14 3 Mr, Hatchett’s Experiments on a Substance t 
But by sulphuric acid, from 480 grains of oak, I obtained 
210 grains, or about 45 per cent, of coal, which burned not 
like the charcoal obtained from the same wood, but like 
many of the mineral coals ; and this was also observed in the 
combustion of the greater part of the coals obtained by the 
humid way from resinous substances. 
The experiment on oak also appears to refute another 
objection to the vegetable origin of pit-coal, namely, the total 
absence of the alkalis, which on the contrary are so constantly 
obtained from the ligneous parts of vegetables by combustion.* 
But I have shewn, that when these bodies are carbonized in 
the humid way either by muriatic or by sulphuric acid, not 
any alkali can be obtained from the ashes of coals so formed ; 
and this seems also to be a farther proof, that the humid way 
has been employed in the operations of nature to convert the 
above mentioned substances into pit-coal ; for supposing fire 
to have been the agent, it does not appear easy to conceive 
how the alkali could have been destroyed or separated.'f 
* Kirwan’s Geological Essays, p. 320. 
•j- Some have attempted to account for the absence of alkali in the Bovey coal and 
common pit-coal, by supposing that the vegetable bodies (from which these have 
been formed) were previously deprived of alkali by simple lixiviation during their 
immersion in water. But in page 127 of this Paper, I have shewn that the submerged 
/>ak of Sutton, although deprived of its tannin, still retained its potash, which cer- 
tainly would not have been the case if the latter like the former could have been 
separated from the wood by mere solution. When wood is reduced to ashes, the 
alkali becomes completely denuded by the destruction of the woody fibre, and 
consequently may be immediately taken up by water ; but when wood is converted 
into coal in the humid way by -means of an acid, then it seems to me that two effects 
