Commercial carbolic acid is prepared solely from coal-tar by a method of which the following is an outline. When coal-tar is distilled the most volatile products—benzol, toluol, cumol, &c., first come away, after which when the temperature rises from 150° C. to 200° C. crude carbolic acid distils over. This distillate is mixed with a strong solution of caustic potash, and the resulting carbolate of potash is in its turn treated with sulphuric acid, which decomposes the carbolate, liberating carbolic acid, which rises to the surface as an oily layer, and is removed by a syphon. The product is purified by washing and repeated rectification, and finally cooled down to 10° C., when it forms whitish acicular crystals, from which the unsolidified acid is drained away. Crystallized carbolic acid of commerce retains a strong naphthalic odour, from which it may be freed for medicinal or other purposes by a method recommended by Professor Church. Into 1 tt> of the crystallized acid he pours 20 & of cold distilled water, care being taken that the whole of the acid shall not be dissolved. The mixture is repeatedly shaken till from 2 to 3 ounces of the acid only remains undissolved, in which residue the whole of the impurities are retained. From this, the aqueous solution is syphoned off, and if necessary, filtered, and then pure powdered common salt is added to it till the salt will no longer dissolve. After standing some time the whole of the carbolic acid rises to the surface, and floats as a yellow oily layer, which as it contains 5 per cent, of water will not crystallize. It may be crystallized by distilling from a little lime, and the product collected up to 185° C. will possess only a faint pleasant aromatic odour. Pure carbolic acid crystallizes in long colourless needles; it melts at 35° C., and boils about 187° C. It is soluble in all proportions in alcohol, ether, and strong acetic acid, but dissolves only sparingly in water. It does not redden litmus paper; it exerts a powerful corrosive action on the skin; its aqueous solution coagulates albumen; and it unites with animal substances, preserving them from decomposition, and removing, the offensive odour from putrefying matter.

The extensive manufacture and employment of carbolic acid are, in a large degree, owing to the exertions of the late Professor Crace Calvert, who was the first to manufacture it in the crystalline form. The development of the aniline colour industry also communicated an impetus to the manufacture of carbolic acid, as the one is, in a sense, a secondary product of the other. A great many useful applications have opened up for the employment of the acid in addition to its extensive medicinal and antiseptic uses (see Antiseptics). For domestic, sanitary, and medicinal use, carbolic acid is prepared in various states of purity and strength. Toilet and medicated soaps, tooth powder, disinfecting powder, <fcc., are all prepared containing definite proportions of the acid. A large quantity of crude carbolic acid is employed under the name of creosote for impregnating wood for railway sleepers and piles, and for engineering purposes generally,—a method of preserving wood discovered and patented by Mr John Bethell.

Carbolic acid is, however, most largely consumed in the preparation of several dyeing materials, which are second only in importance to the colours derived from aniline. Picric or carbazotic acid is a brilliant yellow dye-stuff, much used for wool and silk dyeing, prepared by very cautiously addingin small quantities nitric acid to crystallized carbolic acid, or to a mixture of carbolic acid with sulphuric acid. From picric acid in its turn two derivatives are obtained.

isopurpuric acid and picramic acid, but these have only a limited application in dyeing. Coralline, a dye in extensive use, yielding a variety of fine red shades, is obtained by heating together two parts of oxalic acid, three of carbolic acid, and four of sulphuric acid to a temperature of from 140° C. to 150° C. Peonine, or red coralline, is a product of coralline obtained by acting on it at a temperature of about 130 β C. with a concentrated solution of ammonia. It yields on wool and silk a very rich durable Turkey-red-like shade. Aurine, or yellow coralline, is made by mixing together oxalic acid, carbolic acid and sulphuric acid, the same as for ordinary coralline, but the mixture is submitted to a less elevated temperature. It dyes fine yellow and orange shades on animal fibres. Phénicienne, or rothine, is a dye producing shades varying from a deep garnet red to a chamois colour, made by adding to carbolic acid a mixture of nitric and sulphuric acids. Fol’s yellow is manufactured by heating to 100° C. a mixture of five parts of carbolic acid and three of powdered arsenic acid. Besides these various other dyes having carbolic acid for their basis have been introduced and some of them are commercially established.