TO THEIR STATE OF IQNIZiTION MACGREGOE. 243 



l a and lp will be characteristic of the ions and will not depend 

 upon the salt from which they have been dissociated. A certain 

 amount of evidence has been accumulated which may be said to 

 point in this direction. In the case of several properties it has 

 been shown that for solutions of considerable dilution, the 

 difference between the values of the property for solutions of 

 two salts (ap and bp) having a common ion and the same 

 molecular concentration, is independent of what the common 

 ion may be ; and the value of the difference divided by the 

 number of gramme-equivalents per litre of the salts in solu- 

 tion has been taken to be approximately the difference between 

 the constants l a and l b . Results of this kind have been 

 obtained by Valscn and Bender for density and refracting 

 power, by Kohlrausch for electrical conductivity, by Raoult for 

 the depression of the freezing point, by Traube * for the change 

 of volume on solution, by Rontgen and Schneider for compress- 

 ibility, and by Jahn for the electromagnetic rotation of the 

 plane of polarization. 



Applying the above expression, we have for the difference 

 in the values of a property per unit of molecular concentration, 

 ( P ap- P bp) /n = k a p (! ~ %>) - k bp( l ~ a bp ) + l p (%- % ) + l a a ap- l b a bp' ( 12 

 arid at infinite dilution 



Had the experiments referred to been all carried out at extreme 

 dilution, as were those of Kohlrausch, afterwards extended by 

 Loeb and Nernst^, the evidence would be quite satisfactory. 

 But in general they have been made at only moderate dilution, 

 and it is obvious from (12) that the approximate independence 

 of the common ion on the part of (P P ftp ) /n, may be quite 

 consistent with considerable variation in l a l b . It is clear that 

 the first three terms of (12) may readily mask any variation 

 in the last two, and that, if the last two did not vary, l a l b 

 could not in all cases be the same. 



* Ztschr. anorgan. Chemie, iii. (1892), p. 1. 

 t Ztschr. fur phys. Chemie, ii. (1888) p. 948. 



