50 



PROBLEMS IN PHOTOSYNTHESIS 



Fig. 26. The two-vessel method (photograph taken in Prof. Warburg's institute). 



in the horizontal plane in the thermostat at 20° C with a frequency of 210 

 per min and an excursion of 1 cm. The irradiation of the vessels — with 

 which we shall deal in § 30 — must be identical for both vessels because the 

 conditions for the two-vessel method are only met if the chemical processes 

 in both vessels are the same. It is therefore also imperative that the bottoms 

 of the two illuminated vessels are exactly identical in size and form, because 

 only then can light absorption be equal. This can be tested easily by means 

 of the Ulbricht sphere since the absorption values in both vessels should be 

 the same. 



Numerical example: 



Large vessel 



Va = 13.75 ml Vr = 7.00 ml 



It follows from equation 7 that at 25 ° C 



A'o, = 1.286 mm- Acq, = 2.087 mm'' 



