BITU'3IEN, a Latin word used by Tacitus, Pliny, and other Roman writers. A considerable number of combustible mineral substances are sometimes arranged under the head of Bitumens ; but their pro perties 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, namely, Asphaltum [AsrlisLrum], and a softer kind called Elastic Bitumen, which we shall now describe.
Elastic Bitumen, sometimes called Fossil Caoutchouc, is a rare mineral product, which has hitherto been found in three places only : 1st, in the Odin mine, near Castleton in Derbyshire, in a Secondary Limestone, accompanied by asphaltum, calcareous spar, fluor, blend°, galena, and pyrites ; 2nd, in a coal-mine of Montrelais, a few leagues from Angers in France, it occurs among quartz and calcareous crystals, in the veins of grit of the Coal Formation ; 3rd, in a coal-mine near South Bury in Massachussets, United States.
Elastic Bitumen possesses the following characters :—It is brown, or blackish brown, and translucent in small portions ; it is soft and elastic like caoutchouc, but sometimes it is as bard as leather : it has the property, like caoutehouc, of effacing pencil-marks. Its density varies from to It fuses readily, and at a higher tempera ture it takes fire and burns with a sooty flame : it sometimes leaves one-fifth of its weight of ashes, composed chiefly of silica and per oxide of iron. If the Derbyshire Elastic Bitumen be subjected to distillation, it yields acidulous water and volatile oil, resembling that of naphtha in smell: the oil is neither acid nor alkaline, slightly soluble in alcohol, but readily so in ether ; after the distillation of the water and oil, a brown viscid mass remains in the retort, which is insoluble in water or alcohol, but is dissolved by ether and by potash.
If the distillation be longer continued, an empyreumatie oil resembling that of amber is obtained, and a black shining coal remains.
When the Elastic Bitumen of Montrelais is similarly treated, there is obtained a yellow bitter fetid oil, which is lighter than water and insoluble in alcohol, hut it dissolves in the alkalies.
Elastic Bitumen swells when put into oil of turpentine or of petro leum ; ether and oil of turpentine when boiling extract a kind of soft resin from the English and French bitumen, and this remains after the evaporation of the solvent this resin is of a brownish-yellow colour, is bitter and inelastic ; its weight is nearly half that of the bitumen employed.
It is but slightly soluble in alcohol, but readily in potash ; it is inflammable, and burns with a smell of petroleum ; that portion of the bitumen which is insoluble in the ether and oil of turpentine, is a grayish dry mass, resembling paper ; it burns with difficulty, and carbonises; potash dissolves only a part of it. If after separating these two principles they are mixed together, the bitumen does not regain its elasticity.
Concentrated sulphuric acid does not act upon Elastic Bitumen ; but when long boiled with nitric acid it yields resin, tannin, and a little nitroperic acid. According to the analysis of M. Henry, jun., the Elastic Bitumen consists of at the Cape of Good Hope, and also in India and China." Selby observes that its geographical distribution "seems confined to Europe, extending nearly to the confines of Asia; " but it was in the collection formed in the neighbourhood of Trebizoncl by Keith E. Abbott, Esq.,