112 CONVERSION OF TANNIC INTO GALLIC ACID. 
iQimersed in the water, the acid that produces the noise is 
dry acid. Vessels to receive the acid are now placed below 
the retorts, and luted with clay ; and the retorts are sub- 
jected to a strong heat until the acid ceases to drop into the 
vessels. Dry acid is thus obtained ; but if it be desired to 
obtain Nordhausen sulphuric acid, a quantity of acid, con- 
centrated to 66°, must be introduced into the receiving 
vessels, when they are placed below the retorts ; and by 
the admission of the dry acid the density of the acid in the 
receiver will be increased to 67°, 68°, and 69°, according to 
the quantity of dry acid that enters the receiver. By this 
means sulphuric acid is obtained perfectly clear, and never 
coloured like the Nordhausen sulphuric acid, nor charged 
with earth or other foreign matters. — Chem. Gaz, 
ART. XXIX.— ON THE CONVERSION OF TANNIC INTO 
GALLIC ACID. 
By C. Wetherill. 
The following experiments were made with a view to 
ascertain whether a substance is contained in tannic acid 
which constitutes this acid when conjoined vv^ith gallic acid. 
The author is led from his investigation to regard tannic as 
isomeric with gallic acid dried at 212°, and to derive the 
latter from it by the fixation of water. The tannic acid 
used in the experiments was prepared according to 
Pelouze's method, and was purified by solution in spirit, 
and subsequently in water. It was white, and was per- 
fectly precipitated from its solution in water by sulphate of 
quinine, so that the liquid filtered from the precipitate was 
