308 Mr. Hatchett's additional Experiments 
formation of the artificial tanning substance, I still feel on this* 
point very considerable doubt ; for I have constantly observed, 
that diluted nitric acid, acts upon charcoal more effectually, in 
the formation of the tanning substance, than when it is em- 
ployed in a concentrated state ; and it appears therefore very 
probable, that hydrogen may have been afforded by a portion 
of water decomposed during the process. For admitting that 
the new compound (formed by the action of nitric acid 
upon charcoal) may possess a certain degree of affinity for 
hydrogen, this being exerted simultaneously with the affi- 
nity for oxygen possessed by nitrous gas, may (especially 
when the last is in a nascent state) effect a decomposition of a 
portion of v/ater, the hydrogen of which would therefore enter 
into the composition of the tanning substance, whilst the oxygen 
would supply the place of part of that which had been taken 
from the nitric acid. 
Many of the properties of the tanning substance prepared 
from coal by nitric acid are very remarkable, particularly 
those which have been noticed in § 111. experiments F. and G. ; 
for surely it is not a little singular, that this substance when 
burned should emit an odour so very similar to animal matter, 
notwithstanding that the tanning substance had been prepared 
from pure vegetable charcoal. And again in experiment G. 
the portion which had not been precipitated by solution of isin-; 
glass, was, when dried, found to possess a strong vegetable 
odour very analogous to oak bark, although charcoal is inodor- 
ous, and isinglass very nearly so. 
But, after all, the most extraordinary properties of this sub- 
stance are certainly those which so nearly approach it to the 
vegetable principle called tannin; for it perfectly resembles 
