66 IOWA ACADEMY OF SCIENCE 



DISCUSSION. 



The observed electromotive forces of all the possible concen- 

 tration cells of the type: 



Ag— AgN0 2 , c l— 1.0 N NH 4 N0 3 — AgN0 3 ,c,> — Ag 



may be found in Tables III, IV, VII, VIII, XI and XII. The 

 observed values are small, as we should expect. While they 

 are incumbered, doubtless, with slight errors, they are approxi- 

 mately of the right order of magnitude. In all cases the posi- 

 tive electrode was found in the more concentrated solution. 

 Conductivity data are not available for the solutions in the binary 

 mixtures containing pyridine as one of the components. It is 

 therefore impossible to give the calculated values in the mixed 

 solvents. In the pure solvents, water, methyl alcohol, and ethyl 

 alcohol, the values obtained agree closely with those obtained by 

 Fan*, 16 thus confirming his statement that the Nernst equation 

 does hold for concentration cells in these solvents. 



During the present year the equivalent conductances of solu- 

 tions of silver nitrate in pure pyridine have been carefully deter- 

 mined by Mr. H. L. Dunlap of this laboratory. Repeated deter- 

 minations give the following values for the equivalent conduct- 

 ance at infinite dilution : 



x °° at 0°=51, Xo ° at 25°=71. 



In attempting to calculate the electromotive forces of concen- 

 tration cells in pyridine from Mr. Dunlap 's conductivity data, 

 it was found that the calculated values deviate considerably from 

 those observed. They are peculiar in the following respects: 

 When the normal solution constitutes one-half of the concentra- 

 tion cell they are smaller than the observed values, but if the 

 concentrations in each of the half-cells are less than .5 N they 

 are larger. Furthermore, it will be observed that with the more 

 concentrated solutions the calculated electromotive forces show 

 reversal of sign. 



The deviations between the observed and calculated values 

 for the electromotive forces of concentration cells in pure pyri- 

 dine must be attributed to one or both of two causes, — either the 

 solution pressure of the metal varies with the concentration of 

 the dissolved silver nitrate, or, owing to polymerization and sub- 

 sequent ionization, the equivalent conductivity is not a true 



lc Loc. cit. 



