78 ELECTRICAL CONDUCTIVITIES, ETC. 



hydrated in aqueous solution. Those in Table II crystallize with very different 

 amounts of water, but all with fairly large amounts of water. These substances 

 are, therefore, much hydrated in aqueous solution. 



It should be noted that the sulphates, single and double phosphates, chromates, 

 bichromates, ferro- and ferricyanides,etc, are omitted from both of the above tables. 

 The relations here under discussion do not apply to these more complex substances. 



Let us now compare the temperature coefficients of conductivity, expressed in 

 conductivity units per degree rise in temperature, for some of those substances 

 which have slight hydrating power, with the corresponding coefficients for some of 

 those compounds which have a much greater power to combine with water. 



The volumes range from 8 to 1024, and the temperature coefficients are calculated 

 between 25 and 35, and between 50 and 65. It will be seen, in general, that the 

 substances in Table I have much smaller coefficients of conductivity at all dilutions 

 and all temperatures than those in Table II. This is true, even when we take into 

 account the fact that the substances in Table I are binary electrolytes each mole- 

 cule breaking down into two ions; while those in Table II are nearly all ternary elec- 

 trolytes, each molecule yielding three ions, while the two salts of aluminium are 

 quaternary electrolytes, each molecule breaking down into four ions. 



Another fact of equal importance is brought out by comparing the results in Table 

 I with one another, and similarly those in Table II with one another. If the tem- 

 perature coefficient of conductivity is a function of the decrease in the complexity of 

 the hydrate formed by the ion, with rise in temperature, then we might expect that 

 those substances which have equal hydrating power would have approximately the same 

 temperature coefficients of conductivity. 



An examination of the above tables will show this to be true. The substances in 

 Table I all have slight hydrating power, as would be expected from the fact that 

 they all crystallize with little or no water. It will be seen that their temperature 

 coefficients of conductivity are all of the same order of magnitude. 



The compounds in Table II have different hydrating power, but all have very 

 great hydrating power. Most of them, however, have hydrating power of the same 

 order of magnitude. Indeed, this would be expected, since most of these substances 

 crystallize w r ith six molecules of water. There are a few substances in this table 

 which crystallize with less than six molecules of water. Thus, barium chloride crys- 

 tallizes with only two molecules, yet it forms hydrates of comparable complexity* 

 with those substances which crystallize with larger amounts of water. That its 

 temperature coefficients of conductivity are of the same order of magnitude as the 

 other substances in the table is, therefore, entirely in keeping with the above rela- 

 tion. The hydrates formed by barium nitrate have not yet been worked out, so 

 that it is impossible to say whether or not it presents an exception to the above 

 relation, it crystallizing without water. 



Manganous chloride crystallizes with only four molecules of water, yet the work 

 of Jones and Bassettf has shown that it forms hydrates about as complex as the 



*Carnegie Institution of Washington Publication No. 60. 



tAmer. Chem. Journ., Z3, 562 (1905); Carnegie Institution of Washington Publication No. 60, 

 pp. 75 and 76. 



