Oleum Lini, B.P. Linseed Oil.
Related entries: Linseed
Linseed oil, or Flax Seed oil, is obtained by expression, at ordinary temperatures, from the dried ripe seeds of the flax, Linum usitatissimum, Linn. (N.O. Lineae), cultivated almost universally in temperate and tropical regions, chiefly Russia, India, United States, Canada, and Argentina. It is also official in the U.S.P. Linseed oil occurs, when freshly prepared, as a viscid, yellow liquid, having a faint, but distinct, odour, and a bland taste. The commercial oil, however, has a marked odour, and often an acrid taste, due to oxidation from exposure to the air. Specific gravity, 0.930 to 0.940 (0.925 to 0.935 at 25°). Saponification value, 187 to 195. Iodine value, not less than 170. The oil should not congeal above -20°, and should only slightly redden moistened blue litmus paper. Freedom from non-drying oils, which may be present as adulterants, is indicated by the oil thickening on exposure to air, a thin layer spread on glass forming a hard, transparent varnish. It should be completely saponifiable by alcoholic potassium hydroxide, and the resulting soap should be completely soluble in water without leaving an oily residue (absence of mineral oil and resin oil). If 2 mils of the oil be warmed and shaken in a test-tube with an equal volume of glacial acetic acid, and, after cooling, ½ decimil (0.05 milliliters) of sulphuric acid be added, a greenish colour should be produced (a violet colour under these circumstances would indicate the presence of resin or resin oil).
Insoluble in alcohol; soluble in absolute alcohol (1 in 40), soluble in all proportions of turpentine, ether, chloroform, or carbon bisulphide, forming clear solutions.
Constituents.—The chief constituent of the oil is linolein, a mixture of the glycerides or glyceryl esters of linolic, linolenic, and isolinolenic acids, three isomeric bodies possessing similar physical properties, and sometimes described generally as linoleic acid. Other constituents are olein, stearin, palmitin, and myristin—the glycerides or glyceryl esters of oleic, stearic, palmitic, and myristic acids.
Action and Uses.—For medicinal purposes recently expressed linseed oil is preferable. It has been used internally as a laxative, in doses of 30 mils (1 fluid ounce), but its taste is disagreeable. A rectal injection of 60 mils (2 fluid ounces) of the oil, given night and morning, has been highly recommended for piles. It is applied externally as a soothing application for burns, especially in the form of Carron oil (see Linimentum Calcis cum Oleo Lini). Linseed oil is largely used in the arts for its properties as a drying oil. Refined linseed oil is prepared by treating linseed oil with 1 to 2 per cent. of concentrated sulphuric acid; the charred mass carries down with it the bulk of the impurities contained in the crude oil. Boiled oil is linseed oil which has been heated with litharge, or other suitable "driers," to a temperature of about 150°, so that metallic salts of the fatty acids are formed and cause the oil to dry more quickly.
Dose.—15 to 30 mils (½ to 1 fluid ounce).
- Liniment of Lime with Linseed Oil.