THE THEORIES OF PHOTOSYNTHESIS 13 



was constantly evolved in the flask, and by the combined action 

 of the electrolysis of the KHCO3 solution, and the CO2 which 

 was run into the flask, potassium bicarbonate was continuously 

 being, formed. These are the conditions which Stoklasa consid- 

 ered essential for the formation of formaldehyde. However, no 

 formaldehyde was ever obtained. 



It is important to note that in these experiments formic acid 

 was found to be the only reduction product. Even without the 

 nascent hj^drogen an aqueous solution of carbon dioxide can be 

 reduced to formic acid by exposure to ultraviolet light. Larger 

 amounts of formic acid are formed from potassium bicarbonate, 

 which is probably due to the fact that solutions of the latter salt 

 contain a higher concentration of HCO3 ions than does a solution 

 of carbonic acid. In view of these facts, the old idea proposed 

 by Erlenmeyer that formic acid may play an important role in 

 the photosynthetic process gains new significance. 



As was mentioned above repeated attempts have been made to 

 obtain formaldehyde from formic acid by means of exposure to 

 ultraviolet light and sunlight. Many of the plant acids do yield 

 formaldehyde on being exposed even a short time to sunlight. 

 However, it was never possible to detect a reduction of formic 

 acid to formaldehyde. On the other hand, it has been possible 

 to synthesize a sugar-like substance from formic acid by means 

 of sunlight or ultraviolet light. When solutions of formic acid 

 were exposed to sunlight or ultraviolet rays, for from ten to fifty 

 hours, and the water was then distilled off, there remained a 

 yellow, non-volatile syrup. This substance has many of the 

 properties of a sugar — it reduces Fehling's solution as well as 

 Tollen's solution. Algae develop in solutions thereof in the dark, 

 so can evidently use the substance as a source of carbon. When 

 oxidized with nitric acid, oxalic acid is formed therefrom. 



Unfortunately the amount of this substance formed in any one 

 experiment is not sufficiently large so that the necessary chemical 

 investigations can be made. This is due to the fact that the ac- 

 tion is reversible, that is, not only is the substance formed in the 

 light, but light also easily decomposes it; so that what is finally 

 obtained is the difference between these two actions proceeding 





