Salicylic Acid, a product of salicine, carbolic acid, and other substances. (See Salicine.) When salicylol is acted on by chromic acid or potassium hydrate, it becomes oxidized, forming potassium salicylate, with evolution of hydrogen (C7H6O2+HOK=C7H6KO3+H2). The potassium salicylate is decomposed by the action of hydrochloric acid, liberating salicylic acid, C7H6O3, with production of potassium chloride (C7H5KO3+HCl=C7H6O3+KCl). Oil of wintergreen (Gaultheria procumbens) also yields, by distillation with potash, methyl alcohol and salicylic acid. The latter may also be formed by passing dry carbon dioxide into warm phenol (carbolic acid), to which at the same time are added small pieces of sodium. The reaction forms sodium salicylate, from which salicylic acid may be obtained by the action of hydrochloric acid. It is this manner of producing salicylic acid which gives it importance both in a scientific and commercial point of view. Two German chemists, Kolbe and Lautemann, chose carbolic acid to experiment upon, with a view to produce salicylic acid, and its discovery is therefore not an accident. Salicylic acid crystallizes from an alcoholic solution by spontaneous evaporation in large, monoclinic, four-sided prisms.
From a hot aqueous solution it separates on cooling into slender needles, often an inch long. It melts at 266° F., and gives off phenol at a higher temperature. It has a sweetish sour taste, and reddens litmus paper strongly. It does not act on polarized light. It is very slightly soluble in cold, quite soluble in hot water, and still more in alcohol; and boiling oil of turpentine dissolves about one fifth of its weight. The acid solution imparts a deep red color to ferric salts. Salicylic acid has recently attracted much attention as a powerful anti-ferment, taking the place of carbolic acid or phenol as a dressing to wounds and ulcers, and as a general antiseptic. "When considerably diluted it is almost odorless and tasteless, and in moderate quantities it has no poisonous effects. It prevents the souring of worts and beer, and is used by glue manufacturers to arrest putrefaction.