182 THE FORCE INCLUDED IN PLANTS. [MEMOIR XL 



interesting subject. It had been asserted by Rumford 

 that many other substances besides the leaves of plants 

 would evolve oxygen gas. He specified raw silk and 

 cotton fibres. My investigation commenced by an exam- 

 ination of this assertion. I soon found that two totally 

 distinct things had been confounded. Ordinary water 

 contains, as has been said, carbonic acid in solution, but 

 it also necessarily contains the ingredients of atmospheric 

 air. To this, for the sake of distinctness, the perhaps in- 

 correct designation of water-gas may be given. Since 

 oxygen is very much more soluble than nitrogen, this 

 dissolved gas differs in composition from atmospheric 

 air. It is relatively richer in oxygen. 



I very soon found, on exposing raw silk, spun glass, 

 and other such fibres, immersed in water, to the sun, that 

 Rumford's assertion was correct gas -bubbles were set 

 free; but his inference was incorrect the gas did not 

 come from decomposed carbonic acid ; it was merely the 

 water-gas of the water. I was thus able to separate the 

 true from the false portion of the experiment. And 

 though I thus dispose of the subject in a few words, it is 

 perhaps due to the labor that was expended to say that 

 it cost several weeks of uninterrupted work and many 

 scores of analyses before I felt absolutely certain that 

 this was the indisputable interpretation of Rumford's 

 experiments. 



Now as a guide to a correct exposition of the experi- 

 ments that I have to relate, it must be borne in mind that 

 the assumption of a green color by a germinating plant 

 and the decomposition of carbonic acid by it are identical 

 events. Or, perhaps, to speak more correctly, the latter 

 is the cause, the former the effect. 



At that time very incorrect views of the nature of the 

 sun -rays were entertained. It was believed that they 

 contained three distinct principles: (1) heat, (2) light, (3) 



