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..
1) Expose powdered Nutgall to a damp atmosphere for twenty-four hours. (2) Add Ether to form a paste, and let it stand, closely covered, for six hours. (3) Express this in a close canvas cloth, between tinned plates, reduce the resulting cake to powder and mix with sufficient Ether and express as before. (4) Mix the expressed liquids and allow the mixture to evaporate spontaneously. Tannic Acid remains. 2Hc7h5o5 - H2O=Hc14h9o9.
Gharacters.-A light yellowish, amorphous powder, usually cohering in form of glistening scales or spongy masses, odorless, or having a faint characteristic odor, and a strongly astringent taste; gradually turning darker when exposed to air and light.
In about 1 part of water, and in 0.6 part of Alcohol; also in about 1 part of Glycerin, with the intervention of a moderate heat; freely soluble in diluted Alcohol, sparingly in absolute Alcohol; almost insoluble in absolute Ether, Chloroform, Benzol or Benzin.
Dose, 1 to 20 gr.; .06 to 1.20 gm.
1. Collodium Stypticum. - Styptic Collodion. Tannic Acid, 20; Alcohol, 5; Ether, 25; Collodion, to 100. By solution.
2. Trochisci Acidi Tannici. - Troches of Tannic Acid. Tannic Acid, 6; Sugar, 65; Tragacanth, 2 gm.; Stronger Orange Flower Water, a sufficient quantity to make 100 troches. Each troche contains about 1 gr.; .06 gm. of Tannic Acid.
Dose, 1 to 3 troches.
3. Unguentum Acidi Tannici. - Ointment of Tannic Acid. Tannic Acid, 20; Benzoinated Lard, 80.
4. Glyceritum Acidi Tannici. - Glycerite of Tannic Acid. Tannic Acid, 20; Glycerin, 80
Tannic acid is one of the most important drugs, because it coagulates albumin and gelatin with great readiness; that is to say, it tans the tissues, for it is by coagulating the interstitial fluid in skins that tannic acid converts them into leather. The coagulated albumin or gelatin powerfully resists putrefaction. If an albuminous discharge is taking place from a sore or mucous surface and tannic acid is applied, the excreted fluid is coagulated, and the coagulum forms a solid protecting layer which prevents further discharge. As the tannic acid soaks into the tissues it coagulates the albuminous fluids there also, and this still further hinders the discharge of fluid, therefore it is an energetic astringent. If bleeding is taking place, tannic acid of course coagulates the blood as it flows and the clots plug the vessels; at the same time the coagulum formed within the tissues, by its contraction, constricts the blood-vessels, and thus tannic acid becomes a powerful haemostatic. It has no noteworthy direct effect on the blood-vessels themselves. Tannic acid is mildly depressant to sensory nerves. Like other acids it is irritant, but it is very feebly so, and consequently its action in this direction is more than counterbalanced by its strongly astringent effects.
Gastro-intestinal tract. - Because tannic acid coagulates the mucous secretions and the fluids in mucous membranes, it makes the mouth dry and feel stiff when locally applied; in the stomach large doses prevent the secretion of gastric juice, decrease the flow of mucus, and may cause vomiting. For these reasons, and also because it precipitates pepsin, it interferes with digestion. It will check gastric haemorrhage. In the intestine is is either converted into gallic acid, or forms alkaline tannates, and until these alterations it acts as an intestinal astringent, controlling intestinal bleeding and causing constipation; but this acid and these salts have no astringent properties, therefore when, as is often the case, drugs containing large amounts of tannic acid act as powerful intestinal astringents, we must suppose that the amount of tannic acid taken is large enough for the conversion of it, into salts or gallic acid, to take place slowly. It is absorbed chiefly as gallates, and to a much less extent as tannates.
Remote effects. - Gallates and undecomposed alkaline tannates circulate in the blood, but they have no power to coagulate albumin, nor have they any astringent influence when locally applied, therefore it is difficult to believe that tannic acid has any remote astringent or haemostatic effects; some claim that it has, but they have not proved their case. It is excreted in the urine of animals as gallates with traces of tannates, but in man no derivative of it can be detected in the urine or other excretions, so that any which has been absorbed is entirely decomposed in the body. Any excess passes out in the faeces as tannates and gallates. Many vegetable substances, as logwood, depend for their astringent properties on the tannic acid they contain.