64 
THE TANNINS. 
An unidentified variety, collected from the leaves of 
Rhus glabra, and in many respects the counterpart of 
the Chinese galls, was allowed to become air-dried, and 
then found to contain 61.70 per cent, of tannic acid, 
12.93 per cent, of moisture, and 2.04 per cent, of ash. 
Some previous experience has shown that the white-oak 
galls if allowed to become air-dried lose their tannic 
acid, presumably by the development of the insect, so 
that, to determine the tannin value, either the galls in 
the moist state must be employed, or they must be sub¬ 
jected to sufficient artificial heat to destroy the insect. 
