The veins of asphaltum sometimes take fire acciden tally, and arc extinguished with much difficulty. In the parish of St John's, in Barbadoes, a slave roasting po tatoes on the side of a hill, accidentally set fire to a small vein near the surface, which remained burning slowly, and almost imperceptibly, during five years. It was not attended with any danger to the neighbour hood. Other veins taking fire are frequently extin guished by the earth which surrounds them falling in and choking the flame. A rich mine of asphaltum be ing discovered in Alsace in the year 1759, it was at first wrought with great success. In the course of ex fodiation, a spring burst out, bearing a great quantity of this bitumen on its surface. A lamp having been brought within half a foot of the water, the asphaltum, which was probably in an imperfect state of induration, took fire, and continued burning a considerable time.
Different explosions were heard in the mine, and many of the workmen so severely injured, that it was judged prudent at that period to abandon it.
Asphaltum is supposed merely to be the softer bitu mens in the highest state of induration, which seems extremely probable, as well from its constituent prin ciples, as from different analogies in the situations Where it is found. Intelligent chemists have advanced a rational theory, that the progressive changes of naph tha into petroleum, mineral tar, mineral pitch, and as phaltum, arise from the gradual dissipation of part of the hydrogen of the bitumen, and consequent disengag ing of carbon. But what regards chemical analysis, will
more properly be resumed under another head. Mr Hatchets, from an examination of that brought from 'Trinidad, concludes, that what has there hitherto been supposed pure mineral pitch, is in reality only a porous stone of the argillaceous genus much impregnated with bitumen.
Asphaltum was anciently employed by the Egyptians in embalming their dead. That of the Dead Sea is now carried by the Arabs to Damietta, where it is said to be employed in dyeing. The asphaltum of Trinidad is ex tremely ductile when mixed with a little grease, and thence becomes very useful in pitching ships. It is likewise employed in different varnishes. When adul terated with pitch, the deceit may be detected, by its having too strong an odour, for when pure it exhales a slight bituminous smell if rubbed, and also by its ad hering to the fingers and melting. See Philosophical Transactions, 1789, p. 65 ; Nichoison's Philosophical Journal, vol. ii. p. 201 ; Journal de Scavans, 1759 ; Hughes' Natural History of Barbadoes ; Parkinson's Or ganic Remains of a former World, vol. i.; Linmean Transact. vol. viii ; and Murray's Chemistry, vol. iv. p. 497.