An explosive prepared by steeping cotton-wool in a mixture of equal volumes of strong nitric and sulphuric acids. The cotton, after drying, is not perceptibly altered in appearance, but its weight has increased about 70 per cent., and it has become very inflammable. It is largely used instead of gunpowder, over which it possesses several advantages. The explosive power of one pound of gun-cotton is more than three times that of the same weight of gunpowder. Collodion, used by photographers, is gun-cotton combined with alcohol and ether. Celluloid is gun-cotton combined with camphor and other substances.