HISTORY OF THE GALLIC A£ID. Q\ 



feeen subjected to the press, the two liquors are to be mixed, 



and evaporated by a very gentle heat. Thus we obtain a dark 



brown substance, very brittle, which being reduced to a fina 



powder, and digested in very pure alcohol, tinges.it of a very 



faint straw colour. A second infusion extracts scarcely any 



colour, and leaves a brown residuum, which is tannin nearly » 



pure. The two alcoholic tinctures are then to be mixed, and 



distilled in a small retort, till seven-eighths have passed over.* 



The remaining liquor on cooling becomes nearly solid : water 



is poured on this, and by gently heating a limpid solution is ■■.. % 



obtained with very little colour. , j 



If this solution be evaporated, very small and very white 

 prismatic crystals arc obtained. The mother-water affords yet, 

 more, but they are commonly a little coloured : these however, 

 may be rendered very white by washing them with water. By 

 this process a pound of galls affords half an ounce ol crystals* 

 They are extremely light. , 



The processes of Scheele, Deyeirx, and Richter, have afford- Gallic acid 

 ed advantageous results ; but they differ with respect to the Hu^nidway 1 

 purity of the acid. The acid produced by the first, as Ber- contains tan* 

 thollet observes, retains a great deal of tannin ; that by the . T 



second is perfectly white; that by the third likewise .contains > 



tannin. 



By Richter's process the acid, after being purified, is of a In RichteWs -.. 

 pale straw colour. I attempted in vain to bring it to the state JjJjjJJlt J"^ 

 of purity mentioned by the author. I found, that if the evapo- tions in alcohol 

 ration, desication, and subsequent solution in alcohol were con- a ^d. mp °" 

 tinued, a certain quantity of acid was decomposed every time; 

 m> that the alcoholic tincture, instead of being more transpa- 

 rent, became brown. There is a certain point therefore, where 

 we must stop, if we would preserve the whole of the acid and 

 its properties. 



Mr. Bcrthollet tiied different modes of purifying Scheeie's Berthollet pn- 

 acid. That which succeeded best with him was treating the " xi ^ e l £^ a 

 acid with oxid« of tin recently precipitated from its solution in 

 an acid. 



This experiment I repeated. The following is the method Th»« repeated 

 I pursued, and the phenomena I observed. h T the auth * r - 



After having separated the oxide of muriat of tin by an 

 i; alkaline 



