Gun-cotton

the acids on cotton-wool—a form of cellulose. See Gun-cotton . There are varieties of all these compounds produced, by the substitution of different numbers of equivalents of hypo nitric acid, but the names are specially given to the most highly nitrated forms. Picric acid , the salts of which form the well-known picrates , is made by the action of the acids on carbolic acid. To heighten the effect of the lower forms of nitro-substitution compounds they are usually mixed with an oxidizing agent, such as nitrate or chlorate , which supplies the deficient oxygen. This is exemplified in Schultz’s wood powder (which see), and Reeve’s gun felt. The picrates are similarly treated. Ammonium picrate mixed with nitre forms Abel’s picric powder (Burge ’s powder). This has been used as a bursting charge for shells. Mixtures of two high explosives have also been used, as in glyoxiline, invented by Prof. Abel, which is gun-cotton saturated with nitro-glycerine. Explosive effect depends upon three elements,—1st, the volume of the gases produced taken at a standard temperature; 2d, the heat evolved in the chemical reaction; 3d, the time consumed in the development of the gases. Explosive effect is directly proportional to the first two of these elements, and inversely proportional to the third. According to Bertholet, nitro-glycerine gives out twice as much heat and three and a half times as much gas as an equal weight of gunpowder, but this gives no idea of their relative explosive effects, as the element of time in the detonating explosives is so short that it cannot be calculated. So nearly is this element absent that we may consider these explosions as almost perfect Impulsive Forces. To secure ballistic effect requires the gradual application of force. When motion is imparted to a body the inertia developed is inversely proportional to the time consumed in imparting it. This resistance to motion becomes enormously great when the detonating explosives are used. For this reason their ballistic effect is small. The force which should give the projectile motion is expended in producing molecular changes in both projectile and gun. The same quality, however, fits them especially for blasting and torpedoes, where shattering effect is desirable.