154 DISCUSSION OF EVIDENCE. 



than those in table 49. In making this comparison we must, of course, 

 take into account the fact that the substances in table 48 are binary 

 electrolytes, each molecule breaking down into 2 ions, while the sub- 

 stances recorded in table 49 are all ternary electrolytes, each mole- 

 cule breaking down into 3 ions, except the two salts of aluminium 

 which are quaternary electrolytes, each molecule yielding 4 ions. Even 

 taking all of these facts into account, the temperature coefficients 

 of conductivity for the slightly hydrated salts are much smaller than 

 those for the strongly hydrated compounds. This is exactly what 

 would be expected. The complexity of the hydrates of slightly 

 hydrated salts could change only a little with rise in temperature. 

 Consequently, the mass of the hydrated ion would change only slightly 

 with rise in temperature, and this effect of temperature on conductivity 

 would be very small. 



Another relation manifests itself when we compare the results in 

 table 48 with one another, and those in table 49 with one another. If 

 the temperature coefficient of conductivity is a function of the decreas- 

 ing complexity of the hydrate formed by the ion, as the temperature 

 is raised we should expect that those substances which have equal 

 hydrating power would have approximately the same temperature 

 coefficients of conductivity. 



The substances in table 48 have only slight hydrating power, shown 

 by the fact that they crystallize with little or no water. The fact is, 

 their temperature coefficients of conductivity are all of the same order 

 of magnitude. 



The salts in table 49 have different hydrating power, but all have 

 great power to combine with water in aqueous solution. A large 

 number of these compounds have approximately the same hydrating 

 power, as would be expected from the fact that many of them crystal- 

 lize with 6 molecules of water. Barium chloride crystallizes with only 

 2 molecules of water, yet forms hydrates of complexity comparable 

 with the other salts 1 in this table. Its temperature coefficients are of 

 the same order of magnitude as those of the other substances in the 

 table. Manganous chloride with 4 molecules of water of crystalliza- 

 tion, and copper chloride with 2, form hydrates of the same degree of 

 complexity as the other salts in this table. Their temperature coef- 

 ficients are in keeping with this fact. The chloride of aluminium 

 crystallizes with 6 molecules of water and the nitrate with 8. These 

 salts, as has already been pointed out, break down yielding 4 ions 

 each. Their temperature coefficients are larger than those of the 

 ternary electrolytes. 



The more dilute the solution, the more complex the hydrate formed 

 by the molecule or the ion. This is but the expression of the action 



Carnegie Inst. Wash. Pub. No. 60, pp. 75, 76. 



