1904.] 



Theory of Amphoteric Electrolytes. 



161 



the more rapidly as the dilution is small. It will be noticed that d 

 varies with the dilution much more rapidly than «, which for high 

 values of k b becomes nearly independent of the dilution. What is most 

 deserving of attention is that although for k^/K = 1000 the value of 

 the acid constant Jc a is still nearly a million times greater than the 

 value of the basic constant the acidity of the amphoteric substance 

 is greatly diminished at small dilutions, being for example, at v = 10 

 only one-tenth of that of a simple acid with the same constant. 

 Although the concentration of the chief conducting ion of acids is thus 

 greatly diminished, this diminution may be more than compensated by 

 the comparatively great concentrations of the slower ion HX + which 

 appear at the same low dilutions. 



With regard to the negative ions OH - and XOH~, it may be seen 

 from (5) that in the cases above considered b cannot exceed the value 

 10~ 10 , and may thus be neglected in comparison with the other ions. 

 It follows that the concentration of the remaining negative ion c is 

 equal to the sum of the concentrations of the positive ions, viz., a + d. 



All calculations made from the conductivities of solutions of 

 amphoteric electrolytes have hitherto proceeded on the assumption 

 that the same method of treatment might be adopted as that applicable 

 to simple electrolytes. This is, as we see, far from being the case, and 

 we may now consider what manner of results amphoteric electrolytes 

 with the above constants would yield if their conductivities were 

 treated in this erroneous fashion. Perhaps this is rendered most 

 clearly apparent by calculating what values the Ostwald dissociation 

 " constant" would assume at different dilutions when deduced by the 

 ordinary process from the conductivities. 



The molecular conductivity /x^ corresponding to H + , XOH~ at infinite 

 dilution may be taken as from 350 — 370 at 25° when referred to 

 reciprocal Siemens units. The molecular conductivity of HX + , XOHr 

 under the same conditions would be 60 — 70. From every concentration 

 of HX + , then, we may obtain a concentration of H + having equal 

 conducting power, by dividing ^ by a number varying from 5 to 6 

 according to the substance considered. If we add this quotient to the 

 real value of a we obtain a false value a, which is assumed as the value 

 of a in the simple calculation of the dilution constant. The subjoined 

 table contains the values of the apparent Ostwald dilution constant h 

 for the amphoteric electrolytes considered above when calculated in the 

 customary way from the values a = a + d/5 and a = a + d/Q. In each 

 case the constant has been multiplied by 10 5 . 



For ki/K = 1 it will be observed that a fairly good constant k may 

 lie got, the values for the greater dilutions approximating within the 

 limits of experimental error to the true value k a . For hjK = 10 the 

 values of k are no longer even approximately constant, increasing 

 rapidly with the dilution to attain a value at v = 1000 approaching 



