ON THE BOILING POINTS OF AQUEOUS SOLUTIONS OF ELECTROLYTES. 231 



times less molecules in solution than some of those which ionize less, when these com- 

 mence to hydrate. 



One sees, therefore, that in case many ions are immediately formed, hydration 

 commences in dilute solutions, and that where the salt ionizes feebly a greater con- 

 centration is reached, sometimes a very much greater (pages 220, 221, and 230). 



This indicates that the commencement of hydration is dependent on the number 

 of ions in solution, not on the number of molecules, and indicates that the ions 

 hydrate. 



With regard to the non-electrolytes, Roth # finds that for various non-electrolytes 

 considered there is a divergence of about 2 per cent, from the depression constant ; the 

 meaning of which is that, so far as his observations went, there was no hydration. 



P. W. Robertson, with t regard to the esters in phenol solution, finds " that 

 they have either a high initial depression and a negative rate of association, or associate 

 slightly in dilute solutions and thus exhibit a minimum." Although these results were 

 obtained from phenol as solvent, nevertheless they are interesting from the standpoint 

 of hydration. 



Loomis | found for non-electrolytes " that depression of the freezing point is either 

 the same at all concentrations or changes gradually when referred to one thousand 

 grammes of the solvent." 



These results indicate that some non-electrolytes hydrate, others do not. 



The results I have obtained for non-electrolytes are in harmony with those of 

 Loomis, Roth, and Robertson. 



In this respect possibly the electrolytes resemble the non-electrolytes, in some 

 instances their molecules hydrate, in others not. 



Hydration Data. 



We have now reached a point when it is desirable to obtain hydration data. 

 Consequently I have made out the following formulae for (1) both molecular and ionic 

 hydration, (2) ionic hydration only, and (3) molecular hydration only, so that calculations 

 may be made of the number of molecules of water combined with one molecule or ion 

 of salt, or with each according as hydration may be looked upon as only molecular, ionic 

 alone, or both molecular and ionic. 



To obtain these results it was essential to know the number of grammes of combined 

 water, i.e. the amount of solvent taken up by the salt particles, or combined with these. 



I. To obtain the number of grammes of combined or associated solvent. 



If C be the value of the so-called boiling-point constant obtained at a certain 

 concentration, we have 



c= W ^L AE > ■ ....... (1). 



(1 +w - la)A.w 



* Zeit. phys. Chemie, 43, 539-564 (1903). t Jour. Chem. Soc, Oct. 1905. 



X Rev. Phys. 12, 220 (1901). 



