coatings for the same length of time, a few blows of the hammer being sufficient to clear the castings.
An Armstrong gun is constructed of a number of separate pieces, all of wrought iron except the breech, screw, and vent piece, which are of cast steel; the vent is touched with copper to withstand the gunpowder. The tube is made up of three inner and three outer coils, and the trunnion piece and coil.
Great difficulty is experienced in forging masses of wrought iron sufficiently large except for pieces of very small calibre; the ancient guns were constructed of a number of rings and longitudinal bars; the latter were arranged inside, and grasped together by the rings, which were placed outside. The Armstrong ordnance are made up of a number of wrought iron rings, welded together with others shrunk over the internal tube.
Steel is obtained by combining good bar iron with carbon, by the process of cementation, alternate layers of the iron and charcoal being placed in closed troughs of tire-brick, where they are exposed to a very high temperature for about sixty hours. The metal produced is known from the appearance of its surface as blistered steel. Shear steel is produced by cutting and welding bars of blistered steel. Cast steel is made by fusing bars of blistered steel, and casting them into ingots. Ordnance is made of the latter material, which, Giving to its tenacity and elasticity, is superior to wrought iron. But it is an expensive material, and the after operations of turning and boring the gun are very difficult and costly owing to its extreme hardness.
The following examinations and proofs of a gun are made. The first is by a very ingenious instrument, called Desaguilier’s, by which the smoothness and regularity of the bore is tested, and also whether its axis is identical with that of the piece. A somewhat different process is employed in the case of mortars and howitzers. The external dimensions of the gun are taken by various instruments. The strength of ordnance is tested by the fire proof. The guns being laid on the ground in front of a butt with their muzzles towards it slightly elevated, are loaded with their proper proof charges, and fired by means of a galvanic battery, which is placed in a splinter-proof building, and the current of electricity conveyed to the tubes in the guns through copper wires. The gun is then searched by a long rod having a number of steel springs at the extremity, each of which has a spike attached; these springs are released from a grasping ring when at the bottom of the bore. Any flaw in the metal is at once detected in passing the searcher up and down. The soundness of the metal is tested by the water proof. A hollow wooden plug, covered with leather, is fixed in the muzzle of the gun by chains which pass round the trunnions, and is connected with the main pipe of the water works; a pressure of about 50 lbs. on the square inch is obtained, and water is forced into the bore until it issues a continuous stream from the vent, a wooden plug is then inserted in the latter, and a few more strokes given by the engine. If any water has penetrated through the thinnest part—the neck—the metal is unsound. The last test is the sun proof. After two or three days, the bore being supposed to be perfectly dry, is examined by reflecting the sun rays into it by means of a mirror, and if any part appears wet, it indicates a flaw. The sighting process is the last operation. In the construction of carriages, wheels, &c., ash, elm, pine, fir, oak, African oak, and sabrin from Cuba, are the materials employed. The timber is cross-cut and planed, and all the holes necessary for rivets, bolts, &c., bored by machinery. The various parts of the carriage are finished off and put together by hand.
Gunpowder is made at Waltham, and subjected to four proofs. In the Laboratory various combustible compositions are made, the main ingredients employed being sulphide of antimony, sulphate of arsenic, chlorate of potassa, shell lac, rosin, fulminate of mercury, Kitt and Luten composition.
The operations of mixing compositions, mealing powder, and grinding charcoal and clay, require extreme care in the manipulation of ingredients, great accuracy being essential in weighing the proportions, and in reducing the particles of the different substances to the proper degree of fineness.
Compositions are mixed by a copper slice upon a wooden table, and afterwards pressed through sieves of different degrees of fineness. Powder is mealed on a beechen table, having grooves cut on its surface, and then worked about in small quantities by a man with an oval rubber of beech-wood.
The operation of making fuses, filling carcases and light balls, the manufacture of percussion-caps, bullets, Congreve, and signal rockets, with the making of the cases, and the driving of the composition in the latter case, may also be seen. Solid shot are cast, two models, each half of the size of the shot, being used, and a mould. The metals are melted by coke in a furnace of fire-brick. In the case of common shell a core in addition is necessary to obtain the requisite hollow in the interior. The moulding box for solid shell, like the model of cast iron, is perforated with a number of holes to allow of the escape of the gases evolved by the heated metal.
By taking the railway-train from the Arsenal Station, the visitor will escape passing through the unsavoury streets which lie between it and the Dockyard. To those familiar with the larger yards of Portsmouth and Keyham, the scene will present no novelty; but those who have not had the advantage of seeing those magnificent establishments, may spend an hour agreeably in inspecting that of Woolwich, with its enormous chimney-shaft,—a landmark for miles,—the engine-house, the saw-mills with their marvellous machinery, the huge Nasmyth’s hammer,—which can crack a nut-shell so as not to break the kernel, or snap a thick iron bar with equal facility on the anvil,—the glowing furnaces, the building slips, with the shipwrights hammering with an incessant din on the grand three-decker piled up beam on beam, to which access is gained by inclined planes reaching to the top of the enormous structure. The yard is nearly a mile in length. The masting shears, the docks, the gun-boats, the steel-plated