BITUMEN. A considerable number of combustible mineral substances are sometimes arranged under the head of bitumens; but their properties vary greatly in some respects, as, for example, with regard to solidity, fluidity, and colour. The term bitumen is however usually applied to two varieties, a harder kind called asphaltum [ASPHALTUM], and a softer kind called elastic bitumen. Naphtha is a fluid kind, and petroleum semi-fluid.
Elastic bitumen, sometimes called fossil caoutchouc, is a rare mineral product. It is found in the Odin mine, near Castleton, in Derbyshire; in a coal-mine of Montrelais, a few leagues from Angers, in France ; and in a coal-mine near South Bury, in Massachusets, United States.
Elastic bitumen is brown or blackish brown, translucent in small portions, soft and elastic like caoutchouc, but sometimes hard as lea ther. Its density varies from 0.9053 to L233. It fuses readily, and at a higher temperature it takes fire and burns with a sooty flame. It is but
slightly soluble in alcohol, but readily in potash.
According to the analysis of M. Henry, jun., the elastic bitumen consists of In Texas there has recently been discovered a bituminous lake very similar to that of Trin idad. It is situated in Jefferson about 100 miles from Houston. It is about a qu'arter of a mile in circumference. In the summer months there is a spring near the middle of the lake where an oily liquid like petroleum continually boils up from the bottom ; this liquid gradually hardens on exposure to the air, and forms a black pitchy substance. It burns, when lighted, with a clear bright light, but gives out a very pungent odour. During the winter the bitumen in the lake presents a hard surface, and is covered with water having a somewhat sour taste.