42 A STUDY OF THE ABSORPTION SPECTRA. 



SUMMARY. 



Glycerol solutions of the cobalt salts investigated were found not to 

 show any of the fine red cobalt bands. Rise in temperature of the more 

 concentrated solutions caused the yellow absorption band at ^5100 to 

 widen and to broaden out, so as finally to absorb all the red and thus cause 

 the solution to appear blue. 



Concentrated aqueous solutions of cobalt chloride show an enormous 

 increase in the absorption with rise in temperature. Between quite narrow 

 ranges of temperature there is a very great increase in the red absorption 

 in the region of the finer bands. As the concentration is increased the 

 temperature at which this great increase in the absorption takes place is 

 lowered. For the more dilute solutions the widening of the absorption 

 with rise in temperature is quite symmetrical. 



The effect of rise in temperature on the absorption of cobalt nitrate 

 and cobalt sulphate is quite small as compared with the effect on the 

 chloride. 



The presence of calcium or aluminium chloride with cobalt chloride 

 in water causes the effect of temperature on the absorption to be greater, 

 and causes the red absorption to take place in more dilute solutions, than 

 it does in pure cobalt chloride solutions. The temperature at which the 

 absorption in the red increases so greatly may be called the " critical color 

 temperature." 



The " critical color temperature " seems to depend upon the existence 

 of some solvate or peculiar condition of the cobalt molecule. The critical 

 color temperature is much higher in water and glycerol than for other 

 solvents. In a similar manner the water and glycerol bands are more 

 persistent than the alcohol or acetone bands. It is important that a com- 

 plete study be made of the critical color temperature for the various cobalt 

 salts, and for the same salt in different solvents and when mixed with other 

 salts. At the same time a study of the characteristic cobalt bands could 

 be made. 



A preliminary test was made to find if the presence of N0 3 and water 

 had the same hypsochromous effect 1 on the cobalt bands as it has on the 

 uranyl bands. Unfortunately no bands of any strength have as yet been 

 detected for cobalt nitrate in water. 



1 Strong: Phys. Rev., 29, 555 (1909). 



