1100 THE LIGHT FACTOR. II. QUANTUM YIELD CHAP. 29 



The value used by Warburg and Negelein, Qp = +1.09, was determined 

 by gas analysis, in much stronger light than was used for quantum yield 

 determinations. Warburg now redetermined the Qp value in less intense 

 light, manometrically, by means of two sets of measurements in one vessel 

 filled with two different volumes of liquid (5 and 8 ml.). He found a Qp 

 value of +1.07, practically identical with the quotient used by Warburg 

 and Negelein. 



Furthermore, Warburg and Kubowitz could find no evidence of a "gas 

 burst" in the first few minutes of illumination, except for a comparatively 

 small effect, observed at the higher light intensities, especially when foam- 

 ing occurred in the reaction vessel (c/. fig. 29. 4A). 



With the belief in the validity of the original experimental procedure 

 thus strengthened, Warburg and Kubowitz proceeded to make new de- 

 terminations of the quantum yield by the one-vessel method. The vessel 

 was not silvered to better observe bubble formation (which Warburg con- 

 sidered the most serious source of error) ; readings were made without inter- 

 ruption of shaking. The light used was mostly the yelloAV mercury lines 

 (578 m^) with an intensity of 325-2920 erg/cm. ^ sec. 



To minimize effects caused by sluggish gas exchange, a smaller fluid 

 volume was used than in 1923 and two glass beads were put into each vessel 

 to act as stirrers. Curves such as those in figure 29.4B and C were con- 

 sidered by Warburg as confirmation of the interpretation of pressure dis- 

 turbances at the beginning of the light and dark periods, as consequences 

 of this sluggishness. He described these disturbances as "symmetric," 

 meaning that the two disturbances cancelled each other and the y values 

 therefore were the same, whether they were determined from the steady 

 rates, omitting the measurements in the first few minutes of light (?'. e., 

 from slope AB), or by interpolation, as in figure 29.1 {i. e., from slope CD). 

 This procedure is equivalent to integration of the gas exchange over the 

 whole period of the experiment, including the two transition intervals. 



This obviously does not apply to the curve in figure 29. 4A, where the pressure in- 

 crease in the first minute is faster than afterward. Calculation from the steady* 

 state (slope AB) gives in this case a I/7 value 25% higher than that obtained by inte- 

 gration (slope CJ)). 



Table 29. Ill summarize.-^ the results. Warburg concluded from these 

 experiments that the limiting quantum yield in weak light is 0.25 and that 

 it declines to about 0.20 at 1500 erg/cm.^ sec. He suggested, as general 

 explanation of the smaller values found bj^ other observers, failure to cul- 

 ture algae of the highest efficiency; but his description of the methods of 

 culture revealed no significant difference from those used by Emerson or 

 Rieke. 



