328 FORMATION OF COAL. 



last of which had not been observed, until its exist- 

 ence in these gases was pointed out tyBischoff. The 

 analysis of fire-damp after it had been treated with 

 caustic potash showed its constituents to be, 



Gas from an 

 abandoned Gerhard spas- Gas from a 



mine near Sa 8 e near Lu ~ mhie near 

 Wallesweiler. "enthal. Liekwege. 



Vol. Vol. Vol. 



Light carburetted hydrogen &/-S6 83-08 89-10 



Olefiantgas 6-32 1-98 16-11 



Nitrogen gas 2*32 14-1)4 4-79 



100-00 ' 100-00 100-00 



The evolution of these gases proves that changes 

 are constantly proceeding in the coal. 



It is obvious from this, that a continual removal 

 of oxygen in the form of carbonic acid is effected 

 from layers of wood-coal, in consequence of which 

 the wood must approach gradually to the composi- 

 tion of mineral coal. Hydrogen, on the contrary, 

 is disengaged from the constituents of mineral coal 

 in the form of a compound of carbo -hydrogen ; a 

 complete removal of all the hydrogen would convert 

 coal into anthracite. 



The formula C36 H22 O22, which is given for 

 wood, has been chosen as the empirical expression 

 of the analysis, for the purpose of bringing all the 

 transformations which woody fibre is capable of 

 undergoing under one common point of view. 



Now, although the correctness of this formula 

 must be doubted, until we know with certainty the 

 true constitution of woody fibre, this cannot have 



