318 DECOMPOSITION OF WOOD, COAL, ETC. 



ducts of the processes of decomposition termed 

 decay and putrefaction. We can easily ascertain by 

 analysis the manner in which their constituents 

 have been changed, if we suppose the greater 

 part of their bulk to have been formed from woody 

 fibre. 



But it is necessary before we can obtain a distinct 

 idea of the manner in which coal is formed, to con- 

 sider a peculiar change which woody fibre suffers 

 by means of moisture, when partially or entirely 

 excluded from the air. 



It is known, that when pure woody fibre, as linen, 

 for example, is placed in contact with water, con- 

 siderable heat is evolved, and the substance is con- 

 verted into a soft friable mass which has lost all 

 coherence. This substance was employed in the 

 fabrication of paper before the use of chlorine, 

 as an agent for bleaching. The rags employed 

 for this purpose were placed in heaps, and it was 

 observed, that on their becoming warm a gas was 

 disengaged, and their weight diminished from 18 

 to 25 per cent. 



When sawdust moistened with water is placed 

 in a closed vessel, carbonic acid gas is evolved in 

 the same manner as when air is admitted. A true 

 putrefaction takes place, the wood assumes a white 

 colour, loses its peculiar texture, and is converted 

 into a rotten friable matter. 



The white decayed wood found in the interior 

 of trunks of dead trees which have been in 



