Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/347

Rh GUNPOWDER 327 lateci in the same machine at the same time, but dogwood charcoal being now used for small-arm powders, one descrip tion only is usually made, so that but two long screens are require:! to define the higher and lower limits as to size of grain; for example, all that will pass through a 12 -mesh and be retained upon a 20-mesh screen would be &quot; rifle- fine-grain&quot; (R.F.G.) powder, suited as to size for the Snider and Martini rifles. Modifications of this machine are used by private makers, the grain being usually separ ated into various sizes by hand-sieves. Pebble or cubical powders for heavy ordnance are granu- Cube- lated, or &quot; cut,&quot; in special machines which divide the press- cutting cake first into strips, and then again cross-ways, into cubes mac &quot; m of | inch and 1-|- inch length of edge respectively. This is effected by two pairs of gun-metal or phosphor-bronze rollers, which have straight cutting edges arranged at -suit able intervals along their surfaces, the slabs of press-cake being fed vertically between the first pair of rollers. The resulting strips are carried along upon a board, by means of a skeleton band, which receives each strip of cake C QO

-Granulating machine. A, hopper, with raising arrangement; B, endless band; C,C,C,C, four pairs of rollers; D,D,D, short screens ; E,E, long screens ; F, box for dust ; G, box for grain ; H, box for chucks ; K, bottom board. between two laths of wood; they then drop from the board upon an endless canvas band a little below, travelling in a direction at right angles to their previous motion, and are conveyed endways to the second pair of rollers. To prevent the strips of cake from fouling one another, the board upon which they first fall has a reciprocating motion given to it by means of an endless chain, one link of which is studded view. Slope-reels are open at both ends, fixed at an angle of about 4, and are used for fine-grain powders as they come from the machine, when they contain more dust than the larger grain, especially if made from dogwood charcoal ; the powder is poured in at the higher end, and received in barrels at the other end. The larger grained powders are dusted for about half an hour in a horizontal reel, with closed ends, the charge being from 250 to 300 Ib ; one end of the reel is made to lower for the purpose oi unloading. Both kinds of reel are enclosed in cases to receive the dust, which, as before, is sent back to the incorporating mills for 40 minutes or so. The theory of glazing gunpowder has already been dis- Glazin cussed. All descriptions are glazed, for varying periods, in glazing barrels or &quot; churns&quot; (fig. 8), which are usually about FIG. 7. Rollers of cube-cutting machine. to a bracket underneath the board ; consequently, as the board travels backwards, the strips are deposited at inter vals, in echellon, upon the canvas band. The diagram (fig. 7) shows a portion of the machine. The cubes, &c., fall into a small reel fixed at a slope beneath the machine, which allows the dust and fragments to pass between its wires while the properly sized pebbles or cubes are delivered into boxes. The large 1^-inch powder has, however, after wards to be picked over by hand. listing. All grain from the granulating machine is called &quot; foul- grain,&quot; and has to be deprived of its dust in reels, consisting of a cylindrical frame- work about 8 feet long by some 2 feet in diameter, covered with a dusting cloth or canvas of from 18 to 56 meshes to the linear inch, according to the size of grain. These reels gre either&quot;horizontal&quot;or &quot;slope,&quot; accord ing to the position in which they are fixed and the object in Fio. 8. -Glazing barrels. A, elevation, showing door of case ; C, hoppers for loading ; B, section through barrel (showing opening in dotted lines). 5 feet long by 2 to 3 feet in diameter, and revolve some 34 times in a minute; however, barrels of much greater diameter and less length are occasionally employed, revolv ing at a slower rate. The charge for each barrel is ordinarily 400 tt&amp;gt;, and the fine-grain powders are mixed with a pro-