85 
matter. It is easy to obtain the comparative 
value of different substances for the use of the 
tanner, by comparing the quantities of precipitate 
afforded by infusions of given weights mixed with 
solutions of glue or isinglass. 
To make experiments of this kind, an ounce or 
480 grains of the vegetable substance, in coarse 
powder, should be acted upon by half a pint of 
boiling water. The mixture should be frequently 
stirred, and suffered to stand 24 hours ; the fluid 
should then be passed through a fine linen cloth, 
and mixed with an equal quantity of solution of 
gelatine, made by dissolving glue, jelly, or isin- 
glass, in hot water, in the proportion of a drachm 
of glue or isinglass, or six table-spoonfuls of jelly, 
to a pint of water. The precipitate should be col- 
lected by passing the mixture of the solution and 
infusion through folds of blotting-paper ; and the 
paper exposed to the air till its contents are quite 
dry. If pieces of paper of equal weights are used, 
in cases in which different vegetable substances are 
employed, the difference of the weights of the 
papers, when dried, will indicate with tolerable 
accuracy, the quantities of tannin contained by the 
substances, and their relative value, for the pur- 
poses of manufacture. Four- tenths of the increase 
of weight, in grains, must be taken, which will be 
in relation to the weights in the table. 
Besides the barks already mentioned, there are 
a number of others which contain the tanning 
principle. Few barks, indeed, are entirely free 
from it. It is likewise found in the wood and 
leaves of a number of trees and shrubs, and is one 
g 3 
