THE PREPARATION OF TANNIC ACID. 85 
cess, as the middle layer contains some of the acid, 
which, however, may be recovered by distilling the 
ether and water under reduced pressure. The upper 
layer consists of ether holding in solution resin, color¬ 
ing-matter, and gallic acid. 
Another method of purification consists in dissolving 
the acid in water almost to saturation, and allowing to 
stand to separate the resin and other, insoluble impuri¬ 
ties. The clear liquid is removed by decantation, and 
there is added to it a clear saturated solution of com¬ 
mon salt, to this is added some solid sodium chloride in 
order to completely precipitate the acid, which is col¬ 
lected on a filter, dried carefully, and dissolved in a 
mixture of alcohol and ether, or in acetic ether. Lowe 
recommended to agitate the mixture after addition of 
salt with acetic ether. In either case the solvent is 
recovered by distillation, the residue dissolved in water 
and agitated with ether, the latter separated, and the 
aqueous solution distilled on a water-bath to dryness 
under reduced pressure, which causes the acid to become 
light colored and porous. Glucose is the most tenacious 
impurity, resulting in part from the decomposition of 
the tannic acid during each purification. 
The following process, a combination of some previ¬ 
ously-proposed methods, has been used by the author 
with complete success, although, like other processes, 
it is attended with considerable loss, which, however, 
might in part be obviated if the quantity desired were 
sufficient to warrant it. 
Ten grammes of tannic acid are dissolved in 200 cc. 
of water, and to the unfiltered solution a 10-per-cent, 
solution of lead acetate is added drop by drop with con- 
8 
