Definition. - An organic acid, C6H1(OH3)COOH + H1O, usually prepared from tannic acid.

Description and Properties. - White or pale fawn-colored, silky, interlaced needles or tricolinic prisms; odorless, having an astringent or slightly acidulous taste; permanent in the air. Soluble in 87 parts of water and in 4.14 parts of alcohol at 25C.

Dose. - 5-20 grains (0.3-1.2 Gm.) [15 grains (1 Gm.), U. S. P.].

Physiological Action. - Gallic acid resembles tannic acid in its action, but does not coagulate albumin, and therefore does not possess the local influence of the latter.

Therapeutics. - Externally and Locally. - Gallic acid is seldom used externally. Locally, tannic acid is preferable, but gallic acid is effectual applied as a glycerite, I dram-i ounce (4.0-32.0 Gm.), in cases of tonsillitis and pharyngitis. Gallic acid and stramonium ointment in equal parts form an unguent for hemorrhoids. In alcoholic solution it is applied to the membrane of diphtheria.

Internally. - It is doubtful if gallic acid has any distinct indications.

Administration. - Gallic acid is not to be combined with iron. It is administered in powder or pill form. The glycerite and the ointment are used locally.