Petroleum
Previous to the discovery of the value of petroleum as an illuminating agent, the only artificial light for domestic and other similar uses was the tallow-candle and dirty oil-lamp; but when whale and other animal oils became too costly, resort was had to natural tar and bituminous slate in order to obtain illuminating-oils, and lamp-oils were for a long time prepared from wood, resin, and other substances. The manufacture of coal-oil was introduced into this country about 1853, being confined to districts where bituminous coal could be mined at a cheap rate.
When the value of coal-oil had become recognized, rock-oil or petroleum began to claim attention as a ready means of supplying these oils cheaply, as it was found to be analogous in its properties to that distilled from soft coal. It is probable that the petroleum now found in the earth is the product of original decomposition, and of subsequent distillation. Petroleum is, however, rarely found in contact with bituminous strata of any kind, being usually found in fissures of sand rocks, which fissures serve two purposes--one, to give space for the formation and expansion of the hydrocarbon vapor; the other, to furnish receptacles for the condensed oils. To obtain this oil, one of these fissures must be pierced by a well, when in some instances the oil is forced with such velocity as to produce a jet one hundred feet high. This oil is found in great quantities on the shores of the Caspian Sea; at Burmah, in the East Indies; and in Pennsylvania, Canada, and many other parts of the American continent. Fine specimens of naphtha are found in several parts of Italy. The purer kinds of rock-oil, which are almost colorless and very thin, are NAPHTHA, while the more viscid and darker liquids are PETROLEUM. The variations of color and consistence in rock-oils is owing to the pitchy and fatty substances being more dissolved in those oils that are most fluid. The word petroleum (rock-oil) is used to designate the forms of bitumen that are of an oily consistence, the bitumen passing by insensible gradations into the volatile naphtha on the one hand, and semi-fluid mineral tars on the other. Among its distillates are carbon-oil, paraffine, naphtha, gasoline, and benzine. Besides its use for illuminating purposes, it is now recognized as a fuel on both steamships and locomotives, as well as for ordinary domestic and manufacturing purposes. The products of petroleum that have proved most valuable in medicine are the filtered-paraffine residues, as cosmoline, vaseline, etc., widely used, plain and medicated, as ointments. See BITUMEN.