7Q HISTORY OF THE GALLIC ACID, 



Base of gallic The gallic then, like other vegetable acids, is eomposscd of 



and carbon?* oxigen, hidrogen, and carbon. If but a small quantity of hi- 

 drogen, can be obtained, it is because water is formed during 

 the decomposition of the acid, so that the hidrogen passes over 

 only when very little oxigen remains to act on the carbon. 



I have attempted to shew, that the gallic acid is a compound. 

 Its formation by Scheele's process appears to me to favour this 

 opinion. In fact, if the quantity of acid extracted from the 

 aqulous infusion exposed to the air be compared with that af- 

 forded by sublimation, I conceive it is not difficult to account 



AcidofScheele.for the increase. There can be no doubt, that acetic acid 



med in the liquor, which, acting on a portion of tannin and ex 

 tractive matter, constitute the gallic acid of Scheele : but this com 

 bination is rendered moreintimate, and somewhat different, by the 

 action of caloric; of which we have a proof when the acid is 



Sublimed acid, obtained by sublimation, for not only is the tannin decomposed, 

 but the acid remains combined with a volatile oil which is for- 

 med. Perhaps this acid contains a small portion of tannin in 

 very intimate combination, whence no doubt arises its property 

 of giving a momentary blue with sulphat of iron, though its pre- 

 sence cannot be demonstrated. This acid then must have dif- 

 ferent properties from that of Scheele: and if it were possible to 

 assimilate it to other vegetable acids, the benzoric would it be 



,., that, which it would have the greatest analogy. Mav it be con- 

 not a moriifica- ' = . 

 tion of the sidered however as a modification of the gallic acid? I think 



& allic * not. It is the same with other vegetable acids: and it is probable, 



Acetous the that there exists no modification of them. The acetous appears 



only vegetable f j^ t ] lc so j e vegetable acid : it desolvcs and retains in various 



acid, . " 



forming others proportions a number of the immediate products of vegetables,, 



by various ad- am ] ,j n ^ e processes to which we subject vegetable substances, 



«htions inti- ..... , . . 



mately combi- we facilitate its combination in a more intimate manner; and 



red with it. frequently even augment the quantity of this acid. Already 

 several chemists have admitted the possibility of the acetic acid's 

 dissolvingand remaining combined with fixed andempyreumatic 

 oils, and animal matters: they have even gone so far as to imi- 



Instanccs. tate acids of this sort. The formic, pyrolipic, pyrotartarous, 



and pyromucous, have been classed by Messrs. Fourcroy and 

 Vauguelin among the compound acids : it is the same with tho. 



lactic, 



