Page:The American Cyclopædia (1879) Volume VIII.djvu/344

 330 GUNPOWDER burn progressively from its surface to its cen- tre. It is obvious that the pressure due to any particular position of the shot will depend upon the total amount of gas developed ; and hence, if we can retard the combustion in the initial and accelerate it in the terminal stages, we can, in part at least, accomplish the desired end. At all events, we can reduce the initial gas development in two ways : first, by dimin- ishing the amount of surface presented for igni- tion by a given weight of powder, which is done simply by increasing the size of the grain ; secondly, by decreasing the rate at which com- bustion progresses into each grain, which is done by increasing the density of the grains, and thus closing more tightly the pores through which ignition penetrates their mass. The effect of diminishing the initial pressure with- out a compensating increase of the terminal pressures would be a reduction of the velocity of the shot. This may be restored by an in- crease of the charge, which augments again the initial pressure, but not to such an extent as to carry it beyond the limit of safety. By increasing the size and density of the grains American Lenticular. Hexagonal. FIG. 1. Forms of Gunpowder. while increasing the charge, artillerists have retained control of the energy of gunpowder, and at the same time have actually increased the velocities of even the largest projectiles. For instance, in 1864 the American 15-inch gun, when using 50 Ibs. of powder and a shot of 450 Ibs., showed a pressure of about 15,000 Ibs. and an initial velocity of 1,100 ft. per sec- ond. At present (1874) the same gun and shot, with 120 Ibs. of powder, give about 22,- 000 Ibs. pressure and 1,730 ft. initial velocity. Another improvement consists in giving to the grains definite geometrical forms. The advan- tage of this modification results not so much from the form itself, as from the fact that the action of the individual grains is much more likely to be uniform. In the process of press- ing the powder, by the methods which have been in use for many years, great irregularities of density always occur ; and as the explosive property is more influenced by the density than by any other quality, the advantage of securing uniformity in this respect is manifest. Geometrical or "pellet" powder requires a mould for each grain, whereby the density can be regulated with far more precision than by the old method. A leading variety of these geometrical forms is the prismatic, in which the grains are hexagonal prisms, about an inch in length and diameter. Each prism is perfo- rated with seven holes, one tenth of an inch in diameter, parallel to the axis. They are sym- metrically packed into a cartridge, of very small bulk in proportion to its weight. This form of powder is used for large rifled (Krupp) guns in the Russian, Prussian, and Austrian service, and its performance is excellent. Short cylinders have been used by the English, but they have been supplanted recently by pebble powder. Lenticular powder (grains in the form of lenses) has been tried in this country, but with indifferent results. The central portions, as a necessary result of the mode of pressing, were much less dense than the peripheral, and therefore burned too rapidly. Grains which had been ignited in the gun and extinguished in the air, and collected afterward, showed that the middle portions only had been con- sumed, leaving a ring of the denser portions. Ritter prismatic powder is simply the prismatic form just described, but without the perfora- tions ; it has been used in Belgium only. In recent experiments under the United States government, pellets in the form of two trunca- ted pyramids, having a common hexagonal base, have been employed ; and the results appear to be better than those obtained by any other nation. The irregular, large-grained powder, used in heavy guns, receives the name mam- moth powder in this country, and pebble pow- der in England; but these titles indicate no essential difference. Gunpowder is classified, according to the size of the meshes through which the grain is sifted, into 11 numbers, from to 10, the latter being the finest rifle powder, and the former the mammoth. In classifying it according to quality, each maker has his own method and nomenclature. In the United States government service it is classified into : 1, musket ; 2, mortar ; 3, cannon ; 4, mam- moth powder. Two sieves are used for sepa- rating the grains of each class, all the grains be- ing required to pass through the larger, and none through the smaller. The sizes of the meshes in decimal parts of an inch are : CLASS. Large. . SmalL Musket 06" 08" Mortar 10 06 Cannon 86 25 Mammoth 90 60 The density of granular powder is either the absolute density, which is that of the grains themselves, or the gravimetric density, which is that of a quantity of grains with their inter- stices. The absolute density ranges from 1'60 to 1'80, the most common figure being about 1*75. The gravimetric density is generally about equal to that of water. Sporting pow- der is made with especial care, of the purest saltpetre and sulphur, and the most carefully