SECT. XXII. CHARCOAL. 455 



while the other parts of the plant are dissipated, it 

 is plain that charcoal must be the residuum of 

 woody fibre, and that the quantity of the one must 

 depend upon the quantity of the other, if they are 

 not rather to be considered as the same. 



Charcoal may be obtained from almost all parts 

 of the plant whether solid or fluid, and it is ren- 

 dered perceptible by means of combustion. It 

 often escapes however, during combustion, under the 

 form of carbonic acid, of which it constitutes one 

 of the elements. 



From a variety of experiments made on different 

 plants and on their different parts, it appears that 

 the green parts contain a greater proportion of 

 charcoal than the rest. But this proportion is 

 found to diminish in autumn, when the green parts 

 begin to be deprived of their glutinous and extrac- 

 tive juice. The wood contains more charcoal than 

 the alburnum, the bark more than both. But this 

 last result is not constant in all plants because the 

 bark is not a homogenous substance, the outer parts 

 being affected by the air and the inner parts not. 

 The wood of the Quercus Robur, separated from 

 the alburnum, yielded from 100 parts of its dried 

 substance 1Q75 of charcoal ; the alburnum 17*5 ; 

 the bark 26 ; leaves gathered in May 80 ; in 

 September 26.* 



But the quantity of charcoal differs also in dif- Proponio 

 ferent plants, as well as in different parts of the plants?* 



* Sauss. sur la Veg. chap. v. sect. x. 

 4 



