Oleum Sinapis Expressum, Expressed Oil of Mustard.
Related entries: Sinapis, B.P., Mustard. - Sinapis Albae Semina, B.P., White Mustard Seeds. - Sinapis Nigrae Semina, B.P., Black Mustard Seeds. - Oleum Sinapis Expressum, Expressed Oil of Mustard. - Oleum Sinapis Volatile, B.P., Volatile Oil of Mustard.
Expressed oil of mustard is obtained by pressure from the seeds of Brassica sinapiodes, Roth., and Brassica alba, Boiss. (N.O. Cruciferae), cultivated in most civilised countries. The yield of oil is from 31 to 33 per cent., and 25 to 26 per cent., respectively. The oil from black mustard seed is obtained as a by-product in the manufacture of the volatile oil, and occurs as a brownish-yellow liquid, having a mild taste. Its chemical composition closely resembles that of rape oil. Specific gravity, 0.916 to 0.920. It contains from 2.3 to 4 per cent. of solid fatty acids, including arachidic acid, unsaturated erucic acid, and a liquid fatty acid. Free fatty acids—about 1 per cent.—have also been found. Solidifying point, -17°; saponification value, 173 to 175; iodine value, 96 to 110. The oil from white mustard seed occurs as a golden-yellow coloured liquid, having a burning taste. The physical and chemical constants of the oil appear to be very similar to those of the black seed oil, the iodine value being the chief point of difference. Specific gravity, 0.914 to 0.916; solidifying point, -8° to -16°; saponification value, 170 to 174; iodine value, 92 to 97.
Action and Uses.—Expressed oil of mustard has mild rubefacient properties, and is employed as an application to the chest in place of camphorated oil, and to rub rheumatic joints. The oil obtained from white mustard seed is used for lubricating, and also for burning; that from black mustard seed is used for making soap, and is not suitable for burning.