Oleum Graminis Citrati, I.C.A. Oil of Lemon Grass.
Synonym.—Indian Oil of Verbena.
Oil of lemon grass, or Indian melissa oil, is obtained by distillation from the entire herb, Andropogon citratus, DC. (N.O. Gramineae), which is widely cultivated in India. It is official in India and the Eastern and West Indian Colonies. Oil of lemon grass occurs as a reddish-yellow or brownish-red, mobile liquid, having a very strong odour, resembling that of verbena. Specific gravity, 0.895 to 0.905. Optical rotation, not more than +3° or -3°. The West Indian oil is lighter in density (0.878 to 0.882), although it contains a high percentage of citral; it is less soluble in alcohol owing to the presence of an olefinic terpene, which rapidly resinifies. Adulteration with fatty oils or petroleum may be recognised by the reduction of the citral content. Acetone has been used as an adulterant, and is readily detected by fractional distillation.
Soluble in 70 per cent. alcohol (forming a clear solution with two or more parts).
Constituents.—The chief constituent of the oil is citral, C10H16O, an optically inactive aldehyde, which boils at 228° to 229°, and may be present to the extent of 75 to 85 per cent., but should not be below 70 per cent. It may be determined by shaking 5 mils with 50 mils of a boiling 30 per cent. solution of sodium bisulphite, measuring the oily layer of non-aldehydic bodies, which separates on cooling, and deducting from the volume of oil originally taken. The oil also contains traces of an isomer of citral; geraniol, C10H18O; methylheptenone, C8H14O; traces of citronellal, C10H18O, possibly linalool, and the terpenes limonene and dipentene, which occur to the extent of about 10 per cent., together with a trace of cymene.
Action and Uses.—Oil of lemon grass was formerly given internally as a carminative; it is used mainly in perfumery and as a source of citral.
Dose.—½ to 2 decimils (0.05 to 0.2 milliliters) (½ to 3 minims).