152 



DISCUSSION OF EVIDENCE. 



rise in temperature on both of these factors would be to increase the 

 velocities of the ions and, consequently, the conductivity. 



Another factor must, however, be taken into account. That many 

 ions in aqueous solutions are strongly hydrated seems now quite 

 generally accepted. We have seen that these hydrates are relatively 

 unstable and break down with rise in temperature. The simpler the 

 hydrate formed by an ion, the smaller the mass of the ion; the smaller 

 the mass of the ion, other things being equal, the less resistance it 

 will offer when moving through the solvent. Therefore, rise in tem- 

 perature should increase the velocity of the ion. 



TABLE 48. Temperature coefficients of conductivity. 



If decreasing complexity of the hydrate formed by the ion with 

 rise in temperature plays any prominent part in determining the large 

 temperature coefficient of conductivity, since the complexity of such 

 hydrates would decrease more with rise in temperature, we should 

 expect to find that the ions which have the greatest hydrating power 

 would have the largest temperature coefficients of conductivity. This 

 is a concrete and, it would seem, necessary consequence of the hydrate 

 theory in aqueous solutions. Further, it is one which can be tested 

 directly by experiment. Is it true? 



We have seen that the hydrating power of a salt, or the ions into 

 which it dissociates, is approximately proportional to the number of 

 molecules of water with which it crystallizes. This is the same as to 

 say that the salt which has the greatest power to bring water with it 

 out of solution is the one, other things being equal, which would hold 

 the largest number of molecules of water in combination with it in 

 solution. The question is, therefore, is there any relation between 



