CARBON DIOXIDE CONSUMPTION 



851 



dropping mercury electrode by a stationary mercury electrode, or by a 

 Pt point electrode. (Concerning a rotating electrode, see Kolthoff 1940.) 

 Kaiitsky discovered the extreme sensitivity of the phosphorescence 

 of certain dyestuffs, e. g., trypaflavine adsorbed on silica gel, to traces of oxy- 

 gen. Franck and Pringsheim (1943) investigated this quenching effect 

 quantitatively and found that 50% quenching is obtained at a partial 

 pressure of 5 X 10~^ mm. O2. Pollack, Pringsheim and Terwood (1944) 

 and Franck, Pringsheim and Lad (1945) applied this method to some 

 problems of photosynthesis, e. g., oxygen production by single flashes of 

 light. Figure 25.4 shows the results obtained with a 2 second flash and 

 several 0.03 second flashes of illumination in a suspension of Chlorella. 

 The reason why the "oxygen bursts" recorded in the figure last for 1 minute 

 or more is that the oxygen produced durng the flash is only gradually 



4 5 



TIME, mia 



Fig. 25.4. Oxygen production by Chlorella in single light flashes (measured 

 by the phosphorescence method) (after Pollack, Pringsheim and Terwood 

 1944). Large peak: 2 sec. illumination; small peaks: 0.03 sec. illumination. 



carried away by the stream of nitrogen from the cell suspension into the 

 vessel containing the phosphorescent gel. The apparatus, as constructed 

 by Pringsheim and co-workers, could be used for the measurement of rates 

 down to 5 X 10 ~^ cc. 02/min. However, the method is only useful under 

 anaerobic, or almost anaerobic conditions, since, in the presence of more 

 than 10~^ mm. O2, the quenching becomes practically complete. 



4. Measurements of Carbon Dioxide Consumption 



Like the liberation of oxygen, the consumption of carbon dioxide in 

 photosynthesis can be measured either by the traditional methods of 

 chemical analysis, or by physicochemical methods. Absorbers for carbon 

 dioxide are well known; any alkaline material (e. g., lime or baryta) can 

 be used for this pui-pose, and the quantity of absorbed carbon dioxide 



