208 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



for potassium formate, for example. Since the transference number of 

 hydrochloric acid in formic acid is not known, it is uncertain whether 

 or not the hydrogen ion in formic acid possesses an abnormally high 

 conducting power. The evidence, however, indicates that the chloride 

 ion possesses a conducting power not greatly smaller than that of the 

 formate or hydrogen ion. The limiting value of the conductance of 

 ammonium chloride can scarcely be lower than 52. 13 The value is some- 

 what uncertain because of the solvolytic reaction between the salt and 

 the solvent. However, assuming probable values for the ionization con- 

 stants of ammonium formate and hydrochloric acid and pure formic acid, 

 it can be shown that the fraction of salt transformed to acid and base 

 by reaction with the solvent cannot affect the conductance by more than 

 a few units. If we assume, therefore, the value 52 for the limiting value 

 of the equivalent conductance of ammonium chloride, and assuming for 

 the conductance of the ammonium ion the value 18.8, which follows from 

 the value 70.4 for the limiting value of the equivalent conductance of 

 ammonium formate, we obtain for the limiting value of the conductance 

 of the chloride ion the value 33.2 and for the hydrogen ion 42.8. This 

 indicates that the conductance of the hydrogen ion in formic acid does 

 not differ greatly from that of the chloride ion in the same solvent. The 

 exceptionally high value found for the conductance of the hydrogen and 

 the formate ions, like that of the chloride ion, is presumably due to the 

 relatively smaller dimensions of these ions compared with those of the 

 positive ions in formic acid. 



It has also been suggested that the pyridonium ion, C 6 H 5 NH + , pos- 

 sesses an abnormally high conducting power in pyridine. 14 This, how- 

 ever, rests upon a false accepted value for the conductance of typical 

 salts in pyridine. The conductance of pyridine hydrochloride at a dilu- 

 tion of 32 liters and 25 in pyridine has been found to be 27.4. The 

 conductance of sodium iodide in pyridine at a dilution of 57.7 liters and 

 18 is 23.6. 15 In general, at these concentrations, the conductance of 

 solutions in pyridine changes but little with concentration. Conse- 

 quently the conductance of sodium iodide in pyridine at 32 liters would 

 differ but little from that at the lower concentration. On the other hand, 

 the conductance at 18 is materially lower than at 25 because of the 

 greater viscosity of the solution at the lower temperature. Assuming a 

 viscosity correction of two per cent per degree the conductance of sodium 

 iodide at 25 would be approximately 27.0. In other words, the con- 



"Schlesinger and Calvert, J. Am. Chem. Soc. 33, 1924 (1911). 



14 Hantzsch and Caldwell, loo. cit. 



15 Ottiker, Dissertation, Lausanne (1907); Kraus and Bray, J. Am. Chem. Soc. 35, 

 1379 (1913). 



