The Romance of Modern Chemistry

EXPLOSIONS AND EXPLOSIVES mixture, possibly explosive, of coal gas and air, and if we were to carry a naked flame in search of the leak, we should be as foolish as the miner who goes into a “gassy” mine with a lighted candle. To produce an explosive mixture of air and coal gas about 6 per cent, of the latter is sufficient, so that one cannot be too care- ful. The only safe course is to begin by ventilating the house thoroughly, so that the proportion of gas may be reduced below the explosive limit. In explosions of this kind, where both parties to the combustion are gaseous, the amount of gas produced by the explosion is relatively less than in those cases where the original unexploded substance is a solid. The increase in volume is in fact due solely to the high temperature caused by the heat of the combustion. If coal gas and air, in the proportion of 1 to 5 by volume, are exploded in a very strong closed vessel so that no expansion is possible, a pressure of 7 to 8 atmospheres is developed, and the maxi- mum temperature reached is nearly 3500° Fahi’enheit. Explosions in which the oxygen necessary for the combustion is supplied in the form of air are actually employed as sources of energy in gas- and motor-engines. The pressure developed when a mixture of gas or petroleum with air is exploded is used to move a piston, and the longitudinal motion of the piston is converted into circular motion as in a steam-engine. It has been said that fire is a good servant but a bad master, and the remark is true in reference to explosive as well as to ordinary combustion. If instead of using a mixture of two gases we take a solid combustible material, and mix it intimately with some other substance which not only contains a large proportion of oxygen but is fairly ready to part with 170