130 Extensions of photosynthetic experimentation 



m/i was isolated by the following filters ; 5 cm. water, 2 cm. 5% C11SO4. 10H 2 O, 

 1 cm. tartrazin (20 mg./lOO c.c. H2O), and 1 cm. Didym-plate (Schott-Jena). 



The intensity of this green light beam was about 15 //mol. quanta (330 mm. 3 ) 

 per min., or one hundred times that first employed by us at Urbana and twenty-five 

 to fifty times that used in Bethesda. The green light beam was split by four totally 

 reflecting prisms into two beams of equal intensities. These were measured by a 

 bolometer (Lummer-Kurlbaum) of 9 cm 2 , area, standardized against an American 

 National Bureau of Standards lamp obtained through the courtesy of Dr Curtis 

 J. Humphreys, Chief of the Radiometry Section. The manometric actinometer was 

 standardized against the bolometer. 



IV. The Two-Vessel Method 



The divided light beam effected an improvement in the employment of the two- 

 vessel method since the two vessels could be illuminated and darkened simultane- 

 ously. The two vessels, each with its equal-sized thermobarometer, were fastened 

 on two opposite sides of the thermostat. The two branches of the divided light 

 beam entered the thermostat in horizontal directions and were reflected by two 

 45° mirrors into the two vessels. 



A second improvement that made efficiency determinations possible at high 

 light intensities was the employment of increased motion of the cell Suspension in 

 vessels of increased volume. In our very earliest experiments it was sometimes 

 observed that in the smaller of the two vessels then employed (v = - 13 c.c, 

 i) F = 7) the motion of the liquid was inhibited by striking the upper wall, whereas 

 in the larger vessel (v = 20 c.c, vf = 7) the liquid could swing freely, the conse- 

 quence being that the motion of the cell suspensions in the two vessels was clearly 

 different, and stronger in the greater vessel. We have now used as the smaller vessel 

 the volumes v — 20 c.c. and vf = 7, and as the larger vessel the volumes v = 30 

 c.c. and vf = 7. The bottom area of both these vessels was again about 7.5 cm. 2 . 

 The vessels were shaken by horizontal motion at the increased rate of 220 per min., 

 and when the helmets (male parts) of the attaching manometers were hollow, no 

 splashing in the manometer capillaries occurred no matter how rapid the shaking. 

 No foaming occurred even in experiments of 7 hr. duration. 



In these two vessels of 20 and 30 c.c. volume, the 7 c.c. of cell Suspension could 

 swing freely and showed during the motion of the vessels the same geometrical 

 outline, that is, a downwardly concave surface with a height lowest in the middle 

 that was not less than one-half the height at the ends of the vessels. 



These remarks will emphasize that the two-vessel method applied to bio- 

 photochemistry needs special considerations not demanded by routine manometry, 

 especially when high light intensities and light actions are involved. Not only is 

 equal physical equilibration in the two vessels demanded, but also equal intermit- 

 tency of illumination. The unusual y (CO2/O2) values of photosynthesis reported in 

 the literature* are in our opinion caused in part by inadequate motion of the smaller 

 vessel. In fact, such y values can often be normalized by increasing the shaking rate. 



* Zusatz 1961. By R. Emerson. 



