Production of Essential Oil—Though cultivated in gardens for culinary use, common thyme is not grown in England on a large scale. Its essential oil (Oleum Thymi), for which alone it is of interest to the druggist, is distilled in the south of France. In the neighbourhood of Nîmes, where we have observed the process, the entire plant is used, and the distillation is carried on at two periods of the year, namely in May and June when the plant is in flower, and again late in the autumn. The oil has a deep, reddish-brown colour, but becomes colourless though rather less fragrant by re-distillation. The two sorts of oil, termed respectively Huile rouge de Thym and Huile blanche de Thym, are found in commerce. The yield is about 1 per cent.
Oil of thyme is frequently termed in English shops Oil of Origanum, which it in no respect resembles, and which was never, so far as we know, found in commerce.[1785]
Chemical Composition—The only constituent of the herb that has attracted any attention is the above-named essential oil. This liquid by fractional distillation is resolved into two portions: the first, more volatile and boiling below 180° C., is a mixture of two hydrocarbons, Cymene, C₁₀H₁₄ ([see page 333]), and Thymene, C₁₀H₁₆, the latter boiling at 165° C.
The second, named Thymol, C₁₀H₁₄O, which may also be extracted from the crude oil by means of caustic lye, has been described in our article Fructus Ajowan, at page 303. Commercial oil of thyme is said to be sometimes fraudulently deprived of thymol by that treatment.
Uses—Oil of thyme is an efficient external stimulant, and is sometimes employed as a liniment. Its chief consumption is in veterinary medicine. Thymol has been proposed as a disinfectant in the place of carbolic acid, in cases in which the odour of the latter is objectionable. The herb is not used in modern English medicine, but is often employed on the Continent.
HERBA ROSMARINI.
Herba Anthos; Rosemary; F. Romarin; G. Rosmarin.
Botanical Origin—Rosmarinus officinalis L., an evergreen shrub, attaining a height of 4 feet or more, abundant on dry rocky hills of the Mediterranean region, from the Spanish peninsula[1786] to Greece and Asia Minor. It generally prefers the neighbourhood of the sea, but occurs even in the Sahara, where it is collected and conveyed by caravans to Central Africa.[1787] It does not succeed well in Germany.
History—Rosemary[1788] is mentioned by Pliny, who ascribes to it numerous virtues. It was also familiar to the Arab physicians of Spain, one of whom, Ibn Baytar (13th cent.), states it to be an object of trade among the vendors of aromatics.[1789] In the middle ages rosemary was doubtless much esteemed, as may be inferred from the fact that it was one of the plants which Charlemagne ordered to be grown on the imperial farms.
It was probably in cultivation in Britain prior to the Norman Conquest, as it is recommended for use in an Anglo-Saxon herbal of the 11th century.[1790] In the “Physicians of Myddvai” a curious chapter[1791] is devoted to the virtues of Rosemary, called “Ysbwynwydd, and Rosa Marina in Latin.” The essential oil was distilled by Raymundus Lullus[1792] about a.d. 1330. John Philip de Lignamine,[1793] a writer of the 15th century, describes Rosemary as the usual condiment of salted meats.