ACEDUM GALLICUM 143 



Preparation of Tannic Acid. Powdered nutgall is exposed to damp atmos- 

 phere for twenty -four hours, then made into paste with washed ether. Allow to 

 stand six hours, then express in canvas cloth between tinned plates. After powder- 

 ing the pressed cake, again make into paste with washed ether. Repeat the 

 former process and allow the mixed liquid to evaporate spontaneously. 



ACTION AND THERAPEUTIC PROPERTIES. When taken into the digestive 

 tract some of it is changed into gallic acid and absorbed as such; 

 while some may be taken up as a soluble alkaline tannate. 



Because of its power and lack of toxicity, tannic acid is one of 

 the most widely used of all the astringents, either in the form of the 

 tannic acid itself or of one of the various vegetables containing it. 



Locally applied it may be used to overcome relaxation, as in spongy 

 gums, mercurial sore mouth, hemorrhoids, and chronic sore throat. 



To check hemorrhage it may be used whenever the source of 

 flow can be reached directly, as in epistaxis, haematemesis, hemor- 

 rhage from the bowels, etc. 



Tannic is useful as an antidote against a number of poisons in- 

 cluding most of the irritant metallic salts, especially those of antimony 

 and iron. Dose: 8 gr. (0.6 Gm.). 

 OFFICIAL PREPARATIONS. 



Preparations commonly employed: 

 Unguentum Gallae (20 per cent.). 



Acidum Tannicum, Dose: 10 to 20 gr. (0.6 to 1.2 Gm.). 



Trochisci Acidi Tannici, Each I gr. (0.06 Gm.). 



Glyceritum Acidi Tannici (20 per cent.) f . .Local use. 

 Unguentum Acidi Tannici (20 per cent.), . .Local use. 

 Collodium Stypticum (2 per cent.) Local use. 



105 b. ACIDUM GALLICUM, U.S. GALLIC ACID. Usually prepared 

 from tannic acid. Also prepared by exposing moistened powdered 

 nutgalls to the action of the air for a month or more; a peculiar 

 fermentation sets in which converts the tannic acid into gallic acid; 

 this is extracted by expression and purified by filtration and crystal- 

 lization. It is in light, silky, acicular needles, colorless when pure, 

 but as usually seen in the shops, of a more or less pale brownish 

 color; inodorous; taste sourish and astringent. It differs from 

 tannic acid in its sparing solubility in cold water, and in not precipi- 

 tating gelatin or alkaloids from their solutions. It is less astringent 

 than tannic acid, and inferior to it in all respects except where the 

 astringent effect must be reached through the medium of the general 

 circulation. When applied locally, gallic acid acts as a mild astrin- 

 gent, but does not cause coagulation of the blood, for which reason 

 it is not used locally in the control of hemorrhage. Dose: 5 to 30 gr. 

 (0.3 to 2 Gm.). 



105 c. PYROGALLOL, U.S. PYROGALLIC ACID. A triatomic phenol, 

 C 6 H 3 (OH) 3 , obtained chiefly by the dry distillation of gallic acid. 

 It is in light, white, shining laminae, or in fine needles, becoming 

 gray or darker when exposed to the air or light, and should therefore 



