QUANTUM YIELD 



1949 



that this linearity was found to continue up to 30 or even 40 times the 

 compensation rate (in other words, up to {R + P)/R ^ 30 or 40). Since 

 the rate of respiration of the cells, used in this work, was given as about 

 one volume oxygen per volume of cells per hour, their saturation rate of 

 oxygen production by photosynthesis must have been (at 20° C.) in excess 

 of 40 times their own volume per hour. (The more commonly reported 

 values for oxygen production by Chlorella cultures are 25-30 times the cell 

 volume per hour, c/., e. g., table 28.V, or Tamija and Huzisige, 1949.) 



I 



30 60 90 120 150 180 210 240 270 300 330 

 -y min. continued illuminotion 



Fig. 37D.27A. Oxygen liberation by a dilute Chlorella suspension (initial ab- 

 sorption, 6.2%) (after Warburg et al. 1953). Upper curve: smaller vessel; lower 

 curve: larger vessel. X546 m^, incident flux, 4.1 /xeinstein/min. Quantum require- 

 ment (I/7' = 4.1) calculated without respiration correction, at 18X compensation 

 (P + R = ISR). 



The (relative) absorption (10-25% of incident monochromatic light at 

 546, 578 or 644 m/x) was measured in an integrating sphere, while the (ab- 

 solute) quantum flux was determined by the pheophorbide-thiourea acti- 

 nometer. 



The actinometer had a volume of 184 cm.', containing 120 ml. liquid. A quantum 

 yield of 1.0 was assumed to prevail in the actinometric reaction up to a light flux of about 

 1 /icinstein per minute. We will see below that a quantum yield of 0.7 had been given by 

 Burk and Warburg in 1951 for an apparently similar 120 ml. actinometer, also with 

 pheophorbide as sensitizer, between 1 and 5 peinstein per minute; the reasons why the 

 quantum yield was raised to 1.0 in the new experiments, were not explained. 



As illustrated by fig. 37D.27A, oxygen liberation remained nearly 

 constant for 4V2 hours. During this time, absorption changed somewhat 



