MANUFACTURE. In the manufacture of gun powder great care is necessary, especially in the selection of the ingredients. The potassium ni trate, or nitre, as obtained commercially, con tains potassium. and sodium chlorides and sul phates, sand, and organic matter amounting to nearly five per cent. For the removal of these impurities the potassium nitrate is dissolved in hot water, and after boiling the solution is filtered through bags of coarse cloth into crys tallizing vessels, where it is continually agitated while cooling, so that fine crystals may be formed. The crystals are then washed in distilled water, and while still moist are stored in bins for use. For the making of the charcoal small wood of about 10 years' growth is preferred. Alder and willow are mostly used in the United States and Great Britain, while in France dog wood is preferred, and in Germany the willow, alder, and dogwood are employed. The wood should be straight, perfectly sound, entirely free from bark, and felled during the spring of the year when its moisture is at its maximum. The carbonization is accomplished in cast-iron retorts set in bricks, and the time of burning varies from three to five hours, according to the nature of the powder for which the charcoal is desired, and at a sufficiently high temperature to drive off all volatile matter.
After cooling, the charcoal is carefully hand picked, and then ground to powder in a mill. The sulphur employed is usually the best com mercial article, but this still contains from four to six per cent. of gangue. The sulphur is puri fied by distillation in a large iron retort, and the sublimed sulphur received in a condenser, from which it is removed in the liquid form and cast into moist wooden molds. When thoroughly cold the sulphur is broken up into large lumps and finely ground to powder. The ground ingredi ents are carefully weighed, and the proper pro portions mixed in a cylindrical drum of gun metal or copper in charges of 50 pounds and upward. The mixture is then hand-sifted to re move foreign substances, and again mixed in an incorporating mill, in which, by means of dis tilled water, the charge is kept sufficiently moist to prevent its scattering as dust. This operation is continued for several hours, and the mill-cake is then reduced to meal by passing through roll ers. The meal is then pressed into cakes by a hydraulic press, and the resulting press-cake broken into pieces of different sizes, according to the variety of powder which it is desired to pro duce. A series of rollers next converts the press
cake into grains, which are rough- and porous on the surface, and very angular in shape. It is freed from dust by placing it in revolving reels, and then glazed by causing the grains to rub against each other in revolving wooden barrels. The final operation, called drying, consists in heating the glazed powder in large chambers at a temperature of from 52° to 54° C. (126° to 129° F.) for twenty-four hours. `Pebble,' pris matic,' and similar names were given to forms of military powders that were used especially for artillery, and were made essentially as just described, except that the press-cake was cut into the shapes indicated by their names. (See EXPLOSIVES.) The black powder once used for military purposes by the United States, Great Britain, Russia, Sweden, Italy, and France, consists of potassium nitrate 75 parts, char coal 15 parts, and sulphur 10 parts. Other nations used slightly different proportions, ranging from potassium nitrate 77 parts down to 61.5 parts. The sulphur is the most constant of the ingredients, while the charcoal varies from 23 to 12.5 parts.
Brown or cocoa powder received its name from the color of charcoal used. It con sisted of about the following proportions in the dried powder of the usual ingredients: Nitre 79 per cent., sulphur 3 per cent., and charcoal 18 per cent., although when in ac tual use it contained about 2 per cent. of moisture. The charcoal used was a lightly baked material, and the percentage of carbon that it contained was,therefore but slightly higher than that of the wood or straw from which it was made. This variety of gunpowder found its chief use in heavy breech-loading guns in the forms of hexagonal prisms. The rate of combus tion of the brown powder is slower than that of the black, and therefore for equal muzzle veloci ties of the projectile it produces less pressure in the powder-chamber of the gun than black pow der; also it yields a thinner smoke than the latter. This variety of powder gives on explosion a greater quantity of heat, and a smaller volume of permanent gases than does an equal weight of black powder. Brown powder has been dis placed by smokeless powder (q.v.) and other high explosives. See EXPLOSIVES.