118 
evaporated, however, the colour deepened, and pass- 
ed to brown, affording at length a black carbona- 
ceous residuum. If the vessel contained no oxygen, 
light did not act on the colour of the solution, and 
nitrogen gas experienced no diminution. Light, 
therefore, says M. Berthollet, favours the attraction 
of oxygen, and the combustion of the colourable mat- 
ter, which at first is imperceptible, and gives to the 
solution only a yellow colour ; but soon afterwards 
it is perfected by the action of heat, and the liquor 
becomes brown, and leaves a black residuum *. 
363. With all due deference, however, to the opi- 
nions of this eminent and philosophical chemist, we 
must venture to protest against the employment of 
the term combust ion >> to express that combination 
which oxygen, in these instances, is supposed to form 
with the colourable matters of the solution ; for 
neither in the circumstances of their union, in the 
phenomena which attend it, nor in the results which 
are afforded, does this combination at all resemble 
the ordinary process of combustion. If that process 
be rightly defined, the combination of oxygen with 
certain bodies, accompanied by the phenomena of 
light and heat, and terminating in the destruction of 
the properties of the combustible matter, then no 
process in which such phenomena are not observed, 
and such results afforded, can, with propriety, be 
named combustion. If the mere union of oxygen 
with combustible matter were sufficient to constitute 
combustion, then the living functions of vegetation 
* Elemens de Fait de la Teinture, vol. i. p. 54. 55. 
