The property which this powder possesses, of being inflamed by a blow or a stroke, determined its application, as priming, to percussion guns; but it soon gave place to fulminating mercury, on account of several inconveniences attending it, the principal of which are, to cause a great foulness, and to have a corrosive action on iron. Various methods have been tried to neutralise the effect of the acid; but the most successful results were accompanied by such a diminution of the explosive force of the mixture, as to have led to its discontinuance as a priming for firearms.

Howard's powder, or fulminate of mercury, is at present generally employed for the guns of sportsmen, on account of its easy inflammation, and its inaction upon iron. It is a salt formed of oxide of mercury, and a peculiar acid composed of one atom of nitrogen, one of oxygen, and two atoms of carbon. Since the compo

sition of this powder has been known, it has been named fulminate of mercury. When it detonates by a blow or by heat, the mercury and nitrogen are set at liberty in the state of vapour; and from the carbonaceous deposit observed on the surfaces on which it has been made to detonate, it is very probable that half the carbon which it contains forms, with the oxygen, carbonic acid, and that the other half is deposited or dispersed.

The fulminate, when dry, detonates very readily by a blow of iron upon iron, a little less readily by a blow with iron upon bronze, still a little less by that of marble on glass, marble on marble, or glass on glass: it inflames, however, with sufficient facility in these different circumstances, to be almost sure of causing the explosion at every blow. The blow of iron upon lead inflames it, but with great difficulty, and that of iron upon wood is quite ineffectual.

The fulminate always inflames easily by friction, especially by that of wood against wood. It detonates less readily by that of marble on marble than of iron upon iron, and, lastly, of iron upon wood or marble.

The fulminate which has been pulverised detonates

with more difficulty, particularly by friction, than that which is in crystals. Moistened with five per cent. of water, the fulminate loses a great deal of its inflammability: it detonates, however, with the blow of iron on iron; but the portion struck burns alone, and without flame, nor does it communicate inflammation to that which is not struck.

If the fulminate be mixed with ten per cent. of water, it will be still more difficult to inflame it. It disappears, however, by a blow of iron upon iron, but without flame and noise the part struck burns alone, and projects the other. Moistened with thirty per cent. of water, it still detonates, sometimes under the muller (wood on marble), during the manipulations; but the detonation is partial, and is not communicated to the rest of the mass: the muller is merely raised under the hand of the workman. According to the new arrangements adopted in the manufactory of priming powders situated in the plain of Jory, near Paris, since the explosion which entirely destroyed it, more than 200,000,000 of caps have been manufactured at that establishment, without any other accident than a piece of marble broken under the muller, as above mentioned.

The character of the powders eminently inflammable is to detonate at the moment of their inflammation, even when only very small quantities are employed, and to act on surrounding bodies as a moving power actuated by great velocity. The best made common powder is extremely far from having such a rapid inflammability as fulminate of mercury, and especially as fulminate of silver; and no firearms, loaded with either of these fulminates, with the same charge as common powder, can resist their explosive action, although the volume of elastic fluids produced in the first case is smaller than in the second. Whatever charge of the fulminate of mercury may be put into a firearm made with the known metals, it will speedily be destroyed; for during the charging of the primings or matches with the fulminate weakened with common powder, the punches of tempered cast steel,

with which the powder is pressed to the bottom of the capsules, are speedily furrowed by the explosions which occur every moment, although the gases produced have a free passage by the sides of the punches. The report details a series of experiments which place in a striking point of view the rapidity of explosion and irresistible power of this singular composition.

The quantity of fulminating mercury necessary for a `priming is so small, that it is in a manner unmanageable; and this circumstance naturally led to the expedient of mixing it with common powder, to increase the bulk of the priming: but this is not the chief advantage of the mixture. Pure fulminate of mercury communicates inflammation to powder but with difficulty, and at much smaller distances than when it is mixed with bruised or very fine powder: this is a consequence of the instantaneousness of its inflammation. If it is alone, the elastic fluids have lost the greater part of their caloric before reaching the powder, and can no longer inflame it; but if it is mixed with very fine powder, the latter is carried to the charge while in a state of ignition, and sets fire to it. In the trials of mixture of the fulminate with various substances, made rather with a view to preserve the priming from humidity than to change the composition of the powder, it was found that many were unfavourable to the explosion of the fulminate, although mixed with it only in very small proportions: such are oil, tallow, resin, and wax.

Of the different sorts of priming hitherto employed in France, there have been used, 1st, the fulminating powder in grain; 2d, the powder in pastilles covered with lead or paper; 3d, the powder in grains varnished; 4th, the waxed primings; 5th, the caps or capsules; and 6th, tube primings. The powder in grains is very dangerous, for the explosion of a single grain determines that of the whole mass. It is almost entirely disused. The other primings have not the same inconvenience, having a covering in common with those called waxed, and with caps, which are almost the only ones in use.

The waxed primings were in use with sportsmen when proposed by M. Vergnaud for the infantry. Every one contains three centigrammes (nearly half a grain English) of fulminate of mercury, and one centigramme of bruised gunpowder, and are enveloped with a coating of wax applied by hand, which defends them very well from the action of moisture, and prevents them from exploding simultaneously. They fix also very readily to the pan, and may be easily and safely carried, protecting them from the heat of the sun and of other bodies which might determine their agglomeration. They have the inconvenience of causing great foulness, and giving a little more smoke and smell than cap primings. Their present price in commerce is about seven francs per thousand.

The ciap primngs are most in use at present, and form at least 99 per cent. of the consumption: those for the guns of sportsmen contain in each priming 0·017 grammes of fulminate of mercury, mixed with six tenths of its weight of bruised gunpowder. These primings very well resist the action of humidity, and take fire after several hours' immersion in water.

Their very regular and solid form allows of their being fixed on the chimney of the touch-hole by mechanical means, which will be very advantageous for military fusils. In the explosion, the copper cap is torn sometimes divided and projected; but by hollowing the head of the percussion hammer, the copper is no longer projected except towards the ground.

The copper caps are made by means of a fly press with great rapidity. The primings sometimes take fire during the manufacture; but the inflammation communicates but very rarely to the small number of those under manipulation. They are easily carried, and without danger. Their present price in commerce is 33 francs per thousand. "At this moment," say the French reporters, we cannot say which sort of priming, the waxed or the cap priming, would be preferable for military service."

CHAP. VI.

QUALIFICATIONS PROPER FOR A WHITESMITH.-FORGING, SWAGING, AND FILING. APPARATUS FOR BORING SOLIDS AND CYLINDERS. TURNING LATHES.-COMMON WHITESMITH'S LATHE.— DOG AND DRIVER, AND CHUCKS. MAUDSLAY'S LATHE, CHUCK,

AND REST. TURNING TOOLS.

-

SLIDE LATHES. VARIOUS METHODS OF PRODUCING SCREWS. INSIDE SCREWS, OR BOXES. SAWING CAST IRON WHEN RED-HOT. CUTTING HARDENED STEEL WITH SOFT IRON.

THE whitesmith, or brightsmith, as the term implies, is an artificer who makes and finishes articles chiefly in iron or steel with a bright surface, by means of the file and the turning-lathe, in contradistinction to the blacksmith, who furnishes the productions of his forge either in a rough state, as from the hammer, or, at most, as blackened over with smoke or pitch. Originally, the whitesmith fabricated many of those articles for domestic use, as fire-irons, fenders, grates, &c., which have since become objects of separate manufacture. A modern whitesmithery establishment generally comprises the ingenuity and conveniences requisite for the production of every description of work, from what is called blacksmithing in its lowest, to what is termed machinemaking or engineering in its highest degrees. Hence, a first-rate whitesmith is not only required to understand generally the qualities of common iron and steel, and the methods of forging, welding, and otherwise working them; he must likewise have a competent knowledge of the principles of mechanical science, the laws and combinations of machinery in all the technical varieties of their application, and so much of mathematics as pertains to the accurate calculation and distribution of force, momentum, friction, &c., as may enable him to apply with success and economy all the understood theories of his business, and to direct him in the prosecution of new experiments.

He should likewise be a tolerable draughtsman; not