THE PREPARATION OF TANNIC ACID. 79 
in a cylindrical percolator, the upper end of which is 
narrow in order that it may be stopped to prevent the 
evaporation of the solvent. The lower end of the perco¬ 
lator is plugged with cotton and connected with a flask, 
ether is poured on the powder, and the ethereal solu¬ 
tion of the galls allowed to collect. This solution soon 
separates into two layers, the upper of which consists of 
ether, gallic and ellagic acids, resin, and fat, with some 
tannic acid, while the lower is a solution of moderately 
pure tannic acid in water and ether. The percolation is 
discontinued when the lower layer ceases to increase in 
volume. The two layers are then separated, and the 
lower one evaporated to dryness on a water-bath, by 
which means the acid is obtained in a porous mass. 
There have been, since the publication of this pro¬ 
cess, numerous modifications of it suggested, but the 
principle remains the same. The product is not abso¬ 
lutely pure tannic acid, but a mixture of that compound 
with gallic acid, coloring-matter, resin, and glucose. 
It is, however, a process that is adapted to working 
with large quantities, where there are facilities for 
recovering the ether. 
In order to obviate using so much ether, many 
methods have been offered as superior to the above, 
notably one by extracting with water and precipitating 
with lead acetate. It is, however, a wasteful process 
and is difficult and tedious to perform. 
Mixtures of alcohol, ether, and water in various pro¬ 
portions have been suggested for percolating galls, in¬ 
stead of the commercial ether alone. Four parts of 
ether and one part of alcohol have been recommended 
as the most suitable solvent, although thirty parts ether 
