A stearoptene obtained from the volatile oils of Thymus vulgaris (Labiatae), Monarda punctata (Labiatae), and Carum Ajowan (Ptychotis Ajowan) (Umbelliferae).

These oils contain thymol and thymene, C10H16, which is fluid. The thymol is separated by saponifying with caustic soda and treating the separated soap with hydrochloric acid, or from a distilled fraction of the oil by exposure at a low temperature. It may be purified by recrystallisation from alcohol.

Characters. - Large oblique prismatic crystals having the odour of thyme and a pungent aromatic flavour. They sink in cold water, but on heating the mixture to a temperature of 110° to 125° F. (43.3° to 51.7° C.) they melt and rise to the surface. The crystals volatilise completely at the temperature of a water-bath.

Solubility. - Slightly soluble in cold water, freely soluble in alcohol, ether, and solutions of alkalis.

Reactions. - A solution of thymol in half its bulk of glacial acetic acid, warmed with an equal volume of sulphuric acid, assumes a reddish-violet colour.

Impurity. - Carbolic acid.

Test. - Water saturated with thymol when treated with a few drops of test solution of ferric chloride should not give a blue colour (absence of carbolic acid).

Dose. - Internally, 1/2-10 gr. For spray, 1 in 800 of hot water. As ointment, 5-30 gr. to 1 oz. of petrolatum. As inhalation, 6 gr. to an ounce of warm water.

Action. - In respect of its physiological action, thymol appears to stand between carbolic acid and oil of turpentine. Like carbolic acid, it destroys low organisms, and is a powerful antiseptic. In higher animals it acts as a local irritant and anaesthetic to the skin and mucous membranes. When absorbed it paralyses the nerve-centres in the cord and medulla, like carbolic acid, lessening reflex action, slowing respiration, and lowering the blood-pressure and temperature. In poisonous doses it causes weakness, drowsiness, coma, and death. It differs from carbolic acid in being less volatile and less easily oxidised. Its action as a disinfectant is more permanent, and at the same time more powerful than that of carbolic acid. It is less irritating to the skin or mucous membrane, and does not act as a caustic like carbolic acid, and is a less powerful poison to mammals. Its action on the nerve-centres is a paralysing one from the first, and is not preceded by excitement as in the case of carbolic acid. While in the body it appears to effect tissue-metabolism, for in animals poisoned by it the liver is found quite fatty, as in phosphorus-poisoning. It appears to be eliminated by the respiratory and urinary organs, and to cause irritation of these organs during the process of excretion. In poisoning by it the bronchial mucous membrane is extremely congested, the secretion of mucus increased; the lungs congested, and sometimes consolidated; the kidneys inflamed, and the urine albuminous or bloody.

Uses. - It has been used as an antiseptic instead of carbolic acid for dressing wounds; as an application to skin diseases, ringworm, eczema, psoriasis; as a gargle, spray, or inhalation in sore-throat, bronchiectasis, and phthisis, or as an injection in ozaena. Internally it has been used in diabetes and vesical catarrh.