62 



WORK OF J. N. PEARCE. 



70 1 



ular lowering of the freezing-point. A similar minimum was noted by Jones and 

 Bassett 1 for concentrations ranging from 0.102 normal to 0.153 normal. It has been 



assumed hitherto, by Jones and his 

 coworkers, that the minimum in the 

 freezing-point lowering always occurs 

 in that concentration where the effect 

 due to decrease in dissociation is just 

 counterbalanced by the effect due to 

 hydration. The values of L' and M 

 also show that the abnormality of the 

 freezing-point lowering is greatly aug- 

 mented by the relatively great hydrat- 

 ing power of the ions, since it is the 

 ions with which we are chiefly con- 

 cerned in the dilute solutions. A 

 glance at column H shows us at once 

 the great hydrating power of the ions 

 in dilute solution. The values of H 

 decrease regularly with increase in 

 concentration to 0.10 normal. From 

 that concentration on, the decrease in 

 hydration is very slight as the concen- 

 tration increases. In these concentra- 

 tions the combined effect upon the 

 freezing-point lowering, due both to 

 the dissociation and to the hydration 

 of the ions, is small, compared with the effect due to the undissociated molecules. 

 If we refer to the literature 2 bearing upon the relation between the water of 

 crystallization of a salt and the 

 temperature at which it crystallizes 

 we see that, over a definite range of 

 temperature, the amount of water of 

 crystallization is constant. If, then, 

 we eliminate the hydration due to ^ 

 the ions, we should expect to find the 

 number of molecules of water com- 

 bined with one molecule of the salt 

 to be a constant for a definite range 

 of temperature. This is clearly shown 

 by the values of H for the more con- 

 centrated solutions. 



The values of M are plotted in fig. 23 against the concentrations as abscissae. 

 The curve shows, at a glance, that the amount of water held in combination from 

 the dilution at which the minimum occurs is a linear function of the concentration. 



0.10.25 0.5 



0.75 1. 



Concentration 

 Fig. 22. 



0.10.25 0.5 



0.75 1. 



Concentration 

 Fig. 23. 



1.5 



lAmer. Chem. Journ., 33, 54S (1905). 



'Bassett: Ibid., 34, 294 (1905). 



