CASTOR OIL, the fixed oil obtained from the seeds of the castor oil plant or Palma Christi, Ricinus communis, belonging to the natural order Euphorbiaceae. The botanical name is from Lat. ricinus, a tick, from the form and markings of the seed. The plant is a native of tropical Africa, but it has been introduced, and is now cultivated in most tropical and in the warmer temperate countries. In size it varies from a shrubby plant to a tree of from 30 to 40 ft. in height according to the climate in which it grows, being arborescent in tropical latitudes. On account of its very large beautiful palmate-peltate leaves, which sometimes measure as much as 2 ft. in diameter, it is cultivated as an ornamental plant. In the south of England, with the habit of an annual, it ripens its seeds in favourable seasons; and it has been known to come to maturity as far north as Christiania in Norway. Plants are readily grown from seed, which should be sown singly in small pots and placed in heat early in March. The young plants are kept under glass till early in June when they are hardened and put out. The fruit consists of a three-celled capsule, covered externally with soft yielding prickles, and each cell develops a single seed. The seeds of the different cultivated varieties, of which there are a great number, differ much in size and in external markings; but average seeds are of an oval laterally compressed form, with their longest diameter about four lines. They have a shining, marble-grey and brown, thick, leathery outer coat, within which is a thin dark-coloured brittle coat. A large distinct leafy embryo lies in the middle of a dense, oily tissue (endosperm). The seeds contain a toxic substance, which makes them actively poisonous; so much so that three have been known to kill an adult.
The oil is obtained from the seeds by two principal methods - expression and decoction - the latter process being largely used in India, where the oil, on account of its cheapness and abundance is extensively employed for illuminating as well as for other domestic and medicinal purposes. The oil exported from Calcutta to Europe is prepared by shelling and crushing the seeds between rollers. The crushed mass is then placed in hempen cloths and pressed in a screw or hydraulic press. The oil which exudes is mixed with water and heated till the water boils, and the mucilaginous matter in the oil separates as a scum. It is next strained, then bleached in the sunlight, and stored for exportation. A considerable quantity of castor oil of an excellent quality is also made in Italy; and in California the manufacture is conducted on an extensive scale. The following is an outline of the process adopted in a Californian factory. The seeds are submitted to a dry heat in a furnace for an hour or thereby, by which they are softened and prepared to part easily with their oil. They are then pressed in a large powerful screw-press, and the oily matter which flows out is caught, mixed with an equal proportion of water, and boiled to purify it from mucilaginous and albuminous matter. After boiling about an hour, it is allowed to cool, the water is drawn off, and the oil is transferred to zinc tanks or clarifiers capable of holding from 60 to 100 gallons. In these it stands about eight hours, bleaching in the Sun, after which it is ready for storing. By this method 100 lb of good seeds yield about 5 gallons of pure oil.
Castor oil is a viscid liquid, almost colourless when pure, possessing only a slight odour, and a mild yet highly nauseous and disagreeable taste. Its specific gravity is .96, a little less than that of water, and it dissolves freely in alcohol, ether and glacial acetic acid. It contains palmitic and several other fatty acids, among which there is one - ricinoleic acid - peculiar to itself. This occurs in combination with glycerin, constituting the greater part of the bulk of the oil.
The active principle to which the oil owes its purgative properties has not been isolated. It is, indeed, probable that it is formed in the intestine, as a result of some decomposition as yet unknown. The dose is from a drachm to an ounce. The pharmacopoeial mixture is best avoided, being almost uniquely nauseous. By far the best way to administer the oil is in capsules. It acts in about five hours, affecting the entire length of the bowel, but not increasing the flow of bile except in very large doses. The mode of its action is unknown. The oil will purge when rubbed into the skin or injected per rectum. It is an invaluable drug in temporary constipation and whenever a mild action is essential, as in pregnancy. It is extremely useful for children and the aged, but must not be employed in cases of chronic constipation, which it only aggravates, whilst relieving the symptoms.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)