Oleum Arachis, I.C.A. Arachis Oil.
Related entry: Oils
Synonym.—Oleum Nucis; Nut Oil; Earthnut, Groundnut or Peanut Oil.
Arachis oil is obtained by expression without heat from the seeds of Arachis hypogaea, Linn. (N.O. Leguminosae), a native of Brazil, cultivated in West Africa, India, China, and America. The seeds contain 43 to 45 per cent. of the fixed oil. The oil occurs as a pale yellow or greenish-yellow liquid, having a faint nutty odour, and bland nutty taste. Specific gravity, 0.916 to 0.921 (I.C.A., 0.918). It becomes turbid at 3°, and solid at -5°. Iodine value, 83 to 100; saponification value, 188 to 196.6; melting-point of mixed fatty acids, 28° to 30°. On exposure, the oil thickens very slowly, and becomes rancid. Bleached arachis oil is manufactured in France, is nearly colourless, and almost free from taste; it has been used for adulterating lard oil and olive oil. Arachis oil saponifies slowly, but yields a firm white soap with very little odour.
Soluble in ether or chloroform; insoluble in alcohol.
Constituents.—The chief constituent of arachis oil is olein, but the oil also contains the glycerides of arachidic, hypogaeic, lignoceric, and linolic acids, while the "stearine" which separates from it at low temperatures contains arachin. The oil yields about 20 per cent. of arachidic acid.
Action and Uses.—Arachis oil is official in India, the African, Eastern, and Australasian Colonies, where it may be used as a substitute for olive oil in making ointments, liniments, and plasters.