HISTORY OF THE GALLIC ACID. ^1 



lactic, the composition of which was pointed out at the sama 

 time by those chemists, Mr. Thenard, and myself: lastly we 

 have proof too, according to Mr. Thenard, of the existance of 

 this acid in the urine and sweat, as well as in the sebacic and 

 ozonic acids. I might farther add to these observations (if we 

 were not persuaded, that the acetic acid is found every where) 

 thr:t it exists in the vegetable as in animal matters, where it is 

 almost always si ate of combination ; and that, an equilibri- 

 um in (he prop uli'ins being once established, it gives rise to com- 

 pounds hitherto unalterable, and the affinity of which cannot 

 be destroyed, but by reducing them to their primary elements, 

 oxigen, hidrogen, carbon, and nitrogen. 



From the facts announced in this memoir it follows: 

 1st, That thegallic acids of Scheele and of Richter differ essen- Recapitulation, 

 tially from that obtained by sublimation; and that the crys- 

 tallized is preferable as a reagent, on account of the constant 

 uniformity of the colour it gives with iron. 



2ndly, That this acid appears to be composed of acetic acid 

 tannin, and extractive matter ; and that it cannot be com- 

 pletely freed from tannin by crystallization. 



3dly, That the acid obtained by sublimation contains no 

 tannin, at least that can be ascertained by acting on glue j 

 and that it cannot, on any occasion, supply the place of the 

 crystallized acid. 



4thly, That the sublimed acid, appears likewise to be com- 

 posed of acetic acid, united with a peculiar aromatic vola- 

 tile oil. 



5thly, That by means of water, poured into the ethereal tinc- 

 ture of galls, or ether containing the sublimed acid, an oily 

 matter is separated. 



6'thly, That there is no process known for purifying Scheele's 

 acid completely: that is to say, we cannot take from it the 

 whole of its tannin, without reducing it to the state of acetic 

 acid; which proves, that theportion of tannin it retains is 

 necessary to constitute gallic aciJ, and that to this are owing 

 its excellent properties in the art ofcdying. 



7thly, That the red oxide of mercury, and oxide of tin, as 

 well as carbon, decompose this acid. 



8thly, That by distilling galls with water acetic acid may be 



obtained ; 



