THE CHEMISTRY OF PHOTOSYNTHESIS 265 



nitely established by cle la Motte '" who ol)tainecl adipic acid by the reduc- 

 tion of saccharic acid with hydrindic acid. 



Another contribution to the theory was made through the investigations 

 of the Russian chemist Butlerow.-" By the action of methyl iodide on 

 silver oxalate he had obtained a white solid substance which he called 

 dioxymethylene and to which he ascribed the formula CjHiOo. By treat- 

 ing the substance with alkalies he obtained a sugarlike substance which he 

 called methyleneitan, with the formula CoHioOq and which he considered 

 a sugar: "C'est le premier exemple de la production synthetique d'une 

 substance ayant les allures d'un corps sucre au moyen des composes les 

 plus simples de la chimie organique." After Hofmann had discovered 

 formaldehyde in 1869 and had shown that Butlerow's dioxymethylene was 

 a polymerized form of his formaldehyde, which from vapor density de- 

 terminations had the formula CHoO, the question arose as to how six 

 formaldehyde molecules could unite to form a hexose molecule and conse- 

 quently what was the distribution of the hydroxyl groups in a hexose such 

 as glucose. 



A few years later this question was discussed by Baeyer ^^ in his inter- 

 esting paper entitled ''Uel^er die W'asserentziehung und ihre Bedeutung 

 fiir das Pflanzenleben und die Gahrung.'' He showed that more than one 

 hydroxvl group was very rarely united to a single carbon atom, the group 



OH 



C in most cases spontaneously goes over into C= O. In glyoxylic 



\ 



OH 

 and mesoxalic acids both forms are known as is also the case with chloral- 

 hydrate ; the presence of negative elements as O and CI seem to stabilize 

 the double hydroxyl grouping. These views were applied to the formation 

 of sugar from formaldehyde as indicated by Butlerow's experiments. 



Baeyer's theoretical deductions on this subject have been so much 

 quoted and have, in fact, been taken as the starting point of a great deal 

 of work on photosynthesis that it may not be amiss to give here his own 

 words : 



"Ein Vorgang von grosser Wichtigkeit gehort aber jeden falls hierhin, 

 namlich die Bildung von Methylenitan aus dem Aldehyd der Ameisensaure, 

 Nach Butlerow ensteht ein zuckerartiger Korper, wenn man die wassrige 

 Losung des Formaldehyds mit Alkalien versetzt. Der Formaldehyd hat 

 nach Hofmann's Untersuchungen in Gasform die Zusammensetzung COH2, 

 aber nights hindert, ihn in wassriger Losung als CHslOH). anzusehen. 

 Wenn man nun annimmt, dass je ein OH eines Moleciils mit je einem H 

 eines andern Wasser bildet, und dass die dadurch frei gewordenen 

 C-Afifinitaten sich mit einander verbinden, so bekommt man bei 6 Moleciilen 



"De la Motte, Ber. chcin. Gcs., 12, 1572 (1879). Kiliani, ibid., 19, 1128 (1886). 

 *> Butlerow, Ann. Chem., HI, 242 (1859) ; Compt. rend., 53, 145 (1861). 

 "Baeyer, Ber. chem. Ges., 3, 63 (1864). 



