QUANTUM YIELD MEASUREMENTS BY THE MANOMETRIC METHOD 1091 



were the same as in Warburg's work. The quantum yields calculated from 

 ten experiments at 578 m/u ranged from 0.18 to 0.24, and those calculated 

 from six measurements at 546 mn, from 0.17 to 0.20. 



Thus, Rieke found Warburg and Negelein's results reproducible, but 

 only by strict adherence, not merely to the original method of culturing 

 of the algae, but also to Warburg's schedule of illumination. Wassink, 

 Vermeulen, Reman and Katz (1938) noted another peculiarity— the quan- 

 tum yields determined according to the procedure of Warburg and Nege- 

 lein, were affected by temperature — they increased from 0.11 to 0.20 when 

 the temperature was changed from 0° to 29° C. 



Another peculiar observation was made by Rieke, who found that the 

 kind of water used in the preparation of the algal culture had an effect on 

 the quantum yield. Emerson and Lewis (1938, 1939) confirmed this. 

 They used water from seven different sources, and obtained, under other- 

 wise identical conditions, variations in the quantum yield from 0.16 to 

 0.27. 



The lowest values were obtained in glass-distilled water; addition of a stock niixture 

 of "microelements" (B, Zn, Co, Mn, Mo, Cr, Ni, Co, W, Ti, V) increased it markedly; 

 a similar result was achieved by an increase in the amount of ferrous sulfate in the nu- 

 trient mixture (apparently, this compound contained all the micronutrients as impuri- 

 ties). 



Emerson and Lewis found that, for securing the highest yields, the cells 

 had to be grown for 5 or 10 days at 15-20° C, 20 cm. from four grouped 60 

 watt lamps followed by 3 days 30 cm. from a single 100 watt lamp. In 

 agreement with Wassink and co-workers, they found a temperature effect — 

 the highest quantum yield was observed at 10° C. At least 5% CO2 had 

 to be present during the quantum yield measurement, and the light in- 

 tensity could not exceed 350 erg/cm. ^ sec. 



These experiments could have been interpreted as indicating possible 

 reasons for the low yields observed at Wisconsin, and thus supporting the 

 validity of the results of Warburg and Negelein, if a new difficulty had not 

 appeared. Emerson and Lewis found that, by combining all the favorable 

 factors, 7 values could be obtained that were considerably above Warburg 

 and Negelein's value of 0.25. With 10 min. illumination periods, 7 values 

 up to 0.31 were obtained; and these were further increased by making 

 the illumination periods even shorter-. Since even a quantum yield of M 

 presented grave difficulties from the point of view of thermochemistry, 

 yields of one third or higher were clearly incompatible with the accepted 

 over-all reaction of photosynthesis. 



Emerson and Lewis suspected (1938, 1939) that the oxygen production 

 in the first minutes of illumination may occur by reduction of accumulated 



