When the incorporation is completed the mill cake, as the mixture is now called, is re moved from the bed and runners by means of a copper chisel and wooden mallet. It is partly in the form of a compact cake and partly fine meal and in this condition it is put into the press. This is a powerful hydraulic press with a rectangular box which is divided into com partments of the desired width by means of copper or gun-metal plates. When the spaces between the plates have been filled with mill cake, pressure is applied which causes the parti cles to cohere, and the gunpowder is taken from the press in sheets having an area equal to that of the plates and a thickness dependent on the width of the filling space, the amount of the pressure applied and the duration of its application. Sometimes the press plates are corrugated like waffle irons, as for instance, in the manufacture of waffle and of hexagonal powders, and sometimes they are replaced by a press block filled with molds in each of which a separate grain is pressed, as in the manu facture of cocoa or prismatic powder. The operation of pressing is a most important one, since the density of the finished powder de pends upon it and, as it is markedly affected by even slight changes in atmospheric conditions, it is a very nice one.
The press cake passes to the corning or granulating machine, where it is cut into grams. This machine consists of a hopper into which the charge is fed, an elevating band, an endless revolving table, four pairs of rollers and sev eral sets of screens for sorting the grains ac cording to size into boxes placed to receive each different size. The rollers, which are of gun-metal, are corrugated or provided with teeth, the upper two being coarser than the lower, and they are adjusted to the size of grain required. When the hopper has been emptied a clutch is relieved which stops the machine and at the same time rings a bell which notifies the operator of the fact for, as the machine is self-feeding, the workmen are not obliged to be present while it is at work. The grains are now freed from dust by pass ing through horizontal cylindrical sieves such as are used in flour-mills and they are then glazed by rotation in wooden barrels where, by the friction of the grains against each other, their angles are rounded off and a hard polished surface is imparted to them whereby they be come better able to bear transportation and are less likely to absorb moisture. Sometimes the grains are coated with graphite which is put in the glazing barrel with them. Though but four ounces of graphite are used to 1,200 pounds of gunpowder it is considered objec tionable for use with fine grain regulation powder as it delays ignition and fouls the piece, yet it improves powder to be used in fixed ammunition, in that it enables the grains to readily pack close together. As more dust is formed during the glazing process the grains are again put through the dusting reels and are then exposed for a day in the drying house to a temperature of from 125° to 130° F. The finished powder is packed in 1-pound tins or 25 pound kegs, though other sized packages are produced to some extent. According to the size or form or structure of the grains gun powder is known as waled powder, superfine, designated by the mark F.F.G.; fine grain, F.G.; large or coarse grain, L.G.; large grain for rifles, R.L.G.; mammoth, pebble, pellet, cubical, hexagonal, sphere-hexagonal, waffle, Fossano or progressive, and cocoa or brown prismatic powder. Mealed powder is in the
form of dust and is used for driving fuses for ammunition and in pyrotechny. Fossano or progressive powder is formed by pressing mill cake to a density of 1.79, then breaking this press cake into one-eighth to one-quarter inch grains, mixing these grains with a prescribed quantity of fine grain powder, pressing this mixture to a mean density of 1.76 and breaking this press cake into grains about two and one half inches square by one and three-quarter inches thick. By this means a grain of varying density was obtained which burned progres sively. This feature was introduced into pow der-making by Prof. R. Ogden Doremus of New York, but was developed in Europe. Cocoa or brown prismatic powder is the final stage of development of the compressed per forated grain invented by General Rodman of the United States army. In experimenting with the 15-inch and 20-inch smooth-bore guns in vented by him, General Rodman found that he could reduce the initial pressures, while secur ing the desired velocities, by using perforated discs of compressed powder which were of a diameter equal to the calibre of the gun and between one and two inches in thickness. He styled this charge a ((perforated cake cartridges and in his 'Properties of Metals for Cannon and Qualities of Cannon Powder,) published in Boston, Mass., 1861, he mathematically dem onstrated that at the beginning such discs pre sented the minimum of free surface to com bustion but as the powder burned there was a constant enlargement of the perforations, whereby the area of surface exposed to com bustion was constantly increased and that therefore the volume of evolved gases in creased as the volume of the chamber, due to the travel of the projectile, increased, in con sequence of which the pressure was more uni formly distributed along the bore than it had been with the granulated powders hitherto em ployed. Owing to difficulties in manufacture and use, Rodman later found it convenient to build up his charges with perforated hexagonal prisms of comparatively small size. The Civil War prevented the further development of this novel idea in powder-making in this country at that time, but a Russian military commis sion, which visited the United States during the Civil War, was so impressed by what Rod man had accomplished, that on its recommenda tion the manufacture was taken up and carried on in Russia on an extensive scale, and it soon spread to other countries. About 1880 Ger many adopted cocoa powder, which was a brown prismatic powder with a single canal, the grains having the form of an hexagonal prism, one inch in height by 1.36 inches in diameter and a density of 1.86. This powder, however, differed from ordinary gunpowder both in the kind of charcoal used and in the proportions of the components. The charcoal was underburned or red charcoal made from rye straw, and the composition was saltpeter 80 50 per cent, charcoal 16.00 per cent, sulphur 2.50 per cent and moisture 1 per cent. Cocoa nowder was so successful for use in modern high-powered rifle guns that it was sought for by all military nations and the want was met in this country by substituting for the rye straw charcoal red charcoal from wood and carbohydrates, such as sugar, and this brown prismatic powder was used in our modern large calibre guns until displaced by smokeless powder.