372 CONVERSION OF WOOD INTO MINERAL COAL. 



the form of combustible oils. The composition of 



both of these coals is obtained by the subtraction 



of 3 atoms of carburetted hydrogen, 3 atoms of 



water, and 9 atoms of carbonic acid from the formula 



of wood. 



C36H22 022 = wood 



C12 H9 021 



3 atoms of carburetted hydrogen C 3 H6 

 3 atoms of water . . H 3 03 



9 atoms of carbonic acid . C 9 018 



Mineral coal C24 H13 O 



Carburetted hydrogen generally accompanies all 

 mineral coal ; other varieties of coal contain volatile 

 oils, which may be separated by distillation with 

 water. (Reichenbach.) The origin of naphtha is 

 owing to a similar process of decomposition. Caking 

 coal from Caresfield, near Newcastle, contains the 

 elements of cannel coal, minus the constituents of 

 olefiant gas C4 H4. 



The inflammable gases which stream out of clefts 

 in the strata of mineral coal, or in rocks of the coal 

 formations, always contain carbonic acid, according 

 to a recent examination by BischofF, and also car- 

 buretted hydrogen, nitrogen, and olefiant gas ; the 

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

 istence in these gases was pointed out by Bischoff. 

 The analysis of fire-damp, after it had been treated 

 with caustic potash, showed its constituents to be. 



Gas from an 



abandoned Gerbard's pas- Gas from a 



mine near sage near Lu- mine near 



Wallesweiler. isenthal. Liekwege. 



Vol. Vol. Vol. 



Light carburetted hydrogen 91-36 8308 79-10 



Olefiant gas. . 632 1-98 16-11 



Nitrogen gas . . 2-32 14-94 4-79 



100-00 100-00 10000 



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 composition 



