ether, and the nitroglycerin is dissolved in a part of the acetone before it is added so as to reduce its sensitiveness. The ingredients and solvent having been placed in the "mixer," the workmen withdraw from the building, and the process of incorporation is begun. It requires from one to two hours to effect thorough incorporation, at the end of which time the powder appears as a pasty mass. The powder is next compressed into a solid cake preparatory to passing through the graining press. Until recently the paste was rolled into sheets of varying thickness by passing it between steam-heated rollers, and the fin ished powder is still frequently The sheets of powder are placed in a drying house, where the bulk of the remaining solvent is driven off, when they are again rolled to eliminate the "blisters" formed by the escape of the solvent from the interior of the sheets, as well as to perfect the incorporation. FIG. 4. FIG. 5. In case of the "flake, sheet," or "strip" powders, as the powder comes from the rolling machine, it is of the consistency of indiarubber and the thinner sheets or strips are perfectly translucent. Recently the perforated cylindrical grain, either single or multiperforated (see Figs. 4 and 5), has almost entirely superseded the earlier forms of flake and strip powder. In making the cylindrical-grained powders, the paste is placed in a large cylinder (made of cast iron or steel), which has a piston entering through its head. The piston is generally actuated by hydraulic power, and serves first to compress the paste and then to force it through a die attached to the base of the press. To prevent clogging of the dies the paste is first forced through a plate perforated with very fine holes. By varying the diameter (or form) of the die the same press may be used for pressing and molding powders for use in guns of all calibers. In case of powders of small diameters, such as filite, cordite, etc., the thread or cord is either reeled at once, as it emerges from the press, on drums, and the drums are then transferred to the drying house, where they remain until practically all of the solvent is driven off; or it is received on a canvas belt which passes over steam-heated pipes and is discharged into wire baskets, which are subsequently placed in the drying house until the cord or thread is ready for granulation. For small-arm powder the threads are passed under revolving knives and cut into very short cylinders, which are dusted and sometimes glazed as described in the case of ordinary gunpowder. The diameters of powders intended for guns of larger caliber vary according to the gun, and the grains are both perforated and cut into lengths as the powder emerges from the dies. Properties of Smokeless Powders.-The color of smokeless powder varies from a grayish yellow to dark brown, and from being translucent to entire opaqueness. When glazed they resemble ordinary gunpowder, except in form of grain, but upon cutting through the grain or washing off the graphite the color peculiar to the composition of the powder is readily seen. In texture they are smooth, and are either very hard and brittle or they are tough and of the consistency of indiarubber. They are insoluble in water and are practically unaffected by it. They are insensitive to shock of impact or to the passage of a bullet through them. They are more difficult to ignite than black powder and charges are generally primed with the latter to insure ignition. They leave very little residue in the bore of a gun. Recapitulation.-1. Smokeless powders may be divided into two classes, viz: (1) Those consisting of guncotton alone. (2) Those consisting of guncotton and nitroglycerin. 2. In both classes of smokeless powders the guncotton is dissolved1 and reduced to a gelatinized mass and then pressed into grains of regular shape. 3. The form of grain adopted by the United States is a cylinder which for guns of small caliber has but one central perforation, while the grains for guns of larger caliber are multiperforated. 4. Smokeless powders differ radically from ordinary gunpowder in physical properties as well as in their composition. 'The substance formed by dissolving guncotton is technically called a "colloid." Colloids when ignited even in a closed chamber do not explode, but burn regularly in parallel surfaces. It is this property of colloids that renders them available for use in guns. CHAPTER V EXPLOSIVE COMPOUNDS GUNCOTTON AND NITROGLYCERIN As gunpowder is the best-known example of explosive mixtures, so guncotton and nitroglycerin may be taken as the best known, and with their derivatives the most generally used types of explosive compounds. Guncotton.-As its name implies, this is an explosive derived from cotton, and is made by dipping or steeping pure dry cotton in a mixture of the purest and strongest nitric and sulphuric acids. The purification of the cotton before being immersed, the conversion of the cotton into guncotton, and the subsequent purification of the guncotton are lengthy processes attended with considerable difficulty, and requiring complicated machines, but the principles governing these steps are easily understood. For practical reasons the cotton used in the manufacture of guncotton is "cop waste" (or "weaver's waste”), which consists of the tangled clippings from the spinning rooms of cotton-mills. It therefore generally contains more or less oil, dirt, and moisture (water). When impure or unclean cotton is immersed in the acid mixture, the impurities (oil, dirt, etc.) are acted upon by the acids and form compounds which are unstable and liable to explode during manufacture, and, if not removed, lead to the subsequent decomposition of the guncotton. The presence of moisture during the immersion of the cotton serves to dilute the acid mixture and to cause heat,1 which The heat is caused by the water uniting chemically with the sulphuric acid. also gives rise to the formation of unstable compounds, whose action is as just described. The use of weak acids or too short an immersion prevents the complete conversion of the cotton into the highest and most stable form of guncotton, such as is used for military purposes.1 Manufacture of Guncotton.-The following is an outline of the processes of manufacture of guncotton followed by the best factories in this country and abroad: 1. The "cop waste" is first thoroughly cleansed and dried. 2. The acids are mixed in the proportions of 1 part of nitric to 3 parts of sulphuric2 and allowed to cool. 3. The cotton is immersed in the proportions of 1 part of cotton to 10 parts of acid for the period of ten minutes. 4. Nearly all of the acid is squeezed out of the guncotton, which is next placed in an earthenware crock and allowed to remain ("digest") for twenty-four hours. 5. All remaining traces of acid are removed by wringing, washing, and boiling the guncotton. 6. The guncotton is reduced to the fineness of corn meal in a machine similar to an ordinary paper-pulping machine. 7. The guncotton pulp is washed, first in fresh water, and then in water containing lime, caustic soda, and marble dust.3 8. The water is drawn off and the guncotton drained until 1 When cotton is acted upon by mixtures of nitric and sulphuric acid various products are obtained, nearly all of which are more or less explosive and more or less stable, depending upon the strength of the acids and the length of time the cotton is subjected to their action. Only the highest grade of guncotton, obtained as described above, is sufficiently stable for military purposes. This product is called "trinitrocelluluse." 2 The sulphuric acid is added to absorb any original moisture present in the waste or nitric acid, as well as the water formed during the conversion, so as to preserve the necessary strength of the nitric acid. 3 This last solution is used to neutralize or destroy any possible trace of acid that might remain in the guncotton. |