CHAPTER III GUNPOWDER-Continued The processes described in the preceding chapter refer particularly to the manufacture of powders the sizes of the grains of which do not exceed in diameter 4 inch. When a charge of such powder is burned in the bore of a gun the flame rushes rapidly through the spaces between the grains, causing very rapid combustion and correspondingly rapid formation of gas. With ordinary cannon powder it has been found that seveneighths of the entire charge is consumed before the shot passes over one-third the length of the bore; this action of the powder causes excessive pressures at or near the base of the bore of the gun, due to the fact that the evolution of gas is greatest while the velocity of the projectile is least. Special Powders.-Experiment has shown, however, that the amount of gas evolved at the first instant of inflammation and the combustion of the charge can be measurably controlled by the size and form of the grain and the density of the powder. The first two conditions regulate the area of surface exposed to combustion, while by increasing the density of the powder greater resistance is offered to the penetration of the hot gases through the grains, and the rapidity of burning is thereby controlled. These principles are now so universally recognized that special powders differing in these features are manufactured for use in guns of different calibers in order to secure the best results. Such powders are called special powders. The forms of grain adopted for such powders are regular geometrical figures, such as hexagons, cubes, and prisms, the resulting powders being known as hexagonal, cubical (or pebble in England, where this form is used), and prismatic. Hexagonal Powder. This powder is still retained in the United States Army for use in certain old guns. Each grain is formed of two truncated six-sided pyramids, which are united base to base, the plane of union being therefore a hexagon. (See Fig. 1.) The uniform size and shape of the grain insure uniformity in position and size of the interstices in the cartridge; this insures uniformity in density of loadings which, with uniform density of the grains, produces uniform and low pressure, and uniform and high velocities. FIG. 1. Manufacture of Hexagonal Powder. The ingredients themselves, the proportions of the ingredients, and the processes of manufacture of hexagonal powder are similar in every respect to those already described up to the completion of the "mill-cake." The following modifications are peculiar to this powder: Mealing. The "mill-cake," broken with wooden or copper mallets, is revolved in a cylinder of wire-woven cloth with wooden balls until it is mealed. Pressing. The mealed powder is then moistened and carefully pressed between metallic plates containing dies which correspond to the truncated six-sided pyramids already described. The powder comes from this machine in polyhedral grains connected along their hexagonal edges. Granulating. The press cake is passed through rollers armed with teeth set at an angle of 120 degrees to the axis which separate the grains. Glazing. The powder is next glazed by being run into a glazing barrel containing highly glazed small-grained powder (rifle or mortar). Brushing. The powder is next passed repeatedly through the brushing machine. This consists of a frame with brushes revolving near an inclined plane, along which the powder is made to pass by the motion of the brushes. Drying. The powder is next dried, and then carefully examined; its density and granulation determined, a difference of two grains (or granules) to the pound being enough to condemn the powder. Rebrushing, Redrying, and Packing.-If the results of the preceding examination are satisfactory, the powder is again passed through the brushing machine, redried, brushed a third time, and then packed in barrels. FIG. 2. Prismatic Powders. In selecting the original shape for special powders, several practical considerations led to the adoption of regular geometrical figures, one of the first experimented with being the right hexagonal prism. The earlier prismatic powders contained seven perforations (see Fig. 2) in the direction of the axis of the prism, one in the center, and one within each angle. It was soon discovered, however, that it was impossible to make the walls of the prisms sufficiently strong to resist the action of the heated gases rushing through the perforations, the result being that the prisms were broken up and reduced practically to fine-grain powder. A single perforation was therefore substituted, and as thus modified the perforated prismatic powders were used by the majority of military nations of the world in all guns of large caliber. The best-known prismatic powder is the brown or cocoa powder. (See Fig. 3.) The characteristic color (brown) of this powder is derived from the charcoal used, which is slightly carbonized or charred rye straw, while the proportions of the ingredients are as follows: FIG. 3. Saltpeter.... Sulphur.... Charcoal..... 80 parts. 2 to 3 parts. 18 to 17 parts. The theory of this powder is that ignition occurs first in the interior of the grains (i. e., along the central perforation), and the combustion proceeds uniformly outward until the entire prism is consumed. By this action of the powder, which is rendered possible by the shape of the grain and the high and uniform density of the powder (1.86), the smallest surface of combustion is exposed to inflammation at the instant of ignition, when the velocity of the projectile is least, and constantly increases as the projectile moves down the bore and acquires its greatest velocity. The result is moderate and uniformly sustained pressures on the gun, with uniform and high initial velocities.1 Recapitulation.-1. Small-grain powders burn too rapidly and irregularly to be used in guns of large caliber. 2. Special powders burn more slowly and uniformly, so that excessive pressures on the gun are avoided, and more uniform and higher velocities are imparted to the projectile. 3. The perforated prismatic powders are the best special powders. 4. The granulation of prismatic powders is uniform, and the rate of their combustion is regulated by varying the composition. 1The sizes of the grains of brown powder are practically uniform, being of the same dimensions for 8, 10, and 12-inch rifles. The rate of combustion of these powders is regulated by varying their composition, the rate decreasing as the caliber of the piece increases. CHAPTER IV SMOKELESS POWDERS Although black and brown powders are still used to a very limited extent, all military powers have, within the last twenty years, adopted smokeless powder for use in guns of all calibers. Smokeless powders differ radically from ordinary gunpowders, both in composition and granulation. Although various substances have been experimented with, all military smokeless powders may be divided into two classes: 1. Those consisting of guncotton alone. 2. Those consisting of guncotton and nitroglycerin. In the United States powders of the second class are used in small arms, rapid-fire, field, and siege guns, while those of the first class are used in all other guns. Manufacture of Smokeless Powder. The wet guncotton as it comes from the pulping machine is transferred to an apparatus called "dehydrator," which consists of a steel cylinder, one end of which is fitted with a perforated plate. A heavy solid-headed piston works longitudinally in the cylinder. The first action of the piston is to express the water contained in the guncotton. Alcohol is then poured into the dedydrator and forced through the guncotton until the alcohol runs from the dehydrator of the same strength as when introduced. Sufficient alcohol is allowed to remain in the guncotton to act as a solvent. The guncotton is removed from the dehydrator in the form of a moist cake, is broken up, put into the "mixer," and the requisite amount of ether added to thoroughly dissolve the guncotton. In powders of the second class acetone is used as the solvent instead of alcohol and |