30 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



average distance which the conducting particles would have to travel 

 between these electrodes would remain fixed. If the cell were filled to a 

 height of I centimeters and if the conductance of the solution between 

 the pair of electrodes were A, then, since the electrode area is equal to 

 the reciprocal of the concentration, i.e., to I/ 1, it follows that the specific 

 conductance of this solution would be: 



Therefore, in order to compare the conducting power of a solution of a 

 given electrolyte at different concentrations, we divide the specific con- 

 ductance of the solution by the concentration and compare the values 

 of this ratio, namely the values of A. Similarly, in comparing the con- 

 ducting power of solutions of different electrolytes in the same or different 

 solvents at the same concentration, the values of the equivalent con- 

 ductance of the electrolytes at that concentration are obviously to be 

 compared. The equivalent conductance is a measure of the conducting 

 of an equivalent amount of material. In comparing the conducting 

 power of solutions, therefore, we require the values of the equivalent 

 conductance A for these solutions. 



Values of the equivalent conductance of typical electrolytes in water 

 at 18 are given in Table III. 19 The concentrations in this case are ex- 

 pressed in equivalents per liter. It will be observed that as the concen- 

 tration of an electrolyte in water decreases, its equivalent conductance 

 increases. For a decrease in the concentration in the ratio of one to two 

 between normal and half normal, the equivalent conductance of a binary 

 electrolyte increases approximately 30%. For a corresponding decrease 

 in concentration between 1 and 0.5 milli-equivalent per liter, the equiva- 

 lent conductance increases less than 1%. It is apparent, therefore, that 

 as the concentration decreases, the equivalent conductance approaches a 

 limiting value. 



The relation between the equivalent conductance and the concentra- 

 tion is shown graphically in Figure 1, where values of the equivalent 

 conductance of aqueous solutions of KC1, NaCl and LiI0 3 are plotted 

 as ordinates and the logarithms of the concentrations as abscissas. The 

 curves for different electrolytes are evidently similar in form. As the 

 concentration decreases, the equivalent conductance apparently ap- 

 proaches a definite value as a limit. A curve of this type, however, does 

 not lend itself to a determination of the limiting value which the con- 

 ductance approaches as the concentration 'decreases indefinitely. For 



19 Noyes and Falk, J. Am. Client. Soc. 3^, 454 (1912). 



