54 ABSORPTION OF LIGHT BY WATER CHANGED 



in the transparency of the water and the solution throughout this region is, 

 however, not very great. From 1.1/j towards the longer wave-lengths, as 

 we come down the descending arm of the curve towards the second water- 

 band, the water in the case of the magnesium chloride (as in the case of cal- 

 cium chloride) becomes much more opaque than the solution, the differences 

 here being of the same order of magnitude as those with calcium chloride. 



Fig. 15 gives the results for magnesium chloride with a depth of layer of 

 1 cm., and the same relations hold as in fig. 14, for the relative transparency 

 of the water and of the solution. The water becomes the more transparent 

 from 1.22/z to 1.34/z. For the longer wave-lengths the solution becomes 

 more transparent until the region 1 .41/j is passed. For wave-lengths longer 

 than 1.41/* the transmission of both solution and water is practically zero 

 that is, they both become opaque to the longer wave-lengths. 



The results in fig. 16 bring out some new features of interest and impor- 

 tance. These are the results that were obtained with aluminium sulphate. 

 The new feature shown by the curve for aluminium sulphate, as compared 

 with those for calcium chloride and magnesium chloride, is that at the 

 minimum of the curve corresponding to wave-length 1/j the solution is 

 more transparent than the corresponding water. Beyond the wave-length 

 1.04ju the water becomes the more transparent with aluminium sulphate as 

 with magnesium chloride. Beyond the wave-length 1.17/z the solution 

 becomes more transparent in this case as with magnesium chloride and 

 calcium chloride. 



If we turn to fig. 17 the relations are as follows. In the region of 1.2ju the 

 water is the more opaque. From 1 .29/* to 1 .36/j the water becomes the more 

 transparent. From 1.36// to the longest wave-length studied, the solution 

 again becomes more transparent than the corresponding layer of water. 



An examination of all the results thus far obtained bearing on this prob- 

 lem leads us to conclude that the greater transparency of the solution as 

 compared with the water in the solution must be due to some action of the 

 dissolved substance on the solvent water. The question remains, what is 

 this action? 



EXPLANATION OF THE RESULTS. 



We have seen from our earlier work on the absorption spectra of solutions, 

 which has been in progress in this laboratory continuously for the past eight 

 years, that the solvent can have a marked effect on the power of the dis- 

 solved substance to absorb light. This was first shown by Jones and 

 Anderson, 1 and a large number of examples of this effect have since been 

 found by Jones and Strong. 2 We interpreted the effect of the solvent on the 

 power of the dissolved substance to absorb light as due to a combination 

 between a part of the liquid present and the dissolved substance. This 

 enabled us to explain a large number of facts which were brought to light for 

 the first time by our investigations of the absorption spectra of solutions. 

 Many of the phenomena which were thus explained, it seemed, could not be 



1 Cam. Inst. Wash. Pub. 110. 2 Cam. Inst. Wash. Pubs. 130 and 160. 



