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58 INTERNATIONAL EXHIBITION, 1876. detonation from shocks and to spontaneous combustion than in the liquid state; it is more convenient to handle; frozen in the state of loose powder, it does not lose the property of exploding from the action of the usual fuse (fifteen grains of fulminating mercury), while, if com pressed into cartridges, it becomes as inexplosive as nitro-glycerine itself; saturated with water, it retains its detonating power, but re quires a larger initial explosion to develop it; ignited in small quantities by a flame, and unconfined, it burns quietly. As already stated, many other absorbents beside kieselguhr have been used. They belong to two distinct classes,—those which in themselves are explosive, and those which are inert. To the former belong gun-cotton, the product being glyoxiline, saw-dust treated with nitric and sulphuric acids, the product being dualin, some modi fication of the elements of gunpowder, the product being variously known as lithofracteur, rendrock, vulcan powder, dynamite No. 2, giant powder No. 2, etc. Among the inert absorbents may be named Boghead coal-ashes, mica scales, artificially deposited silica, etc. While it will generally be admitted that the detonating force of these compounds is derived solely from the nitro-glycerine contained in them, the percentage of which varies greatly owing to differences in their power of absorption, it is far from true that their economic value as explosives can be thus compared. The element of time, which determines whether a blow or a push is delivered, is of primary importance, and should practically determine which compound should be selected. In flint-rock no explosive can compete in force with liquid nitro-glycerine; but for common earth, gunpowder is far more effective. Between these limits most of the nitro-glycerine compounds named above may find a use. The Picrates.—Picric acid was discovered in 1788 by Haussman, when treating indigo with concentrated nitric acid; but it is now often derived from other substances, especially from carbolic acid. It is used in commerce as a dye, being of a brilliant yellow color and unexplosive. Its salts are numerous, and are more or less explosive; the potassium and ammonium salts, often in connection with potas sium nitrate or chlorate, are those usually employed for that purpose. Potassium picrate possesses great explosive energy, but is danger ous to handle from its liability to explode by friction. Designolle’s powder, a mixture of potassium picrate and nitrate, sometimes with a little charcoal added, was formerly considerably used in France, but has ceased to be manufactured since the occurrence of a destruc tive accident. - Brugiere powder, a mixture of ammonium picrate and potassium
