The Romance of Modern Chemistry

MORE ABOUT FUEL mineral matter. Such a primitive method of converting wood into charcoal is frequently replaced by a more scientific procedure, in which the wood is heated in closed vessels or retorts, and provision is made for collecting or condensing any volatile matter. In considering the use of wood as a fuel, we have seen that its ready combustibility is due to its giving off’ in- flammable vapour. It is therefore not surprising to find that when wood is heated out of contact with air a quantity of gas is obtained. The main constituents of this gas are carbon dioxide, carbon monoxide, and marsh gas; the two latter are combustible, and although the gas has not much illuminating value, it may be used to heat the retorts. This is a simple example of the way in which the by-products of a manufacturing operation may be utilised so as to diminish the cost of production. The volatile matter obtained by subjecting wood to dry distillation not only yields a combustible gas, but condenses partly to a tar and partly to a watery liquid. The latter yields acetic acid—the acid of vinegar—and wood spirit; this consists largely of methyl alcohol, and is added to rectified spirits of wine in order to produce methylated spirit. The object of thus “denaturing” ordinary alcohol is to provide a spirit which may be employed for industrial purposes, and which, at the same time, is not drinkable. Whether the latter condition is fulfilled is doubtful, for it is said that such methylated spirit is consumed as a beverage, to the injury of the revenue. Accordingly, the bulk of methylated spirit now sold has a small admixture of mineral naphtha or light petroleum to render the taste more objectionable. When coal is subjected to destructive distillation the effects are in general the same as those obtained with 144