Section 102. Conductivity and Ionization-Constants. 291 



The measurements of May 30 to June 5, given in table 120, were made 

 with a sample of the acid obtained by recrystallizing three times from 

 conductivity water with the usual precautions the material used in these 

 measurements of May 21 - 25. The agreement of the results with the 

 two samples shows that the material underwent no change in the three 

 crystallizations. Ostwald* obtained the value 0.21 X 10 -6 for the con- 

 stant at 25 without using special precautions. 



Sosman (see Part VII) with solutions prepared both from liquid 

 ammonia and from the pure ammonia water, obtained for the constant 

 of ammonium hydroxide at 18, as the mean of a large number of deter- 

 minations at concentrations from 0.01 to 0.1, the value 17.15 X 10~ 6 , 

 which is identical with that given in table 121. He obtained the value 

 17.9 X 16" 6 as the means of two determinations at 25. This value agrees 

 closely with the value 18.06 X 10~ 6 here presented. Earlier investigatorsf 

 obtained considerably higher results, partly owing to the incomplete 

 elimination of impurities and to the use of other values of the equivalent 

 conductance for complete ionization. 



The results given in the tables show that the constants of the two sub- 

 stances do not vary considerably with the concentration. Sosman, using 

 a much greater range of concentration, also found that the variation of 

 the constant for ammonium hydroxide at 18 was very small. 



It will be observed that with rising temperature the ionization of the 

 acid increases very rapidly, and that that of the ammonium hydroxide also 

 increases, but to a much smaller extent. 



No reliable estimate of the accuracy of these constants can be made. 

 It seems, however, not improbable that the equivalent-conductance values 

 for the acid may be too high by one per cent, owing to the effect of 

 impurities ; and also that its equivalent-conductance values for complete 

 ionization may be in error by one per cent at 18 and 25, and by even 

 2-3 per cent at 0. Under these assumptions the error in its ionization- 

 constant may be 3-4 per cent at 18 and 25, and 5-7 per cent at 0. In 

 the case of ammonium hydroxide, although the values of the equivalent 

 conductance at the higher concentrations are probably somewhat more 

 exact than those for the acid, yet there is an even greater uncertainty in 

 the values for complete ionization, so that the ionization-constants are 

 probably of the same order of accuracy. 



*Z. physik. Chem., 3, 181 (1889). 



fBredig, Z. physik. Chem., 13, 294 (1894). Davidson, Ber. d. chem. Ges., 31, 1612 

 (1898). Hantzsch and Sebaldt, Z. physik. Chem., 30, 296 (1899). 



