24 



STUDY OF ABSORPTION SPECTRA 



subsequent work. The cells containing the solution could then be so 

 adjusted that they would contain just as much water as was present 

 when the percentage transmissions for 20 mm. of water, that is 21 mm. 

 in one cell and 1 mm. in the other, were determined. 



It was found that, although this procedure would save much tune 

 and labor, it can not be recommended where it is desired to do accurate 

 work, since the conditions would not be as nearly comparable as they 

 would be if the absorption of the solvent was determined immediately 



TABLE 9. Depth of cell 10 mm. Transmission of hydrated salts. 



after that of the solution. The latter procedure was therefore adopted. 

 It will be noted that the percentage transmissions for the three series 

 of measurements with pure water (tables 10 and 11) are very concord- 

 ant for both the 1/t and the 1.25/z bands. 



Zinc nitrate, unlike the hydrated chlorides, bromides, and sulphates, 

 presents an apparent exception in the case of the 1/z band (fig. 9) . At 

 the center of this band the solution has the greater absorption, although 

 the difference between the absorption of the solution and that of the 

 solvent is not large. The same phenomenon makes its appearance in 



