NONMANOMETRIC MEASUREMENTS OF QUANTUM YIELD 1119 



(a) Chemical Methods 



Wurmser (1923, 1925, 1926) made a few quantum yield determinations 

 with the green alga Ulva lactuca. Each experiment lasted for several hours, 

 and consisted in the measurement of change in oxygen concentration in solu- 

 tion by Winkler's method. The rate of absorption of Ught was calculated 

 from comparison of transmission by green and discolored thalli (c/. chapter 

 22, page 675), using a theoretical equation to take into account scattering 

 (c/. page 713). Wurmser found, in some of these experiments, energy con- 

 version factors up to 50%, corresponding to quantum yields up to }4- 

 However, the calculated yield in the (weakly absorbed) green light turned 

 out to be so much higher than in the (strongly absorbed) red light, that it 

 indicated probable grave errors in the calculation of absorption. Warburg 

 (1925) therefore did not consider these experiments of Wurmser as sig- 

 nificant confirmation of his own results. 



Briggs (1929) obtained, with leaves of Phaseolus vulgaris, at hght in- 

 tensities 5-10 times stronger than those used by Warburg and Negelein, 

 yields from 7-17 cc. O2/5OO cal absorbed energy; with yellow elm leaves, 

 from 5.3 to 8.9 ml.; with green elm leaves, from 12 to 20 ml.; and with 

 leaves of Samhucus nigra, from 9 to 19 ml. These values correspond to 

 quantum yields <0.1. 



In 1935, Gabrielsen, working with plants of Sinapis alba, calculated, 

 also from gas-analytical measurements, by extrapolating the light curves 

 (fig. 30.8A,B) to zero illumination, e values from 0.13 in blue, to 0.36 in red 

 Hght, corresponding to maximum quantum yields of 0.1 ± 0.02. Gabrielsen 

 did not question at that time the correctness of Warburg's results, and 

 thought that his lower yields must have been due to the use of a less ef- 

 ficient species. 



Later (1947), Gabrielsen repeated these experiments with Sinapis, 

 Corylus and Fraxinus leaves, and found 70-values between 0.082 and 0.078. 



In the first of a series of investigations emanating from the University 

 of Wisconsin, Manning, Stauffer, Duggar and Daniels (1938) determined 

 the quantum yield by gas analysis, comparing the composition of a gas 

 (containing approximately 5% CO2 and 5% O2) conveyed through a Chlo- 

 rella suspension in the light and in the dark. The suspensions were less 

 dense than in Warburg and Negelein's work, absorbing only 10-50% of the 

 incident light; the intensity of the latter (green line from a mercury lamp) 

 was somewhat higher than in Warburg and Negelein's experiments (1000- 

 1750 erg/cm. 2 sec.) ; 60 minute periods of illumination were used. The 7 

 values derived from the absorption of carbon dioxide were not very different 

 from those calculated from the increase in the concentration of oxygen, thus 

 indicating that the quotient Qp was close to unity. 



