26 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



is a function of its viscosity, it may be inferred that in part, at least, 

 the variation in the transference numbers at the higher concentrations 

 is due to the change of the viscosity of the solution. 



It will be observed that the transference numbers for potassium 

 chloride are very nearly 0.5. In other words, in the case of this salt, 

 each ion carries very nearly one half of the current. If the frictional 

 resistance, which an ion meets in its motion through the medium, is inde- 

 pendent of the sign of its charge, then this indicates that the two ions 

 have approximately the same dimensions. This is borne out by the 

 measurements of Washburn 16tt who showed that these ions are hydrated 

 to approximately the same extent. 



The transference numbers of electrolytes are functions of the tem- 

 perature. In Table II 17 are given the transference numbers of a number 



TABLE II. 



CATION TRANSFERENCE NUMBERS (X 10 :l ) OF VARIOUS ELECTROLYTES AS 

 FUNCTIONS OF THE TEMPERATURE. 



Temp. NaCl KC1 HC1 BaCl 2 



387 493 845 437 



10 ... 495 841 441 



18 397 496 833 



30 404 498 823 444 



50 ... ... 801 475 



96 ... ... 748 



of electrolytes at temperatures from to 96 at concentrations in the 

 neighborhood of 0.015 N. In the case of potassium chloride, the trans- 

 ference number varies only very little with the temperature, whereas in 

 that of sodium chloride the transference number of the cation increases, 

 and in that of hydrochloric acid it decreases. As we shall see later, it is 

 a general rule that with increase of temperature the transference numbers 

 of all electrolytes approach the value 0.5. The transference numbers of 

 ions having values greater than 0.5, therefore, decrease with increasing 

 temperature; and those having smaller values increase under the same 

 conditions. 



3. The Conductance of Electrolytic Solutions. The conductance of 

 an electrolytic solution is a function of the various factors which deter- 

 mine its condition, such as concentration, temperature, etc. The quan- 

 tity actually measured is the specific conductance of the solution. This 

 is defined as the conductance in reciprocal ohms of a column of electro- 



"* Washburn, J. Am. Chem. 800. 31, 322 (1909). 

 17 Noyes and Falk, loc. cit. 



