Oxidation Product of Chlorophyll Extracts. 381 



comparative lack of sensitiveness and the fact that it cannot be used 

 quantitatively, must be regarded as most unsatisfactory for work of this 

 type even when applied with great care, since it has no specificity, and the 

 escape of sulphur dioxide from the solution causes the appearance of the red 

 colour in the absence of aldehyde. 



Illumination of Films in an Atmosphere of Nitrogen. 



It was next necessary to determine the nature of the decomposition 

 described above, in order to eliminate it, and thus ascertain whether photo- 

 synthesis was taking place at the same time. With this object in view, 

 films in sealed glass tubes containing alkaline pyrogallate solution were 

 exposed to bright sunlight for periods of one, one and a half, two, and 

 two and a quarter hours, and to sunshine intermittently bright for periods of 

 five and a half and twelve hours (twice). No trace of formaldehyde could be 

 detected in any of these films after exposure. In carbon-dioxide-free films 

 which received equal exposures over potash solution, the amounts formed 

 were always very considerable. 



A tube containing recently boiled water and a film of chlorophyll extract 

 was six times alternately exhausted and filled with nitrogen, which had 

 been passed through potash solution and over copper heated to redness. 

 After the final filling the tube was sealed off and exposed to bright 

 sunlight for two hours, and to diffuse sunlight for a further period of three 

 hours. On examining the film, again no trace of formaldehyde could be 

 found, although the quantity which had been produced in a film similarly 

 exposed over a solution of potassium hydroxide was most distinct. Both 

 films were allowed to stand in vacuo over soda-lime and pyrogallate solution 

 in the dark for three days before being quickly introduced into the tubes, 

 and the sealed vessels remained for four days more in the dark before 

 exposure. 



Illumination of Films in Carbon Dioxide free from Oxygen. 

 Four tubes containing freshly boiled water and chlorophyll extract films 

 were six times alternately exhausted and filled with carbon dioxide freed 

 from oxygen by means of red hot copper, and sealed off after the sixth 

 rilling. The following exposures were given: (a) 12 hours of sunlight, 

 bright at intervals ; (&) 11 hours of bright and 6 hours of diffuse sunlight ; 

 (c) 25 hours of bright and 6 hours of diffuse sunlight ; and (d) 17 days of 

 intermittent sunshine (July 16 to August 2, 1913). In no case was there 

 any evidence that formaldehyde had been formed in the exposed films, 

 although in each case control films, carefully freed from carbon dioxide and 



2 F 2 



