INTO BROWN OR WOOD-COAL. 323 



The formation of both these specimens of wood 

 coal appears from these formulae to have taken 

 place under circumstances which did not entirely 

 exclude the action of the air, and consequent oxi- 

 dation and removal of a certain quantity of hydro- 

 gen. Now the Laubacher coal is covered with a 

 layer of basalt, and the coal of Ringkuhl was taken 

 from the lowest seam of layers, which possess a 

 thickness of from 90 to 120 feet ; so that both may 

 be considered as well protected from the air. 



During the formation of brown coal, the ele- 

 ments of carbonic acid have been separated from 

 the wood either alone, or at the same time with a 

 certain quantity of water. It is quite possible that 

 the difference in the process of decomposition may 

 depend upon the high temperature and pressure 

 under which the decomposition took place. At 

 least, a piece of wood assumed the character and 

 appearance of Laubacher coal, after being kept 

 for several weeks in the boiler of a steam engine, 

 and had then precisely the same composition. The 

 change in this case was effected in water, at a tem- 

 perature of from 334 to 352 F. ( 1 50 160 C.), and 

 under a corresponding pressure. The ashes of the 

 wood amounted to 0*5 1 per cent. ; a little less, there- 

 fore, than those of the Laubacher coal; but this must 

 be ascribed to the peculiar circumstances under 

 which it was formed. The ashes of plants exa- 

 mined by Berthier amounted always to much more 

 than this. 



Y 2 



