EXPLOSIVES 77 EXPLOSIVES of which is a supporter of combustion. The ingredients of these mixtures are frequently not themselves explosives, but may be ordinary combustibles such as carbon, or sulphur, and stable salts such as chlorate or nitrate of potash. In the explosive powder, however, these other- wise harmless substances are incorpo- rated so thoroughly, and are in such a fine state of division, that combustion can be induced almost instantaneously throughout the mass, with a consequent rapid evolution of hot gases, thus pro- ducing the phenomenon known as an ex- plosion. The best known member of this class is gunpowder, now almost obsolete TANKS at all or only a very small percentage. As substitutes for saltpeter, nitrates of sodium, barium, and ammonia have been employed, the latter extensively in the manufacture of "safety explosives" for use in mines. Ammottal consists of a mixture of ammonium nitrate, aluminum and char- coal. Mixtures containing chlorates and perchlorates in place of nitrates have been manufactured and used to a con- siderable extent, but, owing to their un- stable character, have never very largely replaced the nitrate mixtures. 2. Explosive compounds are those sub- stances which are of such a nature as to NITI?ATlON HOUSE EXPLOSIVES — DIAGRAM OF GUN-COTTON FACTORY Key : A. Sulphuric acid E. Mixed acids I. Endless belts B. Sulphuric acid P. Oleum J. Steam trays C. Nitric acid G. Water K. Nitration pans D. Strong waste acid H. Teasing machine L. Beater M. Sand trays N. Poacher for military purposes, but still largely used for sporting purposes, in mining, for fuses and for minor military pur- poses. It consists of a mixture of nitrate of potash (saltpeter), sulphur, and charcoal, the proportions varying somewhat, but being approximately fifteen parts of potassium nitrate to two parts of sulphur and three parts of char- coal. Great care is taken in selecting the sulphur, while the charcoal is pre- pared in special retorts, and the process of manufacture is one requiring much skilled supervision. Many modifications of gunpowder have been made from time to time. In place of charcoal, such materials as coal, coke, peat, sawdust, bran, sugar, starch and many others have been used, while powders have been produced containing either no sulphur Vol. IV — Cyc — P be themselves explosive. Instead of a chemical reaction taking place between two separate substances, the reaction oc- curs within the molecule of a single sub- stance. As a consequence explosive com- pounds are more powerful in their action than mixtures, and modem explosives used in warfare all belong to this class. For the most part they are produced by the nitration of organic compounds and the best known and most widely used is trivHrotoluenc , commonly called T.N.T. This is manufactured by the nitration of toluene in successive stages, mono- nitrotoluene being first produced, then dinitrotoluene, and finally, trinitro- toluene. It occurs as yellow crystals, which darken on exposure to light, but is frequently used as a fused mass. When held in a flame, it does not explode,
