QUA NTUM YIELD MEASUREMENTS BY THE MANOMETRIC METHOD 1111 



B. Experiments at pH 9.2 (Single vessel) 



Average 10.15 



1 ( AOa/ACOo) for "light effect" (p. 1101). 



2 Average of six cycles, single cycles give l/7-values from 2.3 to 14. 

 ^ No significant difference between 10', 20' and 30' cycles. 



* Four cycles gave very closely similar results; one value off. 



^ Cells washed and re-suspended in fresh medium before this measurement because 

 of apparent drop in yield. 



below those which Emerson and co-workers consider correct on the strength 

 of their own manometric experiments, and of the nonmanometric measure- 

 ments performed in various other laboratories. Emerson sees a possible 

 source of such an error in the decision of Warburg and Burk to reverse 

 Warburg's earlier practice, and to make no allowance for the "physical 

 lag" between the time of gas exchange in the chloroplasts and the time 

 Avhen pressure changes are registered in the manometer (cf. below). 



4. Warburg and Burk's claim that this lag was negligible because of 

 fast shaking could not be confirmed by Emerson and co-workers. The 

 fact that in Warburg and Burk's experiments the pressure change often was 

 the same (within the limits of experimental error) in the first, and in the 

 second 5 minutes of a 10-min. light period, can be explained, according. to 

 Emerson, by compensation of the lag by the carbon dioxide burst. Emer- 

 son and co-workers, too, could obtain time curves in phosphate buffer 

 without an apparent induction period; and yet, experiments made in the 

 same two vessels, and with the same rate of shaking, but in carbonate 

 buffer (eliminating the CO2 burst), showed a lag of considerable duration. 



5. In each vessel, taken separately, the physical lag tends to decrease 

 the manometric effect of the transition from darkness to light (and vice 

 versa) and thus to make the calculated "light effect" smaller. This does 

 not mean, however, that the calculated 7 values also must be too small. 

 The quantum yield and the ratio Qp are calculated from the light effects 

 in the two vessels; and whether the calculated 7 value is too small or too 

 large depends on the ratio of the two lags. With the two vessels used by 

 Warburg and Burk, the lag is larger in the vessel with the larger gas space, 

 and this makes the calculated quantum yields too high. The systematic 

 error caused by this unequal lag needs to be only very small (of the order of 

 0.3 mm. per 10 min.) for the calculated 7 to be increased by a factor of two. 



