which possesses the characteristic Properties of Tannin. 135 
black, and was pulverulent. It burned with some flame, 
emitted still a slight vegetable odour, and was reduced to 
ashes much sooner than the coal formed by sulphuric acid, 
but not so speedily as the oak charcoal. The ashes had an 
ochraceous appearance, and were almost devoid of any saline 
substance, excepting a very slight trace of muriate of potash. 
These two experiments therefore prove, 
1st. That wood may by sulphuric acid be converted into a 
coal which in its properties is very different from charcoal, 
although prepared from the same sort of wood ; and that the 
coal thus formed by the action of sulphuric acid, resembles 
by its mode of burning, and by not affording any alkali when 
reduced to ashes, those mineral coals which are devoid of 
bitumen. 
edly. That wood may also be converted into a sort of coal 
by muriatic acid, but in this case some of the vegetable cha- 
racters remain, although, like the former, not any alkali can 
be obtained from the ashes. 
§ VIII. 
Four different solutions have been proposed respecting that 
difficult problem in the natural history of minerals, the origin 
and formation of coal. 
The first is, that pit-coal is an earth or stone chiefly of the 
argillaceous genus, penetrated and impregnated with bitumen. 
But Mr. Kirwan very justly remarks, that the insufficiency 
of this solution is demonstrated by Kilkenny and other coals 
which are devoid of bitumen, and also that the quantity of 
earthy or stony matter in the most bituminous coals bears no 
proportion to the weight of them.* 
* Geological Essays, p. 316. 
