This section is from the book "Materia Medica Pharmacy, Pharmacology And Therapeutics", by W. Hale White. Also available from Amazon: Materia Medica Pharmacy, Pharmacology And Therapeutics..
By exposing a mixture of Nutgall and distilled water in the form of a thin paste, to the air for a month, expressing and rejecting the liquor, boiling the residue with distilled water and filtering, when hot, through purified Animal Charcoal. Hc14h9o9+H2O=2Hc7h5o5.
White, or pale fawn-colored, silky, interlaced needles, or triclinic prisms; odorless; having an astringent or slightly acidulous taste; permanent in the air.
Incompatibles. - Ferric and metallic salts generally, and Spiritus AEtheris Nitrosi.
Dose, 5 to 20 gr.; .30 to 1.20 gm.
Gallic acid has no power to coagulate albumin, and therefore possesses none of the local properties of tannic acid. If it is wished to produce the supposed remote astringent effects of tannic acid, gallic acid may be administered, for tannic acid is in the intestine converted into it.