INTO BROWN OR WOOD COAL. 371 



certain quantity of carbonic acid, its composition 

 indicates very plainly the manner in which it has 

 been produced. 



The coal of the upper bed is subjected to an in- 

 cessant decay by the action of the air, by means of 

 which its hydrogen is removed in the same manner 

 as in the decay of wood. This is recognised by the 

 way in which it burns, and by the formation of car- 

 bonic acid in the mines. 



The gases which are formed in mines of wood coal, 

 and cause danger in their working, are not combus- 

 tible or inflammable as in mines of mineral coal ; 

 but they consist generally of carbonic acid gas, and 

 are very seldom intermixed with combustible gases. 



Wood coal from the middle bed of the strata at 

 Ringkuhl gave on analysis 65*40, — 64*01 carbon and 

 4*75, — 4*76* hydrogen; the proportion of carbon 

 here is the same as in specimens procured from 

 greater depths, but that of the hydrogen is much 

 less. 



Wood and mineral coal are always accompanied 

 by iron pyrites (sulphuret of iron) or zinc blende 

 (sulphuret of zinc); which minerals are still formed 

 from salts of sulphuric acid, with iron or zinc, during 

 the putrefaction of all vegetable matter. It is pos- 

 sible, that the oxygen of the sulphates in the layers 

 of wood coal is the means by which the removal of 

 the hydrogen is effected, since wood coal contains 

 less of this element than wood. 



According to the analysis of Richardson and Reg- 

 nault, the composition of the combustible materials 

 in splint coal from Newcastle, and cannel coal from 

 Lancashire, is expressed by the formula C24 H13 O. 

 When this is compared with the composition of 

 woody fibre, it appears that these coals are formed 

 from its elements, by the removal of a certain quan- 

 tity of carburetted hydrogen and carbonic acid in 



* The analysis of brown coal from Ringkuhl, as well as all those of 

 the same substance given in this work, have been executed in this labo- 

 ratory by M. Kiihnert of Cassel. — L. 



