214 
Book IV. 
Leaves a 
residuum of 
charcodl. 
Tonnodh 
tion. 
Theory of 
Chaptal. 
VEGETABLE SUBSTANCES. 
as is well known, a quantity of charcoal behind it, 
which exhibits the exact form, and even the different 
layers of the original wood. As it is the wood alone 
which undergoes this change, while the other compo 
nent parts of the plant are dissipated, we may form some 
notion of the relative proportion of wood which diffe 
rent plants contain by the proportion of charcoal which 
they yield. Now, the quantity of charcoal yielded by 
1.00 of different trees is, according to the experiments of 
Proust, as follows : 
Black ash ........ 0.25 
Guaiacum 0.24 
Pine.... 0.20 
Green oak . . . . ... 0.20 
Heart of oak . . . ...0.19 
Wild ash ........ 0.17 
White ash ....... 0.17 
From the facts above related, it appears that the 
wood of plants is composed of oxygen, carbon, hydro 
gen, azot, and lime. Mr Chaptal supposes that muci 
lage differs from woody fibre merely in containing less 
oxygen. We are certain at least that mucilage or gum 
is composed of the same ingredients ; and Mr Chaptal 
has shewn, that the juices of plants are partly converted 
into a substance similar to woody fibre by oxy-muriatic 
acid, which imparts to them oxygen *. These juices 
contain both gum and resin : after the formation of 
the woody fibre the resin is still unaltered. This gives 
some probability to his opinion, provided it can be 
proved that extract, by combining with oxygen, assumes 
the properties of wood ; for the precipitate observed 
by Chaptal was undoubtedly extract. 
X Ann. de Chim. xxi. 285.