168 THE DECOMPOSITION OF CARBONIC-ACID GAS. [MEMOIR X. 



oxygen, an observation originally due to Saussure, or 

 some earlier writer; and, 2d, that the act of decompo- 

 sition is due to the LIGHT of tlie sun. This latter ef- 

 fect, obtained by employing colored glasses or absorb- 

 ent media, has not been generally received. Doubt will 

 always hang about results obtained in that way, and 

 nothing but an examination by the prism can be satis- 

 factory. 



In its connection with organic chemistry and physi- 

 ology the experiment of the decomposition of carbonic 

 acid by leaves assumes extraordinary interest. When 

 we remember that this decomposition is the starting- 

 point for organization out of dead matter, that com- 

 mencing with this action of the leaf the series of or- 

 ganized atoms goes forward in increasing complexity, 

 and blood and flesh and cerebral matter are at its ter- 

 minus, it is clear that unusual importance belongs to 

 precise views of this the commencing change. The rays 

 of the sun are the authors of all organization. 



There is but one way by which the question can be 

 finally settled it is by conducting the experiment in 

 the prismatic spectrum itself. When we consider the 

 feebleness of effect which takes place by reason of the 

 dispersion of the incident beam through the action of 

 the prism, arid the great loss of light through reflection 

 from its surface, it might appear to be a difficult opera- 

 tion to eifect a determination in that way. Encouraged, 

 however, by the purity of the skies in America, I made 

 the trial, and met with complete success. 



When the leaves of plants are placed in water from 

 which all air has been expelled by boiling, and exposed 

 to the sun's rays, no gas whatever is evolved from them. 

 When they are placed in common spring or pump wa- 

 ter, bubbles quickly form, which, when collected and 

 analyzed, prove to be a mixture of oxygen and nitro- 



