i go Mr. Hatchett’s Experiments on a Substance , 
and likewise on some former occasions, dissolves the resins, 
but the progress of its effects seems to be conversely that of 
sulphuric acid ; in the latter case, solution precedes decompo- 
sition ; but when nitric acid is employed, decomposition to a 
certain degree precedes solution ; for it at first converts the 
resins into a pale orange-coloured brittle porous substance, 
then into a product, which apparently possesses the interme- 
diate characters of vegetable extractive matter and of resin, 
and lastly, this is converted into the first variety of the tan- 
ning substance, beyond which I have not been able to effect 
any change. 
As coal therefore appears to be the ultimate effect produced 
by sulphuric acid upon the resinous bodies, so does the first 
variety of-the tanning substance seem to be the terminating 
product afforded by the same when acted upon by nitric acid. 
This effect of nitric acid has been already amply discussed, 
neither does it appear necessary that I should here repeat the 
remarks which have been made on some of the simultaneous 
products, such as the vegetable acids ; but amongst the effects 
produced by sulphuric acid, the coal which is formed seems 
to merit some attention. 
§ VII. 
After the tanning substance and the other products had 
been obtained from the resins, balsams, &c. which have been 
mentioned in the beginning of this Paper, the following pro- 
portions of coal remained.*' 
* The weight of the coal obtained from each of the above mentioned substances, 
was estimated after the complete separation of every other product, and after the 
moisture had been expelled by a red heat, in close vessels. 
