Definition. - A mixture of three isomeric cresols obtained from coal tar, freed from phenol, hydrocarbons, and water.

Description and Properties, - A colorless or straw-colored refractive liquid having a phenol-like odor and turning yellowish-brown on prolonged exposure to light.

Sometimes erroneously called crecylic acid. Cresol is methyl phenol, the three isomeric forms being known chemically as ortho-, meta-, and paracresol.

Soluble in water (1: 60) and miscible in all proportions with alcohol and glycerin. Miscible with alkali hydroxide solutions, forming alkali cresolates, homologous with alkali phenolates.

Dose. - Average dose: 1 minim (0.05 Cc). U. S. P.

Hunt writes "much has been written concerning the germicidal and toxic properties of cresol. It is generally held that cresol is more toxic to bacteria than is phenol, but that it is less toxic to higher animals than is the latter." Tollens (Arch. f, exper. Path. u. Pharm., lii., p. 220, 1905) finds that paracresol is more than twice as toxic for mice as is phenol, orthocresol has the same toxicity, while metacresol is less toxic. Thus the toxicity of a cresol will depend upon the relative proportion of the three constituents, and these seem to vary in different preparations; Tollens finds some specimens to be more toxic than phenol. The U. S. Pharmacopoeia does not specifically state the proportions in which the three cresols are present, although it fixes limits for the boiling-point, specific gravity, and solubility. A preparation on the market under the name of tricresol (enterot) is said to contain 35 per cent. of orthocresol, 40 per cent. of metacresol, and 25 per cent. of paracresol; it is soluble to the extent of 2.2 to 2.55 per cent. in water. The physiological action of the cresols is almost identical with that of phenol.

The cresols are constituents of coal tar and other crude antiseptic substances. Being but slightly soluble in water, they are often used in the form of emulsions or are dissolved with the aid of salts or of soap. The official Liquor Cresolis Compositus (q. v.) belongs to the latter class; it is practically identical with the Liquor Cresoli saponatus of the German Pharmacopoeia and the preparation on the market known as lysol.