similar Jigures are such as have the same angles, and whose sides are in the same proportion, as Fig. 17.
31. Equal figures are such as have the same area or contents.
32. A circle is a plane figure, bounded by a curve line returning into itself, called its circum- ference, ABCD, (Fig. 18.) every where equally
distant from a point E within the circle, which is called the centre.
33. The radius of a circle is a straight line drawn from the centre to the circumference, as E F. (Fig. 18.) The radius is the opening of the com- pass when a circle is described \ and consequently all the radii of a circle must be equal to each other.
34. A diameter of a circle is a straight line drawn from one side of the circumference to the other through the centre, as C B. (Fig. 18.) Every diameter divides the circle into two equal parts.
35. A segment of a circle is a part of a circle cut off by a straight line drawn across it. This straight line is called the chord. A segment may be either equal to, greater, or less than a semicirckf which is
GEOMETRY. 355
a segment formed by the diameter of the circle, as C E B, and is equal to half the circle.
36. A tangent is a straight line drawn so as just to touch a circle without cutting it, as G H. (Fig. 18.) The point A, where it touches the cir- cle, is called the point of contact. And a tangent cannot touch a circle in more points than one.
37- A sector of a circle is a space comprehended between two radii and an arc, as B I K. (Fig. 19.)
3S. The circumference of every circle, whether great or small, is supposed to be divided into 360 equal parts, called degrees ; and every degree into ()0 parts, called minutes ; and every minute into 60 seconds. To measure the inclination of lines to each other, or angles, a circle is described round the angular point as a centre, as IK, Fig. 19.; and according to the number of degrees, minutes, and seconds, cut off by the sides of the angle, so many degrees, minutes, and seconds, it is said to contain. Degrees are marked by °, minutes by ', and seconds by "; thus an angle of 48 degrees, 15 minutes, and 7 seconds, is written in this manner, 48° 15' 7".
S9. A solid is any body that has length, breadth, and thickness : a book, for instance, is solid, so is a sheet of paper ; for though its thickness is very small, yet it has some thickness. The boundaries of \ solid are surfaces.
40. Similar solids are such as are bounded by an equal number of similar planes.
41. A prism is a solid, of which the sides are parallelograms, and the two ends or bases are similar polygons, parallel to each other. Prisms are denominated according to the number of angles in the base, triangular prisms, quadrangular, pent- angular, and so on, as Fig. 20, 21, 22, 23. If the
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SrA) GEOMETRY.
sides are perpendicular to the plane of the base, it is called an iqnight prism ; if they are inclined, it is called an oblique prism.
4f^. When the base of a prism is a parallelogram, it is called a paralleloplpedony as Fig. !22. and 23. Hence a parallelopipedon is a solid terminated by six parallelograms.
43. When all the sides of a parallelopipedon are squares, the solid is called a cube, as Fig. 23.
44. A rhomboid is an oblique prism, whose bases are parallelograms. (Fig. 24.)
45. A pyramid, A B, (Fig. 25. and 26.) is a solid bounded by, or contained within a number of planes, whose base may be any rectilinear figure, and whose faces are triangles terminated in one point, B, commonly called the summit, or vertecc of the pyramid.
When the figure of the base is a triangle, it is called a triangular pyramid ; when the figure of the base is quadrilateral, it is called a quadrilateral pyramid, &c.
A pyramid is either regular or irregular, ac- cording as the base is regular or irregular.
A pyramid is also right or ujnight, or it is oblique. It is right, when a line drawn from the vertex to the centre of the base, is perpendicular to it, as Fig. 25. ; and oblique, when this line in- clines, as Fig. 2(5.
46. A cylinder is a solid (Fig. 27. and 28.) ge- nerated or formed by the rotation of a rectangle about one of its sides, supposed to be at rest ; this quiescent side is called the aiis of the cylinder. Or it may be conceived to be generated by the motion of a circle, in a direction perpendicular to its surface, and always parallel to itself.
GEOMETRY. 357
A cylinder is either right or oblique^ as the axis is perpendicular to the base or inclined.
Every section of a right cylinder taken at right angles to its axis is a circle ; and every section taken across the cylinder, but oblique to the axis, is an ellipsis.
As a circle may be considered to be a polygon of an infinite number of sides, so a cylinder may be conceived as a prism having such polygons for bases.
47. A cone is a solid, (Fig. 29. and 30.) having for its base a circle, and its sides a convex surface, and terminating in a point A called the vertex' or apex of the cone. It may be conceived to be generated by the revolution of a right-angled triangle about its perpendicular.
A line drawn from the vertex to the centre of the base, is the axis of the cone.
When this line is perpendicular to the base, the cone is called an upright or right cone ; but when it is inclined, it is called an oblique cone.
If a cone be cut through the axis from the vertex to the base, the section will be a triangle.
If a right cone be cut by a plane at right angles to the axis, the section will be a circle.
If a cone be cut oblique to the axis, and quite across from one side to the other, the section will be an ellipsis, as Fig. 31. A section of a cylinder made in the same manner, is also an ellipsis j and this is easily conceived ; but it does not appear so readily to most people, that the oblique section of a cone is an ellipsis : they frequently imagine that it will be wider at one end than the other, or what is called an oval^ which is of the shape of an e^^. But that this is a mistake, any one may convince himselij by making a cone, and cutthig it acros:-
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35S GEOMETRY.
obliquely : it will be then seen that the section, in whatever direction it is taken, is a regular ellipsis ; and this is the case, whether the cone be right or oblique; except only in one case in the oblique cone, which is when the section is taken in a particular direction which is called sub-contrary to its base.
48. When the section is made parallel to one of the sides of the cone, as Fig. 32., the curve ABC, which bounds the section, is called a _;^Mr<7Z»o/«.
49. When the section is taken parallel to the axis, as Fig. 33., the curve is called an hyperbola.
The curves which are formed by cutting a cone in different directions are called conic sectmis, and have various properties which are of great import- ance in astronomy, gunnery, perspective, and many other sciences.
50. A sphere is a solid, terminated by a convex surface, every point of which is at an equal distance from a point within called the centre. Fig. 34.
It may be conceived to be formed by making a semicircle revolve round its diameter. This may be illustrated by the process of forming a ball of clay by the potter's wheel, a semicircular mould being used for the purpose. The diameter of the semicircle round which it revolves is called the aa:is of the sphere.
The ends of the axis are called 2)oles.
Any line passing tlirough the centre of the sphere, and terminated by the circumference, is a diameter of the sphere.
Every section of a sphere is a circle ; every sec- tion taken through the centre of the sphere, is called a great circle^ as A B, Fig. 34. ; every other is a lesser circle, as C D.
Any portion of a sphere cut off by a plane is called a segment; and when the plane passes
GEOMETRY. 359
through the centre, it divides the sphere into two equal parts, each of which is called a hemisphere.
51. A conoid is a solid produced by the circum- volution of a section of the cone about its axis ; and consequently may be either an elliptical conoidy a hyperbolical conoid y or ^ parabolical co7ioid. When it is elliptical, it is generally called a spheroid. These solids are also called ellipsoid^ hj/perboloid, and paraboloid.
52. A spheroid is a solid (Fig. 35.) generated by the rotation of a semi-eliipsis about the trans- verse or conjugate axis; and the centre of the ellipsis is the centre of the spheroid.
The line about which the ellipsis revolves, is called the adis. If the spheroid be generated, about the conjugate axis of the semi-ellipsis, it is called ^prolate spheroid.
If the spheroid be generated by the semi-ellipsis, by revolving about the transverse axis, it is called an oblong spheroid.
Every section of a spheroid is an ellipsis, except when it is perpendicular to that axis about which it is generated ; in which case it is a circle.
All sections of a spheroid parallel to each other are similar figures.
A frustum of a solid means a piece cut off from the solid by a plane passed through it, usually parallel to the base of the solid ; as the frustum of a cone, a pyramid, &c.
There is a lower and an upper frustum, according as the piece spoken of does or does not contain the base of the solid.
53. Ratio is the proportion which one magnitude bears to another of the same kind, with respect to quantity j and is usually marked thus, A : B.
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360 GEOMETRY.
Of these, the first is called the mUecedejit, and the second the consequent.
The measure or quantity of a ratio is conceived by considering what part of the consequent is the antecedent ; consequently it is obtained by dividing the consequent by the antecedent.
54. Three magnitudes or quantities, A,B,C, are said to be proportional, when the ratio of the first to the second is the same as that of the second to the third. Thus, % 4, 8, are proportional, because 4 is contained in 8 as many times as 2 is in 4.
55. Four quantities, A,B,C,D, are said to be p>i'0' portional when the ratio of the first A to the second B is the same as the ratio of the third C to the fourth D. It is usually written A : B : : C : D, or, if expressed in numbers, 2:4 : : 8:16.
66. Of three proportional quantities, the middle one is said to be a 7nea?i proportional between the other two ; and the last a third proportional to the first and second.
57. Oi'Jbur proportional quantities, the last is said to be a fourth proportional to the other three, taken in order.
58. Ratio of equality is that which equal -numbers bear to each other.
59. Inverse ratio is when the antecedent is made the consequent, and the consequent the antecedent. Thus if 1 : 2 : : 3 : 6 ; then inversely, 2:1 \'.6\o.
60. Alternate proportion is when antecedent is compared with antecedent, and consequent with consequent. Thus if 2 : 1 : : 6 : 3j then by alter- nation, 2 : 6 : : 1 : 3.
61. Proportion by composition is when the ante- cedent and consequent, taken as one quantity, are compared either with the consequent or with the antecedent. Thus if 2 : 1 : : 6 : 3 ; then by com- position 2 + 1 : 1 : : 6 -f 3 : 3, and 2 + 1:2:6+3:6.
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GEOMETRY. 36i
CS. Divided proportion is when the difterence of the antecedent and consequent is compared either with the consequent or with the antecedent. Thus if S : 1 : : 12 : 4 ; then by division 3 — 1:1: : 12 — 4 : 4 and 3 — 1 : 3 ::12 — 4 : 12.
i53. Continued proportion is when the first is to the second as the second to the third ; as the tliird to the fourth ; as the fourth to the fifth ; and so on.
64. Componnd ratio is formed by the muItipHca- tion of several antecedents and the several conse- quents of ratios together, in the following manner :
If A be to B as 3 to 5, B to C as 5 to 8, and C to
D as 8 to 6 ; then A will be D, as z:^^ = i ;
that is, A : D : : 1 : 2.
Q5. To Bisect means to divide any thing into two equal parts.
QQ. To Trisect is to divide any thing into three equal parts.
67. To Inscribe is to draw one figure within another, so that all the angles of the inner figure shall touch either the angles, sides, or planes of the external figure.
68. To Circumscribe is to draw a figure round another, so that either the angles, sides, or planes of the circumscribed figure shall touch all the angles of the figure within it.
69. A Rectangle under any two lines means a rectangle which has two of its sides equal to one of the lines, and two of them equal to the other. Also the rectangle under AB,CD, means ABxCD.
70. Scales of equal parts. A scale of equal parts is a straight line divided into any number of equal parts at pleasure. Each part may represent any measure you please, as an inch, a foot, a yard, &c. One of these is generally subdivided into parts of the next denomination, or into tenths or hundredths.
362 GEOMETRY.
Scales may be constructed in a variety of ways. The most usual manner is to make an inch, or some aliquot part of an inch to represent a foot ; and then they are called inch scales, three-quarter- inch scales, half-inch scales, quarter-inch scales, &c. They are usually drawn upon ivory or box-wood.
71. An aa:iom is a manifest truth, not requiring any demonstration.
72. Postulates are things required to be granted true, before we proceed to demonstrate a propo- sition.
73. A proposition is when something is either proposed to be done, or to be demonstrated, and is either a problem or a theorem.
74-. A problem is when something is proposed to be done ; as some figure to be drawn.
75. A theorem is when something is proposed to be demonstrated or proved.
76. A lemma is when a premise is demonstrated, in order to render the thing in hand the more easy.
77. A corollary is an inference drawn from the demonstration of some proposition.
78. A scholium is when some remark or observa- tion is made upon something mentioned before.
79. The sign = denotes that the quantities be- twixt which it stands are equal.
80. The sign -f denotes that the quantity after it is to be added to that immediately before it.
81. The sign — denotes that the quantity after it is to be taken away or subtracted from the quan- tity preceding it.
Geometrical Problems,
Prob.l. To divide a given line, AB(P1. 4.), into two equal parts.
GEOMETRY. 363
From the points A and B as centres, and with any opening of the compasses greater than half A B, describe arches cutting each other in c and d. Draw the hne c d ; and the point E, where it cuts A B, will be the middle required.
Prob. 2. To raise a perpendicular to a given line A B, from a point given at C.
Case 1. When the given point is near the middle of the line. On each side of the point C, take any two equal distances C ^ and Ce; from d and e, with any radius or opening of the compasses greater than C df or C e, describe two arcs cutting each other in Jl Lastly, through the points^ C, draw the line J^C, and it will be the perpendicular re- quired.
Case 2. When the point is at or near the end of the line. Take any point d, above the line, and with the radius or distance dCy describe the arc e CJf cutting A B in e and C. Through the centre d, and the point e, draw the line e df, cutting the arc e Cfinf. Through the points^ C, draw the line fC, and it will be the perpendicular required.
Prob. 3. From a given point f, to let fall a per- pendicular upon a given line A B.
From the point J^ with any radius, describe the arc de^ cutting A B in e and d. From the points e dy with the same or any other radius, describe two arcs cutting each other in g. Through the points yand g\ draw the liney^'; andjTC will be the perpendicular required.
Prob. 4. To make an angle equal to another angle which is given, as « B ^.
From the point B, with any radius, describe the arc a b, cutting the legs B «, B Z), in the points a and b. Draw the line D e, and from the point D, with the same radius as before, describe the arc ej^
364f GEOMETRY.
cutting T) e in e. Take the distance b c/, and apply it to the arc ej", from e tof. Lastly, through the points, T),J] draw the line D^ and the angle e T>f will be equal to the angle b B a, as was required.
Prob. 5. To divide a given angle, ABC, into two equal angles.
From the point B, with any radius, describe the arc A C. From A and C with the same, or any other radius, describe arcs cutting each in d. Draw the line B d, and it will bisect the angle ABC, as^ was required.
Prob. 6. To lay down an angle of any number of degrees.
There are various methods of doing this. One is by the use of an instrument called a 2^rottYwtor, which is a semicircle of brass having its circumfer- ence divided into degrees. Let A B be a given line ; and let it be required to draw from the an- gular point A, a line making with A B any number of degrees, suppose 20. Lay the straight side of the protractor along the line AB, and count 20° from the end B of the semicircle ; at C, which is 20* from B, make a mark ; then, removing the protractor, draw the line A C, which makes with A B the angle required.
Or, it may be done by a divided line, usually drawn upon scales, called a line of chords. Take 60° from the line of chords in the compasses ; and setting one at the angular point B, Prob. 4, with that opening as a radius, describe an arch, as a b : then take the number of degrees you intend the angle to be of, and set it from b to a, then is « B ^, the angle required.
Prob. 7' Through a given point C, to draw a line parallel to a given line A B.
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Case 1. Take any point cf, in A B ; upon d and C, with the distance C d, describe two arcs, e C, and djl cutting the line A B in e and d. Make r/y equal to e C; through C andjf draw CJi and it will be the line required.
Case 2. When the parallel is to be at a given distance from A B. From any two points, c and df in the line A B, with a radius equal to the given distance, describe the arcs e and^.- draw the line C B to touch those arcs without cutting them, and it will be parallel to A B, as was required.
Prob. 8. To divide a given line A B into any proposed number of equal parts.
From A, one end of the line, draw A c, making any angle with A B ; and from B, the other end, draw B d, making the angle A B r/ equal to B A c. In each of these lines A c, B </, beginning at A and B, set off as many equal parts of any length as A B is to be divided into. Join the points C 5, 46, 37, &c., and A B will be divided as required.
Prob. 9. To find the centre of a given circle, that is, of any one already described. Draw any chord A B, and bisect it with the perpendicular C D. Bisect C D with the diameter E F, and the intersection O will be the centre required.
Prob. 10. To draw a tangent to a given circle that shall pass through a given point, A.
From the centre O, draw the radius OA. Through the point A, draw D E perpendicular to O A ; and it will be the tangent required.
Prob. 11. To draw a tangent to a circle, or any segment of a circle A B C, through a given point B, without making use of the centre of the circle.
Take any two equal divisions upon the circle from the given point B, towards d and <?, and draw the chord e B. Upon B, as a centre with the dis-
366 GEOMETRY.
tance B rf, describe the D.rcfdg\ cutting the chord eBinJl Make dg equal to dj'; through g draw g B, and it will be the tangent required.
Pi^ob. 12. Given three points, A, B, C. not in a straight line, to describe a circle that shall pass through them.
Bisect the lines A B, B C, by the perpendicu- lars a b, ba, meeting at d. Upon d, with the dis- tance ^ A, ^B, or dCi describe ABC, and it will be the required circle.
P7'ob, 13, To describe the segment of a circle, of any length A B, and any height C D.
Bisect A B by the perpendicular D^, cutting A B in c. From c make c D on the perpendicular equal to C D, Draw A D, and bisect it by a per- pendicular ejy cutting Dg in g. Upon g the centre, describe A D B, and it will be the required segment.
Prob. 14. To describe the segment of a circle by means of two rulers, to any length A B, and perpendicular height C D in the middle of A B, without making use of the centre.
Place the rulers to the height at C j bring the edges close to A and B ; fix them together at C, and put another piece across them to keep them fast. Put in pins at A and B, then move the rulers round these pins, holding a pencil at the angular point C, which will describe the segment.
Prob. 15. In any given triangle to inscribe a circle. Bisect any two angles A and C, with the lines A D and CDC. From D the point of inter- section, let fall the perpendicular D E j it will be the radius of the cii'cle required.
Prob. 16. In a given square, to describe a regu- lar octagon.
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GEOMETRY. 367
Draw the diagonals AC and B D, intersecting at e. Upon the points A, B, C, D, as centres, with a radius e C, describe the arcs h e /, k e n, m e g,fe i. Join J n, m h, k /, / «', and it will be the required octagon.
Prob. 17* In a given circle, to describe any re- gular polygon.
Divide the circumference into as many parts as there are sides in the polygon to be drawn, and join the points of division.
Prob. 18. Upon a given line AB, to construct an equilateral triangle.
Upon the points A, and B, with a radius equal to A B, describe arches cutting each other at C. Draw A C and B C, and ABC will be the triangle required.
Prob. 19. To make a triangle, whose sides shall be equal to three given lines, D, E, F, any two of them being greater than the third.
Draw A B equal to the line D. Upon A, with the radius F, describe an arc C D. Upon B, with the radius E, describe another arc intersecting the former at C. Draw A C and C B, and ABC will be the triangle required.
Prob. 20. To make a trapezium equal and simi- lar to a given trapezium A B C D.
Divide the given trapezium ABCD into two triangles by the diagonal D B. Make E F equal to A B J upon E F construct the triangle E F PI, whose sides shall be respectively equal to those of the triangle A B D by the last problem. Upon H F, which is equal to D B, construct the triangle HFG, whose sides are respectively equal to DBC ; then EFGH will be the trapezium required.
By the help of this problem any plan may be copied J as every figure, however irregular, may
368 GEOMETRY.
be divided into triangles. Upon this the practice of land-surveying and making plans of estates is founded.
Proh. 21. To make a square equal to two given squares. Make the sides D E and D F of the two given squares A and B ; from the sides of a right- angled triangle F D E ; dravv^ the hypothenuse FE; on it describe the square E F G H, and it will be the square required.
Proh. 22. Two right lines A B, C D, being given, to find a third proportional. Make an angle H E I at pleasure ; from E make E F equal to A B, and E G equal to CD: join F G. Make E I equal to E F, and draw H I parallel to F G ; then E H will be tlie third proportional required ; that is, EF : EG:: E H: EI, or AB:CD:: C D : E I.
Proh. 23. Three lines being given, to find a fourth proportional. Make the angle H G I at pleasure ; from G make G H equal to A B, G I equal to C D, and join H I. Make G K equal to E F ; draw K L through K, parallel to H 1 ; then G L will be the fourth proportional requii'ed ; that is, G H : G I : : G K : G L, or A B : C D : : E F : GL.
Proh. 24. To divide a given line A B in the same proportion as another C D is divided.
Make any angle K H I, and make H I equal to A B ; then apply the several divisions of C D from H to K, and join K I. Draw the lines he, if, Ic g\ parallel to I K ; and the line H I will be divided in e^f, gy as was required.
Proh. 25. Between two given lines A B and C D, to find a mean proportional.
Draw the right line E G, in which make E F equal to A B, and F G equal to C D. Bisect E G
gp:ometry. 369
in H, and with H E or H G, as radius, describe the semicircle E I G. From F draw F I perpen- dicular to E G, cutting' the circle in I ; and I F will be the mean proportional required.
Proh. 26. To describe an ellipsis.
If two pins are fixed at the points E and F, a string put about them, and the ends tied together at C ; the point C being moved round, keeping the string stretched, will describe an ellipsis.
The points E and F, where the pins were fixed, are called theyoa.
The line A B passing through the foci, is called the transverse axis.
The point G bisecting the tranverse axis, is the centre of the ellipsis.
The line C D crossing this centre at right-angles to the tranverse axis, is the conjugate axis.
The latus rectum is a right line passing through the focus at F, at right angles to the transverse axis terminated by the curve : this is also called the parameter.
A diameter is any line passing through the centre, and terminated by the curve.
A coiyugate diameter to another diameter is a line drawn through the centre, parallel to a tan- gent at the extreme of the other diameter, and terminated by the curve.
A double ordinate is a line drawn through any diameter parallel to a tangent, at the extreme of that diameter terminated by the curve.
The transverse axis A B, and conjugate axis C D, of any ellipsis, being given, to find the two foci, and from thence to describe the ellipsis.
Take the semi-transverse A E, or E B, and from C as a centre, describe an arc cutting A B at F and G ; these are the foci. Fix pins in these
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370 GEOMETRY.
points ; a string being stretched about the points F, C, G, the elUpsis is described as above.
Prob. 27. The same being given, to describe an elHpsis by a trammel.
The trammel is an instrument consisting of two rulers fixed at right-angles to each other, with a groove in each. A rod with two moveable nuts works in this groove ; and, by means of a pencil fixed in the end of the rod, describes the curve. The operation is as follows :
Let the distance of the first pin at B, from the pencil at A, be equal to half the shortest axis ; and the distance of the second pin at C, from A, to half the longest axis ; the pins being put in the grooves, move the pencil at A, which will describe the ellipsis.
Prob. 28. To draw a figure approaching to an ellipsis with a compass to any length A B, and width C D.
Draw B P parallel and equal to E C, and bisect it at 1 ; then draw 1 C and P D, cutting each other at K j bisect K C by a perpendicular, meet- ing C D in O J and on O, with the radius O C, de- scribe the quadrant C G Q.
Through Q and A, draw QG, cutting the qua- drant at G; then draw G O, cutting A B at M^ make E L equal to E M, also E N equal to E O. From N, through M and L draw N H and N I; tlien M, L, N, O, are the four centres by which the four quarters of the figure are drawn.
It must be observed, that this is not a true el- lipsis, but only an approximation to it ; for it is impossible to draw a perfect ellipsis by means of compasses, which can only describe parts of cir- cles. The curve of an ellipsis differs essentially from that of a circle in every part ; and no por-
GEOMETRY. 371
tions of circles put together can ever form an el- lipsis. But by this means a figure may be drawn, which approaches nearly to an ellipsis, and, there- fore, may be often substituted for it when a tram- mel cannot be had, or when the ellipsis is too small to be drawn by it. At the joining of the portions of circles in this operation, the defect is perceivable ; and the best way is not to join them quite, and to help the curve by hand.
Prob. 29. An ellipsis, A C D B, being given, to find the transverse and conjugate axes.
Draw any two parallel lines, A B and C D, cut- ting the ellipsis at the points A, B, C, D ; bisect them in e and^ Through e and fy draw G H, cutting the ellipsis at G and H ; bisect G H at 1 5 and it will give the centre.
Upon I, with any radius, describe a circle, cut^ ting the ellipsis in the four points /^, /, ???, n /join ky /, and w, n ; bisect k /, or m 7Z, at 0 or p. Through the points 0, 1, or I, ^, draw Q R, cut- ting the ellipsis at Q and R ; then Q R will be the transverse axis. Through I draw T S, parallel to k /, cutting the ellipsis at T and S ; and T S will be the conjugate axis.
Prob, 30. To describe an ellipsis similar to a given one A D B C, to any given length I K, or to a given width M L.
Let A B and C D be the two axes of the given ellipsis. Through the points of contact A,D, B, C, complete the rectangle G E H F ; draw the dia- gonals E F and G H : they will pass through the centre at R. Through I and K draw P N and O Q parallel to C D, cutting the diagonals E F and GH, at P, N, Q, O. Join PO and N Q, cutting CD at L and M ; then I K is the trans-. vei'sCj and M L the conjugate axis of an ellipsis, p B 2
^7^ GEOMETRY.
that will be similar to the given ellipsis A D B C, which may be described by some of the foregoing methods.
Proh. 31. To describe a parabola. If a thread equal in length to B C, be fixed at C, the end of a square ABC, and the other end be fixed at F; and if the side A B of the square be moved along the line A D ; and if the point E be always kept close to the edge B C of the square, keeping the string tight, the point or pin E will describe a curve E G I H, called a 'parabola.
The Jbcus of the parabola is the fixed point F, about which the string revolves.
The directrix is the line A D, which the side of the square moves along.
The axis is the line L K, drawn through the focus F, perpendicular to the directrix.
The vertex is the point I, where the line L K cuts the curve.
The latus rectum^ or 'parameter, is the line G H passing through the focus F, at right-angles to the axis I K, and terminated by the curve.
The diameter is any line M N, drawn parallel to the axis I K.
A double ordinate is a right line R S, drawn pa- rallel to a tangent at M, the extreme of the dia- meter M N, terminated by the curve.
The abscissa is that part of a diameter contained between the curve and its ordinate, as M N.
Prob. 32. To describe a 'parabola, by finding points in the curve ; th,e axis A B, or any diameter being given, and a double ordinate C D.
Through A draw E F parallel to C D ; through C and D draw D F and C E parallel to A B, cut- ting E F at E and F. Divide B C and B D, eacli into any number of equal parts, as four j likewise
GEOMETRY. S'^S
divide CE and DF into the same number of equal parts. Through the points 1, 2, 3, &;c. in CD, draw the Unes 1 a,Q b,o c, kc. parallel to AB; also througli the points 1, 2, 3, in C E and D F, draw the lines 1 A, 2 A, 3 A, cutting the parallel lines at the points <2, bj c; then the points a, b, c, are in the curve of the parabola.
P?^ob. 33. To describe an hyperbola.
If B and C are two fixed points, and a rule A B be made moveable about the point B, a string ADC being tied to the other end of the ruler, and to the point C ; and if the point A be moved round the centre B, towards G, the angle D of the string ADC, by keeping it always tight and close to the edge of the rule A B, will describe a curve D H G, called an hyperbola.
If the end of the ruler at B were made moveable about the point C, the string being tied from the end of the ruler A to B, and a curve being de- scribed after the same manner, is called an oppo- site hyperbola.
The foci are the two points B and C, about which the ruler and string revolves.
The transverse axis is the line IH, terminated by the two curves passing through the foci, if con- tinued.
The centre is the point M, in the middle of the transverse axis I H.
The conjugate axis is the line N O, passing through the centre M, and terminated by a circle from H, whose radius is M C, at N and O.
A diameter is any line V W, drawn through the centre M, and terminated by the opposite curves.
A conjugate diameter to another, is a line drawn through the centre, parallel to a tangent with
B B 3
374 PERSPECTIVE.
either of the curves, at the extreme of the other diameter terminated by the curves.
Abscissa is when any diameter is continued within the curve, terminated by a double ordinate and the curve ; then the part within is called the abscissa.
Double ordinate is a line drawn through any dia- meter parallel to its conjugate, and terminated by the curve.
Parameter^ or latus rectum, is a line drawn through the focus, perpendicular to the transverse axis, and terminated by the curve.
Prob. 34. To describe an hyperbola by finding points in the curve, having the diameter or axis A B, its abscissa B G, and double ordinate D C.
Through G draw E F, parallel to C D ; from C and D draw C E and D F, parallel to B G, cut- ting E F in E and F. Divide C B and B D, each into any number of equal parts, as four ; through the points of division, 1, 2, 3, draw lines to A. Likewise divide E C and D F into the same num- ber of equal parts, viz. four ; from the divisions on C E and D F, draw lines to G ; a curve being drawn through the intersections at G, a, Z>, &c. will be the hyperbola required.
PERSPECTIVE.
Perspective is the art of drawing upon a plane surface the outlines of objects, so as to give the same representations to the eye that the objects themselves do in nature.
This art is of the utmost importance in drawing, ^nd its study cannot be dispensed with by those
PERSPECTIVE. 375
who wish to make any proficiency in this art. Some knowledge of it ought to be acquired, previous to the study of every branch of drawing, whether that of the figure, landscape, flowers, &c.; for though its utility may not appear equally evi- dent in all these, yet there are many cases in each, where it is of indispensable necessity ; and an ac- quaintance with it will save the student the trouble of much wrong thinking, and will enable him to avoid many errors which he otherwise must neces- sarily fall into.
It is true, that many people learn to draw without studying perspective, and too many of those whose profession it is to teach this useful branch of edu- cation, do not sufiiciently recommend to their pupils to learn the principles of this science. The reason of this it is not difficult to point out. The study of perspective, like that of geometry, has in itself but few charms, and it is only by being well convinced, that without it we can never hope to arrive at excellence, and by experiencing how much it accelerates and assists us in our practice of drawing, that we can with patience and resolu- tion go through studies that certainly appear to most people dry and unentertaining. Unfortu- nately, from this circumstance, and from the ab- struse and obscure manner in which it is treated off by the generality of writers on the subject, few will take the trouble of making themselves ac- quainted with a science so necessary.
But though the understanding perspective thoroughly^ certainly does require considerable geometrical knowledge, added to great patience and persevering investigation, yet so much as would enable those who draw to avoid making any very
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376 PERSPECTIVE.
glaring blunders, and render their study of drawing much more pleasant and easy, is so far from being difficult, that it is astonishing any one should hesi- tate a moment about acquiring it.
Some part of the blame may, however, be fairly laid to the want of a treatise on perspective, of an easy and popular kind, such as might suit those who have had no opportunities of acquiring a knowledge of geometr3\ It would be in vain to endeavour to supply this deficiency properly in a work of so limited a nature, and which embraces so many subjects as the present; yet though our /, plan will not permit us to treat of it so fully as it deserves, we shall lay down, as concisely as pos- sible, a few of its principal rules, the understand- ing of which will be found useful to beginners in the art of draw ing.
Exjjlanatio}! of the piincipal Terms used in Perspective.
The perspective plane is the surface of the pic- ture itselfi which may be imagined to be a plane of glass placed upright between the spectator and the objects to be drawn. Then, if lines or rays be supposed to come from every part of the objects to the spectator's eye, when viewing them through the glass, they would cut the plane in certain points ; and if these points were connected by lines, they would give the perspective represent- ation. It is upon this simple idea that all the rules of perspective are founded : they are so many methods of finding out the above-mentioned points ; and when the light, shadow, and colour, are added, the whole constitutes a picture exactly resembling the original.
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PERSrECTIVE. 377
Visual raifs are the rays of light which come from the different parts of the objects to our eyes.
Point of sight is the spectator's eye. This has been erroneously confounded with the centime of the picture, as will be seen afterw^ards.
What is called an original line, is any line in Nature, or in the objects themselves, which are to be drawn in perspective.
An original plane is any surface or plane of the objects to be represented.
If we suppose a line to proceed from the eye, parallel to any line in the objects we are viewing, and to continue till it arrive at the picture or perspective plane, the point where it would touch the plane is called the vanishing jJoint of the line.
All lines that are in Nature parallel to each other have the same vanishing points. The reason of this will be easily seen, if the reader considers the method of finding the vanishing point of an original line just mentioned; for the same line which would find the vanishing point of one, will do for them all, and form only one point.
If we could suppose a plane or surface to pro- ceed from the eye of the spectator, in a direction parallel to any side of an object which we view through the plane of glass, and if it continue till it arrive at the glass, the line which it would form by contact with the glass, is called a vanishing line ; and it is the vanishing line of the side of the object which the supposed plane was parallel to.
In every p)icture or perspective plane, there is a point, where a line drawn from the eye perpen- dicular to the picture, would touch it ; this point is called the centre of the picture, and is the same which is often called in old books on perspective, the jioii'i'l of sight. But this is a wrong term tor it;
.37(^ PERSPECTIVE.
the |)oint of sight, strictly speaking, being in tlie sj)ectator's eye, and consequently, not any point in tlie picture. Although, from its name, we should expect to find it always in the middle of the repre- sentation, yet this is by no m.eans the case, for sometimes it is near one of the sides, particularly in what is called parallel perspective ; though gene- i-ally in obhque perspective, it is in the middle of the picture. And here it should be observed, that, strictly and properly, it should always be in the middle of the picture, when circumstances of con- venience will admit of it ; for it is that point which the spectator is supposed to look full against, or which is exactly opposite to his eye when he views a picture, and surely the best way to see a picture, is to look directly against the middle of it. How- ever, in many kinds of perspective drawings, it is not convenient, on account of room, to have this point in the middle, as may easily be imagined by considering Plate 6. Fig. 1., where G is the centre of the picture.
It will be easily conceived, from the description of vanishing points, and the centre of the picture, that this last must be the vanishing point of all lines that are in Nature perpendicular to the picture.
If a plane be supposed to proceed from the eye, as before, parallel to the floor or level ground till it arrives at the picture, the line where it meets it is called the vanishing line of the horizon, or hori- zontal line. This line is of great importance in perspective : the centre of the picture is always somewhere in this line. Its height is necessarily regulated by the height of the eye from the ground ; in landscapes, and views of places, it is generally kept one-third of the height of the pic- ture froin the bottom, though thib yv\\^ i.s not
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always adiiered to ; for when we stand upon high ground, the horizontal hne rises in proportion. Suppose the view to be taken on level ground, the head of a man represented standing on the ground, would come to this line, and that whether the man be near or far off; that is, wherever his feet are, his head must always come to the horizontal line, if he be standing upright on the ground.
Distance of the picture means the supposed dis- tance of the eye from the centre of the perspective plane or picture.
This distance may be chosen at pleasure ; but a judicious choice of it is very important, for the variation of this distance affects every perspective representation, so as to render them either pleasing or distorted. Long distances, in general, give the best representation ; but they are not always con- venient, or to be attained. Experience alone can direct a proper medium.
Parallel pei^spective is where the picture is sup- posed to be so situated, as to be parallel to the side of the principal object in the picture, as a building, for instance. Then the lines on those sides of the building that are parallel to each other continue parallel on the picture, and do not vanish into any point ; while the lines at right angles to the former vanish into the centre of the picture. This will be exemplified in Plate 6. Fig. 1.
The picture being supposed to stand parallel to the side of the house A B C D, the lines A B, DC, which in Nature are parallel to each other, must be made parallel in the perspective representation. But the lines BE, CF, which in Nature are at right angles to A B, and D C, and, consequently, also to the picture, tend towards a point ; and this
380 PERSPECTIVE.
point G, lowiirds which they tend, is the centre of tlie picture.
Oblique persjJective is when the plane of the pic- ture is supposed to stand oblique to the sides of the objects represented ; in which case the repre- sentations of the Hues upon those sides will not be parallel among tliemselves, but will tend towards their vanishing point. This kind of perspective is show^n in Plate 7* Fig. 1.
A hird^s-eye view is a view supposed to be taken in the air, looking down upon the object; and differs from the usual way of drawing perspective views, only in supposing the horizontal line to be raised much higher.
When an object is to be drawn in perspective, all its parts must be measured, so that we may be able to lay them down from a scale of equal parts. Having determined whether it is to be parallel or oblique perspective, the first thing to be drawai is the horizontal line, which is to be put parallel to the bottom of the drawing, and as high above it as the height of a man's head, as H G, Plate 6. Fig. 1., which is five feet six inches above the bot- tom of the house. Next determine on the centre of the picture G, which must be placed so as to leave convenient room for the representation. Fix on C the nearest corner of the object, and draw the perpendicular C B : lay off C D equal to the length of the building, and draw D A and A B. From C, tlie nearest corner, draw C G, to the centre of the picture. C G now contains the line which repre- sents the bottom of the end of the house ; but this is an indefinite representation, of which we do not yet know the exact length. The method of deter- mining this is as follows : Continue the lineDCtoI,
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and make C I equal to the width of the house. From G, the centre of the picture, lay off G K equal to the distance of the picture, the choosing of which must be regulated by taste. Draw I K, cutting C G in F ; then is C F the exact width of tlie house in perspective, which was equal to C I. To find the middle of this end of the house, you cannot divide it by your compasses, because the farthest half will appear less than the nearer ; but if you divide C I into two equal parts in L, and draw L K, it will cut C F into two equal parts per- spectively. Or it may be found more simply thus : Ilaving drawn the lines B E and C F to the centre of the picture, draw the diagonals E C, B F cross- ing each other in M, and raise the perpendicular M N, which is in the middle of the gable-end.
To find the height of the gable, lay its actual height above B E, upon the corner line B C con- tinued, as B O, and draw O G ; this crossing the perpendicular M N, gives N the point of the gable. The top of the chimney must be drawn in the same manner, by laying its real height, taken from a scale on OP, and drawing P G, lay off L m and L72, each equal to half the width, and draw from these points to the distance point k ; this will cut the bottom of the house C F, in the points o andp ; from these draw perpendiculars, which will give the perspective width of the chimney. To obtain its thickness, lay off P Q equal to its thickness, and draw Q (t ; then drawing from a the line a b, you obtain the exact width of the chimney. From b draw b c, and from d draw d c. The other end of the gable may be drawn by two different methods. The first is by supposing the front of the house transparent, and drawing the other end as if seen through it, in the same manner as the end we have
382 PERSPECTIVE.
described, by laying its width from D to R, and drawing to the distance-point K. By raising the perpendicular in the middle, you will meet the ridge-line from the other gable in d. The other method is as follows : Through the centre of the picture G draw the line S T, upwards, and down- wards, and perpendicular to the horizontal line. Then continue the line of the roof B d till it meet S T in S. From A draw A S, which will give the other gable, and S will be the vanishing point for all hues parallel to B rf and Ad; if N E be conti- nued in like manner, it will give T for its vanish- ing point. The doors and windows on the side A B C D are laid down from a scale, because that side, being parallel to the picture, does not vary from its geometrical delineation, except shewing the thickness of the reveals, or edges of the doors and windows. If there had been any windows in the side B E F C, they would be drawn in perspec- tive by the same method that was used for finding the width of the house and the middle of the end ; viz. by laying off the actual dimensions from C upon CI, and drawing from these points to the distance- point K, which would transfer these divisions to the bottom of the house CF, and then perpendicu- lars might be drawn upwards.
This practice is farther explained by the follow- ing rule.
To divide a line in perspective which is parallel to the horizon, and which tends to a vanishing- point, into any number of equal parts; or to divide it in any required proportion.
Let A B be the line going to its vanishing-point C (Fig 2.); and first let it be required to divide that line into six equal parts. Let C D be the hori- zontal line, and AE the ground-line drawn parallel
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PERSPECTIVE. 388
to it. Lay ofF, at pleasure, CD for the distance of the picture, if C be the centre of the picture. Draw a line from D, touching the end B of the line to be divided: draw DBE, cutting the ground- line in £. Then AE represents the actual dimen- sions of the line AB, wliich is seen in perspective. (Here it may be observed, that this gives a rule also for finding the real length of any line which tends to a vanishing-point.) Divide AE into the same number of equal parts into which you pro- posed to divide the given line AB; as Al, 12, 23, &c. Then from these different divisions draw lines to D, cutting the line AB in «, Z>, c, dy &c., which will represent the required number of equal parts, but diminishing in size as they are farther removed from the eye. If it be wished to divide the line AB into any number of unequal parts, or to lay off doors, windows, &c. upon it, the line AE, found as before, must be divided in the required proportion ; and lines drawn from those to D will give the re- quired divisions on AB, from which perpendiculars may be drawn for the doors, windows, he.
To draw a circle in perspective.
The perspective representation of every circle is a regular ellipsis, when the eye is without the circle, which may be demonstrated, by considering that the rays from the circumference of the circle to the eyCj form an oblique cone. But it is well known to those who are acquainted with conic sec- tions, that every section of a cone, whether right or oblique is a true ellipsis, except in one case only, which is, when the section is taken sub-contrary to its base, a situation which happens so rarely in drawings, that it may be disregarded altogether, and the section of a cone, or the perspective of a circle, in all cases considered as a perfect ellipsis.
rERSPECTIVE.
The most correct and easy method of drawing an ellipsis is to find the transverse and conjugate axes, and then to complete the curve by a trammel, or by hand. But as it is very difficult to find the transverse and conjugate axes of the ellipses which are the perspective representations of circles, re- course is generally had to anotlier method of obtaining the curve. The circle is circumscribed by a square, as K L M N, in Fig. 3., and the dia- gonals and the lines across the centre, and paral- lel to the sides, are drawn; also the lines, c/, cdy are drawn parallel to the sides, through the points v;here the circle is cut by tlie diagonals. This square, with all these lines drawn across it, is now put in perspective as follows : Draw A B for the horizontal line, and fix B for the centre of the picture, and A B for the distance of the picture. Make D C equal to the width of the square, and draw C B, DB ; draw C A to the distance-point A, cutting ofFDG equal to the depth of the square; then draw G F, parallel to D C, which completes the perspective of the square ; also draw the diago- nal DF. Take now the distances M^/, cN; and transfer them to D .z-, o C ; from these points x and 0 draw lines to the vanishing point B, cutting the diagonals of the square. The points in this reticu- lated square in perspective, which correspond to those in the square KLMN, where the circle passes through, must now be observed, and a curve traced through them with a steady hand : it will be the perspective required. Even in this process, it is of considerable use to know that the curve you are tracing is a regular ellipsis ; for though you can- not easily ascertain the axes exactly, yet you may ^ery nearly ; and the eye very soon discovers whether the curve which has been drawn, be that of a regular elhpsis or not.
PERSPECTIVE. 3S5
Upon the same principle the row of arches (Fig. 4.) is drawn. The width of the arches and piers is obtained in the same manner as Avas shown in Fig. 2. ; viz. by laying their dimensions upon the ground-line A B, and drawing lines to the dis- tance-point. The curves of the arches are then found, by drawing the lines which correspond to those in half the square, Fig. 3., in the same man- ner as described above for the circle.
Fig. 5. shows the appearance of circles drawn upon a cylinder, when H I is the horizontal line. The circle drawn on the cylinder at that place is seen exactly edgeways, and appears only as a straight line; that next above it is seen a little under- neath; the next still more; and so on, as they rise higher, appearing like so many ellipses of the same transverse diameter, but whose conjugate diameters continually increase in length as they rise above the horizontal line. On the contrary, you see the under sides of the circles drawn below the horizontal lines; but they observe the same law, being so many ellipses whose conjugate dia- meters vary in the same proportion. A little re- flection on this simple example will enable those who draw to avoid many ridiculous mistakes which are sometimes committed, such as showing the two ends of a cask, or the top and bottom of a cylinder, at the same time.
PI. 7. Fig. 1. shows the method of drawing a building, or other object, in oblique perspective. A B is the horizontal line, and C D the ground-line parallel to it as before. Here neither of the sides of the house is parallel to the picture, but each goes to its respective vanishing point. Having fixed on the nearest corner E, draw EB, at plea- sure, for one side, and choose any point F for the
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386
PERSPECTIVE.
centre of the picture; tlieii, to find the other side, lay off' F G equal to the distance of tlie picture, which, as before, depends upon taste only; draw B G and G A perpendicidar to B G, cutting the horizontal line in A, the other vanishing point. Draw now E A for the other side. To cut off" the several widths of the two sides of the house, which as yet are only drawn to an indefinite extent, two distance-points must be laid down, viz. one for each vanishing point. To do this, extend the compass from B to G, and lay the distance taken in it fiom B to H, which will give H for the distance-point of B, and which is to cut off all the divisions on the side E B. Also extend the compasses fi'om A G,. .^nd lay down A I. I is the distance-point of A, and is used for transferring all divisions upon the side E A, from the ground-line C E, These points^ and lines being adjusted, the process is not much different from parallel perspective ; only here, equal divisions on each side of the building, as doors, win- dows, diminish as they recede, in the same way as on the side B E F C, PI. 6. Fig. 1. Take the real length of the side E L, from the same scale used for laying down the horizontal line, and lay it down on the ground-line from E to C, and draw^ C I, cutting off E L for the perspective length of the building. For the other side of the house, lay its widtli down in the same manner, from E to D, and draw D H, cutting off E N for the perspective width. Raise the perpendiculars EM, L K, and N O, for the three angles of the house. Lay the height of the building upon the corner that comes to the ground- line, as E M, and draw MK and M O to their several vanishing points. Also lay all the heights of the doors and windows, and other divisons, upon E M, and draw them to the vanishing points A and B.
PERSPECTIVE. 387
To lay down the widths of the doors and windows, put their actual widths upon C E, and draw from them to the distance-point I, which cuts off all divisions upon the side L E, and then raise the per- pendiculars. The gable-end is found exactly in the same manner as was described in PI. 6. only taking care to use the proper distance-point H. The manner of finding the width of the chimney is different. Lay off b a for the height of the chimney above the top of the gable, and draw a c parallel to the horizontal line ; then put a c equal to the actual thickness of the chimney, and draw a d to the vanishing point A ; draw also c d to the distance- point I, cutting oW admd : then having drawn ef from the nearest corner of the chimney, which was found as in PI. 6. Fig. 1. Draw df to the vanishing point B, cutting o^ efi'oi' the exact per- spective width.
Fig. 2. represents the method of finding the per- spective of a circle in oblique perspective. A B is the horizontal line, C the centre of the picture, and D, E, the distance-points. The process is exactly the same as that just described, the several divi- sions of the reticulated square in PI. 6. Fig. 3. being laid upon the ground-line FG, and from these lines are drawn to the distance-points. The per- spective of the square is then drawn with all the lines across it, and the curve traced through the different points.
By drawing these examples frequently over, to large scale, and reflecting upon them with atten- tion, the student will become familiar with their use J and as they include the cases which most fre- quently occur, he will find great benefit from the knowledge of them.
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38S-
Dtaumg the Figure.
The study of the human figure has always been considered by artists as the most important part of the art. It is the most difficult, and is by many considered as contributing the most of any to general improvement ; though there are some who carry this idea to too great an extent, saying, tliat a person who can draw the human figure well can draw every thing besides. But this, it is well known, is not the case ; there being many artists who can draw the figure very well who cannot draw landscape nor architecture. To draw any thing well requires a particular study. The study of the figure, however, includes all the finest prin- ciples of the art ; and when the eye of the student has been accustomed to copy faithfidly all the mi- nute circumstances which constitute the character ©f a figure, and to attend to the innumerable beau- ties and graceful forms which it presents, he will be better qualified to pursue with advantage every other branch of the fine arts.
In learning to draw the human figure, it is ne- cessary to begin with eacli of the parts separately, and after sufficient practice in that way, to proceed to put them together in the complete figure.
The head being the most important part of the human body, it should be studied first. For this purpose, the student should copy the best drawings he can procure of the eye^ mouthy nose, and ear, separately and on a large scale j and of these, a front view, profile or side view, oblique view, &c.
The best materials for drawing these, as well as all other parts of the figure, is black chalk, or black lead ; the former may be used either upon white
DRAWING THE FIGURE. 389
paper, or upon middle-tint paper ; and in that case, white chalk may be used for laying on the lights. Black lead is only used upon white paper. A piece of soft charcoal may be made use of for first slightly sketching in the general form, which must afterwards be gone over and corrected with the black chalk. The false lines of the black lead may be removed by the Indian rubber ; but we would recommend to be as sparing as possible of this, as it is more improving to endeavour to draw every thing correct and decided at once, and not trust to the being able to erase the lines which are wrong.
The shadows may be laid on by drawing parallel curve lines, according to the situation of the part, crossing them occasionally, and softening them in with more delicate lines, where necessar}^
All the parts of a human figure are composed of curved surfaces : no straight lines are ever admis- sible ; but every line should have a graceful turn ; and it is this circumstance particularly that occa- sions the study of the figure to give so much freedom in drawing.
Care should be taken, that no lines ever cross each other at right angles, which gives a disagree- able net-like appearance ; neither should the cross- ings be too oblique, as then they are confused : a proper medium will be acquired by the study of good drawings or prints j in general, however, crossing should be avoided as much as possible.
Sometimes the shadows are rubbed in, or their edges are softened with a stump, which is a very expeditious way, and produces a fine effect ; but it should be used with discretion, as it is better to execute the shadows in a clear and regular manner by soft lines.
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390 DRAWING THE FIGURE.
Care should be taken not to make the hnes harsh and hard, Hke those of an engraving; they should be softer and more mellow. On this account, draxvings are much better to learn from than prints ; as, by copying the latter, the student is very apt to acquire a dry and hard manner.
But we particularly caution him to avoid copy- ing with a pen all the lines in engravings used for the shadows, which some, who have not been ac- customed to see good drawings, are apt to do.
Many productions of this kind have been exe- cuted with an immensity of labour, and have been thought very fine by those who had but little knowledge of the art ; yet artists, and those who are good judges, always lament to see so much patience and labour misapplied.
In copper-plate engravings, shadows are gene- rally produced by lines : but this arises from the nature of the process ; and in drawing, which is of a very different nature, there is not the same ne- cessity for them. In general it should be ob- served, that the less labour there appears in any drawing the better ; and that though every possi- ble pains should be taken to make drawings or paintings excellent, yet this labour should be al- ways disguised as much as possible, and the whole should appear as if executed with the greatest ease.
*' In learning to draw, it is of more importance than is generally supposed, to copy from the finest works only. The most prejudicial quality of a model is mediocrity. The bad strike and dis- gust ; but those that are not good, nor absolutely bad, deceive us by offering a dangerous facility. It is for this reason that engraving contributes to the progress of the arts, when it is employed on subjects that are judiciously chosen ; but is too
DRAWING THE FIGURE. 391
often preJLidiciul, by the iiidiiieient works it multi- plies without number. But let Raphael be copied by skilful engravers, let a young artist profit by his labours, and works without dignity and ex- pression will soon become intolerable to him ; he will perceive to wiiat an elevation tlie excellence of the art can raise him.
<' The way to avoid mediocrity, is by the study and imitation of beautiful productions ; or, in want of them, of the most finished translations that have been made from them ; for so we may call beautiful prints. Let a young draughtsman study the heads of Raphael, and he will not see without disgust the soi'did figures of indifferent painters. But if you feed him with insipid substances, he will soon lose the taste necessary to relish great excellencies. In the one case he will advance firmly in his career : in the other he will conti- nually totter, and even not be sensible of his own weakness."
Having copied frequently the parts of a face, he is next to proceed to the entire head ; drawing first a front view, then a profile, a three-quarter, and so on ; varying it in every possible direction, till he is thoroughly acquainted with the appear- ance of all the principal lines in every situation. In making these studies, he should be contented at first with drawing mere otitlhies, as they are by far of the most importance ; and it should be remem- bered in general, that to make a good outline is always the most desirable attainment.
The student should now accompany his lessons by making observations on good casts and living models; but more particularly the former, as indi- vidual nature is seldom fine, and there is danger of
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392 DRAWING THE FIGURE.
copying what is bad, and acquiring false ideas of beauty.
By these exercises he will have acquired some facility in handhng his pencil, and he will be thus prepared for the study of the whole figure. But before he can proceed to this with advantage, we would recommend to him the study of anatomy.
An artist who is not acquainted with the form and construction of the several bones which sup- port and govern the human frame, and does not know in what manner the muscles moving those bones are fixed to them, can make nothing of what appears of them through the integuments with which they are covered ; and which appear- ance is, however, the noblest object of the pencil. It is impossible for an artist to copy faithfully what he sees, unless he thoroughly understands it. Let him employ ever so much time and study in the attempt, it cannot but be attended with many and great mistakes ; just as it must happen to a man who undertakes to copy something in a lan- guage which he does not understand, or to trans- late into his own what has been written in another, on a subject with which he is not acquainted.
But it is not necessary for him to study anatomy as a surgeon, nor to make himself acquainted with all the nerves, veins, &c. It is sufficient to study the skeleton, and the muscles which cover them, and of these, he should most particularly make himself familiar with those muscles which most frequently appear and come into action.
For this purpose, he should procure plaster casts of the anatomy of the human body, and consult treatises written upon the subject; and if he have
19
DRAWING THE FIGURE. 303
opportunity, it will be proper afterwards to attend discussions and lectures on anatomy.
He should also use every possible opportunity of making; observations on the actions of the muscles in nature.
Being thus thoroughly prepared, he will be en- abled to draw the human figure with great advan- tage, and he will make a more rapid progress than he could have done without these previous studies.
Symmetry y or proportion^ will be best learned by copying after the antique statues, of which plaster casts may be easily procured. Nature, whicli in the formation of every species seems to have aimed at the last degree of perfection, does not appear to have been equally solicitous in the production of individuals. Parts of individuals are frequently as beautiful as possible, but a complete whole is never to be met with.
The practice of the ancient Greek statuaries was to select from various individuals tlie most beautiful parts, and by combining them to pro- duce figures more perfectly beautiful than nature ever presented.
Till the student has thus imbibed a proper I'elish for beautiful proportions, and been well grounded in their principles, he should not proceed to draw from living models.
In drawing from plaster casts, a good deal de- pends upon choosing a proper view, and placing the model properly with regard to the light, which should always come in obliquely from above, as it generally does in the daytime. If a candle be used, it should be so high as to cast the light downwards upon the model. The light should only come from one part, as cross lights will distract and spoil the shadows.
o94 DRAWING THE FIGURE.
After the student has with indefatigable labour and persevering zeal gone through all these studies, and acquired a facility of drawing the human figure in every possible situation, and under every variety of form and circumstance, a great deal remains for him still to do, before he can be considered as an artist. He has as yet conquered only the mechani- cal difficulties; but his mind must be cultivated, and he has all the higher and more refined parts of his art to study.
It is the business and duty of the naturalist and historian to draw objects as they find them, and represent them with all those imperfections and blemishes to which, as individuals, they are sub- ject. But an ideal painter, and such alone is a true painter, resembles tlie poet; his creative fancy soars above common nature, and he represents objects endued with all that perfection which belongs to the species, but which is rarely found in the individual.
A good choice of subjects for the exercise of his pencil is now to be considered. For this purpose, he should enrich his mind wdtli a great variety of knowledge : historians and poets should be his con- stant companions ; and he should make himself acquainted with the customs and manners of an- cient as well as modern nations.
His invention should, now be continually exer- cised, and free scope should be given to the wildest sallies of his imagination, which, however, should never exceed the bounds of probability.
*' It is indisputably evident," says Sir J. Rey- nolds, " that a great part of every man's life must be employed in collecting materials for the exer- cise of genius. Invention, strictly speaking, is little more than a new combination of those images
DRAWING THE FIGURE. 395
which have been previously gathered and deposited in the memory. Nothing can come of nothing ; he who has laid up no materials, can produce no combination.
" He should study the works of former artists, learn what subjects they have painted, and liow they have treated them. A student unacquainted with the attempts of former adventurers, is always apt to over-rate his own abilities, to mistake the most trifling excursions for discoveries of moment, and every coast new to him, for a newly-discovered country.
" On whom, however, can he rely, or wlio shall show him the path that leads to excellence ? The answer is obvious : those great masters who have travelled the same road with success are the most likely to conduct others. The works of those who have stood the test of ages, have a claim to that respect and veneration to which no modern can pretend. The duration and stability of their fame is sufficient to evince that it has not been sus- pended upon the slender thread of fashion and caprice, but bound to the human heart by every tie of sympathetic approbation.
*' But though these masters should be studied, they should not be servilely followed. The stu- dent, instead of treading in their footsteps, should only keep the same road. He should endeavour to invent on their principles and way of thinking j he should possess himself with their spirit ; he should consider how they would treat his subject, and should work himself into a belief that they are to see and criticise his picture when completed. Every attempt of this kind will rouse his powers."
Whenever a story is related, every man forms a picture in his mind of the action and the expression
396 DRAWING THE FIGURE.
of the persons employed. The power of repre- senting this mental picture on canvass is what we call invention in a painter.
In the conception of this ideal picture, all the little circumstances should be contrived in such a manner, that they shall strike the sp^ectator no more than they did himself in his conception of the story. Thus there must be a principal object, which should receive the principal mass of light ; and though a second and third group may be added, and a second and third m^ass of light, yet they should be all kept so subordinate^ that they do not come in competition with the principal.
In the design or composition of a picture, sini' plicity is of the first importance. The story should be distinctly told, and nothing should be introduced but what is absolutely necessary.
Among the most difficult and important of the higher branches of the art, is the expressions of the passions.
It is not enough for a painter to delineate the most exquisite forms, give them the most graceful attitudes, and compose them well together ; he must express by their actions and countenances the state of their minds ; they must appear to feel and to think.
Many have written, and among the rest the famous Le Brun, on the various changes that, according to various passions, happen in the muscles of the face. They observe, for example, that in fits of anger, the face reddens, the muscles of the lips puff out, the eyes sparkle ; and that, on the contrary, in fits of melancholy, the eyes grow mo- tionless and dead, the face pale, and the lips sink in. It may be of service to a painter to read them
DRAWING THE FIGURE. 397
and such other remarks ; but it will be of infinitely more service to study them in nature itself, from which they have been borrowed, and who exhibits them in that lively manner which neither tongue nor pen can express.
The colouring must be regulated by the same general principles as the composition. Gaudiness and glare ought to be studiously avoided, and a quietness and simplicity should reign through the whole work. In landscapes, distinct and unbroken colours, such as green, red, &c. are seldom or ever admissible ; the tints should be always varied and broken. But in historical subjects frequently, dis- tinct colours are employed, but they must be placed with respect to each other, so that the effect of the whole be hajmonious.
The art of disposing the drapery makes a very considerable part of the painter's study. To make it merely natural is a mechanical operation, to which neither genius nor taste are required; whereas,, it requires the nicest judgment to dispose the dra- pery, so that the folds have an easy communication^ and gracefully follow each other with such natural negligence, as to look like the effect of chance, and at the same time show the figure under it to the utmost advantage.
In the higher style of painting, the difference in the materials of which the drapery is composed,, that is, whether it is silk, linen, woollen, &c. is never remarked ; it is simply drapery, and nothing more.
We have now tre ated, as fully as our limits will permit, of the various excellencies necessary to be acquired by an artist. It will be easily perceived, that to accomplish all these objects is by no means an easy task.
S9S I>RAWING THE FIGURE.
In some, an inclination to pursue the arts appears at a very early period of life, and it is often difficult to ascertain the circumstance which gave that particular impulse to the mind ; though there must always be some accidental circumstance, not depending upon ourselves, that creates in us that desire.
When a boy is possessed of good talents, and has so strong a passion for the arts, that scarcely any thing can restrain him, there can be little fear of his doing well, if suffered to follow the bent of his inclination ; but without this, nothing should induce him to engage in a profession of so arduous a nature, and which requires such unwearied appli- cation. He may learn to draw the correct outlines of buildings, and other regular objects, by the rules of perspective ; but the forming fine pictures, so as to affect the mind, is an art not reducible to rule 5 and though much may be taught, yet much more will ever depend upon the mind of the artist. Here it is that the existence of a quality which distin- guishes one man from another is so obvious. This has been denominated by various appellations,, none of which are capable of being correctly de- fined. It has been called genius^ tastCy souly mind, and a variety of other teims, all of which are inde- finite, and prove that we know but little of our own nature.
It will be foreign to our purpose to enter into any discussion on this subject; but we shall add a pas- sage relating to it from the lectures of the late Sir Joshua Reynolds : " There is one precept," he observes, *' in which I shall be opposed only by the vain, the ignorant, and the idle. I am not afraid that I shall repeat it too often. You must have no dependence on your cAvn genius. If you
DRAWIVG THE FIGURE. 399
have great talents industry will improve them : if you have moderate abilities, industry will supply their deficiency. Nothing is denied to well-directed labour; nothing is to be obtained without it. Not to enter into metaphysical discussions on the nature or essence of genius, I will venture to assert, that assiduity unabated by difficulties, and a disposition eagerly directed to the object of its pursuit, will produce effects similar to those which some call the result of natural pouters. Though a man can- not at all times, and in all places, paint or draw, yet the mind can prepare itself by laying in proper materials, at all times and in all places."
" I cannot help imagining that I see a promis- ing young painter, equally vigilant, whether at home or abroad, in the streets or in the fields. Every object that presents itself is to him a lesson. He regards all nature with a view to his profession, and combines her beauties, or corrects her defects. He examines the countenances of men under the influence of passion, and often catches the most pleasing hints from subjects of turbulence or de- formity. Even bad pictures themselves supply him with useful documents ; and, as Leonardo da Vinci has observed, he improves upon the fanciful images that are sometimes seen in the fire, or are accidently sketched upon a discoloured wall."
"The artist who has his mind thus filled with ideas, and his hand made expert by practice, works with ease and readiness; whilst he who would have you believe that he is waiting for the inspir- ations of genius, is in reality at a loss how to begin, and is at last delivered of his monsters with diffi- culty and pain."
" What then," exclaims Gesner, " must be the fate of those who do not join an inflexible labour
400 DRAWING LANDSCAPES.
fo an habitual meditation? Let the artist who despises or neglects these important means make no pretension to the recompense due to active and sensible minds. There is no reputation for him, to whom a taste for his art does not become his ruling passion ; to whom the hours he employs in its cultivation are not the most delicious of his life ; to whom the study of it does not constitute his real existence and his primary happiness ; to whom the society of artists is not, of all others, the most pleasing ; to him whose watchings, or dreams in the night, are not occupied with the ideas of his art ; who in the morning does not fly with fresli transport to liis painting-room. But, of all others, luihappy is he who descends to flatter the corrupt taste of the age in whicli he lives, w^ho delights himself with applauded trifles, who does not labour for true glory, and the admiration of posterity. Never will he be admired by it ; liis name will never be repeated ; his works will never fire tlie imagination, nor touch the hearts of those fortun- ate mortals who cherish the arts, who honour their favourites, and search after their works.'*
The Drawing of Landscapes.
Every one who wishes to learn to draw land- scapes should begin by the study of perspective. This will enable him not only to understand and draw all the parts of buildings which so frequently form a principal feature in views of places, but will also give him true ideas of the method of ex- pressing distances, the winding of roads, and a variety of particulars that are continually occurring.
Having made himself master of the principal difficulties in perspective, he should next copy
DRAWING LANDSCAPES. 401
some good drawings ; and here it is of great im- portance that what he copies first, shoidd be veinj excellent ; for it is an absurd notion, that indiffer- ent drawings will do to begin with, or to bring the hand in, as it is termed j but, it has been justly ob- served, the most likely effect these can produce will be to put the hand out.
In choosing drawings to copy for beginners, particular attention should be paid to select those where the outlines or forms of the objects are dis- tinctly and correctly drawn, and not those in which a ^ood effect only has been principally aimed at. The first thing to be studied, is to be able to express with the black-lead pencil, decidedly and truly, the forms of all sorts of objects ; and till this is attained, no attempt should be made at finished drawings or pictures.
Black-lead is the most useful material for draw- ing the outlines of landscapes, which are best executed with this alone, and should not be gone over afterwards by the pen, which, except it be very judiciously managed, generally gives an ap- pearance of hardness.
Indian ink alone should be used for the shadows till the student has advanced very considerably ; nor till then should colours of any kind be used. Beginners are always desirous of producing pictures and making coloured drawings ; but nothing is more hurtful than the practising this too early. The first thing to be learned, is to draw forms correctly; next, the mode of shadowing objects truly ; then the ge- neral light and shadow of a drawing, and with this good composition. Ail this is best learned by using black lead, black chalk, white chalk, Indian ink, and these separately or combined, according
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402 DRAWING LANDSCAPES.
to the taste of the student ; avoiding colours till he has made considerable progress.
When colours are employed, they should be used with great caution and judgment. Nothing is so disgusting as to see coloured drawings wdiere the reds, greens, and blues, are laid on in the most violent manner, without any regard to harmony. Those who execute such vile daubings will say, in their defence, that nothing can be greener than grass, nor bluer than the sky ; but they should consider, that nature employs such a multitude of little shadows, and such a variety of different tints intermixed with her colours, that the harshness of the original colour is corrected, and the effect of the whole is very different from a raw and distinct colour laid upon white paper. Though we should have recourse to the study of nature, in preference to any master, for the study of colouring, yet it requires some judgment to know what part of nature is to be studied, and what is to be avoided ; for in nature herself, there are many parts which are bad ; and to copy them, would do more harm than good. The student in colouring may exa- mine, w^ith every possible attention, the colouring of old walls, broken and stained by time and the weatlier, old thatch, old tiles, rotten wood ; in short, all objects which are covered with moss, stains, and tints of various kinds ; there he v/ill find all that is most perfect and harmonious in colour- ing. Let him copy these with every possible care, and avoid as bad all new buildings, new railing, and objects which are of a uniform decided colour. This has been the practice of all the great masters who have excelled in this captivating part of the art. In short, after learning the first principles of
DRAWING LANDSCAPES. 40S
drawing, he cannot too soon have recourse to na- ture ; he will obtain from her the materials for ac- quiring every species of excellence, in a greater degree than from the works of- the first masters. The study of these, however, will greatly abridge his labour, and it should go hand in hand with drawing from nature.
The fewer colours that are used in a drawing, the better, as harmony is most easily preserved; and by the mixture of a few, every possible tint may be obtained.
It was mentioned, when treating on optics, that the sun's rays were considered by Sir Isaac Newton to be composed of seven primitive colours ; but all the vast variety of tints which we see in nature may be formed by the mixture of red, blue, and yellow, in various proportions. If we had pig- ments of these colours perfectly pure, w^e should have no occasion for more than these three ; but this is not the case, and therefore we are obliged to have recourse to materials of other broken tints. The colours that are found to be the most useful in drawing landscapes in water-colours, are, lakej indigo, Prussian-hhie, gamboge, light red, yelloxx) ochre, burnt terra Sienna, hnrnt timber, and Cologne earth. Some of the other colours may be occasion- ally useful, but these are all that are necessary for general use.
The best sort of water-colours are those mixed with gum and made up into cakes, as these may be used by rubbing upon a tile, in the same manner as Indian ink.
Mechanical Drawing.
We have given the name mechanical drawing to that sort of delineation which depends entirely
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404 COPYING DRAWINGS.
on geometrical rules, and which is executed by the use of the ruler and compasses : such as the draw- ing of plans, elevations and sections of buildings, machinery, &c. This species of drawing is of very extensive utility, and is of so easy acquirement that it may be learned by every person in the same manner as writing.
For this purpose the geometrical problems should first be carefully and neatly drawn, and the hand should be accustomed to the use of the compasses and drawing-pen. Then the architectural mould- ings should be studied, as they occur not only in buildings, but also in cabinet-work, machinery, and almost all kinds of implements.
In this kind of drawing the outlines of objects are laid down from actual measurement, by scales of equal parts; and the lines are drawn first with black lead pencil, and afterwards with ink, by means of the steel drawing-pen. The shadows also are added in Indian ink, and are drawn by rules that are established with mathematical precision.
OF THE MECHANICAL MEANS FOR COPYING DRAWINGS.
There are various methods by which those who are ignorant of the art of drawing may copy very accurately the outlines of pictures, prints, and drawings J and these methods are often useful to' those who can draw, and to engravers, when either great expedition or great accuracy is required; though none of them should ever be used by one who is learning to draw.
Tracing a gainst the Light.
Hold the drawing you wish to copy against one of the panes of the window j or have a pane of
COPYING DRAWINGS. 405
glass put in a frame, and fitted up like a music- stand, with a candle behind it. Lay your paper over your drawing, and you will see all the lines of the original distinctly through it, by which means you can easily trace them with a pen or black-lead pencil.
To make Tracing-Paper.
Mix together equal parts of oil of turpentine and drying-oil, and with a rag rub it evenly over some fan, or tissue paper, or any other very thin paper. Hang it by to dry for a day or two, and it will be fit for use. Lay this over the print or drawing you want to copy, and you will see eveiy line dis- tinctly through, so that you can go over them with the black-lead pencil. If you wish to do it in ink, you must mix a little ox's gall with the ink, to make the paper take it, which it would not other- wise do on account of the oil.
To make Camp-Paper,
Take some hard soap, mix it with lamp-black; make it into the consistence of a jelly with water; with this brush over one side of your paper, and let it dry. When you use it, put it between two sheets of clean paper, with its black side down- wards, and with a pin, or stick with a sharp point, draw or write what you please upon the clean paper; and where the tracer has touched, there will be an impression upon the lowermost sheet of paper, as if it had been written or drawn with a pen. It may be made of any colour, by mixing with the soap black-lead, vermillion, &c.
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4^ COPYING DRAWINGS.
Stenciling.
Lay the print or drawing you wish to have copied, over a sheet of paper, and with a pin or needle prick all the outline over with holes, through both the papers. Then take the clean paper with the holes made in it, and lay it upon the paper you wish to have the design transferred to, and dust it over with the powder of charcoal in a small muslin bag J the dust will penetrate through the holes, and leave a correct copy of the original upon the paper.
This pricked paper will do again for any number of copies. This is very useful for ladies who work flowers upon muslin.
TJie Method of Enlarging and Contracting by Sqiuires.
Divide the sides of your original with a pair of compasses into any number of equal parts, and rule lines across with a black-lead pencil from side to side, and from top to bottom. Then having your paper of the size you intend, divide it into the same number of squares, either laj-ger or less, as you would enlarge or contract it. Then placing your original before you, draw, square by square, the several parts, observing to make the part of the figure you are drawing fall in the same part of the squares in the copy, as it does in your original. To prevent mistakes, number the squares both of the original and copy. Tins method is much used by engravers.
To prevent the necessity of ruling across the original, which in some cases m^ay injure it, take a square pane of crown glass, and divide its sides, and
PAINTING TRANSPARENCIES. Wf
also its top and bottom into equal parts: then from each division draw lines across the glass with lamp- black ground with gum-water, and you will divide the glass into squares. Then lay the glass upon the original which you wish to copy, and having drawn the same number of squares upon your paper, pro- ceed to copy into each square on your paper what appears behind each corresponding square of the glass. Instead of a glass, an open frame with threads stretched across will answer the same purpose.
Tlie Pentagraph.
The Pentagraph is an instrument by means of which one may copy, enlarge, or reduce the out- lines of any picture, print, or drawing. They may be had at most mathematical instrument-makers, and are extremely useful for copying plans, maps, and other complicated figures.
PAINTING TRANSPARENCIES.
The effect of this kind of painting is very pleas- ing, if managed with judgment, particularly in fire and moon lights, where brilliancy of light and strength of shade are so very desirable.
The very great expence attending the purchase of stained glass, and the risk of keeping it secure from accident, almost precludes the use of it in ornamenting rooms ; but transparencies form a sub- stitute nearly equal, and at a very small expence.
The paper upon which you intend to paint
must be fixed in a straining-frame, in order that
you may be able to place it between you and the
light, when you see occasion in the progress of
D D 4
408 PAINTING TRANSPARENCIES.
your work. After tracing in your design, the colours must be laid on in the usual method of stained drawings. When the tints are got in, you must place your picture against the window, on a pane of glass framed for the purpose, and begin to strengthen the shadows with Indian ink, or with colours, according as the effect requires, laying the colours sometimes on both sides of the paper, to give greater force and depth of colour. The last touches for giving final strength to shadows and forms, are to be done with ivory-black, or lamp- black prepared with gum-water, as there is no pigment so opaque and capable of giving strength and decision.
When the picture is finished, and every part has got its depth of colour and brilliancy, being per- fectly dry, you touch very carefully with spirits of turpentine on both sides, those parts which are to be the brightest, such as the moon and fire, and those parts requiring less brightness, only on one side. Then lay on immediately with a pencil, a varnish made by dissolving one ounce of Canada balsam in an equal quantity of spirit of turpentine. You must be cautious with the varnish, as it is apt to spread. When the varnish is dry, you tint the flame with red-lead and gamboge, sHghtly tinging the smoke next the flame: the moon must not be tinted with colour.
Much depends upon the choice of the subject, and none is so admirably adapted to this species of effect as the gloomy Gothic ruin, whose antique towers and pointed turrets finely contrast their dark battlements with the pale, yet brilliant moon. Rays passing througli the ruined windows half choaked with ivy, a fire amongst the clustering- pillars and broken monuments of the choir, round
PAINTING TRANSPARENCIES. 409
which are figures of banditti, or others whose hag- gard faces catch the reflecting hght, afford a pecu- liarity of effect, not to be equalled in any other species of painting. Internal views of cathedrals, also, where windows of stained glass are introduced, form beautiful subjects.
The great point to be attained is a happy coin- cidence between the subject and the effect pro- duced. The fine light should not be too near the moon, as its glare would tend to injure her pale silver sight ; those parts which are not interesting should be kept in an undistinguishable gloom, and where the principal light is, they should be marked with precision. Groups of figures should be well contrasted ; those in shadow crossing those that are in light, by which means the opposition of light against shade is effected.
CRAYON-PAINTING
If the limits of our work would have permitted us, we should have here said something respecting this branch of the art ; but upon considering that it is a very inferior mode of painting, being only adapted for portraits, and being so perishable, that it is a pity the talents of any eminent artist should ever be employed in it, we have judged it better to suppress the article altogether, to make room for something of more importance. Those who are desirous of attempting it, may easily be furnished with the crayons ready prepared; and there is nothing particular in their use, which may not be easily acquired by any one who is acquainted with the practice of drawino-.
410
COLOURS.
We shall now give a brief account of the different pigments or colours, which are used either in water or oil, for the purposes of drawing or painting.
Red Colours.
Lakes. This term is used to denote a species of colours formed by the combination of alumine, or the oxyd of tin, with the colouring matters of vegetables.
The lakes chiefly used are red colours, and these are of different qualities, according to the basis and colouring matter employed.
The principal lakes are carminey Florence-lake ^ and madder-lake.
Carmine is a very ricli bright crimson colour, and stands well in water. For the preparation of carmine, four ounces of finely-pulverized cochineal are to be poured into four or six quarts of rain, or distilled water, that has been previously boiled in a jjervter kettle, and boiled with it for the space of six minutes longer (some advise to add, during the boiling, two drachms of pulverized crystals of tartar). Eight scruples of Roman alum, in pov/der, are to be then added, and the whole kept upon the fire one minute longer. As soon as the gross powder has subsided, and the decoction has become clear, it is to be carefully decanted into large cylindrical glasses, covered over, and kept undis- turbod, till a fine powder is observed to have settled at the bottom. The liquor is then to be poured oft from this powder, which is to be gradually dried. From the liquor, which is still much coloured, the rest of the colouring matter may be separated by
COLOURS. 411
means of the solution of tin, when it yields a car- mine little inferior to the former.
Floroitine lake is the kind in general use, known by the name of lake. It is used in water and also in oil, but does not stand, which is much to be lamented, as it is a very beautiful colour, and the is no substitute that Vv^ill completely answer all the purposes of lake.
The best sort may be prepared from the sedi- ment of cochineal that remains in the kettle after making carmine, adding to it a small quantity of cochineal, or Brazil-wood, and precipitating the colouring matter with a solution of tin.
Madder-lake is not so bright and rich a colour as the last-mentioned lakes, but has this valuable advantage, that it stands much better, and it may answer many of the purposes of Florence-lake.
It is prepared nearly in the same manner as the foregoing.
Rose-lake., This is generally called rose-pink. It is a lake made by a basis of chalk, coloured by Brazil or Campeachy v.^ood. It does not stand, and is only used for house-painting and paper- hanging.
VermilUon, a bright scarlet pigment, formed from sulphur and quicksilver. Its goodness is known by its brightness, and by its inclining to a crimson hue. It is a very useful colour in oil, where it stands very well 5 but in water it is apt to turn black.
Red lead, or minium^ is lead calcined till it ac- quires a red colour, by exposing it V\dth a large surface to the fire. This colou.r is very apt to turn black in water, and is therefore seldom used.
Indian red. This colour is sometimes employed to answer some of the pui'poses of lake. It is
412 COLOURS,
difficult to procure the genuine kind, which comes from the East Indies. What is sold for Indian red, is said to be chiefly made in this country.
Venetian red is a nativ e red ochre, rather inclin- ing to the scarlet than the crimson hue : it is not far different in colour from the common Indian red, and is a very good colour.
Spanish'hrown is also an earthy substance, found in the same state in which it is used ; it is nearly of the same colour as Venetian red, but coarser. It is only used for the commonest purposes.
Light red, or burnt ochre. This is common yellow ochre heated red-hot in the fire, till the colour changes from yellow to a red. It is a very excellent colour, both in water and oil, having the quality in common with all the ochres, of standing perfectly well.
Red chalk. This is the same substance as is used for drawing on paper, in the manner of a crayon. It is very much like light red, and is used instead of it, for some purposes. It stands per- fectly well, and may be used both in water and oil.
Burnt Terra Sienna. This colour is made by calcining raw terra Sienna till it acquires a red colour. It is of a very rich tint, and is much used both in water and oil. It stands well in both.
Blue Colours.
Ultramarine is prepared from lapis lazxdi, by calcining and washing it very clean. When ge- nuine, it is an extremely bright blue colour, some- what transparent both in oil and water, and stands perfectly. On these accounts it is of the utmost value, being excellent in every kind of painting,
COLOURS. 413
even in enamel ; but the great price prevents the general use of it.
Ultramarine ashes. This is the residuum after washing the lapis lazuli, in which a portion of the ultramarine still remains. It is very subject to be adulterated. It is not so bright as ultramarine, being, like that colour, with a tint of red and white in it. When genuine it stands well. , i Prussian blue. This colour is iron combined with the prussic acid. It is made in the following manner.
Two parts of purified potash are most intimately blended with three parts of dried and finely pul- verized bullock's blood. The mass is first calcined in a covered crucible, and on a moderate fire, until no more smoke or flame appear ; and it is after this brought to a complete, yet moderate, ignition. Or equal parts of potash and finely-powdered coals, prepared from bones, horns, claws, &c. are min- gled, and heated in a covered crucible to a moderate redness. This done, either of these two calcined masses is, after cooling, lixiviated with boiling water, and the lixivium filtered. Nothing remains now but to make a solution of one part of green vitriol and two parts of alum, and to add to it while yet hot the above lixivium, little by little how- ever, and to separate the greenish-blue precipitate, which then forms by means of a filtre. If after- wards a slight quantity of diluted muriatic acid be affused upon this precipitate, it assumes a beautiful dark-blue colour. The operation is terminated by edulcorating and drying the pigment thus prepared. Prussian-blue is an extremely beau- tiful colour when properly prepared, and stands well. Common Prussian-blue is apt to contain some iron, which causes it to turn greenish or olive.
414 coLOimSi
Verditer is a blue pigment, obtained by adding chalk or whitening to the solution of copper in aqua fortis. The best sort is prepared by the refiners, who employ for this purpose the solution of copper, which they obtain in the process of parting, by precipitating silver from aqua fortis by plates of copper. Common verditer is made from the sulphate of copper, or blue, by the manufac- turers in Sheffield and Birmingham. Verditer is only used for very coarse purposes, chiefly by the paper-stainers. It has been sometimes called Sanders blue, from ignorance of the meaning of the term cendres blues, or blue ashes, which the l^rench call it.
Indigo. This colour is extracted from a plant called Anil, that grows in the East and West Indies. It is not so bright as Prussian-blue, but it is cooler, and has the advantage of being very durable. When dissolved by the sulphuric acid, it forms Scott's liquid blue, so much used for colouring silk stockings, &c.
Smalt. This is glass coloured with cobalt, and oi'ound to a line powder. Its coarseness prevents its being used much for painting in oil or water. It is employed sometimes by stervving it upon a ground of oil-paint. It is also used in enamel- painting. It stands well.
Blue Bice. This is only smalt more finely levi-
gated.
Yellow Colours.
Indian yellow. This is the brightest of all yel- lows for water-colours, and is perfectly durable. It is said to be procured from the urine of the
COLOURS. 415
bufFalo. In the East Indies it is a very common and cheap colour ; the natives there use it com- monly for colouring their calicoes, which they do without any mordant, so that the colour is washed out again when the cloth is dirt}'.
King's 1/elloxv. This colour is orpiment refined, which is a substance dug out of the earth, and consists of sulphur joined to arsenic ; or it may be prepared by subliming sulphur with arsenic. It is of a very bright yellow, but does not stand very well ; and great caution should be used in employ- ing it, as it is a strong poison.
Naples yelloxc. This is a very durable and bright pale yellow ; it comes from Naples, and is supposed to be prepared from lead and antimony.
Yellow ochre. This is an earth coloured by oxyd of iron. It is a cheap colour, and not very bright ; but is valuable on account of its standing well.
Roman ochre. This is a superior kind of yellow ochre.
Dutch pink. This pigment is formed of chalk coloured with the juice of French berries, or other vegetables affording a yellow colour. It does not stand, and is chiefly used for common purposes.
Gamboge is a gum brought from the East Indies. It readily dissolves in water, and is a fine bright yellow. It is used only in water, and is very serviceable.
Massicot is an oxyd of lead, prepared by calcin- ing white-lead. It is very little used, the colour not being very bright.
Gall stones. This is a concretion or hard sub- stance, formed in the gall-bladders of beasts j or it'
416 COLOURS.
may be obtained from the gall of animals. It is a very rich colour, but does not stand.
Raw Terra Sienna^ is a native ochrous earth brought from Italy. It is a fine warm colour, and stands well.
French berries. A liquor may be extracted from these, which is useful as a stain for some coarse purposes ; but it does not keep its colour.
Turmeric root, and sqffro?i, may be used for si- milar purposes.
Ora7ige lake is the tinging part of annatto pre- cipated together with the earth of alum. It does not stand.
Brown pinli is the tinging part of some vegeta- ble substance precipitated upon the earth of alum. It is of a fine rich greenish yellow, but does not stand in water.
Green Colours.
There are few colours that are useful as greens ; accordingly, it is the practice with artists, to form their greens by the mixture of blue and yellow colours. By varying these, a vast variety of" green tints may be obtained.
Sap green. This colour is the concreted juice of the buckthorn-berries. It is never used in oil. It is employed chiefly in flower-painting and co- louring prints, he.
Ve?Yl?gris. If plates of copper, moistened from time to time with vinegar, be left exposed to the air, they will be converted into a green oxyd, Called verdigris : this is an imperfect oxyd of copper, combined with a small portion of acetic acid, carbonic acid, and water. It is prepared in
COLOURS. 4^17
large quantities, chiefly in France near Montpel- lier, by stratifying copper-plates with the husks of grapes yet under vinous fermentation, which soon grow acid, and corrode the copper. After the plates have stood in this situation for a sufficient time, they are moistened with water, and exposed in heaps to the air. The verdigris is scraped off from their surface as it forms.
Verdigris is of a bluish-green colour, but has no body, and does not stand. It is only used for very coarse purposes. It answers best when used in varnishes.
Distilled verdigris^ sometimes called crystals of verdigris, is prepared from common verdigris, by dissolving it in vinegar. It is of a very bright green, and is used chiefly for varnishes, and in co- louring maps, &c.
Brown Colours.
Bistre is the finer part extracted from the soot of burnt wood. It is much used for sketches in water-colours, being a transparent warm colour.
Cologne earth. This is a mineral substance of a dark blackish brown colour. It is a very useful colour ; though what is generally sold in the shops for Cologne earth is an artificial mixture of several colours.
Raw timbre is a native ochreous earth, of a light brown. It stands well.
Burnt umhre. This is only the last mentioned , colour, calcined in the fire. It then acquires a rich deep brown, and is of great use, being a fine colour, and standing perfectly well.
Asphaltum. This colour is used in oil, and is of a very rich deep brown. It is a transparent or glazing colour. It will not work in water, but
VOL. II. E E
4-18 COLOURS.
when dissolved in turpentine, it becomes a useful substance for giving deep and spirited touches to drawings.
White Colours.
Flake White is corbonate of lead, formed by cor- roding lead with vegetable acids, or vinegar.
White-lead is the same colour as flake white, only of an inferior quality. It is the only white used in oil-painting, and is a very useful colour •, but in water it always turns black, and should never be used.
Pure carbonate of lime is very useful as a white in water-colours, as it stands perfectly well.
Egg-sJiell white, and oyster-shell tchite, are only egg-shells, or oyster^shelis calcined, by which the animal gluten is destroyed, leaving the lime be- hind, which soon attracts the carbonic acid again from the atmosphere. Well washed Spanish white, or common whitening, answers tlie same purpose.
Black Colours.
Lamp black is the soot of oil, collected after it is formed by burning. It is very generally used, both in oil and water, and stands perfectly well.
Ivory black is the coal of ivory or bone, formed by giving them a great heat, while they are de- prived of all access of air. It is of a more intense black than lamp black.
Blue black is the coal from burning vine-stalks in a close vessel. It is like ivory black, with a tint of blue.
Indiaii ink has been already described in page S46.
419
OF ENGRAVING.
Engravings or graving, as it is sometimes called, is the cutting lines upon a copper-plate, by meaps of a steel instrument, called a graver.
This was the first way of producing copper-pl^te prints that was practised, and is still much i^sed in historical subjects, portraits, and in finishing land- scapes.
The tools necessary for this art are, gravers, a scraper, a burnisher, an oil-stone, a sand-bag, an oil-rubber, and some good charcoal.
The gravers are instruments of tempered steel, fitted into a short wooden handle. They are of two sorts, square and. lozenge : the first is used iji cutting very broad strokes, the other for fainter and more delicate lines.
The scraper is a three-edged tool, for scrapii^g off the burr raised by the graver. Burnishers ar.e for rubbing down any lines that are too deep, or burnishing out any scratches or holes i^ the cop- per: they are of very hard steel, wejl rounded and polished.
The oil-stone is for whetting the gravers, etch- ing-points, &c.
The sand-bag, or cushion, is for laying the plate upon, for the conveniency of turning ijt r,ound in any direction.
The oil-rubber and charcoal are for polishing the plate when necessary.
As great care is required to whet the graver nicely, particularly tlie beljy of it, the two an^le^s of the graver which are to be held next the pliajte, must be laid flat upon the stone, and rubbed steadily, till the belly rises gradually above the
E E 2
420 ENGRAVING.
plate, so as that, when you lay the graver flat upon it, you may just perceive the light under the point ; otherwise it will dig into the copper, and then it will be impossible to keep a point, or execute the work with freedom. In order to this, keep your right arm close to your side, and place the fore-finger of your left hand upon that part of the graver which lies uppermost on the stone. When this is done, in order to whet the face, place the flat part of the handle in the hollow of your hand, with the belly of the graver upwards, upon a moderate slope, and rub the extremity, or face, upon the stone, till it has an exceedingly sharp point, w^hich you may try upon your thumb-nail.
When the graver is too hard, as is usually the case when first bought, and which may be known by the frequent breaking of the point, the method of tempering it is as follows : Heat a poker red-hot, and hold the graver upon it, within half an inch of the point, till the steel changes to a light straw colour ; then put the point into oil, to cool ; or hold the graver close to the flame of a candle, till it be of the same colour, and cool it in the tallow ; but be careful either way, not to hold it too long, for then it will be too soft ; and in this case the point, which will then turn blue, must be tempered again. Be not too hasty in tempering ; for some- times whetting will bring it to a good condition, w^hen it is but a little too hard.
To hold the graver, cut off that part of the handle which is upon the same line with the belly, or sharp edge of the graver, making that side flat, that it may be no obstruction.
Hold the handle in the hollow of your hand; and, extending your fore-finger towards the point, let it rest on the back of the graver, that you may
ENGRAVING. 421
guide it flat and parallel with the plate. Take care that your fingers do not interpose between the plate and the graver ; for they will hinder you from carrying the graver level with the plate, and from cutting your strokes so clean as they ought to be.
To lay the design upon the plate, after you have polished it fine and smooth, heat it so that it will melt virgin-wax, with which rub it thinly and equally over, and let it cool. Then the de- sign which you lay on must be drawn on paper, with a black-lead pencil, and laid upon the plate, with its pencilled side upon the wax ; press it down, and with a burnisher go over every part of the design, and when you take off the paper, you will find every line upon the waxed plate which you drew with the black lead pencil ; then with a sharp pointed tool trace all your design through the wax upon the plate, and you may then take off the wax, and proceed to work.
Let the table, or board you work at, be firm and steady ; upon which place your sand-bag with the plate upon it ; and, holding the graver as above directed, proceed in the following manner.
For straight strokes, hold your plate firm upon the sand-bag with your left hand, moving your right hand forwards; leaning lighter where the stroke should be fine, and harder where you would have it broader.
For circular or crooked strokes, hold the graver stedfast, moving your hand or the plate, as you see convenient.
Learn to carry your hand with such dexterity, that you may end your stroke as finely as you began it ; and if you have occasion to make one part deeper or blacker than another, do it by de-
E E 3
422 ENGRAVING*
grees ; and that you may do it ^vith greater exact- ness, take care that your strokes be not too close nor too wide.
In the course of your v/ork scrape off the roughness which arises, with your scraper; but be careful, in doing this, not to scratch the plate ; and that you may see your work properly as you go on, rub it with the oil-rubber, and wipe the plate clean, which will take off the glare of the copper, and show what you have done to the best advantage.
Any mistakes or scratches in the plate may be rubbed out with the burnisher, and tlie part levelled with the scraper, polishing it again afterwards lightly with the burnisher, or charcoal.
Having thus attained the use of the graver, ac- cording to the foregoing rules, you will be able to finish the piece you had etched, by graving up the several parts to the colour required ; beginning, as in the etching, with the fainter parts, and advanc- ing gradually with the stronger, till the v/hole is completed.
The dry point or needle (so called because not used till the ground is taken off the plate) is prin- cipally employed in the extremely light parts of water, sky, drapery, architecture, &c.
To prevent any obstruction from too great a degree of light, the use of a sashj made of trans- parent, or fan paper, pasted on a fiamc, and placed sloping at a convenient distance between your work and the lights will preserve the sight ; and when the sun shines, it cannot possibly be dis- pensed with.
4>23
ETCHING.
Etching is a manner of engraving on copper, in which the lines or strokes, intead of being cut with a tool or graver, are corroded in with aqua fortis.
It is a much later invention than the art of en- graving by cutting the lines on the copper, and has many advantages over it for some purposes, though it cannot supersede the use of the graver entirely, as there are many things that cannot be etched so well as they can be graved.
In almost all the engravings on copper that are executed in the stroke manner, etching and graving are combined, the plate being generally begun by etching, and finished with the graver. Landscapes, architecture, and machinery, are the subjects that receive most assistance from the art of etchinsr ; for it is not so applicable to portraits and historical designs.
We shall first describe the various instruments and materials used in the art.
Copper-plates may be had ready prepared at the coppersmiths, by those who reside in large towns ; but when this cannot be had, procure a piece of pretty thick sheet-copper from a brazier, rather larger than your drawing, and let him planish it well ; then take a piece of pumice-stone, and with water rub it all one way, till the surface is as smooth and level as it can be made by that means : a piece of charcoal is next used with water, for polishing it still farther, and removing the deep
E E 4
4f24 ETCHING.
scratches made by the pumice-stone ; and it is then finished with a piece of charcoal of a finer grain, with a Uttle oil.
Etching-points or 7ieedles are pointed instruments of steel, about an inch long, fixed in handles of hard wood, about six inches in length, and of the size of a goose-quill. They should be well tem- pered, and very accurately fixed in the centre of the handle. They must be brought to an accu- rately conical point, by rubbing upon an oil-stone, with which it is also very necessary to be provided. Several of these points will be necessary.
A parallel-ruler is necessary for drawing parallel straight lines with. This is best when faced with brass, as it is not then so liable to be bruised by accident.
Compasses aj'e useful for striking circles and measuring distances.
Aqua fortis, or what is better, spirits of nitre, (nitrous acid,) is used for corroding the copper, or hiting-in, as it is called. This must be kept in a bottle with a glass stopple, for its fumes destroy corks. A stopple made of wax will serve as a sub- stitute, or a cork well covered with wax.
Bordering-xvaa\ for surrounding the margin of the copper-plate when the aqua fortis is pouring on. This may be bought ready prepared, but it may be made as follows.
Take one-third of bees-wax to two-thirds of pitch J melt them in an iron ladle, and pour them, when melted, into v/ater lukewarm ; then mould it with your hand till it is thoroughly incorporated, and all the water squeezed out. Form it into rolls of convenient size.
Turpentine varnish, is used for covering the cop- per-plate with, in any part where you do not wish
ETCHING. ' 425
the aqua fortis to bite. This may be diluted to a proper consistence with turpentine, and mixed with lamp-black, that it may be seen better when laid upon the pkite.
Ectching-ground is used for covering the plate all over with, previous to drawing the lines on it with the needles. It is prepared in the following manner.
Take of virgin-wax and asphaltum, each two ounces, of black pitch and Burgundy pitch, each half an ounce ; melt the wax and pitch in a new earthenware glazed pipkin, and add to them, by degrees, the asphaltum, finely powdered. Let the whole boil till such time as that, by taking a drop upon a plate, it will break when it is cold, on bend- ing it double two or three times between the fingers. The varnish, being then enough boiled, must be taken off from the fire, and letting it cool a little, must be poured into warm water, that it may work the more easily with the hands, so as to form into balls for use.
It must be observed, first, that the fire be not too violent, for fear of burning the ingredients ; a slight simmering will be sufficient j secondly, that while the asphaltum is putting in, and even after it is mixed with them, the ingredients should be stirred continually with a spatula ; and thirdly, that the water into which this composition is thrown, should be nearly of the same degree of warmth with it, to prevent a kind of cracking, which happens when the water is too cold.
The varnish ought always to be harder in sum- mer than winter, and it will become so if it be suffered to boil longer, or if a greater proportion of the asphaltum be used. The experiment above mentioned, of the drop suffered to cool, will de-
4S6 ETCHING.
termine the degree of hardness or softness that may be suitable to the season when it is used.
To lay the ground for etching, proceed in the following manner : Having cleaned the copper- plate with some fine whiting and a linen rag, to free it from all grease, fix a hand-vice to some part of it where no work is intended to be, to serve as a handle for managing it by when warm. Roll up some coarse brown paper, and light one end ; then hold the back of the plate over the burning paper, moving it about until every part of it. is equally heated, so as to melt the etching-ground, which should be wrapped up in a bit of taflfety, to prevent any dirt that may happen to be among it, from mixing with what is melted upon the plate. If the plate be large, it will be best to heat it over a chafing-dish with some clear coals. It must be heated just sufficient to melt the ground, but not so much as to burn it. When a sufficient quantity of the etching-ground has been rubbed upon the plate, it must be dabbed, or beat gently, while the plate is hot, with a small dabber, made of cotton, wrapped up in a piece of tafFety, by which oper- ation the ground is distributed more equally over the plate than it could be by any other means.
When the plate is thus uniformly and thinly covered with the varnish, it must be blackened by smoking it with a wax taper. For this purpose twist together three or four pieces of wax taper, to make a larger flame, and while the plate is still warm, hold it with the varnished side downwards, and move the smoky part of the lighted taper over its surface, till it is made almost quite black ; taking care not to let the wick touch the varnish, and that the latter get no smear or stain. In laying the etch- ing-ground, great care must be taken that no par-
ETCHING}. 427
tides of dust or dirt of any kind settle upon it, as that would be found very troublesome in etching ; the room, therefore, in which it is laid should be as still as possible, and free from dust*
The ground being now laid) and suffered to cool, the next operation is to transfer the design to the plate.
For this purpose a tracing on oiled paper must now be made, from the design to be etched, with pen and ink, having a very small quantity of ox's gall mixed with it, to make the oiled paper take it; also a piece of thin paper, of the same size, must be rubbed over with red chalk, powdered, by means of som.e cotton i Tlien laying the red chalked paper, with its chalked side next the ground, on the plate, put the tracing over it, and fasten them both together, and to the plate, by a little bit of the bordering wax.
When all this is prepared, take a blunt etching needle, and go gently all over the lines in the tracing ; by which means the chalked paper will be pressed against the ground, and the lines of the tracing will be transferred to it : on taking off the papers, they will be seen distinctly.
The plate is now prepared for drawing through the lines which have been marked upon the ground. For this, the etching-points or needles are employed, leaning hard or lightly, according to the degree of strength required in the lines. Points of different sizes and forms are also usedj for making lines of different thickness, though commonly this is effected by the biting-in with the aqua fbrtis.
A margin or border of wax must now be formed all round the plate, to hold the aqua fortis when it is poured on. To do this, the bordering wax
428 ETCHING.
already described must be put into lukewarm water to soften it, and render it easily worked by the hand. When sufficiently pliable, it must be drawn out into long rolls, and put round the edges of the plate, pressing it down firm, and forming it with the fingers into a neat wall or margin. A spout must be formed in one corner, to pour off the aqua fortis by afterwards.
The nitrous acid (spirits of nitre) is now to be diluted with four or five times as much water, or more (according as you wish the plate to be bit quick or slow,) and poured upon the plate. In a few minutes you will see minute bubbles of air filling all the lines that have been drawn on the copper, which are to be removed by a feather ; and the plate must be now and then swept, as it is called, or kept free from air bubbles. By the more or less rapid production of these bubbles, you judge of the rapidity with which the acid acts upon the copper. The biting-in of the plate is the most uncertain part of the process, and nothing but very great experience can enable any one to tell w^hen the plate is bit enough, as you cannot easily see the thickness and depth of the line till the ground is taken off.
When you judge, from the time the acid has been on, and the rapidity of the biting, that those lines which you wish to be the faintest are as deep as you wish, you pour off the aqua fortis by the spout, wash the plate with water, and dry it, by blowing with bellows, or by the iire, taking care not to melt the ground.
Those lines that are not intended to be bit any deeper, must now be stopped up with turpentine- varnish mixed with a little lamp-black, and laid on with a camel's-hair pencil ; and when this is
ETCHING. 429
thoroughly dry, the aqua tbrtis may be poured on agahi, to bite the other hues that are required to be deeper.
This process of stopping-out and biting-in is to be repeated as often as there are to be lines of dif- ferent degrees of thickness, taking care not to make any mistake in stopping-out wrong lines.
It is also necessary to be particularly careful to stop-out with the varnish, those parts from which the ground may happen to have come off by the action of the acid, otherwise you will have parts bit that were not intended, which is csdledjoul- biting.
When the biting-in is quite finished, the next operation is to remove the bordering-wax and the ground, in order that you may see what success you have had ; for till then, this cannot be known exactly.
To take off the bordering-wax, the plate must be heated by a piece of lighted paper, which soft- ens the wax in contact with the plate, and occa- sions it to come off quite clean.
Oil of turnpentine is nov/ poured upon the ground, and the plate is rubbed with a bit of linen rag, which removes all the ground. Lastly, it is cleaned off with whitening.
The success of the etching may now be known, but it is necessary to get an impression taken upon paper by a copper-plate printer. This impression is called a proof.
If any parts are not bit so deep as were in- tended, the process may be repeated, provided the lines are not too faintly bit to admit of it. This second biting-in the same lines, is called re-bitingy and is done as follows : Melt a little of the etching- ground on a spare piece of copper, and dab it a
430 ETCHING.
little, to get some on the dabber; then, having cleaned out, with whiting, the lines that are to be re-bit, heat the plate gently, and dab it very lightly with the dabber. By this, the parts between the lines will be covered v/ith the ground, but the lines themselves will not be tilled up, and consequently will be exposed to the action of the aqua fortis. This is a very delicate process, and must be per- formed with great care. The rest of the plate must now be varnished over, the bordering wax put on again, and the biting repeated in the same manner as at first.
If any part should be bit too deep, it is more difficult to recover it, or make it fainter : this is ge- nerally done by burnishing the part down, or rub- bing it with a piece of charcoal. This will make the lines shallower, and cause them not to print so black.
Should any small parts of the lines have missed altogether in the biting, they may be cut with the graver ; which is also sometimes employed to cross the lines of the etching, and thus to work up a more finished effect.
Dry-pointing is another method employed for softening the liarsh effects usually apparent in an etching. This is done by cutting with the etching- point upon the copper without any ground or var- nish, which does not make a very deep line, and is used for covering the light, where very delicate tints and soft shadows are wanting. By varying these processes of etching, graving, and dry-point- ing, as is thought necessary, the plate is worked up to the full effect intended j and it is then sent to the writing engraver, to grave whatever letters may be required to be put upon it.
431
MEZZOTINTO SCRAPING.
This art is of later origin than the last, and is not of such difficult execution. In mezzotinto prints the shadows are not formed by lines or hatches, but much resemble Indian ink. It differs in the pro- cess, however, from aquatinta, although the effect is not very different.
Mezzotinto is chiefly employed in portraits and historical subjects ; and aqua tinta for landscape and architecture.
The tools necessary for mezzotinto scraping are the grounding-tool, burnishers, and scrapers.
To lay the mezzotinto ground, lay your plate, with a piece of flannel under it, upon your table; hold the grounding-tool in your hand perpendi- cularly ; lean upon it moderately hard, continually rocking your hand in a right line from end to end, till you have wholly covered the plate in one di- rection : next cross the strokes from side to side, afterwards from corner to corner, working the tool each time all over the plate, in every direction, almost like the points of a compass ; taking all possible care not to let the tool cut (in one direc- tion) twice in a place. This done, the plate will be full, or, in other words, all over rough alike, and would, if it were printed, appear completely black.
Having laid the ground, take the scrapings of black chalk, and with a piece of rag rub it over the plate ; or you may smoke it with candles, as before directed, for etching.
Now take your drawing, and having rubbed the black with red chalk-dust, mixed with flake-white, proceed to trace it on the plate.
4^2 AQUA TINTA.
To form the lights and shadows, take a blunt needle, and mark out the outlines only, then with a scraper scrape off the lights in every part of the plate, as clean and smooth as possible, in propor- tion to the strength of the lights in your drawing, taking care not to hurt your outlines.
The use of the burnisher is to soften or rub down the extreme light parts after tlie scraper is done with ; such as the tip of the nose, forehead, linen, &c. which might otherwise, when proved, appear rather misty than clear.
Another method used by mezzotinto scrapers, is, to etch the outlines of the original, as also the folds in drapery, making the breadth of the sha- dows by dots, which having bit to a proper depth with aqua fortis, they take oft' the ground used in etching, and having laid the mezzotinto ground, proceed to scrape as above.
When your plate is ready for taking a proof or impression, send it to the copper-plate printer, and get it proved. When the proof is dry, touch it with white chalk where it should be lighter, and with black chalk where it should be darker ; and when the print is retouched, proceed as before, for the lights ; and for the shades use a small ground- ing-tool, as much as you judge necessary to bring it to a proper colour ; and when you have done as much as you think expedient, prove it again ; and so proceed to prove and touch till it is entirely to your mind.
AQUA TINTA.
Aqua'tinia is a method of producing prints very much resembling drawings in Indian-ink.
ENGRAVING IN AQUA TINTA. 433
The principle of the process consists in corrod- ing tlie copper with aqua fortis, in such a manner, that an impression from it has the appearance of a tint laid on the paper. This is effected by cover- ing the copper with a powder, or some substance which takes a granulated form, so as to prevent the aqua fortis from acting where the particles adhere, by this means causing it to corrode the copper partially, and in the interstices only. When these particles are extremely minute and near to each other, the impression from the plate appears to the naked eye exactly like a wash of Indian-ink ; but when they are larger, the granulation is more dis- tinct ; and as this may be varied at pleasure, it is capable of being adapted with great success, to a variety of purposes and subjects.
This powder, or granulation, is called the aqua^ tinta grai?iy and there are two general modes of producing it.
We shall first describe what is called the powder- grain, because it was the first that was used.
Having etched the outline on a copper-plate, prepared in the usual way by the coppersmith (for which see tlie article etching), some substance must be finely powdered and sifted, which will melt with heat, and when cold will adhere to the plate, and resist the action of aqua fortis. The sub- stances which have been used for tliis purpose, either separately or mixed, are asphaltum, Bur- gimdy-pitch, rosin, gum-copal, gum-mastich ; and in a greater or less degree, all the resins and gum- resins will answer the purpose. Common rosin has been most generally used, and answers toler- ably well ; tliough gum-copal makes a grain that resists the aqua fortis better.
VOL. ir, F F
434 ENGRAVING IN AQUA TINTA.
The substance intended to be used for the grain must now be distributed over the plate as equally as possible ; and different methods of performing this essential part of the operation have been used by different engravers, and at different times.
The most usual way is to tie up some of the powder in a piece of muslin, and strike it against a piece of stick held at a considerable height above the plate; by this, the powder that issues falls gently, and settles equally over the plate. Every one must have observed how uniformly hair-powder settles upon the furniture after the operations of the hair-dresser. This may afford a hint towards the best mode of performing this part of the pro- cess. The powder must fall upon it from a con- siderable height, and there must be a sufficiently large cloud of the dust formed. The plate being covered equally over with the dust, or powder, the operator is next to proceed to fix it upon the plate, by heating it gently, so as to melt the particles. This may be effected by holding under the plate lighted pieces of brown paper, rolled up, and moving them about till every part of the powder is melted ; this will be known by its change of colour, which will turn brownish. It must now be suffered to cool, when it may be examined with a magnifier, and if the grains or particles appear to be uni- formly distributed, it is ready for the next part of the process.
The design or drawing to be engraved must now be examined, and sucli parts of it as are perfectly wnite are to be remarked. Those corresponding parts of the plate must be covered, or stopped out (as it is called) with turpentine-varnish, diluted with turpentine to a proper consistence to work freely
ENGRAVING IN AQUA TINTA. 43^
with the pencil, and mixed with lamp-black to give it colour ; for if transparent, the touches of the pencil would not be so distinctly seen. The mar- gin of the plate must also be covered with varnish. When the stopping out is sufficiently dry, a border of wax must be raised round the plate, in the same manner as in etching, and the aqua fortis properly diluted with water poured on. This is called biting in, and is the part of the process which is most uncertain, and which requires the greatest degree of experience. When the aqua fortis has lain on so long that the plate, when printed would produce the lightest tint in the drawing, it is poured off, and the plate washed with water, and dried. When it is quite dry, the lightest tints in the drawing are stopped out, and the aqua fortis poured on as be- fore, and the same process is repeated as often as there are tints to be produced in the plate.
Although many plates are etched entirely by this method of stopping out and biting in alternately, yet it may easily be conceived, that in general, it would be very difficult to stop round, and leave out all the finishing touches, as also the leaves of trees and many other objects, which it would be impos- sible to execute with the necessary degree of free- dom, in this manner.
To overcome this difficulty, another very ingeni- ous process has been invented, by which these touches are laid on the plate with the same ease and expedition as they are in a drawing in Indian-ink. Fine \vashed whiting is mixed with a little treacle or sugar, and diluted with water in the pencil, so as to work freely, and this is laid on the plate covered with the aqua-tint ground, in the same manner, and on the same parts as ink on the draw- ing. When this is dry, the whole plate is varnished
FF 2
436 ENGRAVING IN AQUA TINTA.
over with a weak and thin varnish of turpentine, asphaltum, or mastich, and then suffered to dry, when the aqua fortis is poured on. The varnish will immediately break up in the parts where the treacle mixture was laid, and expose all those places to the action of the acid, while the rest of the plate remains secure. The effect of this will be, that all the touches or places where the treacle was used will be bit in deeper than the rest, and will have all the precision and firmness of touches in Indian-ink.
After the plate is completely bit in, the border- ing-wax is taken off, by heating the plate a little with a lighted piece of paper ; and it is then cleared from the ground and varnish by oil of turpentine, and wiped clean with a rag and a little fine w^hiting, when it is ready for the printer.
The principal disadvantages of this method of aqua-tinting are, that it is extremely difficult to produce the required degree of coarseness or fine- ness in the grain, and that plates so engraved do not print many impressions before they are worn out. It is therefore now very seldom used, though it is occasionally of service.
We next proceed to describe the second method of producing the aqua-tint ground, which is generally practised. Some resinous substance is dissolved in spirits of wine, as common resin, Burgundy- pitch, or mastich, and this solution is poured all over the plate, wdiich is then held in a slanting direction, till the superfluous fluid drains ofl'j and it is then laid down to dry, which it does in a few minutes. If the plate be then examined with the magnifier, it \\i\\ be found that the spirit, in evapor- ating, has left the resin in a granulated state, or rather, that the latter has cracked in every direc- tion, still adhering firmly to the copper.
ENGRAVING IN AQUA TINTA. 437
A grain is tlms produced with the greatest ease, which is extremely regular and beautiful, and much superior for most purposes to that produced by the former method. After the grain is formed, every part of the process is conducted in the same manner as above described.
Having thus given a general idea of the art, we shall mention some particulars necessary to be attended to, in order to ensure success in the oper- ation. The spirits of wine used for the solution, must be highly rectified, and of the best quality. What is sold in the shops generally contains cam- ])hor, which would entirely spoil the grain. Resin, Burgundy-pitch, and gum mastich, when dissolved in spirits of wine, produce grains of a different appearance and figure, and are sometimes used separately, and sometimes mixed in different pro- portions, according to the taste of the artist, some using one substance, and some another. In order to produce a coarser or finer grain, it necessary to use a greater or smaller quantity of resin; and to ascertain the proper proportions, several spare pieces of copper must be provided, on which the liquid may be poured, and the grain examined, before it is applied to the plate to be engraved. After the solution is made, it must stand still and undisturbed for a day or two, till all the impurities of the resin have settled to the bottom, and the fluid is quite pellucid. No other method of freeing it from those impurities has been found to answer ; straining it through linen or muslin, only fills it with hairs, which are ruinous to the grain. The room in which the liquid is poured on the plate must be perfectly still and free from dust, which, whenever it falls on the plate while wet, causes a white spot, which it is impossible to remove without laying the grain
FF 3
438 ENGRAVING IN AQUA TINTA.
a-fresh. The plate must also be previously cleaned, with the greatest possible care, with a rag and whiting, as the smallest stain or particle of grease produces a streak or blemish in the grain. All these attentions are absolutely necessary to produce a tolerably regular grain ; and, after every thing that can be done by the most exprienced artists, still there is much uncertainty in the process. They are sometimes obliged to lay on the grains several times, before they procure one sufficiently regular. The same proportions of materials do not always produce the same effect, as it depends in some degree on their qualities: and it is even materially altered by the weather. These difficulties are not to be surmounted but by a great deal of experience j aad those who are daily in the habit of practising the art are frequently liable to the most unaccount- able accidents. Indeed, it is much to be lamented, that so elegant and useful a process should be so extremely delicate and uncertain.
It being necessary to hold the plate in a slanting direction, in order to drain off the superfluous fluid, there will naturally be a greater body of the liquid at the bottom than at the top of the plate. On this account, a grain laid in this way is always coarser at the side of the plate that was held lowermost. The most usual way is, to keep tlie coarsest side for the fore-ground, that being generally the part which has the deepest shadows. In large land- scapes, sometimes various parts are laid Avith dif- ferent grains, according to the nature of the subject.
The finer tlie grain is, the more nearly does the impression resemble Indian-ink, and the fitter it is for imitating drawings: but very fine grains have several disadvantages; for they are apt to come off before the aqua fortis has lain on long enough to produce
ENGRAVING IN AQUA TINTA. 439
the desired depth ; and as the plate is not corroded so deep, it soon wears out in printing; whereas coarser grains are firmer, the acid goes deeper, and the plate will throw off a great many more impres- sions. The reason of all this is evident, when it is considered, that in the fine grains, the particles are small and near each other, and consequently the aqua fortis, which acts laterally as well as down- wards, soon undermines the particles, and causes them to come off. If left too long on the plate, the acid would eat avvay the grain entirely.
On these accounts, therefore, the moderately coarse grains are more sought after, and answer better the purpose of the publisher, than the fine grains which were formerly in use.
Although there are considerable difHculties in laying properly the aqua tint grain, yet the corrod- ing the copper, or biting-in, so as to produce ex- actly the tint required, is still more precarious and uncertain. All engravers allow that no positive rules can be laid down, by which the success of this process can be secured ; nothing but a great deal of experience and attentive observation can enable the artist to do it with any degree of cer- tainty.
There are some hints, however, which may be of considerable importance to the person who wishes to attain the practice of this art. It is evi- dent, that the longer the acid remains on the cop- per, the deeper it bites, and consequently the darker will be the shade in the impression. It may be of some use, t'lerefore, to have several bits of copper laid with aqua tint grounds, of the same kind to be used in the plate, and to let the aqua fortis remain for different lengths of time on each ; and then to examine the tints produced in one,
F F 4
440 ENGRAVING IN AQUA TINTA.
two, three, four minutes, or longer. Observations of this kind, frequently repeated, and with diifer- ent degrees of strength of the acid, will at length assist the judgment, in guessing at the tint which is produced in the plate. A magnifier is also use- ful to examine the grain, and to observe the depth to which it is bit. It must be observed, that no proof of the plate can be obtained till the whole process is finished. If any part appears to have been bit too dark, it must be burnished down with a steel burnisher ; but this requires great delicacy and good management not to make the shade streaky ; and as the beauty and durability of the grain is always somew^hat injured by it, it should be avoided as much as possible.
Those parts which are not dark enough must have a fresh grain laid over them, and be stopped round with varnish, and subjected again to the aqua fortis. This is called re-biting, and requires peculiar care and attention. The plate must be very well cleaned out with turpentine before the grain is laid on, which should be pretty coarse, otherwise it will not lay upon the heights only, as is necessary, in order to produce the same grain. If the new grain is different from the former, it will not be so clear nor so firm, but rotten.
We have now given a general account of the process of engraving in aqua tint, and we believe that no material circumstance has been omitted, that can be communicated without seeing the operation ; but after all it must be confessed, that no printed directions whatever can enable a person to practise it perfectly. Its success depends upon so many niceties, and attention tp circumstances apparently trifling, that the person who attempts it must not be surprised if he does not succeed at
ENGRAVING IN AQUA TINTA. 441
first. It is a species of engraving simple and ex- peditious, if every tiling goes on well ; but it is very precarious, and the errors which are made are rectified with great difficulty.
It seems to be adapted chiefly for imitation of sketches, washed drawings, and slight subjects j but does not appear to be at all calculated to pro- duce prints from finished pictures, as it is not sus- ceptible of that accuracy in the balance of tints necessary for this purpose. Nor does it appear to be very suitable for book-plates, as it does not print a sufficient number of impressions. It is, therefore, not to be put in competition with other modes of engraving. If confined to those subjects for which it is calculated, it must be allowed to be extremely useful, as it is expeditious, and may be attained with much less trouble than any other mode of engraving. But even this circumstance is a source of mischiefj as it occasions the produc- tion of a multitude of prints that have no other effect than that of vitiating the public taste.
Engraving in aqua tint was invented by Le Prince, a French artist, who kept his process a long time secret, and it is said he sold his prints at first as drawings J but he appears to have been acquainted only with the powder-grain and the common method of stopping-out. The prints which he produced are still some of the finest specimens of tlie art. Mr. Paul Sandby was the first who practised it in this country, and it was by him communicated to Mr. Jukes. It is now practised very generally all over Europe j but no where mor^ successfully than in this kingdom.
442
WOOD-CUTTING.
Wood-cutting or engraving on wood is a pro- cess exactly the reverse to engraving on copper. In the latter, the strokes to be printed are sunk, or cut into the copper, and a rolling-press is used for printing it ; but in engraving on wood, all the wood is cut away, except the lines to be printed, which are left standing up like types, and the mode of printing is the same as that used in letter- press.
The wood used for this purpose is box-wood, which is planed quite smooth. The design is then drawn upon the wood itself with black-lead, and all the wood is cut away with gravers and other proper tools, except the lines that are drawn. Or sometimes the design is drawn upon paper, and pasted upon the wood, which is cut as before. This art is of considerable difficulty, and there are few who practise it. It is, however, useful for books, as the printing of it is cheaper than that of copper-plates. It Cannot be applied equally well to all the purposes to which copper-plate en- graving is applicable.
ETCHING ON GLASS.
Glass resists the action of all the acids, except the fluoric acid. By this, however, it is corroded in the same manner as copper is by aqua fortis ; and plates of glass may be engraved in the same manner as copper.
There are several methods of performing this. We shall first describe the mode of etching by
ETCHING ON GLASS. 443
means of the fluoric acid in the state of gas. Having covered over the glass to be etched with a thin coat of virgin-wax (which is only common bees- wax bleached white,) draw the design upon it, in the same manner as in etching on copper. Then take some Jluoy^ spar, commonly called Derhijshire spar, pound it fine, and put it into a leaden vessel, pouring some sulphuric acid over it. Place the glass with the etched side lowermost over this vessel, two or three inches above it^ Apply a gentle heat to the leaden vessel ; this will cause the acid to act upon the fluor spar, and dis- engage the gas, W'hich will corrode the glass. When it is sufficiently corroded, remove the wax by oil of turpentine.
This etching may be also performed by raising a margin of bordering-wax all round the glass, in the same manner as on copper, and pouring on the liquid fluoric acid, which acts upon the glass. The method of making this acid was described under the article fluoric acid, in che- mistry.
A third method of etchino; on fflass is as follows : Having put the wax on the glasSj draw your design, and raise a margin all round it. Then ])ut pounded fluor spar, with some sulphuric acid diluted with Vv'ater, upon the glass. The sulphuric acid will disengage the fluoric, which will be absorbed by the water, and corrode the glass.
In all the above-mentioned methods, some of the gas is let loose in the apartment, and is exceed- ingly suffocating. To remedy this inconvenience, an apparatus was contrived by the editor of this work, some years ago, and is found to answer perfectly.
444 ETCHING ON GLASS.
A, Fig. 5., Plate XVII., Vol. 1., is a cylindrical leaden vessel, having a rim B all round it, made like Count Rumfoid's steam rim for cooking vessels, into which is put a little water. Into this rim fits a cover c, having a pipe d coming from it, Mhich is inserted into a large oblong vessel e of sheet lead, or iron well tinned, having a rim and cover similar to the vessel A, only the cover has no aperture. The fluate of lime powdered and the sulphuric acid are put into the leaden vessel A, which is placed upon a stand made of wire, having a lamp to heat the contents of the vessel over it. As soon as the gas is evolved it ascends, and not being able to escape through the rim B, on account of the water, which condenses a portion, it pro- ceeds through the tube into the large vessel e, in which is placed, upon stands of wire, the glass prepared for etching by drawing through a var- nish, as above described.
In this vessel the gas collects, and acts upon the glass : the rim with water prevents any noxious fumes from escaping into the room. The vessel e is placed upon a stand of such a height as to agree with that of the lamp. In this manner the process may be conducted with the utmost ease and elegance.
Beautiful ornaments may thus be etched on glass, and applied to decorate windows, by paint- ing the figure of the ornament on panes of glass with enrgravers' stopping varnish, and tlien ex- posing the panes to the action of the gass in the vessel e. The gas will corrode all the surface of the glass, except where the varnish has been put, and give it much tlie appearance of ground glass, which may be rendered more or less opaque by lengthening or shortening the process. The parts
ETCHING ON GLASS. 445
where the varnish was appUed will continue trans- parent and seem extremely bright. It is to be noticed, when the liquid fluoric acid is used, the lines which have been etched continue still trans- parent ; but when the gas has been employed, the line is white and opaque, as if cut by a wheel.
LITHOGRAPHY.
This art is so called, because the impressions are produced from drawings made on stone. It was invented by Aloys Sennefelder, a German, about the year 1800.
There are several styles of drawing employed in lithographic prints. The chief are, the line manner, and the chalk manner. In the line manner, which is similar in its effect to the line engraving on cop- per of second rate quality, lines are drawn on a stone with a particular sort of ink, by means of pens of various kinds, or a camels-hair pencil.
In both these methods, the same kind of stone is used ; but in the line manner, the stone must be polished smooth with pumice-stone, whereas, for the chalk it is made a little rough, by grinding with sand. The stone must be calcareous and of a light colour. The white lias in this country answers tolerably well, but is not so fit as the German stones.
The lithographic ink is composed of equal parts of tallow, bees-wax, shell lac, and common soap, with a sufficient quantity of lamp-black to colour it. These ingredients are mixed by heating them.
446 LITHOGRAPHY.
and even burning them in an iron vessel. When cold, the mass is rubbed on a tile with water, like Indian ink, and put into a pen or brush.
The lithographic chalk is formed of 2 oz. of tal- low, 2|- oz. of bees-wax, 1 oz. of shell lac, and If oz. of common soap. These are also united by heating as before ; when cold it is cut into slips, and used as a cravon.
When the drawing is made on the stone with the pen and ink, or with the chalk or crayon, some water, having in it a little nitric acid, is poured over the stone, which slightly corrodes the sur- face ; gum-water is then laid on with a brush, and the stone is left to dry ; it is now ready for print- ing from.
To print from the stone, the printer proceeds to wet the surface of it with a sponge with w^ater, and then applies the printing ink, by a roller.
The printing ink, made of equal parts of burnt oil or varnish, and lamp-black, sometimes with the addition of wax and tallow, adheres to the lines which have been drawn wdth the lithographic ink on the stone, while the water prevents it from sticking to the rest of the surface. The lines alone are thus charged with printing ink. Some damped paper is now laid upon the stone, and passed through a press, by v\^hich an impression is obtained. The stone is again wetted, and the printing ink applied for a second impression, and so on.
The process is the same for printing chalk draw- ings ; but they are more difficult to print, and give fewer impressions.
This art has made considerable progress on the continent ; in this country it has advanced more slowly, chiefly from the secresy employed in the
LITHOGRAPHY. 447
processes of printing. On this account, its advan- tages were not well comprehended, it being difficult to institute a just comparison between this and the other species of engraving, which are in this coun- try carried to such a high degree of perfection. It is now, however, rapidly improving, since artists have been induced to take it up, and we shall probably soon' equal, if not surpass, our continental neighbours.
INDEX.
Abstract 44-6
454^
of Mechanics, i. of Hydrostatics, i.
-- ofPneumaticSji. 455
of Hydraulics, i.456
• of Acoustics, i. 458
of Optics, i. 459.
. of Electricity, i. 461
————— of Galvanism, i. 463
of Magnetism, i. 464
of Astronomy, i. 466
Acid Nitrous, ii. 44
Nitric, ii. 45
Hydro-chloric, or muri- atic, ii. 65 — — Sulphurous, ii. 68
Sulphuric, ii. 69
Carbonic, ii. 70
Phosphorous, ii. 76
Phosphoric, ii. 76
Boracic, ii. 76
Fluoric, ii. 77
Fluo-boric, ii. 78
• Siliceo-fluoric, ii. 78
Arsenic, ii. 117
Arsenious, ii. 1 17
Molybdic, ii. 120
Chromic, ii. 126
— — Tunstic, ii. 120
Tartaric, ii. 133
-—, Oxalic, ii. 133
Malic, ii. 133
Gallic, ii. 134
VOL. II. G
Acid Citric, ii. 134
Benzoic, ii. 134
— — Kinic, ii. 134
Acetous, ii. 136
Acetic, ii. 137
Lactic, ii. 139
Uric, ii. 139
Amniotic, ii. 139
Saccho-lactic, ii. 140
Sebacic, ii. 140
Prussic, ii. 140
Formic, ii. 140
Adipocire, ii. 139 Affinity, chemical, ii. 5 Air, mechanical properties of, i. 126 — weight of, 135 — pressure of, 131 — density of, 135 — height of, 135 — elasticity of, 137 — con- densed, 145 Air pump, i. 129 — experi- ments with it, i. 139 — prac- tical directions for using, i. 153 Air gun, i. 157 Air balloons, i. 162 Air atmospheric, chemical pro- perties of, ii. 46 — fixed, ii. 71 Albumen, ii. 138 Alkalie.'j, ii. 78 Alkohol, ii. 135 Alum, ii. 92 Alumina, ii. 91
4.50
INDEX.
Amalgams, ii. 104- Amber, ii. 129 Ammonia, ii. 85 Animal substances, ii. 137 AnimalculcE, method of pro- curing, ii. 339 Antimony, ii. 11, > Aquatinta, ii. 432
Arsenic, ii. 116 Arsenic acid, ii. 117 Astronomy, i. 413 Attraction, i. 12
•-, electrical, 1.324-
— , magnetic, i. 398
, chemical, ii. 4
Aurum musivum, ii. 325
B.
Balance, i. 32 Balloons, air, i. 162 Barometer, i. 147 Barometer gauge, i. 154 Barytes, ii- 89 Battery, electrical, i. 340
, galvanic, i. 383
Beer, ii. 135—153 Bellmetal, ii. 110 Bismuth, ii. 116 Bitter principle, ii. 139
Bitumen, ii. 130
Bleaching, ii. 160
Blood, ii. 140
Bone, ii. 140
Boron, ii. 76
Brass, ii. 110
Bread, manufacture of, ii. 147
Brewing, ii. 153
Bronze, ii. 110
BronzinsT, ii' 28*2
C.
Calico-printing, ii. 196 Calomel, ii. 104 Caloric, ii. 22 Camera obscura, i. 312 Carbon, ii. 70 Camphor, ii. 132 Carbonates, ii. 73 Carbonate of soda, ii. 82
. of ammonia, ii. 85
of lime, ii. 87
^ of magnesia, ii. 89
— of barytes, ii. 90
Carbonic acid, ii. 71 Carbonic oxide, ii. 73. Carburets, ii. 73 Casts, method of making, ii.
289 Catechu, ii. 131—209 Caoutchouc, ii. 130 Cements, various kinds of, ii.
292 Centre of gravity, i. 20 — of
oscillation, i. 82 Centrifugal and centripetal forces, i. 19
Cerium, ii. 124
Chemistry, definition of, ii. 1
• Animal, ii. 141
■ , instrumentsfor, ii.4
Chlorates, ii. 65 Chloric acid, ii. 64 Chlorides, ii. 65 Chlorine, ii. 63 Chromate of lead, ii. 113 Chromium, ii. 123 Chronometers, i. 83 Cinnabar, ii. 104 Clay, ii. 92 Clepsydra, i. 83 Clocks, i. 84 Cobalt, ii. 119 Colouring matter, ii. 131 Colouring used for drawing, ii. 410
Columbium, ii. 124
Combination, chemical, ii. 6
Comets, i. 439
Compass, mariners', i. 402 — 411
, azimuth, i. 412
9
INDEX.
451
Condenser for air, i. ItS Crayon painting, ii. 409
Copal, ii. 129 — method of Cupellation, ii. 215
dissolving it, ii. 24'3 Currying, art of, ii. 211
Copper, ii. 109 Cyanogen, ii. 74 Cotton, bleaching of, ii. 170
D.
Dip, of the magnetic needle,
i. 403 Discharge, electrical, i. 339,
345 Distillation, ii. 8. Diving bell, i. 159 Divisibility of matter, i. 2 Drawing, "ii, 342—348
--, implements for, ii.342 — , the figure, ii. 388 — , landscapes, ii. 400 •, mechanical, if. 403
Drawings, methods of copying,
ii. 404 Dyeing, ii. 178
E.
Earth, considered as a planet, i. 433
Earths, ii. 86
Echo, i. 229
Eclipses, i. 441
Elain, ii. 139
Electricity, i.319 — considered chemically, ii. 35
, atmospheric, i. 346
• , miscellaneous ex- periments in, i. 352
, animal, i. 373
, medical, i. 375
Electrometer, i. 326 Electrophorus, i. 344 Elementary substances, ii. 2 Engraving, ii. 419 Epsom salt, ii. 89 Equator, i. 415 Etching on copper, ii. 423 — — — on glass, ii. 442 Ether, ii. 136 Euchlorine, ii. 64 Evaporation, ii. 8 Extension, i. 5 Eye, description of, i. 249
Fecula, ii. 127 — 148 Fermentation, ii. 134 — 150 Fibrin, ii. 138 Filtration, ii. 7. Fine arts, ii. 342 Fireworks, artificial, ii. 329 Flax, ii. 161 Fluidity, i. 6 Fluates, ii. 78 F'luoboric acid, ii. 78
Fluoric acid, ii. 77 Fluorine, ii. 77 Fluor spar, ii. 77 Fly wheels, i. 62 Fountain, i. 178 Friction, i. 57 F\dling, ii. 172 Fulminating powder, ii. 321 Furnaces, ii. 18
Galvanism, i. 381 Gas, ammonical, ii. 85 Gas, definition of, ii. 26
G.
Gelatine, ii. 137 Geometry, practical, ii. 348 Gilding, ii. 261
G G 2
452
INDEX.
Glass, chemical composition, Gold, ii. 99
ii, 91 — manufacture of, ii. Gravity,!, l^ — specific, i. 117
235 Grottoes, artificial, ii. 330
Glauber's salts, ii. 83 Gum, ii. 126
Glucine, ii. 93 Gunpowder, composition of, 82
Glue, ii. 292 Gypsum, ii. 88
Glutin, ii. 128—148
H.
Hair-rope machine, i. 195 Harmony of sound, i. 228 Hops, ii. 157 Hydraulics, i. 176 Hydrocarbonate gas, ii. 59 Hydrocyanic acid, ii. 74' Hydrogen, ii. 4'9— an acidifying principle, 54?
Hydrometer, i. 120 Hydrostatics, i. 106 Hydrostatic balance, i. 118 Hydrostatic bellows, i. Ill Hydrostatic paradox, i. 109 Hygrometer, 15 i. 2
L
Japanning, li. 248
Impenetrability of matter, i. 2
Inclined plane, i. 43
Ink, method of making, ii. 306 Iridium, ii. 121
— , sympathetic, ii. 308 Iron, ii. 104 — ores of, 106
Ink, Indian, ii. 346 Iodine, ii. 66 Invisible girl, i. 230
Kelp, ii. 213—235
K.
L.
Lac, ii. 129
Lacquering, ii. 258
Landscapes, drawing of, ii. 400
Lead, ii. Ill
Leather, nature of, ii. 201 -^ tanning of, ii. 202
Lever, i.24
Light, velocity of, i. 232 — • refraction of, 234 — con- sidered chemically, ii. 33
Lens, i. 236 — burning, i. 240 — focal distances of, 243
Lime, ii. 87
Linen, bleaching of, ii. 160
Lithia, ii. 84
Lithography, ii. 445
Lixiviatio%ii. 8
Loadstone, ii. 105
Lute, used in chemical ope- rations, ii. 9. 304
N.
Narcotic principle, ii. 1 32 Nickel, ii. 117 Nitrates, ii. 46
Nitrate of potash or nitre, ii.
81 Nitric acid, ii. 45
INDEX.
453
Nitric oxide or nitrous gas, ii.
43 Nitrogen, ii. 39 Nitrous acid gas, ii. 44
Nitrous acid, ii. 44 Nitrous oxide, ii. 40 Nomenclature of chemistry, ii. 19. 142
M.
Machines, compound, i. 48
Machine, electric, i. 322
Magic lanthorn, i. 316
Magnesia, ii. 89
Magnetism, i. 396
Malt, 135—154.
Manganese, ii. 118
Mastic, ii. 129
Matter, i. 1 — its proper- ties, i. 2
Mechanics, i. 1
Mechanic powers, i. 23
Mercury, ii. 103
Metals, ii. 94 — refining of, ii. 215.
Mezzotinto scraping, ii. 431
Microscopes, i. 271
Milk,ii. 139
Mills, i. 67
Mirrors, i. 262
Mixture, as distinguished from combination, ii. 6
Mobility of matter, i. 2
Molybdena, ii. 120
Moon, i. 436
Mordant, ii. 180
Motion, laws of, i. 7 — commu- nication of, i. 58 — regula- tion of, by fly wheels, i. 62
Moving powers, i. 52
Moulding and casting, ii. 284
Mucilage, or gum, ii. 126
Mucus, ii. 138
Multiplying glass, i. 311
Muriate of soda, ii. 83
of ammonia, ii. 86
Muriatic acid, ii. 65
0.
Oil of vitriol, ii. 69 Oil, fixed, ii. 128
volatile, ii. 129
animal, ii. 139
phosphoric, ii. 319
Operations, chemical, ii. 6
Optics, i. 232
Orrery, electrical, i. 333
Osmium, ii. 121 Oxychloric acid, ii. 64 Oxydes, ii. 96 Oxygen, ii. 36 Oxygenated muriatic acid,
used in bleaching, ii. 166 Oxynmriate of potash, ii. 82
P.
Palladium, ii. 122 J'aper, bleaching of, ii. 177 Paradox, hydrostatic, i. 109 Paste,method of making, ii.303 Pasting, ii. 218 Pearlash, ii. 80 Pendulum, i. 80 Perkinism, i. 394 Perspective, ii. 374 ^
Pewter, ii. Ill
Phantasmagoria, i. 316 Phlogiston, ii. 98 Phosphorus, ii. 74— method of
making, ii. 316 Phosphoretted hydrogen, ii. 62 l^hosphoric acid, ii. 76 Phosphuret of lime, ii. 88. 320 Pinchbeck, or princes' metal,
ii. 110 Plaster of Paris, ii. 89
1-54
INDEX.
Plating, ii. 276 Planets, i. 422 — 437 Points, electrical, i. 331 Polarity of the magnet, i. 101 Potash, ii. 79.
-^ , manufacture of, ii. 214
Potassium, ii. 81 Pottery, ii. 228 Precipitation, chemical, ii. 5
Press, Bramah's, i. 115
Prussian blue, ii. 74
Prussic acid, ii. 74.
Pulley, i.41.
Pump, air, i. 129 — sucking, i. 183— lifting, i. 185 — forc- ing, i. 186 — various con- structions of, i. 188
Pyrometer, ii. 30
R.
Recapitulation of the principal
tacts in vol. i. 446 iteceipts, miscellaneous, ii. 316 Reflection of light, i. 261 Refining metals, ii. 215 Refraction of light, i. 234-247 Repulsion, i. 22 , magnetic, i. 400
Resin, ii. 129, 239 — animal re- sins, ii. 140
Retorts described, ii. 9
Rhodium, ii. 121
Ribbands covered with gold by a chemical process, ii. 325
Rupert's drops, ii. 238
S.
Sacchrometer, ii. 157
Saltpetre, ii. 81
Scapement, i. 86
Screw, i. 45
Sea salt, composition of, ii. 83
Selenium, ii. 125
Shock, electrical, i. 335
Silica, ii. 90
Silks, bleaching of, ii. 173
Silver, ii. 101
Silvering, ii. 275
Size, method of making, ii. 304
Soap, chemical composition of,
ii. 84. 128 Soda, ii. 82 — manufacture of,
ii. 212 Sodium, ii. 83 Soldering, ii. 283 Solidity of matter, i. 2. Sound i. 227 Spark, electric, i. 328 Speaking tubes, i. 230 Specific gravities, i. 1 17 — table
of, i. 122 Spectacles, i. 257 Spermaceti, ii. 139
Spouting of water, i. 176
Springs, nature of, explained, i. 116
Staining wood, ii. 313
of ivory, ii. 316
Stains, method of removing, ii. 310
Starch, ii. 127
Stars, fixed, i. 439
Statera, i. 35
Steam engine, i. 206 ■ — inven- tion of, 207 — Savary's, 208 — Newcomen's,211 — Watt's, 216 — Cartwright's, 224 — Highpressure, 224
Steam boats, i. 225
Steam used in bleaching, ii. 169
Stearin, ii. 139
Steel, ii. 105 — a method of making, 337
Strontia, ii. 90
Suction, i. 133
Sugar, ii. 127 — animal sugar, ii. 140
Sulphate of lime, ii. 89
■ of magnesia, ii. 89
INDEX.
4.55
Sulphate of barytes, ii. 90
of iron, ii. 105
of copper, ii. 19
of soda, ii. 83
Sulphur, ii. 67 Sulphuretted hydrogen, ii. 61
Sulphuric acid, ii. 69 Sulphuring in bleaching, ii. 172 Sun considered as the centre of
our system, i. 431 Syphon, i. 179
T.
Tannin, ii. 131 Tanning, ii. 201 Telescope, i. 297
, refracting, i. 297
, binocular, i. 301
, reflecting, i. 303
, acromatic, i. 308
Terella, i. 405 Thorina, ii. 93 Tides, cause of, i. 444 Time keeper, i. 84 Tin, ii. Ill
Tinning, ii. 281 Titanium, ii. 123 Tobacco-pipes, manufacture
of, ii. 234 Tombac, ii. 110 Torricellian vacuum, i. 129 Touch, magnetic, i. 406 Transparencies, method of
making, ii. 407 Trumpet, speaking, i. 231 —
hearing, i. 231 Tungsten, ii. 120
u &v.
Uranium, ii. 124
Vacuum Torricellian, i. 129
Boylean, i. 129 Valves, i. 202
Varnishing, ii. 239 Vegetable substances, ii. 125 Verdegris, ii. 110 Vision, cause of, i. 244
W.
Watches, i. 84 — 89 Water, chemical constituents
of, ii. 54 Water-spouts, i. 175 Wax, ii. 132 Weatlier-glass, i. 150 Wedge, i. 44 Wheel and axis, i. 36
Wheels, bevelled, i. 60 Wheels carriages, i. 101 Wind gauge, i. 152 Winds, various classes of, i. 172 Wood-cutting, ii. 443 Woody fibre, ii. 131 Wool, bleaching of, ii. 171
Zenith, i. 415 Zinc, ii. 114
Z.
Zirconia, ii. 93 Zodiac, i. 419
THE END.
London:
Prluted by A. & R. Spottlswoode,
New-Street-Sqiiare.
CHEMISTRY.
Piatt I.FolJI.
CHEMISTRY
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