DECOMPOSITION OF CARBONIC ACID IN THE YELLOW REGION. gj 



pear. M. BECQUEREL, as appears from the Scientific Memoirs, vol. iii., pi. \x.,Jig. 2, 

 has been more fortunate. Although, in the course of a great many experiments, I have 

 often obtained very beautiful results, in which the lines in the indigo and violet spaces 

 were given in great numbers, and many of them of that degree of minuteness as to re- 

 quire a lens to show them distinctly, it has never yet happened to me to see the fixed 

 lines D and E reproduced on a sensitive surface of any kind. 



2] 8. It may be remarked, in conclusion, that just as we see the colorific rays symmet- 

 rically arranged in these interference spectra, and the chemical results expressed by the 

 decomposition of chloride and bromide of silver crowded into a narrow space, compared 

 with what takes place in the prismatic spectrum, so must the same thing hold for the 

 rays of heat, the apparent distribution of which must be totally altered. 



CHAPTER VI. 



EXPERIMENTS PROVING THAT IT IS IN THE YELLOW REGION OF THE SPECTRUM THAT THE 

 REDUCTION OF CARBONIC ACID BY THE LEAVES OF PLANTS TAKES PLACE. 



CONTENTS : Several Imponderable Principle* in the Sunbeam. Sennebiers Experi- 

 ments to determine to which of these the Effect is due. Experiments of Morren and 

 Daubeny. Defects of the Mode of operating with Absorbent Media and Glasses. 



Decomposition of Carbonic Acid in the Prismatic Spectrum. Process of conducting 

 the Experiment. It is in the Yellow Region that the Decomposition takes place. 

 No Gas is evolved in the Violet. 



219. THE elementary views of the constitution and nature of the spectrum which 

 we have given enable us now to return to the physiological problem under discussion. 

 From Chapter II. we see that the process of digestion of plants, so far as we have yet 

 examined it, may be separated into three different chemical actions. 1st. The absorp- 

 tion of carbonic acid and water. 2d. The evolution of a mixture of oxygen and nitro- 

 gen. 3d. The retention by the plant of carbon, hydrogen, oxygen, and nitrogen. 



220. There has, therefore, been a decomposition of carbonic acid, of water, and 

 probably of some uitrogenized compound. 



221. But these extraordinary decompositions have been produced by the agency of 

 the sun. The most energetic reducing agents which we know are required in the 

 hands of chemists to produce some of these effects. When made red hot, the vapour 

 of phosphorus and also potassium will accomplish the deoxydation of carbonic acid. 

 Plants can do the same at 50 Fah. very readily. 



222. If water be exposed to the light in glass vessels, common observation assures 

 us that it never undergoes decomposition. In the same manner carbonic acid in a jar 

 remains without exhibiting any change. We shall soon discover why. under these 

 circumstances, the powerful reducing agency of light is not called into action. 



