Sex. Syst. Dioecia, Hexandria.
Palm oil is obtained from two species of Elaeis, both natives of Guinea, and to both of which the name of Guinea Oil Palm is equally applicable. The oil resides in the fleshy portion of the fruit, which, in this respect, resembles the olive.
1. Elaeis Guineensis, Jacquin; The True Guinea Oil Palm; The Palm Oil-Tree; Sloane's Jamaica, vol. ii. p. 113, 1725; Avoira, Aubl., Pl. de la Guiane, 1775.
—A native of Guinea; cultivated in tropical America. The drupes are about the size of pigeons'eggs, ovate, somewhat angular, deep orange yellow, collected in heads. They have a thin epicarp, a fibrous, oily, yellow sarcocarp, which covers and closely adheres to the hard stony putamen or endocarp, within which is the seed.
From the sarcocarp is procured palm oil (oleum palmae). This is obtained by boiling the pulp in water, by which the oil separates and floats on the surface.
2. Elaeis melanococca, Gaertner.—The drupes are somewhat smaller than those of the preceding species. Some time since I received from Mr. Warrington a bunch of them, which had been recently brought from Guinea as the fruit from which palm oil is obtained. The flesh of the fruit is oily, and has the well-known odour and colour of palm oil. Gaertner [De Fructibus et Semin. Plant, vol. i. p. 18, 1801.] thought that it might be only a variety of E. guineensis; but Von Martius, [Palmae Brasil, p. 62, tab. 51-56.] who has fully described it, regards it as a distinct species.
At the ordinary temperatures of this country, it is solid, and might, therefore, with more propriety be termed palm butter. It is said that, when quite fresh, it fuses at 81° F.; but that, by keeping, its fusing point rises. Stenhouse [Ann. d. Chemie u. Pharm. Bd. xxxvi. S. 50.] found that very old palm oil required a temperature of 98 ½° F. to fuse it.
Palm oil has a rich orange yellow colour, a sweetish taste, and an agreeable odour resembling that of the rhizome of the Florentine orris. It is soluble in boiling alcohol and in ether. By exposure to solar light it becomes white.
Palm oil requires to be bleached for various uses in the arts, and there are several agents which are used for decolorizing it—viz., chlorine, oxygen, powerful acids (sulphuric, nitric, or chromic acid), and the combined influence of air, heat, and light. [Knapp's Chemical Technology, vol. i. p. 431, 1848.]
Palm oil consists of oleine, palmitine, and colouring matter. As found in commerce, it usually contains also free fatty acids (oleic and palmitic) and free glycerine, and, therefore, may be said to be rancid. The cause of the separation of these acids from the glycerine has not been satisfactorily explained. The quantity of them increases with the age of the oil, and, according to Pelouze and Boudet, [Journ. de Pharm. t. xxiv. p. 385, 1838.] varies from 33 to 80 per cent. of the entire oil. In proportion as the quantity increases, the fusing point of the oil rises. The glycerine which is set free gradually becomes converted into sebacic acid, which is also found in old palm oil. These various changes seem to be effected by a kind of fermentation, to the commencement of which, according to Guibourt, [Hist. Nat. des Drogues simples, 4me édit. t. ii. p. 142, 1849.] the presence of atmospheric air is necessary.
Palmitine is a white solid fat, which is resolved, by saponification and by the fermentation just alluded to, into palmitic add (C32H31O3+HO), considered by Dumas to be identical with ethalic acid—and glycerine (oxide of glycerule).
The Africans use palm oil as a kind of butter. It is now rarely employed in medicine. By the public it is occasionally used by way of friction in bruises, sprains, &c. It is a constituent of the common black bougie. Its ordinary use in this country is in the manufacture of soap and candles. It readily becomes rancid.
The seeds of both species of Elaeis are nutritive. They yield by pressure a fixed oil (palm-seed oil; oleum palmae seminis), which is solid at ordinary temperature. It is devoid of the orange-yellow colour and orris odour of palm oil. It is said to be used in Africa as a kind of butter. It is rarely brought to Europe, but a few years since I obtained from Africa a specimen of it, with a sample of the seeds from which it was procured.