An organic acid, existing naturally in combination in various plants, but largely prepared synthetically from carbolic acid.

Derivation.—Made by passing carbonic dioxide through sodium carbolate at a temperature of 428° F. (220° C.). 2 NaC₆H₅O (sodium carbolate) + CO₂ = Na₂C₇H₄O₃ (sodium salicylate) + C₆H₆O (phenol). Sodium salicylate is treated with hydrochloric acid when salicylic acid is precipitated.

Properties.—Light, fine, white, needle-shaped crystals, odorless, having a sweetish, afterwards acrid taste; permanent in air. Soluble in alcohol, ether and hot water; borax increases its solubility.

Dose.—Horses, 2 to 6 drs.; cattle, ¹/₂ to 1 oz.; sheep, 1 to 2 drs.; pigs, 30 to 40 grs.; dogs, 5 to 20 grs.; should be given well diluted; large doses are recommended for fevers, but smaller doses more often repeated in rheumatism.