234 



L. HOKWITZ AND F. I.. ALLKN 



of 3 to 4 hours, often much longer, before beginning measurements. 

 The partial pressure of oxygen in the carrier gas before entering the 

 vessel was shown to be below 10-« mm. Hg. There is no doubt that 



HYDROGEN + 2% CO2 



30 40 SO 



LIGHT INTENSITY 



60 



70 



Fig. 1. Data obtained with the Franck-Pringsheim oxygen apparatus, compar- 

 ing oxygen evohition from Scenedesmus D3 incubated under hydrogen plus 2% 

 carbon dioxide, and under nitrogen plus 2% carbon dioxide. Relative light 

 intensity is plotted on the abscissa and oxygen pressure X 10* millimeters of 

 mercury, in the gas stream emerging from the reaction vessel, is plotted on the 

 ordinate. 



this partial pressure of oxygen is sufficiently low to permit adapta- 

 tion. 



Uniform illumination of all the cells was obtained by using green 



