THE PREPARATION OF TANNIC ACID. 81 
volume of water, agitated well, and allowed to stand, 
when it will be found that three layers have formed. 
The under, watery layer contains nearly pure tannic 
acid, and is evaporated rapidly in a vacuum, which 
causes the acid to become porous. The upper layers 
are distilled to recover the ether-alcohol, and from the 
residue water extracts a small quantity of impure tan¬ 
nin. The last method can be recommended only where 
it is desired to obtain a pure acid without the trouble 
of additional purification, for if made from Chinese 
galls the product should be as pure as it is possible to 
get the acid in one operation. It is not available as a 
commercial process, on account of its expensiveness, 
since the quantity of solvent recommended is insufficient 
to completely extract the galls. 
The above-mentioned processes have been enumer¬ 
ated in order to criticise them, and at the same time 
furnish information to those who wish to prepare tannic 
acid from galls on a small scale. The following will 
treat the subject from a commercial stand-point, and 
describe what has been a process for producing the 
tannic acid in quantity. 
There are three varieties of the acid in commerce, 
known as— 
Ether-tannin (the German Schaum-Tannin), 
Alcohol-tannin, 
Water-tannin. 
The first is the one best known in this country, although 
one or both of the others may be had of importers and 
manufacturers under the name of “ commercial tannin/’ 
The Chinese or Japanese galls, on account of their 
greater freedom from coloring-matter and larger per- 
