But if we compare the most brittle specimens of the pitch with common specimens of asphaltum, the differences, except as far as smell and taste are concerned, are not so apparent, and the reason of this will be obvious on considering their fundamental similarity of composition. The chief ingredients of both are carbon and hydrogen. By the application of heat, the proportions of these substances are altered in both cases, the hydrogen being abstracted in the greatest ratio, to form the new compound (the oil) in which hydrogen predominates. The ultimate result of both is charcoal. Asphaltum will be found to combine pretty nearly in the same way, with all the substances I have above enumerated as combining with the pitch. Its essential difference however consists in its solubility in naphtha, and by this test they are readily distinguished.
The chemical difference to which these different properties of substances so similar are owing, will be evident on considering some of the circumstances before related. The disproportion of acetic acid and carbonic oxide produced from the wood pitch, when compared with the produce of the bitumen, proves that it contains oxygen and azote in proportions different from those in which the same substances exist in the bitumens; and that in particular it contains a considerable quantity of the former. The result would not repay the toil required to investigate these proportions, which are probably also subject to considerable variation.
It is obvious that this substance is a new compound, formed by the action of fire on vegetable elementary matter; but all that we can determine of its nature is, that in conformity to modern chemical nomenclature, it is formed of carbon, hydrogen, oxygen, and azote. The carbon and hydrogen constitute its basis, as they do that of the bitumens, and the large proportion of oxygen appears to give it the peculiar properties by which it is distinguished from them