CYNIPS QUERCUS FOLII. 



test of the presence of iron in any liquid, and it is also an 

 excellent test of the presence of morphia. 



Tannic acid has been rarely procured in a state of purity. 

 It is found chiefly in the inner bark of the roots and the stems 

 of trees ; sometimes it is contained in the wood, occasionally 

 in the petals of the flowers, varying in character in different 

 plants, owing to its combination with other principles. It 

 has been employed, in its pure state, in uterine haemorrhages ; 

 and M. Cavalier says it has succeeded in stopping these 

 when many other astringents have failed. He gives it in 

 doses of two grains every two hours. For this purpose it 

 can be procured sufficiently pure from a solution of catechu 

 in cold distilled water, filtered and evaporated to dryness. 

 Tannic acid exposed to the air for some weeks is oxidized, 

 and converted into gallic acid. 



The incompatible substances with infusion or decoction 

 of galls are very numerous. Many substances form precipi- 

 tates with these preparations besides those which indicate 

 the astringent character of the galls. Thus the infusion is 

 precipitated by infusions of cinchona, cusparia, and calumba ; 

 solutions of opium, lime-water ; carbonate of potassa ; the 

 acetates of lead ; sulphates of copper and of iron ; nitrate of 

 mercury and of silver and potassio-tartrate of antimony ; all 

 of which are therefore incompatible in prescriptions with it. 

 The sulphuric and hydrochloric acids cause flaky, white pre- 

 cipitates ; nitric acid changes the color, first to deep orange 

 and then to pale orange or yellow; and the astringency of 

 the infusion is also greatly weakened. Although the nitrate 

 of mercury throws down a clotted, bright-yellow precipitate, 

 yet the bichloride, which is more likely to be ordered in con- 

 junction with the infusion of galls, only renders the infusion 

 milky. It is curious that so copious a decomposition of tar- 

 tar emetic should take place on the addition of the solution 

 of that salt to infusion of galls, when no precipitate is pro- 

 duced by it in decoction of oak-bark. No precipitates are 

 thrown down with infusion of quassia, gentian, canella alba, 

 orange-peel, saffron, ammonia, sulphate of zinc, and bichlo- 

 ride of mercury, which may therefore enter into the prescrip- 

 tions with infusions of gall-nuts. By distillation per se, galls 

 have been found to yield a concrete volatile oil, which Profes- 

 sor Branchi, the discoverer, regards as a component of galls ; 

 but some have considered it only the production of the opera- 



7 



