77 
cubic inches of carbonic acid originally present, but 
which had now entirely disappeared, the atmosphere 
was increased by 14.75 cubic inches of oxygen gas, 
and seven cubic inches of nitrogen, which, together, 
supply exactly the bulk of the carbonic acid lost *. 
Similar experiments were made with plants of mcntha 
aquatica, ly thrum salicarta, pinus genevemis, and 
cactus opuntia, and nearly with the same results ; the 
carbonic acid having, in all cases, more or less com- 
pletely disappeared, and its place being supplied by 
nearly an equal quantity of oxygen, with a small 
portion of nitrogen gas f. 
311. The foregoing experiments seem to afford 
undeniable evidence of the decomposition of carbonic 
acid by growing vegetables, when they are exposed 
to the direct rays of the sun, since not only did this 
acid uniformly disappear, in circumstances where no 
substance was present, which could attract or com- 
bine with any considerable portion of it, but a large 
volume of oxygen gas was produced, without the 
vegetables having ua-dergone any change, by which 
they can have been rendered able to supply it. That 
this superabundant oxygen did not proceed from the 
decomposition of the plant, or of the water which it 
contained, is farther proved by the results of the ex- 
periments (305.), made in pure atmospheric air. 
These experiments were purposely made at the same, 
time, with similar plants, and under the same cir- 
cumstances ; and yet, as we have seen, no absolute* 
* Recherches, p. 41. 
f Ibid, p. 44. & *eq. 
