There are two kinds of tannic acid, of which the official one is the gallo-tannic, and is obtained by treating powdered galls with washed ether. (Galls are growths of plant tissue caused by parasitic fungi or insects, whose excretions stimulate the plant cells to an abnormal development. There are many hundred varieties; that from which tannic acid is made being formed on an oak tree, Quercus lusitanica, by the action of the fly Cynips galloe tinctorioe.) Tannic acid is a light, feathery, yellow-white, non-crystalline powder, of faint odor and slightly bitter taste.
Locally applied it is an active astringent, contracting the tissues, and in the case of mucous membranes causing great dryness. It coagulates albumin readily.
It has much greater strength than gallic acid. It is used to overcome relaxed conditions, and to check excessive secretions of the skin and mucous membranes. Parts exposed to friction, as tender feet or sore nipples, may be successfully hardened by the use of tannic acid. It is also a haemostatic.
It is the best chemical antidote for the poisonous alkaloids, but its administration should be followed by emetics and purgatives, as the compounds formed are capable of being dissolved and absorbed in the alimentary canal.
When meant to act on the stomach it is usually given in powder; on the bowels, in pill form; and locally, as an ointment or lotion.
Tannic or gallic acid in some form is contained in and gives character to nearly all of the vegetable astringents, such as castanea or chestnut, catechu, geranium, pomegranate, logwood, hamamelis or witch hazel, kino, coto bark, alder, diospyros or persimmon, mango, Pinus canadensis, and others.
Glyceritum Acidi Tannici. Glycerite of Tannic Acid. Strength, 20 %.
Unguentum Acidi Tannici. Not official. Tannic Acid Ointment. Strength, 20 %.
Trochisci Acidi Tannici. Troches of Tannic Acid. 1 gr. each.
Acidum Gallicum, Gallic Acid.
Gallic acid is also made from galls, and is an astringent similar to, but milder than, tannic acid. It does not coagulate albumin.
It is given in powder and pill, the average dose being gr. xv.-I Gm.