j?8 Conductivity of Aqueous Solutions. Part XL 



that higher transference numbers were obtained with the 0.002 normal 

 solutions than with the more concentrated solutions of both acids confirms 

 the conclusion drawn from the comparison with the conductivity data. 

 The values obtained at 0.002 normal show, moreover, that even at this 

 very low concentration the velocities have not yet become identical with 

 those at zero concentration. 



This change of the transference number may, of course, arise either 

 from an acceleration of the anion or from a retardation of the hydrogen- 

 ion at very high dilution, or from both causes combined. The facts that 

 salts do not as a rule show any change in their transference numbers 

 after a moderate dilution is reached and that their ionization-values cal- 

 culated from freezing-point lowering and other molecular properties agree 

 with those corresponding to the conductance ratio (A/A )* make it proba- 

 ble, however, that it is the fast-moving hydrogen-ion that is mainly, if 

 not wholly, affected. f It is under this (possibly incorrect) assumption, 

 namely, that neutral ions have the same velocity at moderate and at very 

 low concentrations, that the values, given in table 138, of the equivalent 

 conductance of hydrogen-ion at various concentrations were derived. 



The fact that the values of the equivalent conductance of hydrogen-ion 

 are nearly constant for the interval of concentration 0.006 - 0.018 seems 

 to indicate that these are the normal ones, and that the variations at lower 

 concentrations arise from some secondary effect of a general character, 

 determined perhaps by the smallness of the ion-concentration itself. 



The results obtained at the highest concentration (0.05 to 0.06 normal) 

 differ in the case of the two acids, which makes it seem probable that the 

 variation in the stronger solution is due to some different cause, probably 

 one of a specific chemical nature, from that which gives rise to the change 

 at high dilutions. 



As to the bearing of these results on the calculation of ionization- 

 values, it may be said that in the case of largely ionized acids at moderate 

 concentrations it seems in the light of now existing knowledge most appro- 

 priate to divide the observed equivalent conductance of the acid by a A 

 value obtained by adding to the equivalent conductance of the anion that 

 for the hydrogen-ion obtained by the transference experiments above 

 described at the concentration in question. On the other hand in the case 

 of any acid solution in which the few-concentration is less than 0.001 nor- 

 mal the older value (324 at 20 or 315 at 18) for hydrogen-ion is to be 

 preferred. 



*See A. A. Noyes, Z. phys. Chem., 52, 634. 



fit is therefore probable that the decrease in the conductance of strong acids 

 always observed at very high dilutions is not wholly due to impurities in the water. 



