At Colebrook Dale, in Shropshire, there is a spring of petroleum. This was discovered at the depth of about thirty yards beneath the surface of the earth, in digging an archway for the conveying of coals from a very deep pit. The petroleum was at first found to ooze from between the crannies of the rock, but it soon afterwards poured forth in a considerable stream. The utility of this fluid having been made known, large iron pipes were formed from the spring into pits sunk for the purpose of receiving it. From these pits it is conveyed into immense caldrons, where it is boiled until it attains the consistency of pitch. Since the first discovery of this substance, three different springs of it have broken out. One of these is near the celebrated iron bridge; and the fluid that issues from it is almost pellucid, but, at the same time, is thicker than treacle.
Petroleum easily takes fire, and, in burning, yields a strong, sharp, and somewhat unpleasant odour; and a thick and disagreeable smoke. In cold weather it congeals in the open air.
In Pegu, and other parts of the East, petroleum is used in place of oil for lamps. Boiled with a species of resin, it is employed for painting the timber of houses, and covering the bottoms of boats and other vessels. In the latter respect it is considered to be particularly efficacious, by protecting the timber from the attacks of marine worms. It is also used by the inhabitants of eastern countries as a lotion in cutaneous eruptions, and as an embrocation in bruises and rheumatic affections. The ancient Egyptians used it in the embalming of dead bodies. In some countries lumps of earth are soaked with petroleum, and are employed as fuel.
214. MINERAL TAR, or BARBADOES TAR, is a fluid kind of bitumen, somewhat thicker than petroleum, and nearly of the consistence of common tar. It is viscid, of a black, brownish black, or reddish colour.
In burning its smell is disagreeable, but less pungent than that of most other kinds of bitumen. Its weight is somewhat greater than that of water.
In the West Indies, where this substance is principally found, it is applied to many of the purposes for which the preceding species is used; but its principal repute has been obtained from its being thought useful in disorders of the breast and lungs, though this application of it is considered very improper. It is likewise used as an external remedy in paralytic disorders.
215. ELASTIC BITUMEN, or MINERAL CAOUT-CHOUC, has a strong resemblance to Indian rubber. In some instances it is elastic, and so soft as to adhere to the fingers, and in others brittle, and so hard as nearly to resemble asphalt ([216]).
Its colour is yellowish, reddish brown, or blackish. One kind of this mineral, when fresh cut, nearly resembles fine cork, both in texture and colour.
This extraordinary substance, which will expunge the marks of black lead in the same manner as Indian rubber, was first discovered, about the year 1786, in cavities of the lead mine of Odin, near Castleton, in Derbyshire, and it has not hitherto been found elsewhere. Elastic bitumen appears to be a peculiar modification of petroleum, in its passage to asphalt: and probably owes its elasticity to its cellular texture, and to the moisture with which it is combined.
216. ASPHALT, or SOLID BITUMEN, is a brittle substance, of black or brownish black colour, and of consistence somewhat harder than pitch.