A great part of the powder for H. M. Government has at present to be supplied by merchants. The contracts are made out sometimes for them to supply their own saltpetre, and at others for the Government to furnish it pure, at the rate of 77·5 lbs. per barrel of 100 lbs., they finding the other materials and manufacture, a corresponding reduction in price being made: as, however, it has to come up in nearly all respects to the sample, the requirements of which we shall state, certain proofs have to be undergone before being received for the different services. NOTE.--The foregoing is mainly compiled from Robins’s _New Principles of Gunnery_, by Hutton; _Engines of War_, by Wilkinson; and _Projectile Weapons of War_, by J. Scoffern, M.B. ON THE MANUFACTURE OF GUNPOWDER. ~Composition of powder.~ Gunpowder is an explosive propellant agent; a mechanical combination and intimate mixture of saltpetre, charcoal, and sulphur, in certain fixed proportions, the result of successive experiments. ~Ought to keep without deterioration.~ To be effective, Gunpowder should, 1st.--Preserve itself in a good state, whether in magazine or in carriage. ~Leave no residue.~ 2nd.--Leave as little residue as possible after ignition. ~Combine quickness and power.~ 3rd.--Should combine a certain quickness of combustion with great explosive force. SALTPETRE, OR NITRE. ~Nitre.~ ~Where found.~ ~Unfit in natural state.~ The principal ingredient in Gunpowder is an abundant production of Nature, and is a combination of nitric acid with the vegetable alkali. It is never found pure, being always contaminated with other salts and earthy matter. It is principally found in the East Indies, Ceylon, and South America, and is sometimes produced from decayed animal and vegetable matter. It is totally unfit for Gunpowder until it has been refined; for, being combined with muriates of soda, lime, magnesia, and other salts, which absorb moisture, the close contact of the ingredients would be deranged by their presence, the strength of the powder weakened, and the power of resisting the action of the atmosphere greatly lessened. As for the efflorescent salts it may contain, they are noxious only inasmuch as, possessing no particular useful property, they interpose their atoms between the more combustible ingredients, and impede the rapidity of deflagration. ~Two methods of refining.~ There are two methods of refining saltpetre at Waltham Abbey:--1st, the Old Method, of re-crystallizing three times; and 2nd, the New Method, which has only just been adopted, both of which we shall here briefly describe. OLD METHOD. ~Old method.~ ~Saltpetre fuzes at 600°.~