Bitumen, a mineral substance, remarkable for its inflammability and its strong peculiar odour; generally, however, supposed to be of vegetable origin. The name, which was in use among the ancient Romans, is variously employed, sometimes to include a number of the substances called Mineral Resins (see RESINS), particularly the liquid mineral substances called Naphtha (q.v.) and Petroleum (q.v.) or Mineral Oil, and the solid ones called Mineral Pitch, Asphalt (q.v.), Mineral Caoutchouc, &c.; sometimes in a more restricted sense it is applied by mineralogists only to some of these, and by some mineralogists to the solid, by others to the liquid ones. All these substances are, however, closely allied to each other. Naphtha and petroleum consist essentially of carbon and hydrogen alone, 84 to 88 per cent. being carbon; the others contain also a little oxygen, which is particularly the case in asphalt, the degree of their solidity appearing to depend upon the proportion of oxygen which they contain, which amounts in some specimens of asphalt to 10 per cent. Asphalt also contains a little nitrogen. It seldom occurs quite pure, but is usually mixed with sand or other inorganic ingredients. Not infrequently it is found impregnating sandstone, limestone, shales, clay-slates, &c. Such is the character of the so-called fetid sandstones and limestones. From certain shales, marls, and slates, mineral oil is distilled in large quantities (see SHALE and MARL). Asphalt occurs plentifully on the shores and floating on the surface of the Dead Sea. It is met with in mass in many other places, as in Trinidad, at Limmer in Hanover, at Lobsan in Alsace, at Val de Travers in Switzerland, &c. Now and again it occurs also, in small quantities, in mineral veins or lodes, where it is often mistaken for anthracite. Closely related to asphalt are the pitch-like minerals called Grahamite and Albertite, which occur in fissures in the Carboniferous system of North America. The latter mineral has likewise been met with in Scotland. Some authorities also include the well-known Boghead Coal (q.v.) under the general head of Bitumen.
One of the most interesting of the bituminous minerals is that called Mineral Caoutchouc or Elastic Bitumen, and for which the new name of Elaterite has been devised, as if to support the dignity of its exaltation to the rank of a distinct mineral species. It is a very rare mineral, only three localities being known for it in the world—the Odin lead-mine in Derbyshire; a coal-mine at Montrelais, near Angers, in France; and a coal-mine near South Bury, in Massachusetts. It is elastic and flexible like caoutchouc, and may be used, like it, for effacing pencil-marks. It is easily cut with a knife. Its colour is blackish, reddish, or yellowish-brown; and its specific gravity is sometimes a little less, and sometimes a little more than that of water. It has a strong bituminous odour, and burns with a sooty flame, its composition being . Several substances occur in nature with a similar composition. Of these the best known is the mineral called Ozokerite. It is brownish, yellowish, or greenish in colour, streaked or spotted, and occurs in rudely fibrous masses, as at Slanik and Boryslaw in Galicia. It dissolves with difficulty in alcohol and ether. Various other natural products have been described as Ozokerite, to which they closely approach in chemical composition, and from which they seem to differ chiefly in their ready solubility in ether.