302 PHOTOSYNTHESIS 



atmospheres, 1.62 cal. of the radiant energy would have to be fixed 

 as chemical energy in order that the first cubic millimeter of gas were 

 formed. With the electric arcs not more than 0.1 per cent of the elec- 

 tric energy can be converted into chemical energy in this manner. With 

 an illumination surface of one square millimeter and an arc lamp of 50 

 volts and 10 amperes, at a distance of 5 cm., the first gas bubble from a 

 cubic millimeter of water would appear in about two minutes. 



That dry carbon dioxide is decomposed by ultra-violet light was shown 

 by Herchefinkel ^-° who illuminated this gas over mercury and obtained 

 carbon monoxide and the yellow oxide of mercury. 



In 1910 D. Berthelot and Gaudechon ^-^ endeavored to test the old 

 ideas of M. Berthelot, published almost half a century before, that photo- 

 synthesis consisted in a decomposition of carbon dioxide into carbon 

 monoxide and oxygen, and that the former was reduced by hydrogen 

 formed by the decomposition of water into hydrogen and oxygen, formal- 

 dehyde being formed. They found that in ultra-violet light carbon dioxide 

 is decomposed into carbon monoxide and oxygen, especially if there is 

 a substance present to react with the oxygen formed, as phosphorus or 

 hydrogen. Carbon monoxide also reacts with hydrogen to form formalde- 

 hyde. As water is decomposed in ultra-violet light into hydrogen and 

 oxygen, they were able to obtain formaldehyde from carbon monoxide and 

 water. The formaldehyde polymerized rapidly in ultra-violet light. They 

 were not able to obtain formaldehyde directly from carbon dioxide and 

 water, only from carbon dioxide in the presence of hydrogen. Usher 

 and Priestley '^" then reported that they were able to obtain tests for 

 formaldehyde by exposing quartz tubes containing water and carbon diox- 

 ide to ultra-violet light. It is not without interest that when they used 

 open dishes containing water and placed these immediately beneath the 

 lamp, they also obtained tests for formaldehyde even when no carbon 

 dioxide was bubbled through the water. This formaldehyde must have 

 originated from the action of the ultra-violet light on the dust or other 

 impurities which got into the water or from atmospheric carbon dioxide. 

 The latter must have been very small, while it is well known that there 

 are a great many substances which form formaldehyde in ultra-violet light. 



Immediately following these publications appeared those of Stoklasa ^-^ 

 and his collaborators. The results of these authors are again at variance 

 with those of Berthelot and Gaudechon and of Usher and Priestley. Stok- 

 lasa concluded : that by the action of ultra-violet light on water and car- 

 bon dioxide in the absence of potassium hydroxide neither formaldehyde 

 nor carbohydrates are formed. Formaldehyde is formed from carbon 

 dioxide by the action of ultra-violet light only when there is present hydro- 



'^ Herchefinkel, Compt. rend., 149, 395 (1909). 

 '"Berthelot and Gaudechon, Compt. rend., 150, 1690 (1910). 

 ^'^ Usher and Priestley, Proc. Roy. Soc, 84 B, 101 (1911). 



"'Stoklasa and Zdobnicky, Biochein. Zcit.. 30, 432 (1911). Stoklasa, Sebor and 

 Zdobnicky, ibid., 41, 2>2>Z (1912) ;. 54, 330 (1913). Lob, ibid., 48, 257 (1913). 



