THE CHEMISTRY OF PHOTOSYNTHESIS 301 



CO ^ HoCO. The final products obtained depend very much upon the 

 amount of water vapor present. Lob was also able to obtain glycoUic 

 aldehyde from carbon monoxide and hydrogen. 



An electrolytic reduction of carbon dioxide under pressures of 10 to 

 15 atmospheres was also accomplished by Fischer and Priziza;^^^ under 

 these conditions formic acid with traces of methyl alcohol were obtained. 

 Though it has also been claimed that carbon dioxide is reduced to formal- 

 dehyde by alpha and beta particles, recent investigations of Lind and 

 Bardwell "^ show that carbon dioxide is not decomposed chemically by 

 alpha-radiation. 



Lunt ^^* was not able to detect any formaldehyde or formic acid in 

 mixtures of carbon dioxide and hydrogen in the corona due to alternat- 

 ing currents of high frequency. 



With the development of the quartz mercury vapor lamp a convenient 

 source of light of short wave length became available. ^^^ These lamps 

 have been made in many different designs for laboratory work so that 

 ultra-violet light of high intensity could be used for a variety of experi- 

 mental work. As carbon dioxide has no absorption bands in the visible 

 portions of the normal spectrum but does show absorption in the ultra- 

 violet, and as it is one of the fundamental principles of photochemistry 

 that there can be no photochemical action without absorption of light, 

 it seemed but natural to try the effect of ultra-violet light on carbon dioxide. 



That water is decomposed by ultra-violet light was reported by Kern- 

 baum ^^® who obtained hydrogen and hydrogen peroxide on illuminating 

 water for ten hours. The formation of hydrogen peroxide from water 

 and oxygen in ultra-violet light was also obser\-ed by Thiele."' Coehn ^^^ 

 found that hydrogen and oxygen unite to form water in ultra-violet light 

 and that the latter is also decomposed into detonating gas by the light. 

 There is thus attained an apparent equilibrium which is not altered by a 

 change of temperature of 150° to 800°. Under the conditions of Coehn's 

 experiment the decomposition of water vapor is 0.00087 to 0.0010 per 

 cent; this corresponds to the thermal equilibrium at about 1250°. 

 Weigert ^^® has made the following calculation in order to give an idea 

 of the magnitude of the factors involved in these reactions. For the 

 photochemical decomposition of liquid water into gaseous hydrogen and 

 oxygen, which have an equilibrium pressure at 17° of 3.4 and 1.7 X lO"-® 



"" Fischer and Priziza, Ber. chem. Gcs., 47, 256 (1914). 



"' Stoklasa, Sebor, Zdobnickv, Compt. rend.. 156. 646 (1913). Usher and Priest- 

 ley, Proc. Roy. Soc, 84 B, 102 (1912). Lind, "The Chemical Efifects of Alpha 

 Particles and "Electrons." Chemical Catalog Co.. 1921, pp. 85, 93, 121. Lind and 

 Bardwell, Jour. Aimr. Chem. Soc, 47, 2675 (1925). 



"'Lunt, Proc. Roy. Soc, 108 A, 172 (1925). Moset and Isgarischew, Zeit. 

 Elektrochcvi.. 16. 613 (1910). 



"'Ellis and Wells. 'The Chemical Action of Ultraviolet Rays," The Chemical 

 Catalog Co.. 1925, p. 30. 



"'Kernbaum. Co^npt. rend.. 149. 273 (1909). 



"'Thiele, Zeit. angezv. Chem., 22, 2472 (1909). 



"'Coehn, Ber. chew. Ges., 43, 880 (1910). 



"'Weigert, "Die Chemische Wirkung des Lichts," Stuttgart, 1911, p. 19. 



