76 



WORK OF J. N. PEARCE. 



70 



60 



50 



40- 



X 30 



20 



10- 



Two conclusions are to be drawn from these relations. It will be noted that the 

 molecular hydration and the total amount of water held in combination are the 

 same for any two salts containing a common cation. It seems most probable that 



if the two anions, CI and NO3, possessed very different hydrating power, this influence 

 would manifest itself. It is a well-known fact that organic acids possess little or no 

 hydrating power, and in the work which we have done upon the strong acids 

 hydrochloric, nitric, and sulphuric this has been found to hold in the dilute solu- 

 tions, where the dissociation is practically complete. 



This would lead us to conclude that 

 the hydrating power of any salt is pri- 

 marily a function of the cation. 



In the discussion of the nitrates and 

 chlorides of the alkaline-earth group, 

 attention was called to the fact that 

 the hydrating power of those salts is 

 an inverse function of the atomic vol- 

 umes. 



In the case of the salts of cobalt, 

 copper, and nickel which we have stud- 

 ied, we have to do with cations which 

 have approximately the same atomic 

 volumes. 



As stated by Ostwald, the migration 

 velocity of an organic acid decreases 

 with increase in the mass of the anion, 

 as well as with increase in the mass of 

 the cation in case of the organic bases. 

 We should expect, then, to obtain larger 

 values for conductivity than those given 

 by the alkaline earth metals. Experi- 

 ment shows the opposite to be the fact. 

 We are, therefore, forced to believe that 

 the effect of the atomic volume of the ions upon the conductivity is more than 

 compensated for by the relatively large volume of the ionic complex. 



Bredig 1 pointed out the fact that the migration velocities of elementary cations 

 are a periodic function of the atomic weights. When plotted in a curve, where the 

 orciinates represent velocities and the abscissas the atomic weights, it will be seen 

 that the alkali metals lie very near the maxima of the curve, along with the halogens. 

 At the extreme minima we find aluminium and chromium. Slightly above these 

 lie the metals of the copper group, zinc, and cadmium, while still higher are to be 

 found the metals of the alkaline earths. 



The significance of this periodic relation between the migration velocities of the 

 cations and the atomic weights has never been satisfactorily explained. 



0.10.25 0.5 



0.75 1. 



Concentration 

 Fig. 30. 



1.5 



2. 



iZeit. phys. Chem., 33, 242 (1894). 



