DECO]MPOSITION OF WOOD, COAL, ETC. 367 



parts of water take part. But the composition of 

 mouldered wood must change according as the 

 access of oxygen is more or less prevented. White 

 mouldered beech-wood yielded on analysis 47*67 

 carbon, 5*67 hydrogen, and 46-68 oxygen ; this cor- 

 responds to the formula C33 H25 024. 



The decomposition of wood assumes, therefore, 

 two different forms, according as the access of the 

 air is free or restrained. In both cases carbonic 

 acid is generated ; and in the latter case, a certain 

 quantity of water enters into chemical combination. 



It is highly probable, that in this putrefactive 

 process, as well as in all others, the oxygen of the 

 water assists in the formation of the carbonic acid. 



Wood coal (brown coal of Werner) must have 

 been produced by a process of decomposition similar 

 to that of mouldering. But it is not easy to obtain 

 wood coal suited for analysis, for it is generally 

 impregnated with resinous or earthy substances, by 

 which the composition of those parts which have 

 been formed from woody fibre is essentially changed. 



The wood coal, w^hich forms extensive layers in 



the Wetterau (a district in Hesse Darmstadt), is 



distinguished from that found in other places, by 



possessing the structure of wood unchanged, and by 



containing no bituminous matter. This coal was 



subjected to analysis, a piece being selected upon 



which the annual circles could be counted. It was 



obtained from the vicinity of Laubach ; 100 parts 



contained 



Carbon ... 57*28 



Hydrogen . . .6*03 



Oxygen , . . 36" 10 



Ashes .... 0'59 



100-00 



The large amount of carbon, and small quantity 

 of oxygen, constitute the most obvious difference 

 between this analysis and that of wood. It is evi- 

 dent, that the wood which has undergone the change 

 into coal must have parted with a certain portion of 



