42 THE SYNTHESIS OF CARBOHYDRATES 



from I o C. to 3 5 C. Wherefore, it is concluded that the carbon 

 dioxide is reduced to formaldehyde, this being the only hydrate 

 having a single carbon atom. 



Other authors consider that formic acid is the more likely 

 intermediate product of early origin. Erlenmeyer was the first 

 to make the suggestion, but it is only of recent years that 

 renewed attention has been given to the possibility. The work 

 of Spoehr has already been mentioned : he demonstrated that 

 carbon dioxide and water are easily reduced to formic acid 

 by means of radiant energy ; from formic acid a sugar-like 

 substance is formed, under conditions such as obtain in an 

 active leaf, which the plant can utilize as a food stuff. He 

 points out that in Grafe's and Baker's work the plants were 

 in reality supplied with formic acid, since formaldehyde is 

 oxidized in the light, and he himself found that plants in- 

 creased in dry weight in an atmosphere of formic acid. Wis- 

 licenus * also supports the formic acid hypothesis. 



Laboratory experiments on the polymerization of formalde- 

 hyde to sugars not infrequently are quoted in support of the 

 formaldehyde hypothesis. 



The first successful attempt to bring about such a polymeriz- 

 ation was made by Butlerow in 1861, who, by the catalytic 

 action of lime water, at the ordinary temperatures, on trioxy- 

 methylene (itself a polymer of formaldehyde), obtained a syrup 

 with a somewhat bitter taste, which he called methylenitan. 

 Subsequently Loew undertook an investigation of the action 

 of milk of lime on formaldehyde, and devised the following 

 experiment. A 4 per cent solution of formaldehyde is mixed 

 with an excess of milk of lime and repeatedly shaken for about 

 half an hour ; after filtering, the mixture is set aside for some 

 days until the pungent smell of formaldehyde has disappeared. 

 The solution, which will now reduce Fehling's solution, yields a 

 colourless syrup with a very sweet taste.f This substance, 

 which is known as crude formose, was examined by Emil 

 Fischer, who found it to consist of a mixture of various 



* Wislicenus : " Ber. deut. chem. Gesells.," 1918, 51, 942. 



fMore recently Ewart (" Proc. Roy. Soc.," Victoria, 1919, 31, 328) has 

 worked out the best conditions for the polymerization of formaldehyde to sugar, 

 and finds that the most rapid reaction is produced by sodium hydroxide in the 

 presence of a neutral calcium salt. 



