CHAPTER II. 



SALTS OF COBALT. 



Jones and Uhler, 1 in their work on the absorption spectra of salts of 

 cobalt and copper, discussed a number of the more important papers 

 dealing with cobalt, so that it is necessary only to make brief reference 

 to them here. 



Babo 2 observed a number of the color changes produced in cobalt 

 salts by change in temperature, or by addition of a dehydrating agent. 

 Similar observations were made by Gladstone 3 and Schiff. 4 



Bersch 5 proposed the view that there are two modifications of the 

 compound CoCl 2 .6H 2 the one red and the other blue and would thus 

 account for the color changes in cobalt salts with rise in temperature. 



Tichborne 6 would also account for these color changes on the basis of 

 hydration, and Vogel's 7 work pointed in the same direction. 



The investigations of Russell 8 on the absorption spectra of solutions of 

 cobalt salts are important. He worked under various conditions, such as 

 with the fused salt, with its solution in concentrated hydrochloric acid, 

 and with solutions in the various alcohols and glycerol. He also studied 

 the effect of changes in temperature on the absorption spectra. He con- 

 cluded, as the result of all of his work, that the color of the aqueous solu- 

 tions was due to the presence of hydrates. 



Potilitzin 9 showed that the conclusion of Bersch, that there are two 

 modifications of the compound CoCl 2 .6H 2 0, is an error, and that the for- 

 mation of blue cobalt chloride from the red modification is always a dehy- 

 dration phenomenon. 



Etard 10 studied the color changes and also the solubility curve of 

 cobalt chloride and iodide, and showed from the sudden changes in the 

 direction of the solubility curves the existence of various hydrates of these 

 salts. He also studied the changes in the absorption spectra of cobalt 

 chloride with changes in temperature. 



Engel u does not believe that any general theory can be advanced to 

 account for the changes in color of cobalt salts, but thinks that the blue 

 color is often due to the formation of double compounds. The blue color 

 of a hot, saturated solution of cobalt chloride he regards as due to a double 



1 Publication No. 60, Carnegie Institution of Washington. 



' Jahresber., 1857, 72. 



' Journ. Chem. Soc., 10, 79 (1859). 



Lieb. Ann., 110, 203 (1859). 



1 Sitzungsber. Wien Akad., n, 56, 726 (1867). 



"Chem. News, 25, 133 (1872). 



7 Ber. d. deutsch. chem. Gesell., 8, 1533 (1875); 11, 913 (1878); 12, 2313 (1879). 



8 Proc. Roy. Soc., 32, 258 (1881). Chem. News, 59, 93 (1889). 



Ber. d. deutsch. chem. Gesell., 17, 276 (1884), and Bull. Soc. Chim. (3), 6, 264 



(1891). 



10 Compt. rend., 120, 1057 (1895); 131, 699 (1900). 

 "Bull. Soc. Chim. (3), 6, 239 (1891). 



11 



