300 PHOTOSYNTHESIS 



ing to Thiel and Strohecker ^°* a strong acid. In what form the carbon 

 dioxide is used in photosynthesis, whether it is dissolved CO2, HCO3-, 

 or CO3- has received Httle attention. Considering the energetics of the 

 reaction, this is a question of considerable importance. There is some 

 evidence (Wilke)^°^ that in water solution carbon dioxide also forms 

 a higher hydrate, C(OH)4. which is a very weak acid. Schaum ^""^ in a 

 theoretical consideration of the mechanism of photosynthesis assumes the 

 formation of C(OH)4, which then undergoes a rearrangement with the 

 formation of a peroxide, the latter, through the action of catalase, analo- 

 gous to the conception of Willstatter and StoU, breaking down to formalde- 

 hyde, water and oxygen : 



C(OH)4 ^ HX(OOH), -^ HXO + H3O + O,. 



Schaper i"' studied the action of carbon dioxide on ferro oxalate. 

 While at ordinary pressures carbon dioxide does not oxidize the com- 

 plex K2Fe(C204)o. at pressures of 40-60 atmospheres about 10 per cent 

 oxidation was observed. At ordinary pressures and saturation of potas- 

 sium oxalate Schaper calculates that equilibrium would be attained when 

 0.2 per cent of the ferro complex had been oxidized. 



A direct reduction of carbon dioxide in water solution to formaldehyde 

 was accomplished by Fenton ^°« by the use of metalHc magnesium. The 

 presence of weak alkalies gready favors the amount of reduction, due 

 probably to bicarbonate formation. Formic acid is also reduced in this 

 manner to formaldehyde. That a similar role should be ascribed to the 

 magnesium which constitutes part of the chlorophyll molecule in the photo- 

 synthetic process there is no reason for believing. 



Many attempts have also been made to reduce carbon dioxide under 

 conditions which more nearly simulated the process of photosynthesis than 

 is the case in the reactions with metallic magnesium or atomic hydrogen. 

 Thus Losanitsch and Jovitschitsch,^^^ Berthelot "" and especially W. 

 Lob ^" have studied the effect of the silent electric discharge on mixtures 

 of carbon dioxide and water. By this means a variety of products was 

 obtained • among these were formic acid and formaldehyde. The follow- 

 incr reactions are involved : 200^ = 2CO + O^ ; CO + H^O = HCOOH ; 

 CO + H2O = CO2 -f H2 ; 3O2 = 2O3 ;2H2 + 30^ = 2H2O2 + O3 ; H^ + 



^"^ Thiel, Ber. chem. Ges., 46, 241 (1913). Thiel and Strohecker, ibid., 47, 945 

 ^914) Vorlander and Straube, ihid., 46, 172 (1913). 



^"nVilke Chcm Ztn 39, 309 (1915). Walker, Jour. Chcm. Soc, 77, 1 (1900). 

 Schiplev and McHaffie. /o«r. Soc. Chcm. Ind., 42, 319, 321 (1923). Kolthoff, 

 Z?/f. iVa/ir. Gf-ntmm., 43, 184 (1922) id , v •. r; ^, / 00 



^Schaum, Bcr. chem. Ges., 51, 1372 (1918). Pusch, Zcit. Elcktrochcm., 22, 



^^^^"^^ Schaper, Zeit. physik. Chem., 72, 320 (1910). 



^"^ Fenton, Jour. Chem. Soc, 91, 687 (1907) ,^oc^n^ 



^** Losanitsch and Jovitschitsch, Ber. chem. Ges., 30, 135 (1897). 



"«Berthelot Combt. rend., 126, 610 (1898); 131. 772 (1900). 



"lL5b, iMndw. Jahrb., 35, 541 (1906) ; Zeit. Elektro chem., 11 745 (1906) ,12 

 282 (1906). Holt, Jour. chcm. Soc, 95, 30 (1909). Gibson, Ann. Bot., 22, 118 

 (1908). 



