GUNPOWDER. 376 GUNPOWDER. in France that the practice of pulverizing and mixing tlie separate materials in wheel mills was first emplo_ved. This method was invented by Cossigny in 1787, and in 1791 a revolving drum was first used for pulverizing, and the wheel mill reserved for mixing and incorporating materials, improved methods and apparatus were brought to the United States by Dupont, a student of La- voisier, and the famous works bearing his name at Wilmington. Del., were founded in 1802. In 1850 these works undertook the manufacture of blasting-])owder, .substituting the nitrate of so- dium for that of potassium, and in 1868 the method previously suggested by Longchamps, Antlion, and Kuhlman, of obtaining the potas- sium nitrate from sodium nitrate and potassium chloride, was adopted. About 18G0 General Rod- man of the United States Army determined to make powder of larger sized grains, which con- sequently was slower burning, and enabled the Ordnance Department to construct guns of larger calibre. From this discovery resulted powders of variously shaped grains, generally symmetrical, and with perforations. By changing the nature of the carbon constituent, and using brown char- coal as described below, the gunpowder was ren- dered still slower biu'ning, and in that form, more or less improved, has been brought down to the jjresent. M.NUFACTURE. In the manufacture of gun- powder great care is necessary, especiallj' 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 tliese 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 w'illow 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 w'ooden molds. AYhen thoroughly cold the sulphur is broken un into larjre 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- met;il or copper in charges of .50 pnimds 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 difl'erent sizes, accoi'ding to the variety of powder which it is desiretl to pro- duce. . 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. ( 120° to 12',)° F. ) for twenty-four hours. 'Pebble,' 'pris- matic,' and similar names were given to forms of military powilers 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 ExpLOSiVE.s.) The black powder once used for military purposes by the United States. Great Britain, Russia, Sweden, Italy, and France, consists of potassium nitrate 75 ]jarts, char- coal 15 parts, and sulphur 10 parts. Other nations used slightly difterent proportions, ranging from potassium nitrate 77 parts dow'n to 01.5 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 iised. It con- sisted of about the following proportions in the dried powder of the usual ingredients: Nitre 711 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 giui than Idack 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 ijowdcr. Brown powder has been dis- ])laced by smokeless powder (q.v. ) and other high explosives. See ExPLO.siVES. Jlining or blasting powder, which is used for blasting purposes (see Bl.v.sting ) . usually has a lower amount of potassium nitrate than mili- tary powder, so as to make it slow burning, and the proportions are from potassivim nitrate 70 parts, sulphur IS parts, and charcoal 12 parts, to potassium nitrate 62 parts, sulphur 20 parts, and charcoal IS parts. The manufacture of blast- ing-powder became an important industry in the United States when the construction of canals and railways and mining operations began to be undertaken on a Inrce scale. 'With the in- creased demand for blasting-powder, which origi-
