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 (Burgess’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.
Express Rifle. A modern sporting rifle of great killing power, used in hunting large or dangerous animals. They were first introduced in England, and have become celebrated in the hands of African travelers and explorers. The principle consists in using large charges of powder and a light bullet, which gives a very high initial velocity and a trajectory practically a right line for 150 or 200 yards, hence the term “Express.” To increase the killing power of the bullet it is made of pure lead and has a hollow point. Upon striking game the bullet spreads outwardly, giving a fearful death-wound. Moreover, for specially ugly game a small explosive cartridge can be dropped into the cavity in the point, making it an explosive bullet. (See [Bullets, Express].) In England a caliber as large as .57 is used for some Express rifles. In the United States a caliber of .45 or .50 is considered sufficient.
Expugn. To conquer; to take by assault.
Expugnable. Capable of being expugned, forced or conquered.
Expugnation. The act of taking by assault; conquest.
Expugner. One who expugns or conquers.
Extend. A term peculiarly applicable to light infantry movements, when the files are frequently loosened, and the front of the line extended for the purpose of skirmishing. When the divisions of a column are made to occupy a greater space of ground, they are said to extend their front.