The Romance of Modern Chemistry

EXPLOSIONS AND EXPLOSIVES blotting-paper, the sulphur and the charcoal, being in- soluble in water, are held back, and a colourless solution runs through the blotting-paper into a vessel placed to receive it. This solution, when allowed to cool or when evaporated a little, will deposit white crystals of saltpetre. What takes place when gunpowder is fired is essentially a combustion of the charcoal, as a result of which large quantities of gas—carbon dioxide, carbon monoxide, and nitrogen—are suddenly evolved. The presence of the sulphur makes it more easy to fire the gunpowder, a lower temperature being sufficient to set it off*; the function of the sulphur is therefore similar to that which it used to fulfil when employed in coating matches. In addition, however, the presence of the sulphur contributes to the rapidity with which the explosion is propagated, and its oxidation by the saltpetre adds materially to the heat evolved in the reaction. The advantage of having the explosive material in a compact solid form can be seen from the fact that when gunpowder is fired in a closed space the pressure developed is about 2000 atmospheres, quite a different magnitude from the pressures obtained in the explosion of coal gas and air. Gunpowder is the oldest explosive known, but it is largely displaced nowadays by so-called “ high explosives,” which, in addition to several other points of distinction, are practically smokeless. Any one can understand the long-cherished desire of the military and naval specialist to find some substitute for gunpowder, which when fired envelops the operator of a gun in a dense cloud of smoke. In the chemical action which accompanies the explosion the potassium from the saltpetre forms other salts, potassium carbonate and potassium sulphate. These 172