360 



PALAEOZOIC TIME — CARBONIFEROUS AGE. 



carbon of the wood is lost as gas, and nearly all the gaseous ingre- 

 dients besides. It has been estimated by* Bischof that 100 parts 

 of wood will not make more than 16 parts of anthracite and 25 

 of bituminous coal. 



Bischof states the conditions and changes as follow : — 

 Ultimate constitution of wood, anthracite, bituminous coal, and 

 asphaltum, — impurities excluded : — 



Wood. Anthracite. Bituminous coal. 



Carbon 49.1 94.04 82.2 



Hydrogen 6.3 1.75 5.5 



Oxygen 44.6 4.21 12.3 



Asphaltum. 

 ....81.6 



If the escaping gases in decomposition are carbonic acid and carburetted 

 hydrogen, the loss of each element for anthracite and bituminous coal would be 



as follows : — 



Carbon 



Hydrogen. 

 Oxygen.... 



Wood. 



49.1 

 6.3 



44.6 



100.0 



For Anthracite. 



Loss. 



34.57 



6.03 



43.95 



84.55 



Coal left, 



14.53 



0.27 

 0.65 



15.45 



Coal left. 



in p. c. 



94.04 



1.75 



4.21 



100.00 



For Bituminous Coal. 



Loss. 



Coal left. 



Coal left in 

 per cent. 



31.0 



18.1 



82.2 



5.1 



1.2 



5.5 



41.9 



2.7 



12.3 



78.0 



22.0 



100.0 



The loss for the anthracite is 60.79 per cent, of carbonic acid, and 24.12 of 

 carburetted hydrogen. 



If the escaping gases were carbonic acid and hydrogen, the last forming 

 water with external oxygen, the whole loss in a similar manner would be — for 

 anthracite 65 per cent., leaving 35 of coal ; and for bituminous coal 58£ per cent., 

 leaving 41J of coal. 



If, again, the part lost is carbonic acid and water, both derived from the ele- 

 ments of the wood, the amount of coal left in case of bituminous coal would 

 be about 54£ per cent. 



There is, therefore, a loss of three-fourths of the wood in the case 

 of bituminous coal, and five-sixths in that of anthracite. Besides this 

 reduction to one-fourth and one-sixth by decomposition, there is a 

 reduction in bulk by compression ; which if only to one-half would 

 make the whole reduction of bulk to one-eighth or one-twelfth. 

 Consequently, it would take eight feet in depth of compact vegetable 

 debris to make one foot of bituminous coal, and twelve feet to 

 make one of anthracite. For a bed of pure anthracite 30 feet thick, 

 like that at Wilkesbarre, the bed of vegetation must have been at 

 least 3G0 feet thick, or, allowing for impurities, over 300 feet. 



(5.) Impurities of the coal. — The impurities of the coal are in part 

 derived from the wood. Silica is contained in the exterior part of 



