essence, does not combine with the alkali and separates. Filter the solution obtained and treat with an acid—hydrochloric acid, for example—which sets free the thymol. The product should be purified by washing, dried, and distilled. Thymol was obtained in fine tubular crystals by Flückiger and Hanbury, who exposed oil of ajowan to a temperature of 0° C.; the oil so treated yielded 35 per cent. of its weight of crystallised thymol. Mr Gerrard says it is stated that oil of thyme yields as much as 50 per cent.
“As found in commerce, thymol consists of irregular broken crystals, nearly transparent and colourless; the taste is burning and aromatic, sp. gr. 1·028, but lighter than water when fused; its melting point is about 44° C. When once completely fused and allowed to cool to the ordinary temperature, it will maintain itself in the fluid condition for several days, but the contact of a crystal will at once cause it to crystallise. It is freely soluble in alcohol, ether, chloroform, benzol, carbon bisulphide, fats, and oils, and but sparingly in water and glycerin. The alkaline hydrates of potash and soda are powerful solvents of thymol; ammonia dissolves it but sparingly.
“The potash and soda solutions are spoken of by some authors as chemical combinations; but the following test will demonstrate them otherwise. When shaken with ether the thymol can be entirely removed, and obtained as a neutral volatile residue.”[232]
[232] “Thymol and its Pharmacy,” by A. W. Gerrard, F.C.S., ‘Ph. Journ.,’ vol. viii, 3rd series, 645.
With sulphuric acid thymol forms crystallisable colugated acid, the thymol sulphuric having the formula HC10H13SO4. Undiluted thymol is an energetic caustic. According to Bucholz, thymol possesses ten times the septic power of carbolic acid, over which it also has the advantage of being non-poisonous, and of giving off an agreeable odour. Although considerably dearer than carbolic acid, the much smaller quantity required to produce an equivalent effect nearly equalises it in point of cost. It is said to have been successfully employed in the antiseptic treatment of wounds in destroying the fœtor arising from ulcerated surfaces and carious bones; in the form of spray during surgical applications, as well as for certain throat affections, and as an ointment and lotion in psoriasis and other skin diseases. When thymol is to be used for lotions, injections, inhalations, or spray solutions, the Paris Pharmaceutical Society recommends 1 part of thymol to be dissolved in 4 parts of alcohol at 90°, and this to be added to 995 parts of distilled water.
Dr Crocker, of University College Hospital, strongly recommends thymol lotion to be prepared with glycerin, which, he says, obviates the drying effect upon the skin produced by aqueous or spirituous solutions of the thymol alone. According to Mr Gerrard, this lotion is prepared by dissolving 1 part of thymol in
120 parts of glycerin, and reducing by water to 600 parts. Dr Symes says he finds milk to be an excellent solvent for thymol, of which it will take up readily to nearly 10 per cent. of its weight. In cases, therefore, in which solutions are required of greater strength than aqueous ones, he recommends the employment of the fluid.
An ointment varying in strength from 1 to 5 parts of thymol to 100 of lard, is said by Mr Gerrard to be employed in our hospitals. In the preparation of this ointment, it is of importance to first dissolve the thymol in a few drops of spirits, and then to mix it with the lard. The neglect of this precaution causes the undissolved particles of thymol present in the ointment to act as a caustic irritant on the skin, and to eat little holes in it. Mr Gerrard found vaseline an unsuitable and objectionable vehicle for the application of thymol, since, after a few days, an ointment prepared with it had its surface covered with minute crystals of thymol.
The ‘Medical Times’ contains the following formula for the preparation of thymol gauze for dressing wounds:—“Bleached gauze, 1000 parts; spermaceti, 500; resin, 50; thymol, 16 parts.” This is said to yield an extremely soft and pliant preparation, excellently adapted for wounds, fitting accurately to them, and absorbing at the same time the blood and secretions from them like a sponge would do. Dr Ranke has pointed out that, in consequence of the great reduction in the amount of secretion from wounds caused by the use of thymol, the consequent consumption of bandages becomes so much less as to more than compensate for the great difference in price between thymol and carbolic acid.
Another advantage possessed by thymol over carbolic acid is that the redness, vesication, and eczema, frequently induced when dressings of the latter agent are used, does not follow the application of thymol dressings.