lie Experiments on a Suhslance which possesses 



also to be corroborated bv the great resemblance which (as 

 has been previously stated) the coals formed artificially from 

 •many vegetable substances bear to the mineral coals, espe- 

 cially as the similarity is not confined to external characters^ 

 but extends to other properties. 



Bv the action of sulphuric acid on vegetable bodies, a 

 much srreater portion of their carbon is converted into coal 

 than v.hen tlie same are subjected to the effects of fire. 



Several examples respecting the resins have been men- 

 tioned in the seventli section of this paper; and the result 

 of the experiment made upon oak perfectly accords with 

 theai. 



IvI. Proust, in the course of some comparative experi- 

 incnts 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 *. 



But by sulphuric acid, from 480 grains of oak I obtained 

 210 crains, or about 45 percent, of coal, which burned not 

 like the charcoal obtained froin the same wood, but like 

 manv 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, tlie 

 total absence of the alkalis, which, on the contrary, are so 

 constantly obtained from the ligneous parts of vegetables by 

 combustion f. But I have shown, 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 further 

 proof that the humid way has been employed in the opera- 

 tions 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 J. 



Every 



* Journal de Physique 1799, torn, xlviii. p. 469. 

 f Kirwan's Geological Essays, p. 320. 



^ Some have attenipetd to account for the absence of alkali in the Bovey coai 

 and common pit coal, by supposing that the vegetahle bodies (from which these 



have 



