278 Prof. J. G. MacGregor on the Calculation of 



It will be observed that while the numbers in the various 

 horizontal rows show a general agreement, they differ very 

 considerably from one another, the extreme differences ranging 

 from 0*7 to 205 per cent. 



He found also that two solutions of Ammonium Acetate 

 and Acetic Acid respectively, which were determined as above 

 to be isohydric, contained, according to Kohlrausch, amounts 

 of the ion CH 3 C00 which were in the ratio 1 : 0'79, a ratio 

 which is only very roughly equal to unity. 



So far as result is concerned these tests are not satisfactory. 

 But the lack of agreement may have been due to various 

 causes : (1) the data for calculation may have been defective ; 



(2) the change of volume which would doubtless occur on 

 mixing, even with very dilute solutions, may have been too 

 great for the application of Arrhenius's deduction ; and 



(3) the difference between the values of fi n in simple solution 

 and in a mixture may be too great to admit of the identifica- 

 tion of isohydric solutions by the method employed. 



On the other hand, Arrhenius has calculated* the conduc- 

 tivities of two dilute solutions containing in each case given 

 quantities of two acids, employing for this purpose a series of 

 approximations based on his own observations of isohydric 

 solutions of the acids ; and the calculated values were found 

 to agree with those observed to within 0*5 and 0'2 per cent, 

 respectively. So far as result is concerned this forms a much 

 more satisfactory test than those mentioned above. But the 

 number of calculations is too small to exclude the possibility 

 of accidental agreement. 



The calculation of the conductivity of a mixture of electro- 

 lytes is so severe a test of the ionisation theory of electrolysis 

 that I have thought it well to test its possibility on a more 

 extensive scalo, especially as a considerable body of material 

 is available for this purpose in the observations of the con- 

 ductivity of mixtures of solutions of Potassium and Sodium 

 Chlorides made by Benderf. The present paper contains 

 the results of calculations of the conductivities of mixtures 

 determined experimentally by him. 



Method of Calculation, 



In order to make such calculations by Arrhenius's method, 

 it would be necessary to make a preliminary determination of 

 a number of isohydric solutions of the two salts, and to restrict 

 the calculations to very dilute solutions. They may be made, 

 however, without such preliminary experiments and without 



* Wiedemann's Annalen, xxx. p. 73 (1887). 

 t Ibid. xxii. p. 197 (1884). 



