194 
the complete decomposition of carbonic acid was ef- 
fected, and the charcoal appeared in the form of a 
black powder *. Mr Davy, also, remarked, that po- 
tassium readily inflamed and oxidated in carbonic 
gas f ; and Dr Henry and Mr Dalton have likewise 
ascertained, that, by a continued repetition of elec- 
tric shocks, this gas may be decomposed, even while 
it retains its elastic form J. In all all these examples, 
however, the decomposition is effected under circum- 
stances absolutely destructive to the vegetable body $ 
and, except when potassium is employed, caloric, or 
the intense agency of positive electricity, is called in- 
to action. 
4-65. But at the ordinary atmospheric temperature., 
and even in a degree below zero (299.), carbonic 
acid is decomposed in plants by the power of solar 
light ; and since this decomposition always precedes 
(378.) the formation of the green colour, and this 
green colour is effected (437.) by the sole agency of 
the chemical rays, it follows, that these rays alone 
are essentially concerned in the operation. If, there- 
fore, these rays, in their chemical action, be consi- 
dered to resemble negative electricity, they must be 
held to exert an attraction towards the carbon or in- 
flammable base, and a repulsion towards its oxygen, 
in the same manner as in the decomposition of wa- 
ter by the negative pole of the Voltaic battery, its 
hydrogen is attracted and its oxygen is repelled. 
Consequently, the oxygen of the acid will pass off in 
* Phil. Trans. 1791, p. 183. f Ibid. 1SO) ; p. 73, 
J Dalton's Chem, Phil, part 2. p. 382. 
