S3 
skin is exposed to solutions containing tannin, it 
slowly combines with that principle ; its fibrous 
texture and coherence are preserved ; it is ren- 
dered perfectly insoluble in water, and is no longer 
liable to putrefaction : in short, it becomes a sub- 
stance in chemical composition precisely analogous 
to that furnished by the solution of jelly and the 
solution of tannin. 
In general, in this country, the bark of the oak 
is used for affording tannin in the manufacture of 
leather : but the barks of some other trees, par- 
ticularly the Spanish chesnut, have lately come 
into use. The following table will give a general 
idea of the relative value of different species of 
barks. It is founded on the result of experiments 
made by myself. 
Table of Numbers exhibiting the Quantity of Tannin afforded 
by 480 lbs. of different Barks , which express nearly their 
relative Values. 
lb. 
Average of entire Bark of middle-sized Oak, cut in 
spring, 
— — — — — of Spanish Chesnut, 
29 
21 
— of Leicester Willow, large 
size, - - 
S3 
• — — of Elm, - 
13 
— — — - — of Common Willow, large, 
11 
— — - — — of Ash, - 
16 
— -of Beech, - 
10 
of Horse Chesnut, 
9 
— of Sycamore, 
11 
— ______ of Lombardy Poplar, 
15 
of Birch, 
8 
of Hazel, 
14 
— ■■■■> of Black Thorn, 
16 
— . — — — - of Coppice Oak, - * 
32 
— — - — — — — — — of Oak, cut in autumn, 
21 
* — - — — — — — of Larch, cut in autumn, 
8 
White interior cortical layers of Oak Bark - 
72 
G % 
