Oleum Thymi. Oil of Thyme.
Related entries: Thymol
Oil of thyme is obtained by distillation from the leaves and flowering tops of Thymus vulgaris, Linn. (N.O. Labiatae), indigenous to the countries bordering on the Mediterranean, and now cultivated in most countries with a temperate climate. It is official in the U.S.P., when it should contain not less than 20 per cent. by volume of phenols. Oil of thyme occurs as a dark reddish-brown or colourless liquid, having a pleasant, strong, thyme odour, and a biting, persistent taste, which is afterwards cooling. Specific gravity, 0.905 to 0.935 (0.900 to 0.930 at 25°). Slightly laevorotatory. The red-coloured oil on being properly rectified yields the "white" oil. White thyme oil, however, is not infrequently ordinary dark coloured oil, with a large addition of oil of turpentine. The most common adulterant is oil of turpentine, which reduces the specific gravity, diminishes the solubility in alcohol, and reduces the phenol content. French oil of turpentine gives a high laevorotation. The percentage of phenols present is approximately shown by shaking the oil with a 5 per cent. solution of potassium hydroxide, and calculating the absorbed portion as thymol. With a drop of ferric chloride solution, oil of thyme yields a greenish-brown colouration, which changes to reddish. The oil frequently goes under the name of origanum oil, but erroneously so, as origanum oil is derived from Origanum hirtum (Trieste), O. Smyrnaeum (Smyrna), and O. Majoranoides (Cyprus). The Cyprus oil is the best quality containing 78 to 84 per cent. of carvacrol, and having a specific gravity of 0.960 to 0.967. The Trieste oil may contain from 60 to 85 per cent. of carvacrol, and has a specific gravity of 0.940 to 0.980. Smyrna oil contains 25 to 60 per cent. of carvacrol and has a specific gravity of 0.915 to 0.945. These oils are usually soluble in 2 to 3 volumes of 70 per cent. alcohol. In addition to carvacrol they contain cymene; and origanene has been found in the Cyprus oil.
Soluble in alcohol (2 in 1); in 80 per cent. alcohol (1 in 1 to 2) in 70 per cent. alcohol, usually 1 in 3, though sometimes 10 or more is required to form a clear solution.
Constituents.—The chief constituents of the oil are from 20 to 45 per cent. of the phenols thymol, C10H14O, and its isomer carvacrol. Other constituents are cymene, C10H14; l-pinene, C10H16, in very small quantity; borneol, C10H18O, linalool, C10H18O, and bornyl acetate, C12H20O2.
Action and Uses.—Oil of thyme is employed in combination with olive and other oils as a rubefacient and counter-irritant in rheumatism, etc. Internally, it is antiseptic, antispasmodic, and carminative.
Dose.—6 to 30 centimils (0.06 to 0.3 milliliters) (1 to 5 minims).