THE CHEMISTRY OF PHOTOSYNTHESIS 307 



about these reactions and the term photocatalysts has been apphed to them 

 rather freely and with httle discrimination as to whether the reactions in 

 question are really cases of catalysis or not. Some attempts have also 

 been made to apply various salts of iron and uranium in the photo- 

 chemical reduction of carbon dioxide. Here again the results are quite 

 contradictory. Moore and Webster ^^- claimed to have obtained formal- 

 dehyde by exposing to sunlight solutions of colloidal uranic and ferric 

 hydroxides, through which carbon dioxide was passed. In this case it 

 is not a question of using ultra-violet light, for glass vessels were used 

 and in some cases a "Uviol" mercury arc. On the other hand, entirely 

 negative results with these conditions were obtained by Baur and Reb- 

 mann and by Spoehr in the work previously cited. 



Other attempts in this direction were made by using chlorophyll prepa- 

 rations in various forms. Several claims of having attained photosynthe- 

 sis in preparations of this nature have been made, the basis of these 

 being the formation of formaldehyde, of hydrogen peroxide or of oxygen 

 in the illuminated preparations. Thus Usher and Priestley ^^^ obtained 

 tests for formaldehyde by using chlorophyll in films of gelatine in the 

 presence of catalase. These, as well as the claims of Schryver ^^* and 

 of Chodat and Schweizer,^^^ have been subjected to criticism by Ewart,^^*' 

 Mameli and Pollacci,^^' Euler,^^* and by Curtius and Franzen.^^*^ 



Of direct bearing on these claims are also the results of Warner ^*° 

 who reported that formaldehyde was produced by the photo-oxidation of 

 the chlorophyll films in air. No formaldehyde was formed when such 

 films were illuminated in a. moist atmosphere of nitrogen or of carbon 

 dioxide. The bleaching of the films was found to be effected by hydro- 

 gen peroxide "in the formation of which carbon dioxide can have no 

 share, since there is no decolorisation in moist carbon dioxide free from 

 oxygen." Extracts of carotin also produce formaldehyde and are bleached 

 under similar conditions. At the same time Wager ^*^ published, a paper 

 giving his results of a study of the action of light on chlorophyll. He 

 comes to conclusions very similar to those of Warner. The decomposi- 

 tion of chlorophyll and formation of aldehyde in the light take place 

 as readily in the absence of carbon dioxide as when this is present. These 

 results clearly show that from the formation of formaldehyde in arti- 



^ Moore and Webster, Proc. Roy. Soc, 87 B, 163 (1913) ; 91 B, 196 (1920). 

 "= Usher and Priestley, Proc. Rov. Soc, 77 B, 369 (1906); 78 B, 318 (1906) ; 

 84 B, 101 (1911). 



^Schrvver, ibid.. 82 B. 226 (1909-1910). 



"'Chodat and Schweizer, Arch. Sci. Ph\. cf Nat. (4), 39, 334 (1915). 

 "«Ewart, Proc. Rox. Soc, 80 B. 30 {1908). 



"'Mameli and Pollacci, Atti. accad. Lined (5), 17, 739 (1908). 

 "*Euler, Zeit. physiol. Chew., 59, 122 (1909). 



"'Curtius and Franzen, Sitcbcr. akad. ]Viss. Heidelberg, Math.-nat. KL. 1912, 7, 

 17. 



Warner, Proc Rox. Soc, 87 B, 378 (1914). 



Wager, ibid., 87 B, 386 (1914). 



140 



