on a Substance possessing the Properties of Tannin. 307 
which I have hitherto postponed, in order that the account of 
the experiments might not be interrupted. 
The first variety is that which is the most easily formed ; and 
from some experiments which were purposely made, I find 
that 100 grains of dry vegetable charcoal afford 120 of the tan- 
ning substance ; but as it is extremely difficult completely to 
expel moisture, or even the whole of the nitric acid which has 
been employed,* an allowance of about three or four grains 
ought to be made, so that after this deduction we may conclude, 
that 100 grains of vegetable charcoal yield 116 or 117 of the 
dry tanning substance. 
The proportions of the constituent parts of this substance I 
have not as yet ascertained ; but from the manner by which it 
is produced, carbon is evidently the base of it, and is the pre- 
dominating essential ingredient. 
From § III. experiment F. it also appears, that the other 
component parts are oxygen, hydrogen, and nitrogen ; for 
when the artificial tanning substance was distilled, ammonia and 
carbonic acid were obtained, exclusive of a very small portion 
of a yellow liquor, which stained the upper part of the retort, 
and which, from its tenacity and insolubility in water and 
alcohol, appeared to be of an oily nature. 
As I had taken every precaution respecting the charcoal 
which had been employed, I was at first induced to consider 
the above facts as almost positively demonstrative of the pre- 
sence of hydrogen in charcoal, but upon farther reflexion, and 
upon weighing some of the circumstances which attend the 
* The most effectual method of expelling the nitric acid, is to reduce the tanning 
substance to powder, and repeatedly evaporate different portions of distilled water 
from it in a glass or porcelain basin. 
R r 2 
