164 HYDRATES IN AQUEOUS SOLUTION. 



Russell* made a fairly extended spectroscopic study of solutions of cobalt 

 chloride. He worked with a fused salt, with its solution in concentrated 

 hydrochloric acid, and with its solution in various alcohols. He showed 

 that the spectrum in the concentrated acid was very similar to that of the 

 fused salt, the two bands being shifted a little towards the blue. The 

 spectrum of cobalt chloride when dissolved in the various alcohols and in 

 glycerol, was practically the same, independent of the nature of the solvent. 



Russell also worked with aqueous solutions at different concentrations, 

 and studied their absorption spectra. He also studied the effect of change 

 of temperature on the various aqueous solutions. He concluded that the 

 color of the aqueous solutions was due to the presence of hydrates in them. 



Potilitzint took up the study of cobalt chloride especially to test the 

 conclusions reached by Bersch that there are two modifications of the 

 compound CoCl 2 .6H 2 0, the one red and the other blue. He showed that 

 when the hexahydrate is warmed to about 52 for four hours, it passes 

 over into the dihydrate, CoCl2.2H 2 O, which is reddish, with a slightly violet 

 tint. The same compound is obtained when the hexahydrate is placed 

 in a desiccator for a few days. At 100 the dihydrate passes over into 

 the monohydrate, CoCl2-H20, which is dark violet in color. When the 

 monohydrate is warmed from 110 to 120, it loses its last molecule of water 

 and yields the anhydrous salt, which is blue. Potilitzin concludes that the 

 transition temperatures from one hydrate to another of cobalt chloride, as 

 given by Bersch, are in error; that there is only one modification of the 

 compound CoCl2.2H 2 0, and that the only other hydrate of cobalt chloride 

 has the composition CoCl 2 .H 2 O. 



The formation of blue cobalt chloride from red, by whatever means effected, 

 is a dehydration process. 



SabatierJ showed that hydrates of cobalt chloride containing less water 

 than the hexahydrate, were formed when hydrochloric acid was added to a 

 strong aqueous solution of the cobalt salt. There seems to be some evidence 

 for the formation of chlorhydrates. He performed similar experiments with 

 copper chloride, and obtained analogous results. 



In 1890 Lescceurll took up a study of the hydrates formed by cobalt chlo- 

 ride. He found also that at 120 the compound CoCl2.2H 2 is produced. 

 When any of the hydrates are heated up to 140, they yield the anhydrous 

 chloride. The compound CoCl2.2H 2 of lilac color, is easily obtained by 

 drying the hexahydrate over sulphuric acid at ordinary temperature. There 

 is no intermediate hydrate such as CoCl 2 .4H 2 O formed. 



* Proceed. Roy. Soc., 32, 258 (1881). 



fBer. d. deutsch. chem. Gesell., 17, 276 (1884), 



JCompt. rend., 107, 42 (1888). 



Ibid., 106, 1724 (1888). 



|| Ann. Chim. Phys., [6] 19, 547 (1890), 



