327 
not afford any sensible quantity of carbonic acid by 
its combustion with oxygen gas *. The hydrogen 
gas, in the former case, must have derived its carbon 
from the plant, and this carbon, during the combus- 
tion, must have united with the oxygen to form car- 
bonic acid. The production of water arose, no 
doubt, from the direct union of oxygen and hydro* 
gen, Awhile the nitrogen proceeded from the air pre- 
viously existing in the plant. 
628. Still farther to corroborate these results, we 
added to about 22 cubic inches of the residual 
air of vegetation 14 inches of oxygen, after both 
gases had been first washed in lime water. Water of 
potassa was then passed into the jar, in the manner 
before related (625.), and the jar was thus complete- 
ly filled by the aeriform mixture and solution. A 
saucer, filled with mercury, was then passed under 
the jar, which was thus removed from the trough, 
and the water on the outside of the jar was removed 
by a sponge, and only a thin film of that fluid co- 
vered the mercury within. By the 16th day, the 
mercury had risen nearly four-tenths of an inch into 
the jar ; and when, at this period, the jar was raised, and 
a diluted acid poured on the alkaline solution, it exci- 
ted in it a very brisk effevescence. These facts suf" 
ficiently testify that carbon is given out both by seeds 
and plants in a form capable of uniting either with 
nitrogen or hydrogen gas; and they consequently 
prove, that the presence of oxygen gas is not neces. 
sary to abstract this substance. 
* Recherches Cbim. sur la Vegetation, p. 211. 
