1124 THE LIGHT FACTOR. II. QUANTUM YIELD CHAP. 29 



Measurements with a photocalorimeter {cf. page 854) were carried out 

 also at Wisconsin, by Magee, DeWitt, Smith and Daniels (1939), and gave 

 7 values from 0.049 to 0.110 (the average of 17 experiments was 7 = 0.077 

 or ITy = 13). No pronounced change with light intensity was noted be- 

 tween 1200 and 8000 erg/cm. ^ sec. 



More recently, Tonnelat (1944, 1946), who worked in Wurmser's lab- 

 oratory in Paris, published similar results of an investigation initiated in 

 1939. Tonnelat measured the heat developed in an adiabatic microcalorim- 

 eter under three conditions: (i) when the calorimeter contained an il- 

 luminated black-bottomed vessel with pure water (heat evolution, £"0); 

 {2) when it contained the same vessel with an equal volume of an algal 

 suspension in the dark (heat evolution, Er, due to respiration) ; and (5) 

 when it contained the same suspension and was illuminated (heat evolu- 

 tion, E = Eo-{- Er - AHc). The energy yield, «, was then: 



(29.3) e = AHc/E = (^0 + Eh - E)/E 



and the quantum yield, according to equation (29.1), assuming X = 530 

 mju (green light isolated by Wratten filter No. 62) : 



(29.4) 7 = e/(4 X 10-5 X 530) = 6/2.12 



Illumination lasted for 16 hours without noticeable deviation from 

 linearity (t. e., presumably, from the constancy of both R and P); even 

 in the very low Ught used (about 1.5 X lO"* einstein of green light/cm 

 min., or 550 erg/cm.^ sec), such long duration of the experiments seems 

 dangerous. The results of Tonnelat's determinations are shown in Table 

 29.VII. 



T.\BLE 29.VII 



Efficiency of Photosynthe.sis (after Tonnelat 1944) 

 Measured with Photocalokimetkr 



Chlorella Energy 



concn., conversion 



Experiment cclls/0.5 cm.^ factor 



(1) Reflecting bottom 32 X 106 0.26 (±0.06) 



(2) Reflecting bottom 33 0.34(±0.05) 



(3) Reflecting bottom 37 0.26 (±0.06) 



(4) Reflecting bottom 56 0.31(±0.05) 



(5) Reflecting bottom 194 0.08(±0.08) 



(6) Black bottom 36 0.12 (±0.07) 



(7) Black bottom 51 0.31 (±0.05) 



(8) Black bottom" 48 0. 18 



" With 0.1% agar. 



Experiment 5 shows that the yield became low in very concentrated 

 suspensions (a result Tonnelat attributed to inhibited gas exchange in the 

 dense layer of cells on the bottom of the vessel, but which also could be due 



2 



