rate at l - 8 gramme eqs. per litre. 



1-0 



5? )5 



1-0 



55 ■>■> 



'74 



)> ): 



70 



>J 5? 



•26 



)) >> 



230 REV. S. M. JOHNSTON 



diminution of the amount of active water and consequent increase of the elevation 

 constant when hydration is not taken into account in its computation. 



The ionization at which the curves change direction gives a means of determining 

 at what ionization hydration commences and the corresponding concentrations may be 

 obtained. 



The following rough approximations for the commencement of hydration have been 

 obtained in this way. 



Cdl 2 commences to hvdrate at 



LiN0 3 



NH 4 C1 



NHJBr 



NHJ 



LiBr 



It has been pointed out that the value of the elevation of the boiling-point constant 

 does not change its apparent value by the ordinary method of computation until a 

 certain ionization is reached. Further, when the equivalent depression of freezing 

 point is plotted against equivalent concentration, the curves exhibit a minimum ; and in 

 the curves when equivalent elevation is plotted against equivalent concentration, as 

 given by Biltz, # Jones and Getman,! and those obtained by my self, \ a minimum 

 also is found. Each indicates that there is no hydration in dilute solutions. 



On this point Jones and Getman § say : " In the dilute solutions there is no evidence 

 of the existeDce of hydrates." 



Passing on to consider hydration more minutely, the question arises — Do the ions, 

 or molecules, or both, hydrate ? 



The answer which Jones and Getman || give to this question is : " It is difficult to 

 say whether it is the molecules, or the ions, or both, that form the hydrates in concen- 

 trated solutions, since all such solutions that we have studied contain both molecules 

 and ions. Since, however, these solutions that are most concentrated and therefore 

 the least dissociated show the greatest amount of hydration, it seems probable that 

 it is the molecules and not the ions that combine with water and form hydrates." 

 This conclusion II has been modified. 



Jones and Getman found the above idea on the fact that the more concentrated 

 solutions are those in which hydration is greatest. Where there are relatively few 

 molecules, there is no hydration. 



If one were only to consider a single salt or a few salts of the same kind, prefer- 

 ably those which ionize highly, then one might see ground for their conclusion ; 

 but when salts which ionize very differently are considered, it is seen that, as a rule, 

 those which ionize highly commence to hydrate at the smaller concentration, and it 

 is these which have the smaller number of molecules at this concentration, and many 



* Zeit. phys. Uhemie, 40, 204 (1902). t Am. Clieni. Jour., 31, 325 (1904). t Page 226. 



§ Am. Chem. Jour., 31, 355 (1904). || Am. Chem. Jour., 31, 356 (1904). IT Am. Chem. Jour., 33, 583 (1905). 



