QUANTUM YIELD MEASUREMENTS BY THE MANOMETRIC METHOD 1101 



Table 29.III 

 Quantum Yields after Warburg (1946, 1948)" 



° Chlorella suspension, 10° C, complete absorption. 450 mm.^ cells in 5 or 8 ml. 

 liquid; bottom area 17 cm.^ The two values in parentheses probably are affected by 

 the light absorption by carotenoids. 



'' P'rom the steady state. 



"^ By integration. 



In discussing Warburg's results, Emerson and his co-workers (1949, 

 1950) pointed out that the pressure changes in the first minutes of ilkimi- 

 nation are affected by two factors : the sluggishness of the manometer (em- 

 phasized by Warburg) and the carbon dioxide burst. In very weak light, 

 the burst may be spread almost uniformly over a 10-15 min. illumination 

 period, and the sluggish transition is then clearly revealed by the initial 

 measurements, as in fig 29. 4B and C. In stronger light, the burst is much 

 more sudden, and its rapid decay overcompensates the effect of sluggish 

 gas exchange, leading to curves such as that in figure 29.4 A. The spread 

 of the burst in low light over the whole illumination period, accentuated bj' 

 the sluggishness of the manometer, may answer one of Warburg's objec- 

 tions — the absence of a visible pressure burst on the low light curv^es (figs. 

 29.4B-D). 



Warburg's other (and main) objection against Emerson's criticism was 

 that a check "under the conditions of the quantum yields measurements" 

 confirmed the validity of the Qr value of apin-oximately -fl, and that an 

 extreme deviation of Qf from unity would have been needed to calculate 

 from Warburg's experimental data (obtained with the one-vessel method) 

 a quantum yield of about 0.1 for the liberation of oxygen in light. To 

 this, Emerson and co-workers answered that Warburg's determination of 

 Qp was based on subtraction of the rate of pressure change in darkness from 

 the rate of pressure change in light (this difference was called the "light 

 effect"). From the comparison of "light effects" in experiments with 

 different amounts of liquid in the same vessel, Warburg derived the ratio 

 AO2/ACO2 for (he light effect; and finding it close to 1, concluded that no 



