which possesses the characteristic Properties of Tannin. 141 
formed from the resinous and other vegetable substances by 
any of the known chemical processes, yet there is every 
reason to believe, that the agent employed by nature in the 
formation of coal and bitumen has been either muriatic or 
sulphuric acid ; and when it is considered, that common salt 
is never found in coal mines except when in the vicinity of 
salt springs, whilst on the contrary, pyrites, sulphate of iron, 
and alum, most commonly are present ; * these facts, together 
with the sulphureous odour emitted by most of the mineral 
coals when burned, appear strongly to evince the agency of 
the latter. That this has been the case, seems also to be 
corroborated, by the great resemblance which ( as has been 
previously stated) the coals formed artificially from many 
vegetable substances bear to the mineral coals, especially as 
the similarity is not confined to external characters, but extends 
to other properties. 
By the action of sulphuric acid on vegetable bodies, a much 
greater portion of their carbon is converted into coal than 
when the same are subjected to the effects of fire. 
Several examples respecting the resins, have been men- 
tioned in the seventh section of this Paper, and the re- 
sult of the experiment made upon oak perfectly accords with 
them. 
Mr. Proust, in the course of some comparative experiments 
on the proportions of charcoal afforded by different kinds of 
wood, obtained 20 per cent, from green oak, and 19 per cent . 
from heart of oak.'f 
* Kirwan’s Geological Essays, p. 324. 
t Journal de Physique, I799, Tome 48, p, 469, 
