The Romance of Modern Chemistry

EXPLOSIONS AND EXPLOSIVES cohesion between the constituent atoms; it is the old story of a house divided against itself. But most of the explosions which come about, intentionally or uninten« tionally, depend on an altogether different principle; they are simply combustions which take place with excessive rapidity, and which result in the production of quantities of gas. In such explosions the element oxygen plays an essential part In the first place, any inflammable gas or vapour will form an explosive mixture with air. The reader must carefully distinguish between “inflammable” and “ex- plosive **; it is not correct to speak of coal gas as “ explosive ”; it is certainly inflammable, and when ignited at a suitable nozzle, burns quietly as long as the supply lasts. Combustion takes place only where air and gas meet A mixture of coal gas with air is, how- ever, a very different thing; it is inflammable at every point—explosive, in fact: combustion once started is rapidly propagated through the bulk of the mixture. Hydrogen similarly forms an explosive mixture with air, and illustrations of this fact are not infrequent in a chemical laboratory. For it often happens that a beginner, preparing hydrogen in a flask by the action of an acid on a metal, applies a light to the issuing gas before all the air has been expelled. The result of this will probably be that part of the flask will adhere to the ceiling, and the rest will be converted into fine dust. That coal gas becomes explosive when mixed with air we are frequently reminded, as from time to time we read of some one who has gone to look for a leak of gas with a lighted match or candle, and has thereby brought disaster on himself and his surroundings. When we can smell gas through a house, the atmosphere there is a 169