FORMATION OF WOOD COAL. 369 



coal appears from these formulae to have taken place 

 under circumstances which did not entirely exclude 

 the action of the air, and consequent oxidation and 

 removal of a certain quantity of hydrogen. 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 elements 

 of carbonic acid have been separated from the wood 

 either alone, or at the same time with a certain quan- 

 tity 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 w^ood 

 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 temperature of from 334° to 352° F. 

 (150°— 160° C), and under a corresponding pres- 

 sure. The ashes of the wood amounted to 0*51 per 

 cent. ; a little less, therefore, than those of the Lau- 

 bacher coal ; but this must be ascribed to the pecu- 

 liar circumstances under which it w^as formed. The 

 ashes of plants examined by Berthier amounted 

 always to much more than this. 



The peculiar process by which the decomposition 

 of these extinct vegetables has been effected, namely, 

 a disengagement of carbonic acid from their sub- 

 stance, appears still to go on at great depths in all 

 the layers of wood coal. At all events it is remark- 

 able, that springs impregnated with carbonic acid 

 occur in many places, in the country between Meiss- 

 ner, in the electorate of Hesse, and the Eifel, which 

 are known to possess large layers of wood coal. 

 These springs of mineral water are produced on the 

 spot at which they are found ; the springs of com- 



