40 PROBLEMS IN PHOTOSYNTHESIS 



As shown in Figure 18, the manometer vessel has two phases: the cell 

 suspension with the volume Fp- and the gas phase with the volume Vq. The 

 vessel connected with the manometer is suspended in a thermostat and is 

 shaken continuously during the experiment. Figure 19, after Burk (7), shows 

 the typical, open-arm, fixed-volume manometer made classic and universal 

 by Warburg. In the manometer vessel O2 is consumed and CO2 evolved and 

 absorbed by KOH. The change of the amount of gas in the vessel causes 

 an experimentally observed vertical displacement of the fluid in the manom- 

 eter arm open to the atmosphere when the meniscus in the closed arm is 

 maintained at a fixed level by means of the adjustable screw and the fluid- 

 filled sac at the base of the manometer. The narrow, even-bore capillary 

 of the manometer arms has an area of 0.5 to 3 mm-. Obviously, exact 

 calibration of the manometer and sensitivity magnification are of the utmost 

 importance (7, 10). The theory of the simple manometer will be discussed 

 in§18. 



The manometer fluid may be either ;\yo-capronic acid or Brodie's solution. 

 The latter contains in each 500 ml water 23 g NaCl and 5 g sodium choleinate 

 plus a few drops of thymol solution. As the relative specific gravities are 

 0.926 and 1 .034, respectively, we find that 



u "760 X 13.6 ,,,^^ 

 760 mm Hg = — = 11160 mm ?5^o-capronic acid 



and 



760 mm Hg = ^'"^ ?^ ^^"'^ = 10000 mm Brodie 



or 



1 mm /jo-capronic acid — 0.068 mm Hg 



and 



1 mm Brodie = 0.076 mm Hg 



§ 17 Light Absorption and Its Measurement 



Figure 20 depicts schematically early, experimental equipment devised by 

 Warburg and Figure 21 shows equipment as used today. The principle is 

 the same in both, the light passing from the source through various filters 

 to give the desired wave-length and entering the thermostat in the horizontal 

 plane. It is then reflected by a mirror inclined at 45 ° and enters the manom- 

 eter vessel from below. The light is then directed on to a bolometer so that 

 its intensity can be measured. This is depicted schematically in Figure 22. 

 It used to be the practice to measure the intensity of the light before it entered 

 the thermostat, as can be seen from Figure 20. However, corrections always 

 had to be made for the difference in permeability the light encountered in its 

 passage through the thermostat. Today, the intensity is measured after the 

 light has passed through the thermostat. The mirror M^ in the thermostat 

 used to be fixed .so that the light was reflected vertically upwards. Now, it 



