OTHER PROPERTIED OF ELECTROLYTIC SOLUTIONS 303 



trolytes, both with and without a common ion. The results of Poma 

 indicate a considerable change in the electromotive force due to the 

 addition of another electrolyte. The effect varies with the concentra- 

 tion and also with the nature of the added electrolyte. At the higher 

 concentrations of added salt, at any rate, the effect is greatly dependent 

 upon the nature of the added electrolyte, the electromotive force due to 

 the addition of a given amount of electrolyte being the greater the 

 greater the tendency of the salt to form hydrates. The sign of the 

 electromotive force, moreover, was found to depend upon the nature of 

 the added electrolyte. 



The results of Poma do not seem to be in good agreement with the 

 results of other investigators who have investigated the electromotive 

 force of similar cells. The potential of the hydrogen electrode in solu- 

 tions of hydrochloric acid in the presence of varying amounts of alkali 

 metal chlorides has been investigated by Chow, 31 who found that, keep- 

 ing the total ion concentration constant, the potential of the electrode 

 in the mixture may be calculated according to Equation 95, the total 

 concentration of hydrogen and of chlorine being employed for the con- 

 centrations of the ions. According to this result, the function J remains 



constant in the mixture, provided the total concentration of the mixed 

 electrolytes is maintained constant. Similar results have been obtained 

 by Earned. 32 The results of Harned indicate that at low concentra- 

 tions the function J l(! has the same value for the mixture as it has for 



o 



the pure electrolyte at the same total salt concentration. At higher con- 

 centrations, according to Harned's measurements, the potential of the 

 electrolyte depends upon the nature of the added electrolyte. It was 

 also found that the potential of the hydrogen electrode in hydrochloric 

 acid suffers nearly the same change due to the addition of equivalent 

 amounts of potassium chloride and sodium bromide. 



As yet, experimental data in this direction are not sufficiently exten- 

 sive to warrant generalizing the conclusions drawn from the investiga- 

 tions referred to above. 



6. Thermal Properties of Electrolytic Solutions. It is only recently 

 that the technique of thermal measurements has been refined to a point 

 where data obtained with electrolytic solutions are sufficiently precise 

 to make an inter-comparison of the various thermal properties of such 

 solutions generally possible. Even now, accurate data are available for 

 only a limited number of systems, as a result of which but few general 



"Chow, J. Am. Chem. Soc. &, 497 (1920). 



"Earned, J. Am. Che m . SQC. 42, 1808 (1920) ; i&itf,, 37, 2460 U9J5), 



