8 WORK OF J. N. PEARCE. 



5. The hydrating power of a salt is, primarily, a function of the cation. The 

 results show that two salts which crystallize with the same amounts of water of 

 crystallization and contain a common cation exhibit hydrating power of the same 

 order of magnitude. 



6. It has been found that the hydrating power of a cation is an inverse function 

 of its atomic volume. Those cations which have the smallest atomic volumes have 

 the greatest hydrating power, and vice versa. We may state the relations thus: 

 The hydrating power of the ions is a function of their atomic weights. 



7. Furthermore, we have found that those cations which have the greatest migra- 

 tion velocities exhibit, also, the smallest hydrating power, and vice versa. This 

 probably accounts for the apparent anomaly which exists in the relation between 

 the migration velocities of the ions and their atomic weights and atomic volumes. 

 The influence upon the migration velocity of the hydration of those ions with small 

 atomic volumes is greater than that of the small hydration of those ions which have 

 large atomic volumes. 



8. In the case of every salt it has been found that the dissociation in the dilute 

 solutions, as measured by the conductivity method, is less than that calculated from 

 the freezing-point lowering. Since the freezing-point and conductivity measure- 

 ments of the dilute solutions were made at approximately the same temperature, 

 the number of the ions present, their velocities, and their hydration are practically 

 the same in both cases. The solutions have, likewise, the same viscosity. There- 

 fore, the friction between the solvent and ion will vary directly as the surface of the 

 latter. This being the case, the greater the dilution the greater wall be the com- 

 plexity of the hydrate, and, consequently, its surface. We should expect to find, 

 therefore, a greater abnormality in the dissociation, as measured by the two methods, 

 the greater the dilution at which the measurements are made. The results show 

 this to be the fact. 



It is only in case of those salts which crystallize in the anhydrous condition that 

 we obtain comparable values for the dissociation as measured by the two methods. 

 These values are found only in those concentrations which lie close to that concen- 

 tration which gives the minimum molecular lowering. 



