from the surface, which assumes a whitish color, but no further change occurs, no matter how long the explosive remains immersed. Unconfined, it burns, when ignited, with a bright yellow flame and a hissing sound, but does not explode. If, however, it is confined and heated to its ignition point, it explodes violently. Heated slowly, it explodes at about 399° F.; heated rapidly, it explodes at 464° F. The exact temperature at which explosive gelatin freezes is not definitely known, but it is probably about 40° F. When frozen, it assumes a crystalline structure and a somewhat paler yellow color than when in its normal condition. Unlike the dynamites previously mentioned, explosive gelatine is much more sensitive to shock when frozen than when in the unfrozen state, and is readily exploded by the impact of bullets. When unfrozen, it is comparatively insensitive to friction, blows, etc. On account of its solid form and plastic nature, its great power and comparative safety, explosive gelatin has been regarded as the ideal military explosive. The original and best grade of explosive gelatin is manufactured by the Nobel Explosive Company of Great Britain. The gelatin manufactured by the Forcite Powder Company in this country is similar in many respects to the Nobel gelatin, but the samples tested seem to have a greater tendency "to leak." Detonators. In order to develop the full force of guncotton, nitroglycerin, and explosives derived from them, they should be detonated. The best-known substance to cause such explosives to detonate is mercury fulminate. Mercury fulminate is itself an explosive, and when dry is very sensitive to all kinds of shocks, and explodes violently when struck, or rubbed or pressed between hard surfaces, or when heated. When moistened so as to contain about 30 per cent. of water it is practically inexplosive. Its most valuable property for military purposes is that it invariably causes "high explosives" to detonate when itself exploded in contact with or very near such substances. When used for this purpose it is mixed with other substances, the usual mixture being 75 parts of mercury fulminate and 25 parts of potassium chlorate, to which is added a little ground glass. The detonator case is a copper capsule about 1 inches in length and inch in diameter. The decomposition is rubbed very fine under water, partially dried and pressed into the capsule, where it dries thoroughly and is covered with a drop of varnish or a thin disk of foil. According to the amount of fulminate they contain, detonators are graded into single, double, treble, etc., force caps. Single force caps contain 3 grains, double 6 grains, etc., up to the strongest or quintuple force cap, which contains 15 grains of fulminate. Detonators are made so as to be fired by means of a "time fuse" or by electricity. The ends of detonators to be fired by time fuse are left open to receive the fuse, while electric detonators are closed by means of a plug made of sulphur and ground glass, through which pass two wires. The ends of the wires are connected by a very fine wire (or bridge) around which is wrapped a wisp of dry guncotton. When the electric current passes through the bridge it heats it and the guncotton is ignited and causes the fulminate to detonate. Recapitulation.-1. On account of their tremendous force, guncotton and nitroglycerin are combined with other substances to modify and regulate their action, the resulting explosives being known as guncotton powders and dynamite. 2. Dynamite is a term which includes all explosives made by absorbing liquid nitroglycerin in a solid material, the absorbent being technically known as the "dope." 1 This term includes guncotton, nitroglycerin, their derivatives, and practically all explosives capable of detonating. 3. Dynamite is made under various names and in many grades, the strength of any particular grade depending upon the amount of nitroglycerin it contains. N. B. For demolitions, submarine mines, and military purposes in general, only the highest grade or strongest dynamite should be used. 4. All guncotton powders and dynamite ("high explosives") should be exploded by means of detonators. 5. Detonators (or "blasting caps") may be fired by a "time fuse" or by electricity. 6. The rate of burning of a time fuse should always be determined before it is used. 7. Dynamite should never be used when frozen, and great precaution should be used when it is thawed. |