Cotton seed oil is obtained by expression from the seeds of Gossypium herbaceum, Linn. (N.O. Malvaceae), and other species of Gossypium, the plants being extensively cultivated in the United States, Egypt, and India. It is official in the U.S.P. It is refined by a method of partial saponification, whereby the dark-red colouring matter of the crude oil is carried down as a precipitate along with the soap formed, the supernatant oil being of a very pale colour. It occurs as a pale yellow, odourless liquid, having a bland, nutty taste. Specific gravity, 0.918 to 0.925 (0.915 to 0.921 at 25°). On cooling to about 12°, particles of solid fat separate, and at a temperature between 0° and -5° the oil becomes solid, or nearly so. Sulphuric acid (specific gravity, 1.6 to 1.7) added to the oil diluted with carbon bisulphide produces a reddish-brown colour. A few mils of the oil shaken vigorously with an equal volume of nitric acid (specific gravity, 1.375), and allowed to stand for some time, up to twenty-four hours, gives a characteristic coffee-brown colouration. On shaking 5 mils of the oil in a test-tube with 5 mils of an alcoholic solution of silver nitrate (made by dissolving 1 decigram of silver nitrate in 10 mils of alcohol, and adding 1 decimil (0.1 milliliters) of nitric acid), and heating on a water-bath for about five minutes, a reddish or brownish colour is produced. If a test-tube containing a mixture of 2 mils of the oil with 2 mils of amyl alcohol, and 2 mils of a carbon bisulphide solution of sulphur (1 per cent.) be heated on a water-bath, and the temperature maintained for some time, the carbon bisulphide evaporates, and the oil acquires a deep-red colouration in the course of five to fifteen minutes. By this test, known as the Halphen colour reaction, it is possible to detect 5 per cent. or less of cotton seed oil in admixture with other oils, provided it has not been previously heated to 200° or over. The nitric acid test mentioned above is a useful confirmatory test, but the silver test is not considered of any great value. Iodine value of the oil, 102 to 108; iodine value of the liquid fatty acids, about 150; solidifying point of the mixed fatty acids, about 32°; melting-point, about 36°.
Sparingly soluble in alcohol, readily soluble in ether, chloroform, and carbon bisulphide.
Constituents.—The oil consists of the glycerides of palmitic, stearic, oleic, and linolic acids. It is a typical semi-drying oil.
Uses.—Cotton seed oil is employed similarly to olive oil in preparations for external use.
Dose.—15 to 30 mils (1/2 to 1 fluid ounce), or more.
The British Pharmaceutical Codex, 1911, was published by direction of the Council of the Pharmaceutical Society of Great Britain.