PROPERTIES OF AQUEOUS SALT SOLUTIONS 321 



more slowly than the product of the valences of the ions. The pro- 

 portionality becomes a fairly close one, however, when the salts are 

 compared at the same molal instead of the same equivalent concen- 

 tration. Thus, with the help of the Kohlrausch concentration func- 

 tion, it is calculated from the preceding values that the un-ionized 

 fractions in ~ molal solution are as follows: 



13 per cent for the uni-univalent salts, 

 29^ per cent for the uni-bivalent salts, 

 41 per cent for the uni-trivalent salts, 

 62 per cent for the uni-quadrivalent salts, 

 55 per cent for the bi-bivalent salts, - 



which are seen to be approximately the required multiples of the 

 constant factor 14. 



Before leaving this subject it should be stated that the results con- 

 form, on the whole, about equally well to the rule that the decrease 

 of equivalent conductivity (instead of ionizatiori) is roughly constant for 

 salts of the same type ; and when the comparison is made at the same 

 equivalent concentration, distinctly better to the rule that the de- 

 crease of equivalent conductivity is proportional to the product of the 

 valences of the ions for salts of different types. When compared at the 

 same molal concentration, however, this rule does not apply. These 

 rules were originally stated by Ostwald. They differ not inconsider- 

 ably from those expressing the change in ionization - - namely, to an 

 extent corresponding to the variations of the conductivities at ex- 

 treme dilution. The deviations are so irregular, however, that, from 

 an empirical standpoint, the choice between the two pairs of rules is 

 arbitrary. In either form these rules seem to justify the inference that 

 the degree of ionization of salts, unlike that of the organic acids and 

 bases, is not primarily a specific chemical property determined by 

 chemical affinity, but that it is determined, at least in the main, 

 by the magnitude of the electric charges on the ions. 



The establishment of the principle in regard to the ionization of a 

 mixture of salts has a direct bearing on the phenomenon of the effect 

 of one salt on the solubility of another with a common ion. It has 

 been usually assumed that in a (not too concentrated) saturated solu- 

 tion the un-ionized molecules of the salt always have the same concen- 

 tration; and, secondly, that the product of the ion-concentrations 

 (each raised to a power corresponding to the number resulting from one 

 molecule) also retains the same value. And the experimental results 

 in several cases have been shown to accord fairly well with these two 

 hypotheses. Yet their simultaneous validity is quite inconsistent with 

 the principle in regard to the ionization in mixtures. In fact, when 

 considered in the light of this principle, the existing data lead to the 

 conclusion that the former hypothesis is not even approximately true, 

 and that the latter one, at any rate in cases where the ionization is far 



