The Romance of Modern Chemistry

CHAPTER XIII MORE ABOUT FUEL IN the foregoing chapter we have discussed the various natural fuels which are available for use without any more than a slight preliminary treatment There are, however, other substances commonly classed as fuels to which no reference has yet been made—for example, charcoal, coke, and coal gas. Although these substances are to be regarded as fuels, they do not belong to the same category as wood, peat, coal, or petroleum. Unlike the latter fuels, they are not obtained directly from Nature; they are produced secondarily from the natural fuels by special treatment. Generally speaking, the secondary fuels, charcoal, coke, and coal gas, are obtained by the process of destructive distillation. This operation sounds rather alarming, but it is one which most boys have performed on a small scale, and the principle of it is comparatively simple. In ordinary distillation, where a liquid is converted into a vapour, and this vapour is condensed by passing through a cooled tube, any products obtained in the distillate were already present in the original liquid. The pro- ducts, however, of a dry or destructive distillation are not present as such in the original substance; they are only produced by its chemical decomposition. The little experiment in destructive distillation which many readers have probably made consists in filling the 142