This section is from the "A Handbook of Useful Drugs" book, by State Medical Examining and Licensing Boards.
An organic acid, HC7H5O3 = C6H4.OH.COOH, generally prepared synthetically from phenol.
Properties : It occurs as fine, white needles or a bulky, white crystalline, odorless powder, possessing a sweetish, subsequently acrid taste. Salicylic acid is only slightly soluble in water but freely soluble in alcohol or in ether. Salicylic acid reacts with alkali hydroxids and carbonates to form water-soluble salts. With solution of ferric chlorid it gives a deep purple color.
Incompatibilities: It is incompatible with salts of iron and with spirit of nitrous ether.
Action and Uses: Salicylic acid is an antiseptic. It is quite irritant to mucous membranes and somewhat corrosive. Internally it has the actions described under sodium salicylate, in which form it is commonly employed. Externally it has been used as an application in pruritus, urticaria, bromidrosis and in some forms of eczema; also in the form of ointments and collodions to soften and remove corns and warts.
Dosage: Internally it is best given in the form of soluble salicylates. (See Sodium Salicylate.) Externally it is applied as an astringent in from 1 to 2 per cent, alcoholic solution or ointment; as an antiseptic, antiparasitic and keratolytic agent, in 2 to 5 per cent, dusting-powder, or ointment, and as a strong keratolytic in proportions up to 20 per cent., best dissolved in collodion. Continuous application to the skin may occasion slight corrosion.