68 IOWA ACADEMY OF SCIENCE 



measure of the concentration of the silver ions. The latter alter- 

 native is in accord with the observation of Neustadt and Abegg 17 

 that in the electrolysis of pyridine solutions of silver nitrate both 

 the silver ion and the nitrate radicle migrate to the cathode, 

 probably as a complex ion. 



"Walden and Centnerszwer 18 have found that the molecular 

 weight of silver nitrate in dilute pyridine solutions is normal, 

 while in the more concentrated solutions it is greater than nor- 

 mal, thus indicating association. Since simple silver ions must 

 be present, if an electromotive force is to exist, it is probable that 

 silver nitrate may ionize both as simple and as complex 

 ions. If the ionization of the complex molecule is just 

 sufficient to form as many particles as there would be if the 

 substance existed as a simple molecule, then the molecular 

 weight should appear to be normal. This is probably the case 

 in the more dilute solutions of silver nitrate in pyridine. 



It is evident from Tables I, II, V, VI, IX, X and from Plate 

 II A that the electrode potentials of silver are much higher for 

 solutions in water, methyl alcohol and ethyl alcohol than for 

 equivalent concentrations in pyridine. On comparing the equiv- 

 alent concentrations, it will be observed that for all binary mix- 

 tures of pyridine with water and with the two alcohols the elec- 

 trode potential increases with the decrease in the proportion of 

 pyridine in the mixture. This increase is very gradual until 

 seventy-five per cent of the pyridine has been replaced by the 

 second solvent. For the water-pyridine mixtures the initial in- 

 crease is apparently a linear function of the per cent of water 

 present. "With further decrease in the proportion of pyridine 

 there is a rapid increase in the value of the electrode potential to 

 its value in the second solvent. The curves for the water- 

 pyridine series show a strong resemblance to the curve found 

 by Hartley, Thomas and Appleby 19 for the surface tensions of 

 the same system. Whether or not any relation exists between 

 surface tension and electrode potential is a question still un- 

 answered. 



For all solvents, simple and mixed, the electrode potentials 

 increase as the concentration of the salt increases. From the 

 curves, Plate II B, it will be observed that, starting with the most 



17 Loc. cit. 



ls Zeit. phvsik. Chem., 55, 321, 190fi. 



"Trans. Chem.. Soc, 93, 549, 1908. 



