340 MR. W. C. D. WHETHAM ON THE IONIZATION OF 



we shall find that at extreme dilution the equivalent conductivity decreases rapidly 

 as concentration is reduced, and in such cases perhaps the best way for the present 

 would be to make no correction for the solvent, but to wait until more about its 

 action is understood. But the equivalent conductivities of acids are much greater 

 than those of salts, owing to the high velocity of the hydrogen ion, and in them the 

 correction for the solvent is therefore smaller. And so to preserve uniformity, the 

 correction is made in the measurements on sulphuric acid which follow. Its effect 

 will not appreciably change the general direction of the curve giving the results. 



Having thus determined the value of the concentration m and of the conductivity 

 k of the substance dissolved, we get Jc/m, the equivalent conductivity. 



In order to express the results in a visible form, we may plot a curve with the 

 values of k/ni as ordinates, and the values of \/m (a number proportional to the 

 average nearness of the molecules of solute) as abscissae. This gives a curve in which 

 the very dilute portion is not crowded together as it would be if we took the values 

 of m itself as abscissae, and, moreover, the fact that most of the curves so drawn come 

 out as straight lines for the greater part of their length seems to indicate that there 

 are theoretical as well as practical reasons for choosing this method. The form of 

 these curves is similar to that of the corresponding ionization curves shown in the 

 diagrams. It will be seen that as the concentration of a solution gets smaller, the 

 value of k/m approaches a limiting value. Its maximum can easily be determined 

 from the curve in such cases as potassium chloride or barium chloride, where the slope 

 of the curve is comparatively small and the limit is reached at moderate dilutions. 

 In cases such as those of potassium bichromate and potassium ferricyanide, the maxi- 

 mum values are more uncertain, and this uncertainty is transferred to the ionization 

 curves deduced from them. 



The maximum value having been estimated, the coefficient of ionization, a, is calcu- 

 lated for each solution by dividing the equivalent conductivity by its maximum value, 

 and the curves given below show the results obtained by plotting the ionizations as 

 ordinates and the values of m* as abscissae. 



It will be noticed that, in order to get these ionization coefficients for a solution of 

 any given concentration, it is not necessary to know the absolute value of the 

 equivalent conductivity. For the purposes of these experiments, then, there was no 

 need to measure the constant of the electrolytic cell. To do so satisfactorily would 

 have involved a redetermination each time the cell was dismounted. The approxi- 

 mate values of the equivalent conductivities have, nevertheless, been calculated for 

 convenience of reference ; but it must be understood that their accuracy is not 

 supposed to be as great as that of the ionizations, which are quite independent of 

 their absolute values. 



SECTION 11. On the Results of the Measurements. 

 Sulphuric Add. As an example of the method of work, and of the way in which 



