on the constituent Parts of astringent Vegetables. 271 
chemical combination with the skin. In no case is there any 
reason to believe that gallic acid is absorbed in this process ; 
and M. Seguin’s ingenious theory of the agency of this sub- 
stance, in producing the deoxygenation oi skin, seems sup- 
ported by no proofs. Even in the formation of glue from 
skin, there is no evidence which ought to induce us to suppose 
that it loses a portion of oxygen ; and the effect appears to be 
owing merely to the separation of the gelatine, from the small 
quantity of albumen with which it was combined in the orga- 
nised form, by the solvent powers of water. 
The different qualities of leather made with the same kind of 
skin, seem to depend very much upon the different quantities 
of extractive matter it contains. The leather obtained by means 
of infusion of galls, is generally found harder, and more liable 
to crack, than the leather obtained from the infusions of barks ; 
and, in all cases, it contains a much larger proportion of tannin, 
and a smaller proportion of extractive matter. 
When skin is very slowly tanned in weak solutions of the 
barks, or of catechu, it combines with a considerable proportion 
of extractive matter; and, in these cases, though the increase 
of weight of the skin is comparatively small, yet it is rendered 
perfectly insoluble in water ; and is found soft, and at the same 
time strong. 
The saturated astringent infusions of barks contain much less 
extractive matter, in proportion to their tannin, than the weak 
infusions ; and, when skin is quickly tanned in them, common 
experience shows that it produces leather less durable than the 
leather slowly formed. 
Besides, in the case of quick tanning by means of infusions 
of barks, a quantity of vegetable extractive matter is lost to the 
