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allowing the mixture to settle for a short time. By this means the water dissolves out the methyl-alcohol, and the mixture of spirit and water readily rises to the surface, in virtue of its low specific gravity, and can be removed by means of a siphon, or by simply pouring it off. As a blasting liquid it is now ready for use. If protected blasting liquid be kept in a closed vessel, it will remain in that state for an indefinite period of time, and ready at any moment to be reduced or rendered fit for action; if, however, it be exposed in an open vessel, it will regain its explosiveness, in periods of time proportionate to the amount or degree of exposure. For blasting purposes, the chief advantage which nitro-glycerine possesses is that it requires a much smaller hole or chamber than gunpowder does, the strength of the latter being scarcely that of the former. A chamber, 34 millimètres in diameter, was made perpendicularly in a dolomitic rock, 60 ft. in length, and at a distance of 14 ft. from its extremity, which was nearly vertical. At a depth of 8 ft., a vault filled with clay was found, in consequence of which the bottom of the hole was tamped, leaving a depth of 7 ft. One litre and a half of nitro-glycerine was then poured in; it occupied 5 ft. A match and stopper were then applied as stated, and the mine sprung. The effect was so enormous as to produce a fissure 50 ft. in length, and another of 20 ft. Nitro-glycerine has, however, one disadvantage. It freezes at a temperature very probably above 92° F., and it is said that even at a temperature of 43° to 46° F. the oil solidifies to an icy mass, which mere friction will cause to explode. It is probable, however, that the freezing-point of the oil lies somewhat lower than is here stated, though as yet no exact determination of the freezing-point of the oil has been made. Great care must be exercised whilst it is in a frozen state, as otherwise it will cause most dreadful accidents.

Dynamite is made by mixing 75 per cent. of nitro-glycerine with 25 per cent. of powdered sand. Dynamite re

tains all the properties of nitro-glycerine for blasting, but is not so dangerous, as it may be handled freely. Explosion is produced by means of a percussion cap in the same manner as with nitroglycerine.

Fulminates.-Fulminate of Mercury. 1. This highly-explosive compound consists of protoxide of mercury united with an acid; fulminic acid, formed of cyanogen and oxygen. Fulminate of mercury is prepared by causing alcohol to react on the acid protonitrate. A quantity of mercury is dissolved in 12 parts of nitric acid of 35° or 40° of Baumé, and 11 parts of alcohol at 86 are gradually added to the solution; while the temperature is slowly elevated, a lively reaction, accompanied by a copious evolution of reddish vapours, soon ensues, when the liquid, on cooling, deposits small crystals of a yellowish white colour. Fulminate of mercury is one of the most explosive compounds known, and should be handled with great care, especially when it is dry, and it detonates when rubbed against a hard body. It dissolves readily in boiling water, but the greater portion is again deposited in crystals during cooling. The fulminating material of percussion caps is made of fulminate of mercury prepared as just stated, after having been washed in cold water. The substance is allowed to drain until it contains only about 20 per cent. of water, and is then mixed with

of its weight of nitre, which mixture is ground on a marble table with a muller of guiacum-wood. A small quantity of the paste is then placed in each copper cap and allowed to dry, the fulminating powder in the cap being often covered with a thin coat of varnish to preserve it from moisture. 2. Weigh out 25 grains of meroury in a watchglass, transfer it to a half-pint pipkin, add a measured oz. of ordinary concentrated nitric acid, sp. gr. 1.42, and apply a gentle heat. As soon as the mercury is completely dissolved, place the pivkin upon the table away from any flame, and pour quickly into it, at arm's length, 5 measured drachms of

moist.

Fulminating Platinum.-Dissolve binoxide of platinum in diluted sulphuric acid, mix the solution with excess of ammonia, a black precipitate is obtained, which detonates violently at about 400° F.

alcohol, sp. gr. 0.87. A brisk action | plosion, and is dangerous whilst still will ensue, and heavy white clouds will arise. When this action has subsided, fill the pipkin with water, allow the fulminate to settle, and then pour off the liquid acid. Collect the fulminate on a filter, and wash with water as long as the washing tastes acid, then dry by exposure to the air. This explodes at a temperature of 360° F., or by being touched by a glass rod which has been dipped in concentrated nitric or sulphuric acid. An electric spark also explodes it.

Fulminating Gold.-Add ammonia to a solution of terchloride of gold; the buff precipitate which it deposits is violently explosive at a gentle heat.

Terchloride of Gold.-Dissolve gold in hydrochloric acid, with one-fourth of its volume of nitric acid. Evaporate on a water bath to a small bulk; when cool, yellow prismatic crystals of a compound of the terchloride, with hydrochloric acid are deposited, from which the hydrochloric acid may be expelled by a gentle heat, not exceeding 250° F. The terchloride forms a red brown deliquescent mass, which dissolves very readily in water.

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Fulminate of Silver. - Dissolve 10 grains of pure silver, at a gentle heat, in 70 minims of ordinary concentrated nitric acid, sp. gr. 1·42, and 50 minims of water. As soon as the silver is dissolved the heat is removed, and 200 minims of alcohol, sp. gr. 0.87, are added. If the nitric acid and alcohol are not of the exact strength here given it may be difficult to start the action, in which case add two or three drops of red nitric acid, which contains nitrous acid. Standard silver, containing copper, may be used for the preparation of the fulminate. If the action does not commence after a short time, a very gentle heat may be applied until effervescence begins, when the fulminate of silver will be deposited in minute needles, and may be further treated as in the case of fulminate of mercury. As the fulminate of silver is exploded much more readily than the fulminate of mercury, it must be handled with the greatest caution when dry. It should be separated into small quantities, each portion wrapped in paper, and kept in a cardboard box, nothing harder than this should be Saltpetre.-Crude saltpetre cannot be brought in contact with it. This mix-used for making gunpowder. The crysture is of no use for percussion caps, being too violent in its action.

Throw-down Detonating Cracker. Screw up a particle of fulminate of silver in a piece of thin paper, with some fragments of a crushed quartz pebble.

Gunpowder. The component parts of gunpower are saltpetre, sulphur, and charcoal, used in the following proportions:-1. English war powder.-Saltpetre, 75 parts; sulphur, 10; charcoal, 15. 2. French war powder.Saltpetre, 75 parts; sulphur, 12.5; charcoal, 12.5. 3. French sporting powder.-Saltpetre, 76 9 parts; sulphur, 9.6; charcoal, 13.5. 4. French blasting powder.-Saltpetre, 62 parts; sulphur, 20; charcoal, 18. There are a number of variations of the above receipts; but the difference, which is purely a matter of opinion, consists principally in varying the quantity of sulphur or charcoal employed.

talline flour, quite free from chloride, is the best for the purpose. The washing process is carried so far that nitrate of silver produces no precipitate in the purified saltpetre. The general rule is to use the saltpetre whilst slightly Double Fulminate of Silver and Am- damp, allowing for the proportion of monia.-Dissolve fulminate of silver in moisture when mixing with the other warm ammonia: the solution, on cooling, ingredients. This saves the processes of will deposit crystals of the double ful- drying and grinding the saltpetre before minate. This is very violent in its ex-mixing with the sulphur and charcoal.

SULPHUR. Refined sulphur in rolls | riorates by keeping. Charcoal that has been too highly burned for war powder is used in the manufacture of blasting powder, as that need not be so inflammable.

is used. This must be reduced to an impalpable powder, which is usually effected by placing the sulphur in hollow wooden drums, having projections, or brackets inside. A number of small brass balls are put into the drum with the sulphur, and the drum is made to revolve for six hours, when the action of the balls and projections reduces the sulphur to very fine powder, which is then extracted through wire gauze. Any small particles of sand, or unequally pulverized sulphur, are then separated by a bolting machine.

CHARCOAL.-The quality of the charcoal depends greatly upon the material from which it is obtained, and the manner in which it is prepared. The soft, woody parts of plants, which yield a friable, porous charcoal, leaving very little ash, are preferred. Black alder, and spindle tree, poplar, chestnut, vinestalks and willow, are most esteemed. Hemp-stalks, fibres of flax, and old linen also yield a very good charcoal. Remove the bark, leaves, and smaller branches, selecting branches from 1 to 2 inches in thickness. These are to be cut into lengths of 5 or 6 feet, and tied in bundles, weighing about 30 lbs. The wood will not be injured by exposure to the rain, as that tends to remove extractive matter. The carbonization is effected either in pits, or in cast-iron cylinders. The yield of charcoal is 18 to 20 per cent., when prepared in pits; and from 35 to 40 per cent. when prepared in the cast-iron cylinders. The process of manufacture is similar to that adopted for ordinary charcoal, the pits or cylinders, however, replacing the ordinary kiln. If the charcoal is intended for sporting powder, it may be withdrawn whilst of a brown colour, when it is called red charcoal. This would make a powder too explosive for war purposes; this must be prepared from the black or distilled charcoal, which is more completely calcined, and is used by all English makers. The best quality has a bluish black colour, is light, firm, and slightly flexible, and should be used immediately it is made, as it rapidly dete

Pulverizing. The required quantities of sulphur and charcoal are thoroughly pulverized, and intimately mixed, by being rolled for about four hours in a cast-iron drum, with numerous small brass balls, at a speed of about 28 revolutions a minute. When the mixture is complete, the powdered sulphur and charcoal is removed from the drum, and a proportionate quantity of saltpetre is added. Great care must be used in weighing out the various ingredients, according to the quality of the powder required, as upon that, and the complete mixing of the materials, the success of the manufacture depends.

Mixing. The powder is put in a mixing machine, which is a leather drum, in which are placed numerous small bronze balls. The machine revolves at from 25 to 30 revolutions a minute, and in about 4 hours' time the mixing is complete.

Granulating. The powder having been damped and pressed into cakes, must then be crushed to the required size of grain. It is first roughly broken into lumps by small mallets; it is then fed into the granulating machine, which is caused to revolve for 35 or 40 minutes, at about 10 revolutions a minute. A small stream of water enters the granulator; the movement of the machine rolling the damp grains constantly among the dry meal powder, causes the latter to adhere to their sur

face, and each grain is thus increased by concentric layers. When the small meal powder is all absorbed by the action of the granulator, the material is placed in a barrel ready for equalization.

Equalizing.-The grains as they come from the granulator are of various sizes, they are therefore sifted over two leather or parchment sieves, one of which is pierced to separate the grains which are too large, whilst the other allows all the dust to pass through, retaining only the grains which are of the desired size.

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The small refuse powder which has passed through the sieve, is again placed in the granulator, and acted upon as before described.

Glazing. The powder is placed in a cask, or barrel, which revolves on its axis at about 40 revolutions a minute; by the friction of the grains against each other they become round, smooth, and polished, in which state the powder will bear the shaking and friction of carriage without injury, and is less likely to absorb moisture than when in rough and angular grains.

Drying. The powder must not be too rapidly dried, a temperature commencing at about 66° F., and gradually increased to 130° or 140° F., is a safe one; the operation requires from 3 to 4 hours, and is best performed in a room warmed by steam pipes or hot-air flues. The powder is then fit for use, and may be packed in sacks, to be afterwards placed in casks, or in double casks; sporting powder is usually packed

in tin canisters.

between the lamp and the block, causes the light to fall directly upon the block.

FIG. 30.

The dotted line shows the direction of

the light; by lowering the lamp this light would take a more horizontal direction, thus enabling the engraver to work farther from the lamp. A shade over the eyes is occasionally used as a protection from the light of the lamp.

block. Of each of these tools several sizes are required.

Pharaoh's Serpents.-Fuse in a crucible equal parts by weight of yellow TOOLS.-These consist of gravers, tintprussiate of potash and flower of sulphur, frequently it is advisable, if the tools, gouges or scoopers, flat tools or heat cannot be well regulated, to include chisels, and a sharp-edged scraper, somea little carbonate of potash; lixiviate thing like a copper-plate engraver's burthe mass with water and filter; the fil-nisher, which is used for lowering the trate will be sulphocyanide of potassium, which, upon being added to a solution of mercury dissolved in nitric acid, gives a copious precipitate of sulphocyanide of mercury; collect this; wash well with water, and dry; roll into a small pyramid, cover with tin-foil, and when dry it is ready to be lit.

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Engraving on Wood. graver's Lamp. · A clear and steady light, directed immediately upon the block to be cut, is a most important point, and in working by lamplight it is necessary to protect the eyes from its heat and glare. The lamp shown in Fig. 30 can be raised or lowered at pleasure by sliding the bracket up or down the standard, it being fixed in the desired position by means of the small set screw. A large globe of transparent glass, filled with clean water, placed

Gravers. The outline tool, Fig. 31, is chiefly used for separating one figure

FIG. 31

A

D

2

from another, and for outlines. A is the back of the tool; B, the face; C, the point; D is technically termed the belly. The horizontal line, 2, shows the surface of the block. All the handles when received from the turner's are circular, but as soon as the tool has been inserted a segment is cut away from the lower part, so that the tool may clear the block. The blade should be very fine at the point, so that the line it cuts may not be visible when the block 's printed, its

chief duty being to form a termination to a number of lines running in another direction. Although the point should be fine, the blade must not be too thin, for it would then only make a small opening, which would probably close up when the block was put in the press. When the tool becomes too thin at the point, the lower part must be rubbed on a hone to enable it to cut out the wood instead of sinking into it. Nine gravers of different sizes, starting from the outline tool, are sufficient for ordinary work. The blades as made are very similar to those used in copperplate engraving; the necessary shape for wood engraving is obtained by rubbing the points on a Turkey stone. The faces, and part of the backs, of nine gravers of different sizes, are shown on Fig. 32;

FIG. 32.

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B

the dotted line, A C, shows the extent to which the tool is sometimes ground down to broaden the point. This grinding rounds the point of the tool, instead of leaving it straight, as shown at A B. Except for the parallel lines, called tints, these gravers are used for nearly all kinds of work. The width of the line cut out is regulated by the thickness of the graver near the point, and the pressure of the engraver's hand.

Tint-tools. The parallel lines forming an even and uniform tint, as in the representation of a clear sky, are obtained by what is called the tint-tool, which is thinner at the back, but deeper at the side, than the graver, and the angle of the face at the point is much more acute, as shown on Fig. 33: A is a side view of the blade; B shows the faces of nine tint-tools of varying fineness. The handle is of the same form as that used for the graver. The graver should not be used in place of the tinttool, as from the greater width of its

two tools, from a comparison of which this statement will be readily understood. As the width of the tint-tool at B is little more than at A, it causes only a very slight difference in the distance of the lines cut, if inclined to the right or the left, as compared with the use of the graver. Tint-tools that are strong in the back are to be preferred as less likely to bend, and giving greater freedom of execution than weak ones. A tinttool that is thicker at the back than at the lower part, leaves the black raised lines solid at their base, as in Fig. 35,

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the block being less liable to damage than in the case of Fig. 36, in which the lines are no thicker at their base than at the surface. The face of both gravers and tint-tools should be kept rather long than short; though if the point be ground too fine it will be very liable to break. When, as in Fig. 37, the face is long, or, strictly speaking, when the angle formed by the plane of the face

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