A Select Collection of Valuable and Curious Arts and Interesting Experiments Part 2

60. COPPER-PLATE PRINTING.--The paper on which impressions from a copper-plate are to be taken, should be moistened, or wet down two or three days previous to printing; this is performed by dipping the sheets in water severally, and then laying them all together under a heavy weight till they are used. When the paper is ready, the copper-plate may be warmed over a chafing dish of coals, and the engraved side completely covered and all the lines filled with common printing ink, or ink made of Frankfort black, finely ground in old linseed oil. This may be done by means of a printing ball, or the ink may be spread on the plate with a smooth stiff brush. The plate may then be wiped with a piece of linen or cotton cloth, and afterward with the hand, being pa.s.sed slowly but hardly over the plate to take off all the ink except what remains in the lines of the engraving; to accomplish which more effectually, the hand may be rubbed occasionally with dry whiting. When the plate is thoroughly cleaned of the redundant ink, it may be laid on the table of a rolling press, and having a sheet of the moistened paper laid upon the face of it, and a piece of fine broad-cloth over the paper, the whole may be pa.s.sed through the press. Then on taking up the paper, it will be found to have received a black impression from the plate, according to the engraving or etching, and the plate may be again carried to the fire, to be blacked again as before. This is the usual manner of printing; but when a rolling press is not at hand, the plate and moistened paper may by other means, be pressed hard and firmly together, and the paper will have received the impression equally as fair. Any of the colours, commonly used in oil painting, being ground very thick in oil may be subst.i.tuted for ink in copper-plate printing. The plate, after being used, should be wiped clean with a piece of flannel, moistened with olive oil.

61. ETCHING LETTERS OR FLOWERS ON GLa.s.s.--Select a piece of gla.s.s that is thick and straight, and lay a coat of melted bees-wax on the fairest side; then with a needle, pen-knife, or any other convenient pointed instrument, trace any design, or picture, which being placed under the gla.s.s, may be seen through the wax; or form any letters or figures on the gla.s.s, carefully cutting or scoring quite through the wax, and making the lines large or small as occasion may require. Then warm a piece of the wax, so as to form it into a roll, about one fourth of an inch in diameter; lay this roll round the work upon the gla.s.s, and press it down so as to make it adhere to the gla.s.s, thus forming a border. Then take some finely powdered fluate of lime, and strew it evenly over the gla.s.s, on the waxed side, that it may fill all the lines in the wax; and then gently pour upon it, so as not to displace the powder, as much sulphuric acid, diluted with thrice its weight of water, as is sufficient to cover the powdered fluate of lime. Let every thing remain in this state for three hours; then pour off the mixture, and clean the gla.s.s by was.h.i.+ng it with spirits of turpentine. The figures which were scored in the wax, will be found engraven on the gla.s.s; while the parts which the wax covered, will be uncorroded.--This gla.s.s plate may be charged with ink, (or any thick oil paint) and impressions may be taken from it on paper, the same as from copper plates, only caution is requisite, that the gla.s.s be not broken by the pressure. _Note._--The fluoric acid, which is partly absorbed by the water, in the above process, being very corrosive, should not be suffered to touch the hands, nor any valuable vessel whatever.

62. TO PRINT FIGURES WITH A SMOOTH STONE.--Take a piece of marble or slate, and form a smooth plane surface on one side, and on this, paint any letters or figures with common oil paint of any colour. When this is dry, wet the stone with water, which will not adhere to the painted figures, especially if the paints were mixed with old linseed oil, that will produce a sharp gloss. Then apply a printer's ink-ball to the plane surface, by which means the dry painted figures will be covered with the ink, while the bare surface of the stone, being wet, will not be blackened or affected by it. Press the figured surface upon some moistened paper, and it will give a fair impression of the painted figures, on the paper. The block of stone must be then dipped in the water, and again inked as before, Thus many impressions may be taken with a tolerable degree of accuracy.

63. TO CUT GLa.s.s WITH A PIECE OF IRON.--Draw with a pencil on paper, any pattern to which you would have the gla.s.s conform; place the pattern under the gla.s.s, holding both together in the left hand, (for the gla.s.s must not rest on any plane surface;) then take a common spike or some similar piece of iron,--heat the point of it to redness, and apply it to the edge of the gla.s.s; draw the iron slowly forward, and the edge of the gla.s.s will immediately crack; continue moving the iron slowly over the gla.s.s, tracing the pattern, and the c.h.i.n.k in the gla.s.s will follow at the distance of about half an inch, in every direction according to the motion of the iron. It may sometimes be found requisite, however, especially in forming corners, to apply a wet finger to the opposite side of the gla.s.s. Tumblers and other gla.s.ses may be cut or divided very fancifully by similar means. The iron must be reheated as often as the crevice in the gla.s.s ceases to follow.

64. BEST CEMENT FOR JOINING GLa.s.s.--If the gla.s.s is not likely to be exposed to moisture, the pieces may be joined by a solution of equal parts of gum-arabic and loaf sugar in water; or if these are not at hand, the white of an egg may answer nearly as well. But a strong water proof cement that is equally transparent, may be made by digesting finely powdered gum-copal, in thrice its weight of sulphuric ether till it is dissolved. This solution may be applied to the edges of the broken gla.s.s, with a camel hair pencil, and the pieces must be put together immediately and pressed close till they adhere.

65. BEST CEMENT FOR JOINING CHINA OR CROCKERY.--Heat a piece of chalk to a full red heat in a fire; and while this is heating, take the white of an egg, and mix and beat together with it, one fourth of its weight of pondered or sc.r.a.ped cheese, (such as is most void of cream, or oily matter is preferable) or the curd that is formed by adding vinegar to skimmed milk;--take the chalk from the fire, and before it is cold, reduce it to powder, and add as much of it to the mixture as will form a thick paste, and beat them anew all together, and use the composition immediately. When this is dry, it will resist, in a great measure, either heat or moisture. A semi-transparent cement, suitable for china ware, may be made by gently boiling the flour of rice with water.

66. TO MAKE A STRONG WATER PROOF GLUE.--Dissolve common glue in water in the usual way, and dip into it some clean paper, sufficient to take up an ounce or more of the glue. When the paper is nearly dry, roll it up, or cut it into strips and put them into a wide mouthed phial or flask, with about four ounces of alcohol; suspend this over a fire so as to boil it gently for an hour, having the cork set in slightly to prevent its taking fire, but not so as to prevent the vapour entirely.

Then take out the paper (the only use of which is to give the glue more surface for the action of the alcohol) and add one ounce of gum-sh.e.l.lac in powder; continue the heat, often shaking the mixture till the sh.e.l.lac is dissolved. Then evaporate it to the proper consistence for use. _Note._--Many experiments have been made, in order to discover some aqueous size, that when dry, would resist moisture: and some have recommended skimmed milk, and others vinegar as a menstruum for the glue. But it does not appear from trial, that either of these are but very little better for this purpose than water; nor is it probable that any similar composition of size will resist moisture much better than common glue, especially if it be mixed with sulphate of lime, or some similar substance by way of support.

67. THE ART OF MOULDING FIGURES IN RELIEF.--Mix together and temper with a solution of gum-arabic in water, one part of clean, sifted wood-ashes, and two parts of fine sulphate of lime. Knead this composition on a board, till it has the consistence of putty. Press a ball of this putty on any medal, coin or carved work in relief, (which must be previously oiled) and let it dry; then take off the mould thus formed, and oil the part that has received the impression of the figure, with olive oil;--make a small orifice through the mould, from the centre, or deepest part of the impression; also, pare off the border of the mould, to within half an inch of the impressed figure.

Then lay a small piece of the putty on the board and press the mould down hard upon it, that it may not only fill the mould, but that the redundant part may be pressed out beyond the border of the mould: raise the mould a little and blow through the orifice, to detach the new moulded figure from the mould. Thus any number of figures may be readily produced, suitable for ornamenting chimney pieces, or mouldings, and which will be very hard when dry, and may be painted with any coloured oil paints, which will also preserve them from moisture.

68. TO CAST IMAGES IN PLASTER.--For this purpose a model of the figure that is to be cast, must be provided, and suspended by a rod or staff, one inch in diameter, and fixed in the top of the head. This model may be made of wood, chalk, or any other substance that is smooth, and sufficiently cohesive to support itself. This being prepared, mix fine sulphate of lime with water, to the consistence of soft putty, and having brushed some olive oil over the model, cover it completely with the plaster, which must be applied, and spread over it with the hands, to the depth of two inches or more. When the plaster is nearly dry, divide it into several parts with a thin blade, so as to take it off from the model without breaking any part. When the several parts of the mould are dry, oil them inside and put them together as before, and bind them with pieces of tape or twine; set the mould upright, and fill it with a fresh mixture of sulphate of lime and water, of as much consistence as may be poured in through the aperture at the head. This plaster should be poured into the mould as quick as possible after being mixed; otherwise it would become too stiff, and be spoiled. The plaster in the mould will soon cohere, so that the mould may be taken off, and the figures may be set up to dry; and the mould being oiled and put together again, is ready for another cast.

69. TO PRODUCE EMBOSSED LETTERS, OR FIGURES ON MARBLE.--Take some of the coloured varnish described at 37, and with a hair pencil, draw the letters, &c. on the marble, (which should be previously well polished,) and also cover with the varnish, every part of the face of the marble that is to remain plain. Lay the marble in a horizontal position and make a border of oil putty round it, and pour on muriatic acid to the depth of half an inch on the marble. When ebulition ceases, the acid may be drained off, and the work examined; and if the letters are not sufficiently prominent, a fresh quant.i.ty of the acid may be added. When the work has been thus corroded to the depth required, the varnish may be washed off with spirits of turpentine.

The acid that has been thus employed need not be lost, for a muriate of lime being thus formed, may be crystallized by a slight evaporation, and preserved for other purposes; or by the addition of a small quant.i.ty of sulphuric acid a sulphate of lime is precipitated, and the muriatic may be poured off and be used again for the same or a similar purpose.

70. TO SOFTEN STONE.--Marble or granite may be deprived in some measure, of the property of cohesion by being heated red hot and then quenched in oil. In this case, the carbonic acid which const.i.tutes the cohesive property of the stone, is expelled by the heat; and the vacuum thus produced in its pores, are in some measure, filled by the oil by the pressure of the atmosphere; by which means the stone acquires a texture quite different from what it had previously. This however, is not often applied to any valuable purpose.

71. TO CHANGE WOOD APPARENTLY, TO STONE.--Provide a block, or plank of soft wood, of the dimensions required, and give it two or three coats of linseed oil, allowing each to dry. Then having prepared some pieces of marble or granite as directed in the last experiment, pulverize them to a gross powder; brush over the wood with a heavy coat of copal varnish (see 47) mixed with an equal quant.i.ty of venice turpentine; let this rest about an hour, and then strew the stone powder over every part of it, so as to cover the surface completely. If marble is to be imitated, the powder of different colours, especially the white and blue, may be prepared separately, and may be strewed on the work in such shades as will appear the most natural. Granite may also be crossed or striped occasionally with streaks of a coa.r.s.er grain, which will give it a very deceptive effect. When the varnish is thus covered with stone, a heavy roller, or round log of wood, having a blanket folded and wrapped round it, should be rolled over the work, that the larger grains, (which of course will be the most exposed,) may the more firmly adhere. In this manner, a very perfect imitation of stone may be given, and the wood thus prepared will be exceedingly durable, and will answer for many purposes, as well as real stone.

72. TO RENDER WOOD, CLOTH OR PAPER FIRE-PROOF.--Dissolve one ounce of alum, half an ounce of sub-borate of soda and half an ounce of cherry tree gum, in half a pint of vinegar. Dip any cloth or pieces of paper, or wood, in this mixture and let them dry;--they cannot afterwards be ignited so as to blaze, but may be considered safe with regard to their taking fire by accident. _Note._--Though this composition is a very powerful preventive against fire, it is too complex for common use, and has too much colour for white cloths or papers; but a solution of one ounce of sub-borate of soda in a pint of water is very transparent and harmless, and will answer in most cases nearly as well.

73. TO PRODUCE FIRE READILY.--_Process 1._ Mix together gently but intimately, two or three grains of chlorate of pota.s.s, and an equal quant.i.ty of loaf sugar, both previously reduced to fine powder:--dip the end of a strip of gla.s.s, or a straw in sulphuric acid, and with it gently touch the powder,--it will instantly burst into flame.

74. _Process 2._--Upon one drachm of spirits of turpentine, in a gla.s.s, pour an equal quant.i.ty of a mixture of three parts of nitric, with one of sulphuric acid. Instantaneous inflammation, accompanied by the production of a large quant.i.ty of black smoke, will be the result.

75. PROCESS 3.--Take a piece of phosphorus of the size of a pin's head, and wrap it in a piece of dry brown paper: rub the paper with a piece of wood, or any hard body, and it will instantly inflame.

_Note._--In handling phosphorus, it is proper to have a piece of paper or cloth intervene between the stick of phosphorus and the fingers; and the phosphorus should be kept under water except when wanted for use.

76. TO MAKE SUPER-COMBUSTIBLE MATCHES.--Prepare any number of small strips or splinters of pine or other light wood, which may be about two inches in length and one twelfth of an inch in diameter; dip one end of each in melted sulphur to the depth of one fourth of an inch.

When they are cold, sc.r.a.pe off most of the sulphur, and dip the ends of them slightly in a paste made of ten parts of chlorate of pota.s.s, five parts of loaf sugar and one part of red lead, mixed and ground together in alcohol. Afterwards they may be readily ignited or kindled at any time by application of the smallest quant.i.ty of sulphuric acid.

For this purpose, the ends of them may be dipped or rather barely touched to the acid in a phial, or, which is a better way, a strip of gla.s.s, or even wood may be dipped in the acid and applied to the match.

77. TO MAKE GUN POWDER.--Pulverize separately, five drachms of nitrate of pota.s.s, one of sulphur, and one of newly burnt charcoal. Mix them together with a little water, so as to make the compound into a dough; form this dough into rolls of the size of a small wire, which may be done by rolling small quant.i.ties between two boards. Lay a few of these rolls together, and cut them into very small grains, and place them on a sheet of paper, in a warm place, to dry. The dough may be prevented sticking to the board while rolling it, by rubbing on the board, a little of the dry compound powder. When the grains are thoroughly dry, they are ready for use or experiment. On the same principle, gun powder is manufactured on the large scale, but then the several parts of the operation, are performed by machinery, otherwise it would be a very expensive commodity.

78. TO MAKE THE COMMON FULMINATING POWDERS.--Grind and mix intimately, three parts of nitrate of pota.s.s, with two of sub-carbonate of pota.s.s, and one of sulphur. If half a drachm of this compound be placed on a shovel, and held over a gentle fire, it will soon explode with a loud report. It is not, however, attended with any danger. If two grains of chlorate of pota.s.s in powder and one of sulphur be mixed together, and wrapped in a piece of strong paper, and the paper be then struck with a hammer, it will also explode with detonation. This experiment may require some caution. _Note._--The percussion powder, such as is used for priming the patent percussion rifles, is composed of chlorate of pota.s.s, and flour of sulphur, with a trifling proportion of charcoal and loaf sugar, being made into a paste or dough with alcohol,--then grained and dried.

79. TO MAKE THE MERCURIAL FULMINATING POWDER.--Dissolve half an ounce of mercury in three ounces of nitric acid, a.s.sisting the solution by a gentle heat. When the solution is cold, pour it upon an equal quant.i.ty of strong alcohol previously introduced into a flask, and apply a moderate heat till effervescence is excited. (Do not forget that the mercurial solution must be poured upon the alcohol, and not the alcohol upon the solution.) A white fume will soon begin to undulate on the surface of the liquor, and flow through the neck of the flask, and a white powder will be gradually precipitated. As soon as any precipitate ceases to fall, quickly pour the contents of the flask on a filter; wash the powder with pure water, and cautiously dry it by a heat not exceeding that of boiling water. The immediate was.h.i.+ng the powder is material, because it is liable to the re-action of the nitric acid; and while any of that acid adheres to it, it is very subject to be decomposed by the action of light. This powder, if very pure and nicely made, explodes by percussion, or a moderate degree of heat. _Experiment._--Place one-fourth of a grain of this powder, between the ends of two slips of paste-board, and paste, or bind them firmly together;--hold the ends of the slips over the flame of a candle, and as soon as it becomes warm, it will explode with a loud report. This composition is less dangerous than the fulminating compounds of gold or silver, as it never explodes spontaneously; but yet it cannot be handled with too much caution. _Note._--The silver powder, or fulminating silver, with which torpedoes and waterloo crackers are charged, is prepared in a similar manner; pure silver being dissolved instead of mercury, but it is too dangerous to be trifled with.

80. TO KINDLE A FIRE UNDER WATER.--Put into a deep wine-gla.s.s, that is small at the bottom, three or four bits of phosphorus, about the size of flax seeds, and two or three times the quant.i.ty of chlorate of pota.s.s, in grains or crystals, and fill the gla.s.s nearly full of water. Then place the end of a tobacco-pipe stem directly on, or over the chlorate and phosphorus, and pour nearly a tea-spoon full of sulphuric acid into the bowl of the pipe, that it may fall directly on the phosphorus; a violent action will ensue, and the phosphorus will burn vividly, with a very curious light under the water.

81. TO LIGHT A CANDLE BY APPLICATION OF ICE.--Attach to the wick of a candle, a small piece, or globule of pota.s.sium (the metallic base of pota.s.s) of the size of a small shot. Apply an icicle or point of ice to the metal, and it will instantly inflame. _Note._--This curious substance, which has the peculiar property of being ignited by coming in contact with ice or water, has been lately discovered by Sir Humphrey Davy. It is produced by making pure pota.s.s a part of the circuit of a powerful Voltaic battery. It cannot be preserved but by being kept immersed in naptha, a kind of oil of which oxygen is not a const.i.tuent.

82. TO FORM LETTERS OR FLOWERS OF REAL FLAME.--Provide a tin chest of about eighteen inches in length, equal in height and one inch in breadth. Chalk any design, of letters or flowers on the face of this chest, and pierce each line with rows of small holes, which should be about half an inch distant from each other.--Make an aperture at the top, through which pour about a pint of a mixture of rum and spirits of turpentine. Place two or three lamps under the bottom of the chest (which must be raised a little from the floor for that purpose) to warm the spirits, but not so as to cause them to boil. Stop the aperture at the top and after eight or ten minutes (which time should be allowed for the vapour to expel the atmospheric air, which otherwise would cause an explosion) apply the flame of a lamp to the pierced lines;--in an instant, all the lines will be covered with flame, which will continue till the spirits are exhausted.

83. TO PRODUCE FLAME OF VARIOUS COLOURS.--This may be effected by mixing certain substances with burning alcohol, or by applying them with the point of a pen-knife, to the wick of a burning lamp or candle. Thus a beautiful rose or carmine coloured flame may be produced by muriate of strontia: this is prepared by dissolving carbonate of strontia in muriatic acid, and evaporating it to dryness.

The preparation for an orange colour, is muriate of lime; (a solution of marble in muriatic acid, evaporated to crystallization) which should be exposed to a moderate heat till it is deprived of its water of crystallization and falls to powder. A fine green tinge is produced by acetate of copper, or boracic acid; which last is procured by adding sulphuric acid to a solution of borate of soda (in hot water) till it has a sensibly acid taste; as it cools, the boracic acid is deposited in crystals on the sides of the vessel. Camphor gives to flame a blue colour; and nitrate of strontia (prepared the same as the muriate) a purple. A brilliant yellow may also be produced by muriate of soda. Any of these preparations being reduced to powder, may be ignited with three or four times their weight of alcohol, which should be previously warmed; and if the vessel that contains it be kept heated also, the combustion will be the more brilliant.

84. TO MAKE SKY-ROCKETS AND FIRE WHEELS.--Grind and mix together, (dry) one pound of gun powder, two ounces of sulphur, two ounces of nitrate of pota.s.s, and four ounces of newly burnt charcoal. Then make several strong paper cases or cartridges, by wrapping some strong paper (being moistened with paste,) fifteen or twenty times round a mould made of wood, which may be one inch in diameter, and ten inches in length. One end of this mould must be made smaller, being only one fourth of an inch in diameter for the s.p.a.ce of an inch of its length.

The paper must be drawn up close round this neck, and strongly bound with twine, being thus brought to a shape similar to the neck of a phial. This neck is called the choke of the cartridge. Take the paper from the mould, and proceed in the same manner with another. When a sufficient number of cartridges are thus made and dry, place one of them in a socket which it will fill up closely, and then fill the cartridge with the above described compound powder, which must be thrown into the cartridge in small quant.i.ties, and each several quant.i.ty must be rammed or beat down very hard, with a suitable sized rammer and mallet. In filling the cartridge, small quant.i.ties of any of the flame-colouring preparations, described in the preceding article, may be added occasionally. When the cartridge is nearly full, some small b.a.l.l.s of cotton, dipped in spirits of turpentine, may be added, to produce the appearance called stars.--These also, may have some muriate of strontia, or boracic acid strewed on them. Then place a circular piece of thick paste board on the materials in the cartridge, having a small hole through it, communicating with the powder below; lay upon this, half an ounce of fine gun powder, and fold the paper down upon it from all sides, cementing the folds firmly with glue, thus giving the end of the cartridge a conical form. Then bore a hole about two thirds of the length of the cartridge from the choke with a gimblet or bit. Fill this hole (which must be as large as the choke, but tapering towards the other end) with fine gun powder, to the choke, and fill the choke with the compound, the outside of which may be moistened a little, the better to keep it in its place. Finish the others in the same manner, and keep them in a warm dry place till used. They are then to be lashed firmly to the end of a light pine rod, with the choke towards the opposite end. The length of the rod, should be about nine times that of the cartridge. The rocket then being elevated by the rod, and being ignited at the choke, the compound inside burning intensely, acts upon the air, and causes it to ascend. The cartridges for fire wheels, are prepared in the same manner, but are generally smaller; and instead of being lashed to a rod, they are lashed to the arms of a wheel, in such manner, that a violent rotary motion is produced by their combustion.

85. TO PRODUCE DETONATING BALLOONS.--Moisten and compress a bladder till no air remains in it, and tie the neck of it upon a perforated cork; set the cork in a flask containing the materials for producing hydrogen gas (see 9.) Thus convey into the bladder a quant.i.ty of the gas, and then remove the cork to another flask, containing two or three ounces of black oxide of manganese, moistened with sulphuric acid, sufficient to form with it a soft paste; apply the heat of a lamp, and oxygen gas will be evolved, and will also rise through the neck of the flask; in this manner, convey into the bladder, nearly half as much oxygen gas, as it previously contained of hydrogen. Then tie the stem of a tobacco-pipe in the neck of the bladder, and dip the bowl of the pipe in a solution of soap in water, (soap-suds) and compress the bladder a little, so as to swell a bubble from the bowl of the pipe;--shake off the bubble, which being lighter than atmospheric air will naturally rise, or float horizontally in the air.

If the flame of a candle be brought in contact with one of these balloons, or floating bubbles, it will explode with a violent detonation, resembling the report of a pistol. If this compound gas be forced into the water, so as to form several bubbles on the surface, and flame be then applied to them, a volley of explosions will be the result. Caution is requisite in these experiments, that the fire be not communicated to the bladder, as such an explosion might not be safe.

86. TO PREPARE A PHIAL THAT WILL GIVE LIGHT IN THE DARK.--Fill a small phial about one third full of olive oil; add to this a piece of phosphorus equal to one tenth of the weight of the oil. Cork the phial and wrap it in paper to exclude the light, and set it, or suspend it in a warm place, but where the heat may not be equal to that of boiling water, till the phosphorus appears to be dissolved. This phial may be carried in the pocket, and whenever the cork is started in the night, the phial will evolve light enough to show the hour on a watch.

87. TO MAKE A PERSON'S FACE APPEAR LUMINOUS IN THE DARK.--Prepare some phosphorized oil, (as directed 27,) and rub it over the face. This oil, though it appears luminous in the dark has not power to burn any thing, so that it may be rubbed on the face or hands without danger; and the appearance thereby produced, is most hideously frightful. All the parts of the face that have been rubbed, appear to be covered with a luminous bluish flame, and the mouth and eyes appear as black spots.--The luminous appearance may also be repeatedly heightened, by the friction of a handkerchief, being rubbed over the luminous part.

88. TO FREEZE WATER IN WARM WEATHER.--Draw a thread through a small gla.s.s tube; close one end and then fill the tube with water. Mix together equal parts of nitrate of ammonia and water, and immerse the tube in this mixture. The water in the tube will be frozen immediately, and may be drawn out by the thread. The same effect may be produced by a mixture of one part muriate of ammonia, one part nitrate of pota.s.s, and three parts of water. For these experiments, the above mentioned salts should be fresh, dry and finely pulverized previous to mixing; the mixture should be made in a tin vessel that is coated inside with bees-wax, and has a flannel wrapper round the outside, and the tube should be immersed quickly, as soon as the ingredients are mixed. To produce a greater, or intense degree of cold, a small vessel of water is first set in one of those freezing mixtures till it becomes very cold, and then the due proportion of the salts are added to that, and the tube, &c. immersed in it. The water in the tube may also be frozen, by continually bathing the outside of it with sulphuric ether: the evaporation of the ether, carries off the caloric of fluidity, and the water congeals.

89. TO CHANGE THE COLOURS OF ANIMALS.--Any black, or dark coloured spots on some animals, especially horses, may be effectually changed to white, by means of any substance that will chafe or blister the skin; thus a white spot of any shape may be produced on a black horse, by shaving off the hair from the part that is to be thus marked, and applying a plaster of spanish flies, or of quick lime moistened with vinegar; this plaster must be cut to the size and form required for the mark, and must be kept bound on, till the skin is blistered, or nearly so. The next coat of hair will infallibly be white. White spots can be changed to black or brown, only by means of oils or grease.

Bacon fat has been recommended for this purpose, but if the oil or fat of a bear can be procured, it will prove more efficacious, as this fat is well known to have a remarkable tendency to darken the colour of animals and even complexions. But either of these, and in fact, many other kinds, will answer this purpose if properly applied, and frequently repeated.