Petroleum, Pharm. Lond. Oleum petrae, Oleum terrae. Rock oil: a fluid bitumen or mineral oil; exuding from the clefts of rocks or From the earth, or found floating on the surface of waters, in different parts of Europe, and more plentifully in the warmer countries; simi-lar, in its general properties, to the oils extracted by distillation from pitcoal, amber, and other solid bituminous bodies. The more fluid petro-lea have been distinguished by the name of naphtha; and the thicker by those of piffafphaltum and piffelaum.

1. Petroleum album. White petroleum: nearly colourless; almost as clear, fluid, and transparent, as water; of a strong penetrating smell, not disagreeable, somewhat resembling that of rectified oil of amber. The principal, or only, part of Europe, in which it is found, is the dutchy of Modena in Italy.

2. Petroleum flavum feu italicum Pharm. Paris. Yellow petroleum: of a clear yellow colour; somewhat less fluid than the former; in smell rather less penetrating, less agreeable, and more nearly allied to that of oil of amber. This also is found chiefly in the dutchy of Modena, and does not appear to differ very materially from the white sort.

3. Petroleum rubrum feu gabianum, five Oleum gabianum Pharm. Paris. Red petroleum: of a blackish red colour; of a thicker consistence, and a less penetrating and more disagree-able smell, than either of the foregoing; found in Italy, and about the village Gabian in Lan-guedoc.

There are many variations of these oils in regard to colour, fluidity, fubtility, and the pungency of their smell and taste: the most fluid are in general the most subtile and pungent. Among us, the finer kinds are rarely to be met with; and even the inferiour sorts are rarely unsophisticated.

Fine petroleum catches fire on the approach of a flaming body, even without the contact of its substance with the flame; and burns entirely away. The hasty affusion of concentrated mineral acids, which raises a violent ebullition with distilled vegetable oils, and generally sets them on fire, makes no great conflict with petroleum: its consistence becomes thicker by this admixture, and its smell more fragrant. By distillation, it loses much of its natural scent, and becomes somewhat more pellucid than at first; a small quantity of a brownish. or yellowish matter, similar to amber (a), remaining behind. Dropt on water, it spreads to a great distance, forming a various-coloured film on the surface. It floats also on rectified spirit of wine, and appears to be indissoluble in this menstruum; but unites with the essential oils of vegetables (a).

(a) Borrichius, Acta medica & philosoph. Hafnienfia, tom. i. obf. 57.

The finer petrolea, more agreeable than oil of amber, and more mild than that of turpentine, partake of the virtues of both. They have been sometimes taken internally in nervous complaints and as a diuretic; but used chiefly as an external stimulant, against rheumatic pains, palsies, chilblains, etc. In these intentions, some mineral oils, procurable among ourselves, are used by the common people, and often with benefit: the empyrical medicine, called British oil, is of the same nature with the petrolea; the genuine sort being extracted by distil-lation from a hard bitumen, or a kind of stone-coal, found in Shropshire and other parts of England.

4. Petroleum barbadense Pharm. Edinb. Bitumen barbadenfe. Piffelaum indicum. Bar-badoes tar: of a reddish black colour, and a thick consistence, approaching to that of treacle or common tar. It is found in several of our American islands, particularly, as is said, in that from which it receives its name.

This bitumen, greatly esteemed by the Americans as a sudorific, in disorders of the bread, and as an external discutient and antiparalytic, is in smell more disagreeable, and both in smell and taste less pungent, than the foregoing petrolea. It is likewise less inflammable, and leaves on being burnt a considerable quantity of ashes. In distillation, it yields an oil different, in regard to its colour, from those afforded by such of the other bitumens as have been examined; appearing, when placed betwixt the eye and the light, of an orange colour, in other positions blue; but losing this variability of aspect in long keeping, and then looking in all situations yellow. This oil, and a balsam prepared by boiling the petroleum itself with one fourth its weight of flowers of sulphur, are directed by the London college to be kept in the shops.

(a), See l'Hiftoire & les memoires de l'acad. roy. des fcienc. de Paris, pour Us annees 1715 & 1726.