ATTENDrSG THE FOBMATfON OF COAL, &c. 259 



castle, gave the formula C^ Hj, Oi. The analysis of 

 coal from the Oakweli Gate colliery, near Gateshead, and 

 from the Hebbum colliery, corresponds very nearly to this 

 formula. Of course the greater number of coals and can- 

 nels will vary from it more or less, but it may be taken as 

 the expression of a general formula. 

 Now 1 atom of wood C. 36 H. 22 0.22 



Minus 9 atoms carbonic acid C. 9 0. 1 8 



„ Satomswater H. 3 O. 3 



„ 8 atoms carburetted hydr. C 3 H. 6 



== C. 24, H. 13, O. the composition of co^ 



So that all the elements of the vegetable fibre have partici- 

 pated in the decomposition; and the wood, in its conversion 

 into coal, has evolved from its structure 9 atoms carbonic 

 acid, 3 atoms water, and 3 atoms light carburetted hydrogen. 

 It would appear, that in the earlier stages of decomposition, 

 when the air had partial access to the decaying matter, and 

 oxygen existed in the mass as a main constituent, that the 

 carbon and hydrogen combined with this agent, in prefer- 

 ence to uniting with each other, as might, from the immense 

 combining or chemical energy of oxygen, have been antici- 

 pated, and that thus, during these periods, only water and 

 carbonic acid would be evolved, or vdth a very minute pro- 

 portion of carburetted hydrogen. The wood coal or brown 

 coal of Lavbach in Hesse-Darmstadt is composed of C. 33, 

 H. 21, O. 16, and differs from fresh wood, therefore, by 

 the elements of 3 atoms carbonic acid and 1 atom of hydro- 

 gen. The wood coal (brown coal) of Ring Kuhl, near 

 Cassel, is much further decomposed, and is losing the woody 

 structure. It contains C. 32, H. 15, O. 9, and differs from 

 wood by the loss of 4 atoms carbonic acid, 5 atoms water, 

 and two atoms hydrogen. There can be no doubt that the 

 surplus hydrogen has been removed in both these cases by 

 external oxidation. The gas eliminated in mines of wood 

 coal is invariably carbonic acid, and never contains carbu- 



