Safety or Flameless Explosives.— These explosives are for use in fiery mines, particularly coal mines, where there is a chance of an acci dent arising through the ignition of the fire damp from the flame or incandescent particles given off by the explosive as the blast is fired. Among the earlier devices employed to pre vent this was the mixing in the dope of the dynamite or with the powder of a quantity of washing soda, alum, Epsom salts or other salt containing a large amount of water of crystalli zation that would be set free when the mix ture was fired. In 1883 Mallard and Le Chatelier discovered that when explosives were detonated unconfined in air containing 10 per cent of methane (marsh-gas), the fire damp could not be ignited if the temperature of de tonation was below 2200° C., owing to the cool ing of the gases due to their rapid expansion and to the retardation of the inflammation of the fire-damp. An investigation by the French Fire Damp Commission showed that, among others, certain salts of ammonia and especially ammonium nitrate, were capable of reducing the temperature of the gases produced by deto nation very materially, the temperature of the gases from explosive gelatine being reduced from 3090° C, when detonated alone, to 1493° C., if detonated when mixed with 88 per cent of ammonium nitrate. In August 1890 the French government prohibited the use of black powder in fiery or dusty mines and permitted the use in them of explosives whose gases are not combustible and the detonation tempera ture of which does not exceed 1900° C., where blasting is to be done in the rock, nor 1500° C., where the work is to be done in the coal seam. Among the explosives designed to meet such conditions and styled abroad safety or flameless explosives are: Ammonite; amvis, aphosite; bellite; benedite; britainite; cambrite; car bonite; Casteau's explosives; dalunenite; Fa vier's explosive; fractorite; Geserick's powder; grisoutine; grisoutite; nitroferrite; progressite; roburite; securite; westphalite ; wetterdyna mite.
Permissible Explosives are those which have passed the tests by the United States Bureau of Mines and which have been placed by it on the Permissible List of Explosives for Use in Coal Mines, established in 1908. There were 137 explosives on the permissible list 15 April 1916 classified as "ammonium nitrate,' 'hy drated," °organic nitrate" and 'nitroglycerin' explosives. Rules for testing and regulations for use of these explosives are supplied in free publications of this Bureau. By the use of these explosives safety in mining coal is in creased.
Smokeless Powders are high powered propellents used as substitutes for gunpowder in firearms and cannon. They are formed of the highest grade of cellulose nitrate only, like indurite, or of the medium grade only, like pyrocellulose powder, or they may be mixtures of different grades together with metallic nitrates like the B. N. powders. Another class are mixtures of cellulose nitrates with nitro glycerin and a restrainer, like vaseline; ballis tite, cordite and flute being examples of this kind. In robin-hood, gold dust, and gelbite,
we have examples of such powders made from nitrosubstitution compounds and oxidizing agents. Other smokeless powders are amberite; Erackett's powder; cannonite; Curtis and Andre's powder; Du Pont powder; E. C. pow der; fulgor ; granulite; hornite; J. B. powder; kolfite; poudre J; poudre S; pyrocollodion; rifleite; Schultze powder and Walsrode powder.
Shell Explosives.— For charging armor piercing and other high explosives shell very stable, insensitive, detonating explosives are required. Nitroglycerin, dynamite, guncotton and explosive gelatin were tried but found too dangerous. Picric acid was known to be powerful and, when condensed by fusion, so msensitive that it could be safely fired from modern guns, but it was found difficult to de tonate it when it was compressed in the shelL Turpin in France in 1886 solved the problem by causing a mercury fulminate detonator to act on pulverulent picric acid contained in a cavity in the compressed picric acid. For attack on warships shells are required that will pass through the armor and explode when on the inside. According to Marshall nitroaromatic explosives, such as picric acid, generally deto nate on the face of the armor. This is accom plished by ammonium nitrate explosives. The first complete demonstration was made at the United States Naval Proving Ground, Indian Head, Md., in 1897 under Capt. W. T. Sampson, U. S. N., when a shell containing 8.25 pounds of Joveite (moronitronaphthalene, picric acid and ammonium nitrate) penetrated a sheet of the harveyized armor of the United States Steamship Kentucky 14.5 inches in thickness and burst on the other side of the plate. Com pressed picric acid is known in France as melinite; in England as lyddite; Germany, granatfilllung 88; Italy, pertite; Japan, shimo site; Sweden, coronite; Spain, picrinite; and Austria, ecrasite. In many instances other sub stances are mixed with the picric acid. Thus in France to reduce the melting point and avoid the formation of cavities from crystallization or "piping" trinitrocresol is mixed with the pic ric acid. A mixture of 60 per cent trinitrocre sol and 40 per cent picric acid is known as cresylite 60/40. It melts at 85° C., but at is sufficiently plastic to permit of its being com pressed into charges which, on cooling, are com pact, amorphous and very homogeneous. In Austria ammonium cresylate is mixed with the picric acid. Since picric acid is corrosive, and may, by action on the metal of its containers, produce dangerously sensitive compounds..and also because the supply of it is limited, trinitro toluene has come to be largely used as the bursting charge for detonating shells. Schnei derite (mononitronaphthalene 10 per cent and anunonium nitrate 90 per cent) is used at Creu sot for this purpose also. Macarite (T. N. T. and lead nitrate) is also used.
Grenade and Bomb Explosives. Ammonal, cheddite, compressed gun cotton, picric acid, smokeless powder, T. N. T., and tonne are used for charging hand grenades and bombs.