Encyclopædia Britannica, Ninth Edition/Ground Nut

GROUND NUT (synonyms, Earth Nut, Pistache de Terre, Monkey Nut, Pea Nut, Manilla Nut), a nut or pod the produce of the Arachis hypogæa, L. (Nat. Ord. Leguminosæ). The plant is an annual of diffuse habit, with hairy stem, with two-paired, abruptly pinnate leaflets. The flowers above ground are sterile, and the pods or legumes are stalked, oblong, cylindrical, about 1 inch in length, the thin reticulated shell containing one or two irregularly ovoid seeds. After the flower withers, the stalk of the ovary has the peculiarity of elongating and bending down, forcing the young pod under ground, and thus the seeds become matured at some distance below the surface. Hence the specific and vernacular names of the plant. Two varieties are recognized in Malacca and Java, a white and a brown, and the seeds are known as minyak katjang (oil bean). Of the history of this plant much has been written. Monardes in 1596 writes of having seen it largely used about the river Maranon in Brazil, and Marcgraf in 1648 gave a description and figure of it. To M. Jaubert, how ever, a colonist at Gore"e near Cape Verd, seems to belong the honour of first recommending it as of commercial value. As to its native country the opinions of botanists are divided between Africa and America. It is extensively cultivated in all tropical and subtropical countries, especially in America, Africa, India, the Malayan Archipelago, and China. The plant affects a light sandy soil, and is very prolific, yielding in some instances 30 to 38 bushels of nuts per acre. The pods when ripe are dug up and dried. The seeds when fresh are largely eaten in tropical countries, and in taste are almost equal to almonds; when roasted they are used as a substitute for chocolate. Even in England large quantities of these "monkey nuts" are consumed by the poorer children. By expression the seeds yield a large quantity of oil, which is used by natives for lamps, as a fish or curry oil, and for medicinal purposes. The leaves form an excellent food for cattle, being very like clover.

Large quantities of seeds are imported to Europe, chiefly to Marseilles, London, Hamburg, and Berlin, for the sake of their contained oil. The seeds yield from 42 to 50 per cent, of oil by cold expression, but a larger quantity is obtained by heat, although of an inferior quality. The seeds being soft facilitate mechanical expression, and where bisulphide of carbon or other solvent is used, a very pure oil is obtained.

The expressed oil is limpid, of a light yellowish or straw colour, having a faint smell and bland taste; it forms an excellent substitute for olive oil, although in a slight degree more prone to rancidity than the latter. Its specific gravity is 916 to 918; it becomes turbid at 3 C., concretes at + 3 to 4 C., and hardens at 4- 7 C. It is a non-drying oil. Ground nut oil consists of (1) oleic acid (C I8 H 31 O 2 ); (2) hypogseic acid (C 16 H 30 2 ), by some supposed to be identical with a fatty acid found in whale oil; (3) palmitic acid (C 1C H 32 O 2 ); and (4) arachic acid (C 20 H 40 O 2 ). The oil is officinal in the Indian pharmacopoeia, replacing olive oil, and it is also used in the adulteration of gingelly oil. In 1874 about 145 million ft> of ground nuts, valued at 1,040,000, were exported from the west coast of Africa, chiefly to Marseilles, London, Hamburg, and Berlin.