326 
vegetation of plants. If, says he, plants be placed to 
grow in a vessel of common air, the v/hole of its oxy- 
genous portion will be gradually changed into car- 
bonic acid ; and if the residual air be afterwards 
washed in lime-water, nothing remains but carburet- 
ted nitrogen gas ; at least, he adds, if oxygen gas be 
added to this residual air, we obtain a fresh portion 
of carbonic acid gas. If, at the commencement of 
the experiment, pure hydrogen gas has been employ- 
ed instead of nitrogen, and the residual air, after 
being washed, be then mixed with oxygen, the for- 
mation of carbonic acid is rendered still more sensi- 
ble, by electrizing the aeriform mixture over lime- 
water, as the acid gas is then at once produced, and 
attracted by the lime-water *. 
627. M. de Saussure, also, relates an experiment 
from which a similar inference may be drawn. He 
placed a plant of ly thrum salicaria in 60 cubic inch- 
es of hydrogen gas, and exposed it to the sun, where, 
like some other plants of the same genus, it vegeta- 
ted for five weeks. On examining the air at this 
period, it was fotind not to suffer any diminution by 
the addition of nitrous gas, neither did it contain any 
carbonic acid ; but when a due proportion of oxy r 
gen was added to it, and it was then fired by the 
electric spark, it yielded water, together with portions 
of carbonic acid and nitrogen gases. Another quan- 
tity of hydrogen gas, which stood by the side of the 
former, but in which no plants had been placed, did 
Physiologic Yeg. ton), iii. p. 116. 
