A drying-room, heated by steam pipes, is fitted with open framework shelves, on which rests small wooden trays about 3ft. long, 1ft. 6-in. in breadth, and 2¹⁄₂in. deep, having canvas bottoms; on each is spread 8lbs. of powder. This room holds about 40 barrels, or 4,000lbs., which remains in it for twenty four hours, and is subjected to a heat of 130° Fahrenheit for sixteen hours, communicated by steam passing through pipes arranged horizontally on the floor of the room. The temperature is raised and lowered gradually, otherwise the too sudden change would be likely to destroy the texture of the grain. The ceiling and roof are fitted with ventilators, through which all the moisture escapes, so that there is a constant current of hot air circulating through the room. It is of the greatest importance that the vapour should be carried off; for, if this is not effectually done, on the decrease of temperature, it would return to its liquid state, and form again on the powder. FINISHING DUSTING. ~Final dusting.~ ~Barrelling.~ The action of heat however produces a small portion of dust; both these powders, therefore, when they leave the stove, are reeled in horizontal reels, clothed with 28 and 44-mesh canvas respectively, for one hour and a half. This perfectly separates any remaining dust, and gives the finishing glaze to the large-grain powder. This is the final process, and the powder thus finished is taken to the barrelling-up house; weighed out into barrels holding 100lbs. each; marked L. G. (large-grain), and F. G. (fine-grain), as the case may be; and stored in magazines. EXAMINATION AND PROOF OF GUNPOWDER. ~Desired properties of gunpowder.~ ~Specific gravity.~ ~Strength.~ ~Purity.~ The great and ultimate object to be attained in the manufacture of Gunpowder is, not so much to produce that which ranges the highest, as one that shall be durable in its texture, not easily deteriorated by atmospheric influence or transport, and one with which equal charges shall produce equal effects. It should present uniformity in the appearance of its grains, which should be angular, crisp and sharp to the touch, not easily reduced to dust by pressure between the fingers, or dusty in handling; its specific gravity should not be under 55lbs. to the cubic foot, (that of Waltham Abbey is generally 58lbs.) taking water at 1000ozs.; its strength is tested by firing three rounds from an 8 inch mortar, throwing a 68-pounder solid shot with a charge of 2oz. this should give a range of from 270 to 300 feet. The distance however, varies considerably, according to the state of the atmosphere, and the density of the powder: for, the greater the density, the less the range in small charges. Half an ounce flashed on a glass plate should leave little or no residuum; should white beads or globules appear, it is a sign of imperfect incorporation. PROOF OF MERCHANT’S POWDER. The following are the different proofs merchant’s powder is subjected to:--