Facts for a History of the Gallic Acid. 3,5 



crystallized is preferable as a re-'agent, on account of the 

 constant unifonnitv of the colour it givesWith iron. 



Sdly, 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 contanis no 

 tannin, at least none that can be ascertained by acting on 

 glue; and that it cannot, on any occasion, supply the place 

 of the crystallized acid. 



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

 posed of acelic acid united with a peculiar aromatic volatile 

 oil. 



3thly, That by means of water poured into the etherized 

 tincture of galls, or ether containing the sublimed acid, an 

 oily matter is separated. 



6thly, 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 the portion of tannin 

 it retains is necessary to constitute gallic acid, and that to 

 this are owing its excellent properties in the art of dyeing. 



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 ; and that it is by the assistance of caloric acting 

 more immediately on galls, that a more intimate union be- 

 tween the acid and the tannin is effected. 



9thly, That the earthy and alkaline gallates likewise afford 

 iicetic acid by their decomposition. 



lOthlv, and finally. That gallic acid, like the other vege- 

 table acids, is composed of oxygen, hydrogen, and carbon. 



If these results be accurate, we n)ay conceive it possible 

 to accomplish its synthesis. Some trials that I have al- 

 ready made give me the hope of succeeding in it. I shall 

 do myself the honour of imparting the further results of my 

 inquiry to the class, if they should be worthy its notice. 



C 2 Vir. Njte 



