CASTOR-OIL is extracted from the seeds of the Ricinus communis, a plant belonging to the natural order Euphorbiaceae, and to the Linnaean class and order Monocotyledonia. This plant, common in Asia, Africa, West Indies, south of Europe, &c., is best known by the name of the Palma Christi, and is now recognised as the gourd (kikayon and kiki) mentioned in Scripture as sheltering the prophet Jonah. In temperate countries this plant is annual and herbaceous, and only reaches 6 or 8 feet in height. But in warmer countries it is more ligneous and perennial, and in India often attains the height of 40 feet. It is of rapid growth, and has large deeply-cut palmated leaves. It throws up a long spike of green flowers, which are succeeded by spiny capsules, each containing three beautifully marbled seeds. The kernel of the seeds contains about 46
per cent. of a fixed oil, which is the castor-oil of commerce. Castor and Pollux || Castoreum. The oil was well known to, and was used by the ancient Egyptians, Greeks, and probably all the oriental nations. In India it is largely used at the present day; and though sometimes obtained by expression, is more commonly prepared by steeping the seeds for a night in cold water, boiling them for two hours, then drying them in the sun, and afterwards pounding or bruising them: the seeds thus bruised are then thrown into water and boiled till the whole oil is extracted, when it rises to the surface and is skimmed off. In the West Indies the seeds are not usually either steeped or boiled previous to bruising, but are bruised, and boiled in water at once. At one time, both in India and in London (as still in America), the seeds were bruised, and the oil obtained by subjecting the mass to strong expression. When so prepared the oil requires to be boiled with water, or at least subjected along with water to a heat of 200°, in order to coagulate the albumen and dissolve out the mucilage which has been expressed along with the oil, and which, if not removed, would cause the oil soon to become rancid. When thus prepared by expression it is called cold drawn castor-oil, and used to be most in esteem; but oil so prepared has no advantages over that prepared carefully by boiling the bruised seeds. The chief supply comes from India. When good it should be a thickish fluid, either limpid or of a very pale yellow colour, with a peculiar nauseous odour, and an oily taste which is very permanent. This oil may be distinguished from almost every other fixed oil by being soluble in ether or in alcohol in all proportions. Hence one of the best tests of its purity is to mix it with its own volume of alcohol. If it be entirely dissolved it is pure; if impure, the oil mixed with it is left undissolved. Bussy and Lecanu regard the oil as composed of three fatty acids; but other chemists dissent from this, and seeing that it is not separable with margarine and claine, like the other oils, and that it is totally soluble in alcohol and ether, regard it as composed of a single peculiar fatty principle. The principle, however, on which its purgative properties depend has not yet been discovered.
In all countries where the castor-oil plant grows, the oil is extensively used for burning; but it is best known for its use in medicine, as one of our best and safest purgatives. It is usually administered plain, or mixed with milk, coffee, port wine, brandy, or aromatic waters, to cover its nauseous taste; or is formed into a soapy emulsion with a few drops of solution of caustic potass. The castor-oil seeds are themselves powerfully drastic purgatives and irritants, so few as twenty seeds having even proved fatal to man. The kernels of from one to three of the fresh seeds suffice for an effectual dose.
Castor-oil pays no duty now; it is therefore difficult to procure late returns of its importations. In 1835 there were imported into Great Britain 1,109,307 lb., of which 670,205 lb. were retained for home consumption.