26 TflE VIIAL 1< UNCTIONS. 



Mr. Palmer. They are proved in a very satis- 

 factory manner by the following experiment of De 

 Candolle. 



Two glass jars were inverted over the same 

 water-bath ; the one fdled with carbonic acid gas, 

 the other filled with water, containing a sprig of 

 mint; the jars communicating below by means of 

 the water-bath, on the surface of wdiich some oil 

 was poured, so as to intercept all communication 

 between the water and the atmosphere. The sprig 

 of mint was exposed to the light of the sun for 

 twelve days consecutively : at the end of each day 

 the carbonic acid was seen to diminish in quantity, 

 the water rising in the jar to supply the place of 

 what was lost, and at the same time the plant 

 exhaled a quantity of oxygen exactly equal to that 

 of the carbonic acid which had disappeared. A 

 similar sprig of mint, placed in ajar of the same 

 size, full of distilled water, but without having 

 access to carbonic acid, gave out no oxygen gas, 

 and soon perished. When, in another experiment, 

 conducted by means of the same apparatus as was 

 used in the first, oxygen gas was substituted in the 

 first jar instead of carbonic acid gas, no gas was dis- 

 engaged in the other jar, which contained a sprig of 

 mint. It is evident, therefore, that the oxygen gas 

 obtained from the mint in the first experiment was 

 derived from the decomposition, by the leaves of 

 the mint, of the carbonic acid, which the plant had 

 absorbed from the water. 



Solar light is an essential agent in effecting this 

 chemical change; for it is never found to take 

 place at night, nor while the plant is kept in the 

 dark. The experiments of Seniiebier would tend 



