38 



thus it appears, that nitrogen gas exerts no direct in- 

 fluence on plants, so it is probable that they produce 

 no change upon it ; and we may conclude, there- 

 fore, that this gas, in its simple and uncornbined 

 form, is altogether inactive in the process of vege- 

 tation. 



30. We have next to inquire into the necessity 

 and use of oxygen gas, and the changes which it 

 undergoes in vegetation. It has been shewn by Dr 

 Ingenhousz, that plants do not, any more than seeds, 

 grow in any species of air unless it contain a portion 

 of oxygen gas, and this gas have access to their 

 leaves : that they vegetate very well in atmospheric 

 air and in oxygen gas ; and, therefore, that this lat- 

 ter gas is necessary to vegetation *. What then are 

 the changes which it suffers in that process ? By the 

 experiments of Dr Woodhouse, we are taught, that 

 plants growing in earth and confined in a glass ves- 

 sel of atmospheric air render it impure, and that car- 

 bonic acid is formed : that when confined in oxygen 

 gas, previously well washed in lime-water, carbonic 

 acid is, in like manner, produced : and that the 

 quicker this acid is generated, the sooner does the 

 plant die f- These facts derive confirmation from 

 the following experiment. Some peas, growing in 

 a small pot of mould to the height of several inches, 

 were placed under a jar of atmospheric air inverted 

 over water ; and a common wine-glass, the foot of 

 which was broken off, was filled with lime-water, 



* Thomson's System of Chemistry, vol. iv. p. 290. 

 f Nicholson's Journal, July 1802, p. 152. 



