oi Fads fur a History of the Gallic Acid. 



acitl rcmaius combined with a volatile oil which is formed. 

 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 sulphate of iron, though 

 its presence cannot be demonstrated. Tliis acid, then, must 

 have different properties from that of Scheele ; and if it were 

 possible to assimilate it to other vegetable acids, the ben- 

 zoic is that to which it would have the greatest analogy. 

 May it therefore be considered as a modification of the 

 gallic acid ? 1 thiuk not. It is the sam^ uith other vegeta- 

 ble acids; and it is probable that there exists no modifica- 

 tion of them. Tire acetous appears to be the sole vegetable 

 acid ; it dissolves and retains in various proportions a num- 

 ber of the immediate products of vegetables, and in the pro- 

 cesses to which we subject vegetable substances, we facilitate 

 its combination in a more intimate manner, and frequently 

 even augmeut the quantity of this acid. Already several 

 chemists have admitted the possibility of the acetic acid's 

 dissolving and remaining combined with fixed and empy- 

 reumatic oils, and animal matters : they have even gone so 

 far as to imitate acids of this sort. The formic, pyrolignic, 

 tartarous, and mucous, have been classed by Messrs. Four- 

 croy and Vauquelin among the compound acids ; it is the 

 same with the lactic acid, the composition of which was 

 pointed out at the same time by those chemists, M. The- 

 nard, and myself: lastly, we have proof too, according to 

 M. Thenaid, of the existence of this acid in urine and 

 sweat, as well as in the sebacic and zoonic acids. I might 

 further add to these observations (if we were not persuaded 

 that the acetic acid is found every where) that it exists in 

 vegetable as in animal matters, where it is almost always 

 in a state of combination ; and that an equilibrium in the 

 proportions being once established, it gives rise to compounds 

 hitherto unalterable, and the affinity of which cannot be de- 

 stroyed but by reducing them to their primary elements — 

 oxygen, hydrogen, carbon, and nitrogen. 

 . From the facts announced in this memoir jt follows : 

 1st, That the gallic acids of Scheele andjof Richter differ 

 Cpsentially froin that obtained by sublimation j and that the 



crystallized 



