Acidum Gallicum, B.P. Gallic Acid.
Related entry: Pyrogallic acid, Oxidised pyrogallic acid - Tannic acid
C7H6O5. H2O = 188.064.
Gallic acid, C6H2(OH)3COOH, H2O, is usually prepared by the hydrolysis of tannic acid. The acid is also official in the U.S.P. It occurs in white or pale brown, odourless, silky needles or prisms. Dried at 100° it loses 9.5 per cent. of its weight. Gallic acid gives a white precipitate with tartarated antimony, the B.P. statement to the effect that its aqueous solution is not precipitated by that compound being incorrect.
Soluble in water (1 in 100), boiling water (1 in 3), alcohol (1 in 8), glycerin (1 in 6).
Action and Uses.—Gallic acid does not combine with protein and has therefore no local astringent action similar to that of tannic acid. It is absorbed and excreted as sodium gallate, but much of it is oxidised in the tissues. It has been largely used as a remote astringent in cases of internal haemorrhage, on the supposition that it induced vaso-constriction, but it does not constrict vessels. It has been used to a less extent in albuminuria, diabetes, and the night-sweats of phthisis; but there is no evidence to show that it exerts a beneficial action in these conditions. It is applied locally in the form of ointment in psoriasis and external haemorrhoids. It is generally administered in mixture form, when it must be very finely powdered and diffused without the aid of a suspending agent. It may also be given in cachets, powders, or pills (massed with about one-tenth of its weight of glycerin). It is incompatible with Spiritus Aetheris Nitrosi and the salts of iron. Gallic acid enters into the composition of several compounds, such as bismuth subgallate (Dermatol), gallic acid anilide (Gallanol), gallic acid methyl ester (Gallicin), and dibromo-gallic acid (Gallobromol).
Dose.—3 to 10 decigrams (5 to 15 grains).
PREPARATION.
- Glycerinum Acidi Gallici, B.P., 1885.—GLYCERIN OF GALLIC ACID.
- Gallic acid, 1; glycerin, 4.
