Azuline —The same firm introduced, towards the end of 1860, a blue dye, derived from rosolic acid, which they called " Azuline." This is prepared by heating for several hours, at about 180° (360° F.), a mixture of 5 parts rosolic acid and 6-8 parts aniline, and which is purified by repeated treatment with sulphuric acid and benzol, constituting, when dry, a red mass having gold_ coloured tints. Though discovei ed before the aniline blues, which have since become formidable rivals, it is still manufactured in competition with them.
Veridine.—In 1863, was produced the first green derived from carbolic acid ; but it bas not beeu able to compete with aniliue greens. It was obtained from a mixture of aniline, and benzoic and resolic acids.
Phenicienne.—This was discovered, in 1863, by M. Roth; it produces fast colours, from a garnet rod to a golden-buff, and is obtained by the action of nitro-sulphuric upon carbolic acid.
Sulpho-carbolic Acid and its Salts.—When one equivalent carbolic acid is slowly mixed and heated with two equivalents concentrated sulphuric acid in an earthenware pan, a definite compound is formed, called sulpho-carbolic acid C81-1080„ which is dissolved out by the addition of water. The heat must be applied carefully, on account of the carbonizing influence of the sulphuric acid. The sulpho-carbolic acid is freed from sulphates by adding carbonate of baryta, which falls to the bottom of the vessel as sulphate of barium, and the liquid acid may be decanted. It forms a great number of definite salts, every one of which is soluble in water. The most important are those of soda, potash, zinc, iron, magnesia, and lime ; all are largely used for pharmaceutical purposes.
Salicylic Acid.—Salicylic acid (to which much attention has lately been drawn), originally a pro duct obtained in the laboratory in small quantities from the plant called Wiutergreen (Gaultheria procumbens), is now being produced from carbolic acid on a commercial scale on the Continent, by the process of.Professor Kolbe, of Leipzic. Carbolic acid is heated with solid hydrated oxide sodium
in a closed iron retort, the temperature being maintained at about 183° (361° F.), till the water, and the excess of carbolic acid, have passed over into a receiver, dry carbonie gas being passed into the contents of the retort iu a continuous stream. The temperature is finally made to exceed 200° (392° F.), the mass becomes solid, and the operation is terminated when but little residual acid distils over. The contents of the retort, after the above operation, contain some salicylate of soda and free carbolic acid ; they are dissolved in water, and by the addition of slight excess of hydrochloric acid to the solution, the salicylic acid is precipitated. It is then washed, and thus purified from all traces of the hydrochlorie acid. The salicylic acid thus produced is a yellowish white powder, devoid of smell, fusing, when pure, at 158° (316° F.), sparingly soluble in cold water, but readily soluble in boiling water. Its chemical composition is 071-1,0a ; or, in other words, 1 equivalent carbolic acid + 1 equivalent carbonic) acid. It may be sublimed unaltered ; but when heated strongly with powdered glass or sand in a retort, it is resolved into carbolic and carbonic acids. It possesses antiseptic properties, though in a less degree than carbolic acid. As a general disinfectant, it cannot become a rival to carbolic acid, owing to its lesser antiseptic power, and its higher pries, this latter being entirely dependent on the oast of the carbolic acid from which it is manufactm•ed. It is, however, being now employed in some of the German hospitals.