The Romance of Modern Chemistry

EXPLOSIONS AND EXPLOSIVES some of it, then, on the supposition that the combustible material yields gaseous products when it is burned, the mixture of the two solids will be a compact explosive. It will be compact because its bulk will be small in com- parison with the volume of the gases produced by its explosion. Common gunpowder is an explosive of this kind. It is an intimate mechanical mixture of the three substances— potassium nitrate (nitre or saltpetre), charcoal, and sulphur. The first and second of these are the essential constituents of gunpowder; the sulphur is present in a smaller pro- portion, and is added for a special purpose which will be explained later. The charcoal and the sulphur, as the reader will under- stand, are the combustible constituents, and the saltpetre, which forms about three-quarters of the gunpowder, is a compound which contains a high proportion of oxygen, and which, moreover, is easily induced to part with some of it; this being so, saltpetre may be regarded as a com- pact form of oxygen. Anyhow, it is easy to show that charcoal and saltpetre, while quite ready to lie down peacefully together at the ordinary temperature, act violently on each other when heated; any one can con- vince himself of this by throwing a pinch of saltpetre on a glowing coal fire. It is very easy to extract the potassium nitrate from gunpowder, and it is worth the reader’s while to try this, since the process illustrates very forcibly what was said in an earlier part of this volume about the separation of the constituents of a mechanical mixture, and shows, too, the kind of simple operations of which the chemist makes daily use. If the gunpowder is boiled with water, and the liquid is then filtered through a paper cone made of 171