233 
short time, air globules began to form on the leaves, 
and in about six hours sufficient air was collected to 
be examined ; it measured two cubic inches and a 
half, and was nearly pure oxygen gas. Since, in 
this experiment, no gas of any kind was held in so- 
lution by the water, and pure oxygen gas was pro- 
duced, it must have arisen, says Mr Davy, from the 
decomposition of the water, by the combination of 
its oxygen with light, and of its hydrogen with the 
vegetable *. 
516. But although it be granted that the water 
employed, and the surfaces of the leaves, were, in this 
experiment, freed from air, yet the aeriform fluid in 
their substance was not expelled. That such a fluid 
exists in leaves, has been clearly established ; and, 
indeed, Mr Davy's own experiments shew, that, 
when leaves are confined either in nitrogen or in hy- 
drogen gas, they afford oxygen gas in sunshine. 
Thus, a small plant of minianet, exposed to the sun 
in twenty-eight cubic inches of hydrogen gas, yield- 
ed two and a half cubic inches of oxygen ; and in 
experiments made with leaves in nitrogen gas, six- 
tenths of a cubic inch of oxygen were obtained f. 
Mr Davy, indeed, supposed this oxygen to proceed 
from the decomposition of the water of the plant ; 
but this is to take for granted the thing that re- 
quires to be proved ; and the supposition cannot be 
received, until the source of fallacy just stated has 
been first disposed of. 
517. If water were decomposed by plants, no good 
* Beddoes's Contributions, p. 159. t I^id. p. 154. 163. 
