44 ABSORPTION SPECTRA OF SOLUTIONS. 



absorbing power of the acetate solution is greater than that of the chloride. 

 A direct comparison of the absorption of the acetate and sulphate solu- 

 tions is not possible from the spectrograms, since the concentrations dif- 

 fered too much; but the indications both from the comparison with the 

 chloride and from visual observations in the red are that the two absorb 

 about the same if concentration and depth of layer are equal. 



The absorption bands of nickel salts seem to be very similar in their 

 behavior to the green band of cobalt. In our study of that band we came to 

 the conclusion that the absorbing power for green light is a property of the 

 cobalt atom, which is only slightly affected by its immediate surroundings. 

 Similarly, it appears from our study of nickel salts that the absorption 

 shown by them is a property of the nickel atom, and there are only a few 

 hints that it is changed very much by the immediate surroundings. 



One of these is the marked widening of the ^ 3960 band in nickel chloride 

 as we approach a saturated solution. Others are the widening of the same 

 band when large quantities of calcium or aluminium chlorides are added, 

 and the appearance of the narrower bands in the orange and red, together 

 with the change in the general absorption there under the same conditions. 

 These point to the fact that the simplest hydrates have a somewhat dif- 

 ferent absorption from the more complex ones, all of which (if there are 

 several) seem to have about the same action on light. More definite con- 

 clusions on this subject must be deferred until the investigation shall have 

 been extended to more compounds and under more varied conditions. 



