290 Fac/s for a Hlslory nf the Gallic yield. 



in these operations, the acid itself, by carbonizing, forms, 

 after a slight combustion, colouring particlt^s. 



For this purpose he boiled red oxide of mercury for half 

 an hour in a solulionof gallic acid, which assumed a blackish 

 colour. He found in the residue revived mercuiy mixed 

 with a charry powder ; he afterwards saturated the liquor 

 with carbonates of potash and soda. These salts did not 

 give him any blue precipitate with the sulphate of iron. He 

 obtained a similar result with the oxide of manganese. 



Other experiments persuaded the author ihatjhose bodies 

 which take up oxygen from the gallic acid brighten its co- 

 lour. " T have made (says M. Bartholdi) a solution of 

 gallic acid as limpid as distilled water, having boiled it for 

 some time with very pure and well pulverized charcoal, 

 which I used in double its weight to that of the acid; it 

 preserved its limpidity as long as I kept it from the influ- 

 ence of the atmosphere, and it precipitated the iron in a 

 black colour." 



M. Bartholdi presumes that we may thus succeed in de- 

 stroying the astringent properly. 



I shall not indulge myself upon the present occasion in 

 any observations ; it will be necessary, in o^der to limit them 

 precisely, to detail the following experiments : 



Extraction of the Gallic Acid. 



There are several processes for extracting this acid from 

 gall-nuts, 



Scheela's Process. — We pour upon one part of gall-nuts, 

 poundedj and passed through a coarse sieve, six parts of cold 

 water. We must then infuse it in a glass bowl for four 

 days, taking care to stir it often j it must be then filtered, 

 the liquor exposed to the free air in the same vessel, covered 

 with a piece of gray paper only : a month afterwards we find 

 this infusion covered with a thick mouldy pellicle, without 

 any precipitate being formed ; it has no longer any astrin- 

 gent taste, but ,t is acid. The liquor is now allowed to rest 

 for fu'e weeks ; there is then formed a precipi'ate two fingers 

 in thickness, and there is a mucous pellicle above it. The 

 infusion is filtered, and again exposed to the air. At the 



end 



