80 
vault illuminated by six lamps, which afforded light 
equal to fifty ordinary candles. For the first twenty- 
four hours, no air was afforded, but at the end of 
that time it collected in considerable quantity ; and, 
on being analysed by M. Vauquelin, was found to 
consist principally of nitrogen and carbonic acid, 
with only -^ of oxygen gas *. These experiments 
shew, that though artificial light renders vegetables 
green, yet it is not sufficiently powerful to decom- 
pose carbonic acid in plants, at least in , any consi- 
derable quantity ; and in this respect, therefore, it re- 
sembles, in its operation, the effects of a weak natural 
light. 
315. The probability of the decomposition of car- 
bonic acid by plants, growing in a weak light, is sup- 
ported by many facts, which seem otherwise incapable 
of explanation. The germination of seeds we have 
seen to produce a considerable consumption of oxy- 
gen ; and it might, therefore, be naturally expected 
that plants should continue to affect the air at least 
in an equal degree. The changes, however, effected 
by plants in a state of full growth and vigour, on 
the surrounding air, says Mr Murray, are much less 
than have been imagined, and, when supplied merely 
with water, they are so inconsiderable as not to be 
very perceptible. Hassenfratz, he continues, inclosed 
growing plants in atmospheric air for a month and a 
half or two months at a time ; and though the plants 
grew, the air remained unaltered in volume, and in 
the proportion of oxygen f. This slowness of change 
* Journ. de Phys. torn. hi. p, 124. 
f Syst. Chem. v. iv. p. 54. 
