Oil of spearmint (Oleum Menthae; Oleum Menthae Crispae) is obtained by distillation from fresh, flowering spearmint, Mentha viridis, and M. crispa, Linn. (N.O. Labiatae), a native of Europe and Asia, cultivated for domestic use as well as for the sake of its oil, most of which is imported from America. It is also official in the U.S.P., where it is directed to be rectified by steam distillation. Oil of spearmint occurs as a colourless, pale yellow or greenish-yellow liquid when recently distilled, but becomes darker and viscid on keeping; it has the characteristic odour, and warm slightly bitter taste of the spearmint, the taste being less pungent than that of peppermint. Specific gravity, 0.920 to 0.940 (0.914 to 0.934 at 25°); rotation, - 36° to - 50°.
Soluble in its own volume of alcohol (95 per cent.), forming a clear solution; also soluble in all proportions of absolute alcohol, and in about its own volume of alcohol (90 per cent.), the solution becoming opalescent on adding more solvent.
Constituents.—The chief constituent of the oil is carvone, which may occur to the extent of about 56 per cent. Boiling-point, 230°. Specific gravity, 0.964. It is an unsaturated ketone, having the formula C10H14O, and is a colourless liquid, smelling strongly of caraway, and solidifying on refrigeration. It combines with hydrogen sulphide to form a crystalline addition compound, but not with bisulphites. Besides carvone, an alcohol, l-limonene and l-pinene have been found, and in Russian spearmint oil, said to be a product of M. aquatica, carvone, linalool, cineol, and l-limonene. The constituent to which the odour of the oil is due is said to be the acetic ester of dihydrocuminol.
Action and Uses.—The properties of oil of spearmint resemble those of peppermint oil, but its flavour is less agreeable.
Dose.—¼ to 2 decimils (0.025 to 0.2 milliliters) (½ to 3 minims).
- Aqua Menthae Viridis, B.P.—SPEARMINT WATER. Syn.—Aqua Menthae.
- Oil of spearmint, 0.1; water, 150. Add the oil to the water, and distil 100. Spearmint water has properties similar to those of peppermint water. Dose.—30 to 60 mils (1 to 2 fluid ounces).
- Aqua Menthae Viridis, U.S.P.—SPEARMINT WATER, U.S.P.
- Oil of spearmint, 0.2; purified talc, 1.5; distilled water, to 100. Average dose.—16 mils (4 fluid drachms).
- Aqua Menthae Viridis Concentrata, B.P.C.—CONCENTRATED SPEARMINT WATER.
- One part of this solution corresponds to 40 parts of spearmint water.
- Spiritus Menthae Viridis, B.P.C.—SPIRIT OF SPEARMINT. 1 in 10.
- Used as a flavouring agent and carminative, in the same way as spirit of peppermint. Dose.—3 to 12 decimils (0.3 to 1.2 milliliters) (5 to 20 minims).
- Spiritus Menthae Viridis, U.S.P.—SPIRIT OF SPEARMINT.
- Oil of spearmint, 10; spearmint, bruised, 1; alcohol (95 per cent.), sufficient to produce 100. The oil is dissolved in 90 of the alcohol, and in this solution the spearmint is macerated for twenty-four hours, the product filtered, and made up to 100 with alcohol (95 per cent.). Average dose.—2 mils (30 minims).