1904] 



Th cor y of Amphoteric Electrolytes. 



16:5 



tion as dilution progressed than that corresponding to Ostwald's 

 dilution law. This assumption, however, is unnecessary, the theoretical 

 discussion already given being competent to explain the facts. 



The increase in the value of h in the range of dilution examined is 

 obviously of the same order as that calculated for hijK = 100. We 

 should therefore expect to obtain from hydrolysis experiments con- 

 ducted with the hydrochloride of the amino-acid a value for the ratio 

 approximating to this number. Winkelblech found from the catalysis 

 of methyl acetate fo/K = 112 in excellent accordance with the theory. 

 He also determined the same ratio from the conductivity of solutions 

 of the hydrochloride and obtained the divergent value 164. The same 

 discrepancy was observed with most of the other substances ho 

 examined. If we consider, however, that the catalysis method 

 measures the concentration of one ion only, viz., hydrion, whilst the 

 conductivity method is coDcerned with a complex equilibrium among 

 at least five kinds of ions, we see that the former is likely to yield 

 the more accurate results. This view receives confirmation from 

 Winkelbleeh's own data. For the few substances with which there is 

 agreement between the catalysis and conductivity methods, it is found 

 that the latter gives concordant values for the ratio at all dilutions. 

 Where, on the other hand, the two methods do not yield the same 

 result, there are also wide divergences amongst the values of the ratio 

 derived from the conductivities at different dilutions. The presump- 

 tion, therefore, is that the catalysis method is more trustworthy than 

 the other. It may be noted in general that the discrepancy is great 

 for monobasic amphoteric acids when the acid constant is great. 



Knowing the ratio fo/K, the value of k a , and the speeds of the 

 various ions, it is possible to calculate the molecular conductivity, and 

 from this the apparent Ostwald dilution constant h . If we take from 

 the preceding table 0*96 x 10~ 5 as the value of Jc at v = 1000, we 

 obtain 1'02 x 10~ 5 as the approximate value of Jc a , since the table on 

 p. 162 shows that Jc a exceeds k by 6 — 7 per cent. With regard to 

 the speeds of the ions we may adopt Winkelbleeh's value /x M = 357 as 

 the sum of the velocities of hydrion and the anion. There is less 

 certainty as to the sum of the velocities of kation and anion. The 

 velocities attributed by Winkelblech to the kation in this and in 

 similar instances are, in my opinion, considerably overestimated. For 

 the amino-benzoic acids he does not give directly the experimental 

 data from which he estimated the velocity of the kations, but 

 presumably the values were obtained by the same method as that 

 which he adopted for other substances, viz., by measurement of the 

 conductivity of the hydrochloride in presence of excess of base.* 

 Owing to the very considerable hydrolysis of such substances in 

 aqueous solution, the results obtained for p. at the experimental dilutions 

 * Compare Bredig, ' Zeit. far physikal. Chem.,' vol. 13, p. 214 (1891). 



