on tbe constituent Parts of astringent Vegetables. 263 
gelatine and 41 of tannin; that from the infusion of Leicester 
willow bark, of 57 parts of gelatine and 43 of tannin ; and that 
from the infusion of Spanish chesnut bark, of 61 parts of gelatine 
and 39 of tannin. 
Two pieces of calf-skin, which weighed when dry 120 grains 
each, were tanned ; one in the strongest infusion of Leicester 
willow bark, and the other in the strongest infusion of oak bark. 
The process was completed, in both instances, in less than a 
fortnight ; when the weight of the leather formed by the tannin 
of the Leicester willow bark w : as found equal to 161 grains; 
and that of the leather formed by the infusion of oak bark was 
equal to 164 grains. 
When pieces of skin were suffered to remain in small quan- 
tities of the infusions of the oak bark, and of the Leicester willow 
bark, till they were exhausted of their tanning principle, it was 
found, that though the residual liquors gave olive-coloured pre- 
cipitates with the solutions of sulphate of iron, yet they were 
scarcely rendered turbid by solutions of muriate of tin ; and 
there is every reason to suppose, that a portion of their extractive 
matter had been taken up with the tannin by the skin. 
I attempted, in different modes, to obtain uncombined gallic 
acid from the solid matter produced by the evaporation of the 
barks, but without success. When portions of this solid matter 
were exposed to the degree of heat that is required for the pro- 
duction of gallic acid from Aleppo galls, no crystals were formed; 
and the fluid that came over gave only a brown colour to the 
solution of salts of iron, and was found to contain much acetous 
acid and empyreumatic oil. 
When pure water was made to act, in successive portions, 
upon oak bark in coarse p owder, till all its soluble parts were 
