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



Thus the first solutions of substances like barium chloride and copper sulphate 

 reach a constant resistance as soon as the measurements are begun, the slight decrease 

 with time being caused by the slow rise of temperature which is going on. In the 

 eases of potassium permanganate and sulphuric acid, however, the resistance goes on 

 rising for nearly, or quite, half an hour after the first addition of stock solution is made. 

 Potassium permanganate shows this phenomenon in the first solution only, the second 

 one keeping constant or slowly decreasing in resistance just as do the solutions of 

 normal salts, but in sulphuric acid it is appreciable in the second solution also. We 

 are thus again led to the conclusion that the action with permanganate, whatever it 

 may be, is completed by the first addition of salt, while a second addition of sulphuric 

 acid is acted on in a similar manner to the first. 



Experiments at higher temperatures have shown that this drop in the curve at 

 extreme dilution occurs in the cases of acids, alkalies, and, to a smaller extent, of 

 carbonates, which are unstable substances whose solutions probably contain a certain 

 amount of alkali. Thus the phenomenon seems to be associated with the presence of 

 hydrogen or hydroxyl ions, and to occur only in solutions which contain such ions. 



Now these ions have two peculiarities. Firstly, they form the constituents of the 

 solvent, water, in which the substances are dissolved ; and, secondly, they are ions 

 which travel in aqueous solutions with abnormally high velocities. These high 

 velocities may, however, be connected with the existence of the ions in the solvent. 



It is possible, in cases where one of the ions of a salt is much more mobile than 

 the other, that the dilution of solution near the two electrodes, which we know to be 

 the consequence of the movement of the ions, is so great at one electrode that the 

 effective resistance of the liquid is increased, even in the small time during which the 

 current flows in one direction. If this were the case we should expect that, in dilute 

 solutions of acids where the equivalent conductivity has passed beyond the maximum, 

 the measured resistance would depend on the rate of alternation of the current. 

 Experiments made with such a solution of sulphuric acid showed that when the 

 speed of the commutator was altered, the variation in resistance was inappreciable, 

 just as it is in cases of other solutions. 



Another possibility is that when one of the ions of the dissolved salt is also a con- 

 stituent of the solvent, there is some action between them, whereby either the 

 number of effective ions or their velocity is reduced. Such an action might require 

 time to reach its completion, and hence is not inconsistent with the gradual rise in 

 resistance which has been previously described. It is a well known fact that the 

 amount of chemical dissociation is greatly reduced when one of the products is already 

 present. Some such relation may explain the phenomenon in question. 



The absolute values of the equivalent conductivities of potassium bichromate and 

 potassium ferricyanide (see below) are, when calculated from the formula? iK 2 O 2 O 7 

 and ^K 3 Fe(CN) 6 , higher than the numbers for any of the other salts used. It is 

 unlikely that the complex anions of these substances should travel faster than simple 



