Chemistry and Physies. 121 
phuric acid, any other substance was formed. The proportions used 
were one measure of acid, sp. gr. 1°840, and four of water; to 500 
cubic centimetres of this, 50 grammes of pure tannic acid, prepared 
after the process of Pelouze, were added, and the mixture boiled until 
it crystallized on cooling ; the liquid then set aside deposits an abund- 
ance of very white gallic acid. 
The liquid neutralized by carbonate of baryta, evaporated, and treat- 
ed wiih ether, gave 12 per cent. of residue, principally gallate of 
baryta with one or two per cent. of a black matter “apparently due to 
Some impurity of the tannin.” In varying the process in different 
Ways the same result was obtained, besides the black substance nothing 
but gallic acid could be detected. The maximum amount of gallic 
acid that could be obtained was 87:4 for 100 of tannin. 
_ From these experiments the author concludes that the transformation 
1S a result of hydration, and that tannin is isomeric with gallie acid dried 
at 100°C. The composition of the two is thus compared :-— 
Gallic acid by Pelouze. Calculated. Tannin by Wetherell. Calculated. 
C 49-56 49-41 C 50-63 Cv 
H 3-70 H, 858 H 364 H, 379 
O 46-74 O, 47-06 O 45°73 O,2 45°28 
_ “ These numbers,” observes Mr. Wetherell, “ correspond very , 
4y4 H, O,,, and finally that when we act upon tannic acid by differ- 
ent reagents, the crystallized gallic acid is formed by the absorption of 
an equivalent of water.” ay xe 
_ [As the true formula of gallic acid is represented by C, H, O, or 
©xygen than were obtained by Mr. Wetherell, whose results agree well 
with those of ists. Moreover it is diffic 
Szconp Sznizs, Vol. v, No. 13.—Jan., 1848. 
