COBALT SALTS. 



33 



atom. Absorption in the red is considered to be due to a simple solvate. 

 In alcohol cobalt chloride has bands at X 3100 and X 3600, and also a green 

 band. In methyl alcohol they find a fairly narrow band at X 5910, one at 

 X 6050; a narrow intense band at X 6240; a wide band at X 6450, and a wide 

 intense band at X 6700. The position and relative intensity of these bands 

 are very different from that of the cobalt chloride water-bands described by 

 Uhler. In acetone broad bands appear at X 5725, X 6200, and X 6780. These 

 do not appear to be broken up into sharper bands under any conditions. 

 By the addition of 5 per cent of water to an ethyl alcohol solution of cobalt 

 chloride, the water-bands are made to appear, while for an acetone solution 

 it requires the presence of at least 10 per cent of water to bring out the 

 water-bands. Cobalt and calcium bromides in water are found to give 

 bands at X 6400, X 6650, and X 6950. Cobalt bromide in acetone has bands 

 in the red that differ quite markedly from those of cobalt chloride in acetone. 



Rizzo 1 has investigated the effect of rise in temperature on the absorp- 

 tion bands of cobalt glass. He gives the following figures: 



From the above summary it will be seen that our knowledge of the red 

 cobalt bands is very small at present. Much more work, similar to that 

 to be described on the uranyl bands, remains to be done. Apparently 

 these cobalt bands are somewhat different from the uranyl bands; at any 

 rate, the bands investigated by Bois and Elias did not break up into fine, 

 3harp bands at very low temperatures. 



In discussing the various spectrograms that show the effect of change 

 in temperature on the absorption spectra of salts, these spectra will be 

 iivided into three kinds: 



The first kind of absorption consists of wide bands, in many cases 

 hundreds of Angstrom units wide. In many of the spectrograms only 

 me edge of the band mav anDear. the other edsre of it lviner in Darts of the 



