ELECTRICAL CONDUCTIVITIES, ETC. 



09 



The salts of cadmium present several points of interest. The chloride crystal- 

 lizes with two molecules of water, while the bromide and iodide crystallize without 

 water. Notwithstanding the small hydrating power of the cadmium ion, its salts 

 conduct less than the corresponding compounds of calcium, strontium, barium, and 

 magnesium. The explanation of this is well known. The halides of cadmium are 

 much less dissociated than the halides of the metals related chemically to it, hence 

 the smaller conductivity. 



The conductivities of the salts of manganese, nickel, and cobalt call for no special 

 comment. Manganese nitrate underwent some decomposition at 35. Nickel ace- 

 tate underwent hydrolysis, the solution having the odor of acetic acid. Salts of these 

 three metals give conductivities that are of the same order of magnitude, and are, 

 indeed, very nearly equal. This would be expected from the relative hydrating 

 power of the manganese, cobalt, and nickel ions. 



The above comments also apply to the salts of copper that were investigated. At 

 65 these salts, in general, underwent decomposition, and the work, therefore, could 

 not be extended to this temperature. The salts of aluminium, iron, and chromium 

 are all quaternary electrolytes, i. e., the molecule breaks down into four ions. The 

 conductivities of these substances are, therefore, large. Many of these salts undergo 

 hydrolysis at the higher temperatures. This is so pronounced with the salts of iron 

 that they could not be studied at all at the higher temperatures. The salts of alu- 

 minium, iron, and chromium crystallize with large amounts of water, i. e., these ions 

 have great hydrating power. The order of magnitude of this power can be seen from 

 the earlier work in this laboratory.* That these substances have very large temper- 

 ature coefficients of conductivity will be seen a little later. 



The salts of uranyl undergo hydrolysis, especially at the more elevated temper- 

 atures. To this hydrolysis there is an appreciable time factor. This accounts for 

 the difficulties encountered by different workers in obtaining concordant results. 



The relations pointed out above will be seen from the table of molecular conduc- 

 tivities on pages 70 and 71. Here the results are given at two dilutions widely 

 removed from one another, and at three temperatures as widely different as possible. 



A DEHYDROLYTIC TIME FACTOR. 



An observation of some importance was made by Mr. Shaeffer. He took four 

 parts of a n/32 solution of chromium chloride. One of these was kept at room temper- 

 ature. A second was heated for two hours to 50, a third for the same time to 05, 

 while a fourth was heated for two hours to 90. All four solutions were then brought 

 to the same temperature and their conductivities determined. The conductivities 

 of all four solutions were taken at 35, at 50, and at 05, and the results are given 

 in the following table: 



Chromium Chlokide. 



"Carnegie Institution of Washington Publication No. 60, pp. 87-93. 



