60 



the water in which they are immersed, may be infer- 

 red also from the experiments of Count Rumford, 

 who found that dried leaves, fibres of raw silk, and 

 even of glass, when placed in similar circumstances, 

 produced a like separation of air. This air varied in 

 quality, being in many cases less pure than that of 

 the atmosphere * ; and Dr Woodhouse found river 

 water to yield chiefly nitrogen gas ! This varia- 

 tion arises no doubt from the nature of the air which 

 the water contains ; for Mr Dalton remarks, that al- 

 though atmospheric air, expelled from pure water, 

 contains 38 fier cent, of oxygen, yet that, by stagna- 

 tion, it loses a part or all of it, notwithstanding its 

 constant exposition to the atmosphere : and this must 

 arise from some impurities in the water which com- 

 bine with the oxygen, since pure rain water lost 

 none of its oxygen after standing in a bottle more 

 than a year J. Hence, then, we see, that to effect the 

 separation of air from water, the organized structure 

 of the leaf is not only not necessary, but that the 

 quality of the separated air is altogether different from 

 what this supposed function of the leaves ought to 

 supply. No proof, therefore, of the absorption and 

 emission of gases, much less of oxygen gas, by the 

 natural functions of leaves, can be derived from these 

 experiments on plants immersed in water : and were 

 the experiments even more precise, they would not 

 in the least apply to the case of vegetables which 

 nourish in the open air. 



* Philosophical Transactions, 1787. 



f Nicholson's Journal, July 1802. 



; Manchester Memoirs, vol. i. new series. 



