34 



STUDY OF ABSORPTION SPECTRA 



nitrate (fig. 13) and the 1.25/1 band for magnesium nitrate (fig. 14). 

 The above relation is shown very clearly in many cases by a study of 

 the curves for hydrated salts. With increasing wave-lengths, as the 

 regions of intense absorption are approached the solution is much more 

 transparent than the solvent. Near 1.2ju, as we approach the 1.25/u 

 band, having in the path of the light 20 mm. of the solution, the solu- 

 tion is usually from 20 to 40 per cent more transparent than the pure 

 solvent. This difference increases as the depth of the solution in the 

 path of the light increases. It is very much less for 10 mm. of solution 



TABLE 13. Magnesium nitrate, ammonium bromide 

 and sodium nitrate. 



than for 20mm., for the same wave-length of light. It requires an intense 

 absorption to bring out these differences in a pronounced manner. A 

 decrease in the concentration of the solution also decreases the differ- 

 ence between the absorption for the solution and for the solvent, as has 

 been pointed out by Jones and Guy. 1 



Non-hydrated salts, under similar conditions, give results in many 

 respects exactly the opposite of those obtained with hydrated salts. 

 Three non-hydrated salts were investigated, and in all three cases the 



'Carnegie Inst. Wash. Pub. No. 190, page 49. 



