32 A STUDY OF THE ABSORPTION SPECTRA. 



they concluded that mercuric and cobalt chlorides in solution form com- 

 pounds. When metallic ions of relatively strong basic properties like the 

 alkaline earths or hydrogen are introduced with chlorine ions into a cobalt 

 chloride solution, there is a greater formation of complex cobalt anions 

 similar to that given by the following equation. 



CoCl 2 + 2Cl < CoCl 4 CoCl 2 + CT * CoCL, 



On the other hand, Zn, Cd, Hg, Sb, Sn, etc., form negative complexes 

 easier than cobalt and hence they will cause the cobalt complexes to break 

 up. 



CoCl 4 <=i CoCl 2 + 2Ci ZnCl 2 + 2Cl <= ZnCl, 



Vaillant 1 has made a quantitative comparison between dissociation 

 and light absorption. In general there is a close parallelism between these 

 two phenomena. For concentrated solutions, however, there are marked 

 differences which suggest other products, and these Vaillant called hydrates. 

 Pfluger, 2 Vaillant and Moore 3 have studied various salt solutions photo- 

 metrically. They find the same absorption coefficients for dilute solutions 

 of sodium, potassium, and barium permanganates, but for concentrated 

 solutions they find differences. They conclude that absorption depends 

 upon ionization. 



A very detailed study has been made by Hartley * of the effect of tem- 

 perature on the absorption spectra of solutions. Hartley considered that 

 the effect of change in temperature was largely due to change in the solva- 

 tion of the dissolved salt. Bois and Elias 5 studied cobaltammonium- 

 rhodamid at 18 and 190 C. At the lower temperature the bands 

 were smaller but were still very diffuse. 



Uhler 6 has studied cobalt salts very systematically. Cobalt chloride 

 in water was found to show rather fine bands at X 6970, X 6610, X 6400 (weak), 

 X 6245 (weak), and X 6095 (weak). In ethyl alcohol bands were found at 

 X 6950, X 6360, X 6150, and X 6000. 



Jones and Anderson 7 have made a detailed study of cobalt salts. 

 Solutions of all the salts studied, except the sulphate, have a region of ultra- 

 violet one-sided absorption. This they consider as due to association or 

 solvation. In addition to the one-sided ultra-violet band, cobalt chloride 

 has a band at X 3300 which disappears very rapidly with dilution. This 

 band they believe is due to some simple hydrate, and they consider that 

 this simple hydrate is only stable in very concentrated solutions or at high 

 temperatures. The green band appears for all aqueous solutions, and is 

 independent of whether the cobalt exists as an ion, molecule, as an aggre- 

 gate, or as a solvate; the absorbing power being apparently due to the cobalt 



1 Ann. Chim. Phys. (7), 28, 213 (1903). 



2 Ann. Phys. (4), 12, 1903. 



I Of* 01 1 



* Dub. Trans. (2), 7, 253, 312 (1900). 



