PROPERTIES OF AQUEOUS SALT SOLUTIONS 313 



Two conclusions are to be drawn from this result. The first is, that 

 complex ions are not present in important quantity in the solutions 

 of these salts. And the second is, that the migration-velocities of the 

 two ions of a salt vary by the same percentage amount, if they vary 

 at all, with changes in its concentration. It is scarcely admissible, 

 however, to regard this last fact even as an indication that the hypo- 

 thesis of constant migration-velocities is correct; for any change in 

 the character of the liquid medium might well affect the velocities of 

 different ions not far from equally. 



Important evidence in regard to this hypothesis and that stating 

 that ions and the un-ionized molecules associated with them have 

 a normal osmotic pressure is, however, furnished by the agreement of 

 the ionization values derived, on the one hand, from the conductivity- 

 ratio, and, on the other, from the properties thermodynamically re- 

 lated to osmotic pressure. Three of these properties have been meas- 

 ured with sufficient accuracy with certain electrolytes to make the 

 results of significance, namely, the freezing-point lowering, the electro- 

 motive force of concentration-cells, and the heat of solution in relation 

 to change of solubility with the temperature. Under the assumption 

 that osmotic pressure and gaseous pressure are equal under identical 

 conditions, a relation between each of these properties and the de- 

 gree of ionization of an electrolyte can be derived with the help of 

 the second law of energetics. Then, either this ionization value may 

 be directly compared with the conductivity-ratio, or, assuming pro- 

 visionally that the latter is a correct measure of ionization, the mag- 

 nitude of the property in question may be calculated, and the result 

 compared with that obtained by direct measurement. In the case of 

 the freezing-point lowering, I have adopted the first of these methods. 

 For the five salts for which both reliable freezing-point determina- 

 tions and accurate conductivity-measurements at exist, the ion- 

 ization values corresponding to both of these properties have been 

 computed. Especial attention was given to the selection of the best 

 value of the freezing-point lowering constant and to the extrapolation 

 of the conductivity for zero concentration, the details of which can- 

 not be here described. The results may be summarized as follows: 



In case of the two uni-univalent salts and the three uni-bivalent 

 salts hitherto carefully investigated, the ionization values derived from 

 freezing-point lowering do not differ from those derived from conduc- 

 tivity, between the concentrations of ^--^ and ^ normal, by more than 2 

 or 3 per cent. 



The five salts referred to are potassium and sodium chlorides, 

 potassium and sodium sulphates, and barium chloride. The two sets 

 of values for potassium chloride, for which an abundant experimental 

 material exists, exhibit no pronounced or systematic differences; but 

 for the other four salts the freezing-point leads to values which are in 



