THE ENERGETICS OF PHOTOSYNTHESIS 61 



time span is h' mm, vessel B has only absorbed the fraction 1 — a of the radia- 

 tion energy. Thus, we have 



1 _ h 

 1 - a ~ V 



Hence, the fraction of light absorbed by the cell suspension is 



a = 1 -- 



With this method neither the photochemical yield of the actinometer reaction 

 nor the vessel constant need be known, as only changes in pressure are meas- 

 ured. For this reason, absorption in the actinometer vessel need not even 

 be complete. 



Numerical example fll): 



Blue light (4360 A) 

 In vessel A : water 

 Pressure change in vessel B in 10 niin: /; = —20 mm 



In vessel A: 4 ^1 cells in 7 ml 



Pressure change in vessel B in 10 min: //' = —13 mm 



a = 1 - ;^ = O.JD 



35% of the light is absorbed by the cells. 



In vessel A: 8 /xl cells in 7 ml 



Pressure change in vessel B in 10 min: /;' = —8 mm 



a = 1 - 1^ = 0.60 



60% of the light is absorbed by the cells. 



In vessel A: 16 )ul cells in 7 ml 



Pressure change in vessel B in 20 min: //' = —7 mm 



82.5% of the light is absorbed by the cells. 



For measurements of the intensity absorption of cell suspensions, the acti- 

 nometer has been superseded by the Ulbricht sphere, as the latter works more 

 rapidly. On the other hand, the actinometer is still of value in measuring 

 quantum intensities because a single reading of the manometer at the end of 

 an experiment immediately indicates the number of incident quanta during 

 the time of illumination. In contrast to the bolometer, the spectral composi- 

 tion of the light need not be known. The bolometer measures i^ and the 

 actinometer integrates the light intensities over time and number of quanta 

 (29,34). 



§ 25 Photodissociation of Iron Carbonyl Compounds 



In 1896 Haldane and Smith (14) discovered the photochemical dissociation 

 of iron carbonyl compounds. They found that the affinity of CO to hemo- 



