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SALICYLIC ACID. 233

ACIDUM SALICYLICUM—SALICYLIC ACID.
Formula.—HCjH.O,.
Derivation.—Salicylic Acid is obtained by combining carbolic
acid with caustic soda, and subjecting this compound to dry car-
bonic acid under the influence of heat, the portion of salicylate
of sodium remaining behind after the carbolic acid distills over
being saturated, in the form of a hot, aqueous solution, with
muriatic acid, which liberates the salicylic acid in small crystals.
The crystals are washed, dissolved in hot water, and by re-crys-
tallization, obtained in the form of a powder of a light brown
color, which is then bleached until it is quite white; but most of
that sold is of a light cream-color with a reddish tinge. The
coloring matter, however, which is present, does not interfere
with its efficacy. It is sometimes obtained from the product of
plants, such as wintergreen. It has no smell, a slight taste, and is
soluble in alcohol and ether and in hot water and glycerine. It
can also be obtained from salicin, the vegetable principle existing
in willow, poplar, etc., and from oil of gaultheria (wintergreen)
and from spiraea ulmariae (meadow sweet).
Medical Properties and Physiological Action.— Salicylic acid is a
powerful antiseptic, and is said to be as effective in small quanti-
ties as any other antiseptic, in arresting putrefactive and fer-
mentative processes. When properly reduced in strength it causes
no pain or irritation in the parts to which it is applied. It will
destroy minute organisms, and a small quantity will arrest vinous
fermentation and prevent the decomposition of animal fluids.
Although free from any poisonous action when administered in a
reasonable quantity, yet in large doses it will cause nausea and
vomiting. It is thought to combine with the soda of the blood,
where it is present as a salicylate. It has little or no affinity for
cold water; but the addition of certain alkaline salts, such as
sodium phosphate, increases its solubility. Combined with sul-
phite of sodium, which is also antiseptic, and water, a solution is
formed which is free from irritating properties and especiallv ap-
plicable to the treatment of zymotic diseases. Glycerine warmed
will dissolve A its weight of salicylic acid, and the solution may
then be diluted with water to any desirable extent.