OXIDATION-REDUCTION POTENTIALS 



195 



imidazole compounds, picoline, pyridine, and nicotine, indicating 

 that the affinity to the reductant is greater than to the oxidant. 

 The nature of the porphyrin also affects the potential, which is 

 lowest with hemochromes of porphyrins with saturated side chains, 

 higher with protoporphyrin, and still higher with spirographis por- 

 phyrin (Barron, 182). The latter is of interest since the respiratory 

 ferment may contain carbonyl groups in the side chains. 



Table IX and Figure 8 illustrate these facts. Table IX is compiled 

 from Barron's papers {180,182,183) and those of Clark {loc. cit.). 



> 



6? 



0.2 0.4 0.6 0.8 1.0 



CONCENTRATION OF NITROGENOUS SUBSTANCES 



Fig. 8. Increase of oxidation-reduction potential on association with bases 

 (after Barron, 180). 



