ON THE BOILING POINTS OF AQUEOUS SOLUTIONS OF ELECTROLYTES. 229 



Cadmium Iodide. 



Grm. eqs. 



Elevation of Ion 



ization 



Elevation 



per Litre. 



Boiling Point. C 



o-eff. 



Constant. 



•445 



•169 



167 



520 



•639 



•218 



146 



516 



1-048 



•286 



119 



519 



1-210 



•354 



115 



521 



1-308 



•436 



113 



519 



1-563 



•517 



107 



522 



1-825 



•577 



101 



510 



2021 



•682 



096 



526 





Cadmium ( 



Chloride. 





Grins, eqs. 



Elevation of 



Ionization 



Elevation 



per Litre. 



Boiling Point. 



Co-eff. 



Constant. 



•330 



•129 



■251 



517 



1-512 



•484 



•132 



520 



2-446 



•754 



T02 



516 



3182 



1-022 



•084 



523 



3-884 



1-154 



•066 



517 



4-390 



1-324 



•061 



525 



4-936 



1-504 



•056 



' 518 



5-892 



1-864 



•048 



517 



6-550 



2-110 



•042 



529 



These several results in combination show that largely different values of the 

 constant for the ion and the molecule are not the cause of the increase of the 

 elevation constant with concentration. Having shown that the high values obtained 

 for the elevation constant are not accounted for by the supposition put forward, we 

 will now consider the hydration theory. 



When curves are drawn (see page 226) for which elevation of the boiling point per 

 gramme equivalent, is plotted against the number of gramme equivalents per litre, 

 these curves exhibit a minimum, and consequently show that, notwithstanding the 

 decrease of ionization, elevation of the boiling point per gramme equivalent increases 

 with concentration after a certain concentration has been reached, the portion of all 

 the curves for concentrated solutions bending towards the equivalent elevation axis. 



On the hydration theory this curvature is at once explained as due to the quantity 

 of active water being diminished through water molecules combining with salt particles 

 (molecules or ions). Consequently the elevation increases as concentration increases, 

 so long as the active water continues to diminish. 



The minimum point is explained by the falling off of hydration until its effect is 

 balanced by change in ionization and the curvature of the portion of the curve between 

 the minimum point and the equivalent elevation axis, as due to increase of ionization. 



As the change in ionization is not very considerable for a small range of con- 

 centration, the fact that between the minimum point and the equivalent elevation axis 

 it has an influence which has a very considerable effect on the curve, indicates that for 

 this portion of the curve hydration must have an inappreciable influence, or, in other 

 words, that for dilute solutions the hydration, if any, is negligible, as has been 

 previously pointed out by various observers. 



For the curves* (fig. 16) for which values of My/m*, have been plotted as ordinates 

 and values of the elevation constant as abscissae, it has been noted that the curves 

 consist of approximately rectilinear portions branching from a common rectilinear trunk 

 at points corresponding to different concentrations in the case of different salts. The 

 branching off of these curves is readily explained on the hydration theory as due to 



* Page 227. 



