or that carbon which there is not oxygen enough present to burn, is deposited in a state of very minute division in proportion as it is volatilized, during the formation of the naphtha or petroleum, the more hydrogenous part of the compound. But if this part is separated without flame, either by a more moderate heat, or by excluding oxygen from it, the carbon is rendered apparent by its affinity of aggregation, which causes it in the end to assume comparatively refractory powers, and a more solid form.
Such are the views I would entertain of the bituminous genus, in which as it is found in Nature, all traces of organization or resemblance to vegetable and animal inflammable matter, have so thoroughly ceased, that we are entitled to give its several species a fair rank among minerals. But there is yet another division of inflammable and subterraneous substances connected with these, of which the claims may appear doubtful. Retaining as they do, the traces of organization, and that sometimes in great perfection, it may be often questioned whether they do not more properly rank with the fossil remains, than with the minerals properly so called. They are well distinguished by the name of Lignites. At one end of this series is placed jet, in which the traces of vegetable origin are nearly obliterated. Surturbrand and the several varieties of brown coal, including Cologne earth, connect it gradually with submerged wood and peat. The experiments I have already related prove that the substance resembling bitumen, which is produced by the action of fire in the ordinary way on vegetables, differs from it essentially, and it has been seen that solubility in naphtha is the readiest criterion by which these substances can be distinguished. To assure myself of the accuracy of this test I mixed the petroleum of coal with the black oil of wood in several proportions, and by the application of naphtha separated the one from the other. By this simple