362 THE CHEMISTRY OF CREATION. 



the element which they set free, and by the 

 powers of vitality to apply it to the different 

 purposes of their economy. 



The following experiment will doubtless be 

 considered decisive as to the chemical influence 

 of plants over carbonic 

 acid. Dr. Priestley took 

 a sprig of mint and put 

 it into a glass vessel (see 

 Fig.) which contained air 

 mixed with a considerable 

 quantity of carbonic acid. 

 He then put it in a posi- 

 tion where it was well 

 THE SPH IG OF MINT. exposed to the light, and 

 left it for a little time. 



He subsequently analysed the air contained in 

 the jar, and to his astonishment found that all 

 the carbonic acid had disappeared, and the air 

 within the vessel contained more oxygen than 

 common air ! De Saussure performed similar 

 experiments; and he found that not only had 

 carbonic acid disappeared, but that actually a 

 notable amount of oxygen had been added to 

 the air, and the plants under examination had 

 also increased in weight. Boussingault per- 

 formed a yet more conclusive experiment. He 

 enclosed a vine-branch in a glass receiver ex- 

 posed to sun-light, and containing air with a 

 certain proportion of carbonic acid gas. The 



