ways to contain a large portion of air * ; and M. 
Coulomb, on piercing an Italian poplar, observed the 
sap to flow out abundantly, with a continued noise of 
air bubbles, which ascended and burst in the ori- 
fice |. These bubbles M. Senebier found, in some 
cases at least, to be carbonic acid ; for if the clear 
sap of the vine was mixed with lime water, a white 
precipitate was formed, which could again be dissi- 
pated with effervescence by a few drops of nitric 
acid J. M. Vauauelin also, in his analysis of the sap 
of the elm, found it to contain lime, which was held 
in solution by carbonic acid, of which there existed a 
considerable excess in the sap ||. These facts, there- 
fore, afford sufficient evidence of the existence of this 
acid gas in the sap of plants, and of its escape when 
this ip comes into contact with the air. 
319. Besides the carbonic acid, which thus enters 
the substance of the plant by the medium of water, 
other gases, dissolved in water, in the same way gain 
admission into the vegetable body. Thus, the expe- 
riments of De Saussure seem clearly to prove, that 
oxygen gas may, in this manner, be carried into the 
vegetable ^J" ; and since nitrogen gas is likewise con- 
tained, in a smaller proportion, in water, it may be 
presumed, that, by a similar conveyance, it gains ad* 
mission also, and is again given out unaltered in those 
* Phil. Transact.- 1805. 
f Phil. Magaz. vol. ix. p. 310. 
J Physiol. Veg. torn. ii. p. 343. 
[I Thomson's Chem. vol. iv. p. %6 e 2. 1st edit. 
H Recherches Chim. p. ill. 
