Page:Once a Week Volume V.djvu/447

 440 implements, moulds for casting shot, grape, chain, and canister, bullets and balls; the manufactories of rockets, percussion caps, and metal fuses; the powder magazines and the gun-carriage department; the store-rooms for saddles and bridles, and arms of every description, with the park of artillery, where nearly 30,000 pieces of cannon, and pyramids of shot and shell to the number of 4,000,000 to 5,000,000, are accumulated.

At the siege of Sebastopol the total number of rounds expended amounted to 253,042: 35 13-inch mortars, 35 10-inch mortars, 11 8-inch mortars, and 20 5½-inch mortars were used. Of these 10 became unserviceable from use, and 3 were destroyed by the enemy. Seven Lancaster guns S 68-pounders, 105 32-pounders, 57 24-pounders, 3 9-pounders, 10 10-inch guns, and 76 8-inch guns were employed; and of the entire number only 41 remained serviceable at the end of the siege.

From these statistics of a single siege it will be seen how indispensable it is to have such a reserve and permanent stock of artillery, which supplies the fleet, the garrisons, and batteries, and army of England. The authorities very properly refuse admission generally to the principal works, on two grounds—apprehension of interruption to the workmen, and of positive danger, as some of the manufactures are conducted in rooms which the persons employed are allowed to enter only with slippered feet. Of some of the more interesting and important processes the reader will no doubt be glad to obtain succinct information, divested of all technicalities.

Gun-metal is an alloy of copper and tin, in the proportions of 100 parts of the first to 10 of the latter. The copper is first reduced to a fluid state, and about ten minutes before it is ready to run the tin is thrown in, which, owing to its fusibility, melts immediately. A piece of ordnance composed of gun-metal requires a less thickness of metal than a cast-iron gun. The bores of bronze pieces become indented by the irregular motion of the shot in passing through them, and after long-continued firing are liable to the defect known technically as 3droop at the muzzle,” owing to the rebounding of the shot within the bore. The cost of bronze ordnance is 187l., the value of pure copper is 124l., of tin 120l., and of gun-metal 80l. per ton. The cast-iron used for ordnance is obtained by mixing the different numbers of pig iron together so as to produce a grey cast-iron of great tenacity with sufficient hardness and fusibility. The quality of the iron depends principally upon the fuel—peat charcoal found at Low Moor and Bowling Iron Works in Yorkshire—used in smelting the ores. Coke is employed with cold blast, as it is superior in tenacity and strength to hot-blast iron made with coal in its raw state. The ores of Sweden and Nova Scotia are preferred from their superior quality, being smelted with charcoal which is free from sulphur, the latter being highly injurious. The specific gravity of the iron from which ordnance is made varies from 7 to 7.2. The fusing point is about 374° Fahrenheit; in cooling it contracts 1.25 per cent. Cast-iron cannot be depended upon for rifled cannon, and if used for these ordnance, requires to be strengthened by shrinking wrought-iron rings or tubes over the portion of the gun in rear of the trunnions. The cost of cast-iron guns is about 21l. per ton: the value of the best English iron is 5l. 10s. per ton, and that of old iron guns 5l. per ton.

Wrought iron is obtained from cast iron in two ways, by the operations of refining and puddling. The greater part of the carbon and impurities is driven off by fusing pig iron for two hours in a blast furnace, after which it is run out and suddenly cooled with water. The refined metal is now placed in a reverberatory-furnace, where it is stirred with an iron rake while it is in a state of fusion, and every particle is exposed to the action of a current of hot air passing over it. The metal now assumes the consistency of a thick paste, and is subjected to the action of the forge hammer or pressure under rollers, by which it is rendered malleable and ductile.

All ordnance are cast in a solid mass, similar in shape to the exterior form of the piece, but larger, to allow for turning down, and that the mass may contract throughout as equally as possible. They are bored and turned by machinery; an additional length of three or four feet of metal, termed the dead head, is given to the piece at the muzzle; as the gun is cast in a vertical position the dross and other impurities run down and collect into this part; by its weight it compresses, and therefore increases the density of the gun, and furnishes a supply of metal to the mass when cooling and shrinking.

The reverberatory furnace consists of a fire-place and a hearth, on which the material to be subjected to the flame is placed; great nicety of regularity of heat is obtained, and the metal does not come into contact with the fuel, a bituminous coal, as in a cupola or blast furnace. The flame rising from the fire-place, as it passes over the ridge of fire-brick which divides the fire-place from the hearth, strikes the arch of the furnace, and is thrown back or reverberated on the material.

In casting iron ordnance, a model of the piece is made of cast iron, or of some hard seasoned wood, in sections of convenient length. The jacket consists of twelve parts; the mould, about three inches thick, is composed of dry angular sharp sand, moistened with water and mixed with strong clay to render it more adhesive. The model is covered over with blacking made of charcoal and coal dust, moistened with clay, to prevent its adhesion to the mould. Each portion of the jacket is rammed separately, and successively placed one over the other. The mould is then formed in a vertical position, and—the model having been extracted—is placed in a stove, where it is gradually and perfectly dried, a process occupying from 12 to 14 hours. Parts of the jacket are then carried to the pit, where they are screwed together and secured in a perfectly upright position. The interior of the mould is coated with blacking. The metal, being brought from the reverberatory furnace, is admitted at the run hole, which has been stopped by a lump of friable clay, and flows into an iron basin lined with loam conveniently near the mouths of the moulds. Castings generally remain in the pit undisturbed for forty-eight hours. They are then taken out and allowed to remain in their earthy