ORIGIN OF COAL AND ITS VARIETIES. 



355 



composition, except that in the latter case some of the carbon and 

 much of the hydrogen and oxygen have passed away in the process of 

 change : 



Vegetable matter, cellulose C36H 6 o0 3 o 



Bituminous coal C 26 H 10 O2 



Anthracite " C 4 oH 8 



Graphite " C pure 



The gradual loss of the hydrogen and oxygen is still better shown in 

 the following table, in which the constituents are given in proportion- 

 ate weights instead of equivalents, and the carbon reduced to a con- 

 stant quantity : 



KINDS OF VEGETABLE MATTER AND COALS. 



Carbon. 



Hydrogen. 



Oxygen. 



Cellulose 



100-00 

 100-00 

 100-00 

 100-00 

 100-00 

 100-00 

 100-00 



16-66 

 12-18 

 9-83 

 8-37 

 6-12 

 2-84 



o-oo 



133-33 

 83-07 

 55-67 

 42-42 

 21-23 

 1-74 



o-oo 



Wood 



Peat 



Lignite 







Graphite " 





Now, there are two modes of decomposition to which vegetable 

 matter may be subjected, viz. : 1. In contact with air ; and, 2. Out of 

 contact with air. The first is partly decomposition, and partly oxida- 

 tion by the air (eremacausis) ; the second is wholly decomposition. 



In Contact with Air. — Under these conditions the carbon of the 

 vegetable matter unites with the oxygen of the vegetable matter, form- 

 ing carbonic acid (C0 2 ) ; and the hydrogen of the vegetable matter 

 unites with the oxygen of the air, forming water (H 2 0). Further, it 

 is evident that, for every equivalent of carbon thus lost, there are two 

 equivalents of oxygen and four equivalents of hydrogen lost, so as 

 always to maintain the same relative propor- 

 tion of H, and O viz., the proportion forming 

 water (H 2 0). The final result of this process 

 is pure carbon. It is very improbable, how- 

 ever, that anthracite or graphite is formed in 

 this way ; for vegetable matter, by aerial de- 

 cay, falls to powder. It is very probable, however — nay, almost certain 

 — that a peculiar substance, pulverulent and retaining vegetable struct- 

 ure in a remarkable degree, called mineral charcoal, found very com- 

 monly in some stratified coals has been formed by partial aerial decay, 

 somewhat as represented in the table. Mineral charcoal has a high 

 percentage of carbon, with very little hydrogen and oxygen. 



Out of Contact with Air. — When vegetable matter is buried in 

 mud or submerged in water, its elements react on each other. Some of 



Cellulose C 3 6H 6 oO S o 



Decayed C 35 H560 28 



More decayed. .C34BU2O26 

 Final result. . . . C 2 i 



