MEMOIR X.] THE DECOMPOSITION OF CARBONIC-ACID GAS. 



MEMOIR X. 



ON THE DECOMPOSITION OF C AKBONIC ACID GAS BY 

 PLANTS IN" THE PRISMATIC SPECTRUM. 



From the Proceedings of the American Philosophical Society, May, 1 843 ; Phil- 

 osophical Magazine, Sept., 1843; American Journal of Science and Arts, Vol. 

 XXVI., 1843; Philosophical Magazine, Sept., 1844. 



CONTENTS: The decomposition of carbonic acid by light formerly at- 

 tributed to the violet ray. It can be successfully accomplished in the 

 prismatic spectrum. It takes place not in the violet but in the yellow 

 ray. Decomposition by yellow absorbent media. Analysis of the gas 

 evolved ; it always contains nitrogen. Decomposition of alkaline car- 

 bonates and bicarbonates. Analysis of the gas evolved in different rays. 



FOR many years it has been known that the green 

 parts of plants, under the influence of sunlight, possess 

 the power of decomposing carbonic acid, and setting 

 free its oxygen. It is remarkable that this, which is a 

 fundamental fact in vegetable physiology, should not 

 have been investigated in an accurate manner. The 

 statements met with in the books are often far from 

 being correct. It is sometimes said that pure oxygen 

 gas is evolved, that the decomposition is brought about 

 by the so-called " chemical rays;" these and a multitude 

 of such errors pass current. So far as my reading goes, 

 no one has yet attempted an examination of the phe- 

 nomena by the aid of the prism, the only way in winch 

 it can be correctly discussed. 



In a paper by Dr. Daubeny, inserted in the Philosoph- 

 ical Transactions for 1836, two facts, which I shall verify 

 in this communication, are fully established. These are, 

 1st, the occurrence of nitrogen gas in mixture with the 



