90 TANNING MATTE&, &6... 



Exoerim nt *^^^^^^^<^ water was poured ; the whole was decanted into 

 &c. ott an arti- a filter, was repeatedly washed, and was afterwards dried 

 ficiai substance without heat. 1'he sawdust then appeared, as I have 

 racters of tan* o^^served, brownish-black, and was pulverulent. It 

 ning matter. burned with some tlame, 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, except- 

 ing 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 af- 

 fording any alkali wben reduced to ashes, those mineral 

 coals which are devoid of bitumen. 



2dly. That wood may also be converted into a sort of 

 coal by muriatic acid, but in this case some of the vege- 

 table characters remain, although, like the former, not 

 any alkali can be obtained from the ashes. 



4VIII. 



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, t\i^t 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 insuf- 

 ficiency 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 bitu- 

 minous coals bears no proportion to the weight of 

 them *. 



The second and most prevailing opinion is, that mineral 

 coal is of vegetable origin, that the vegetable bodies 

 have, subsequent to their being buried under vast strata 

 of earth, been mineralized by some unknown process, of 



Geological Essays, p. 3x6* 



which, 



