IN THE PRESENCE OF STRONGLY HYDRATED SALTS. 45 



solution and the deflection in this case also noted. The deflection produced 

 when the deeper solution was in the path of the beam of light was then 

 divided by the deflection produced by the shallower solution, and this gave 

 the absolute transmission of the solution of the substance in question of 

 known concentration, having a depth of layer of 20 mm. 



This process was repeated for the different parts of the spectrum, chang- 

 ing the wave-length of light from reading to reading b} r only a small amount. 

 The object of using the two depths of the same solution, and then dividing 

 the deflection produced by the deeper layer by that obtained when the more 

 shallow layer was in the path of the beam of light, was to eliminate any 

 effect of reflection from the glass ends closing the cells containing the solu- 

 tions, and also to eliminate any changes in the total amounts of energy sent 

 through the solution, due to slight changes in the intensity of the Nernst 

 glower. From the specific gravity of the solution and its known concentra- 

 tion, the amount of water in a layer of the solution, say 21 mm. in depth, 

 could easily be calculated. Similarly, the amount of water in a layer of the 

 solution which was 1 mm. deep, could also be calculated. Water was then 

 introduced into two cells, and the cells so adjusted that the difference in 

 depths was exactly equal to the depth of the water in the layer of the solu- 

 tion, which was 20 mm. deep. 



The deflection for the water in the deeper cell was then read for any given 

 wave-length of light, and then, at once, the deflection when the light was 

 passed through the more shallow layer of water. The deflection for the 

 deeper layer was divided by the deflection for the shallower layer. The 

 result was the absolute transmission for water with a depth of layer just 

 equal to the depth of water in the solution in question. 



RESULTS. 



The above results for the solution are plotted as one curve and those for 

 water having the same depth as the water in the solution as another curve, 

 wave-lengths being abscissae and transmission ordinates. A comparison 

 of the two curves shows at once whether water in the free, uncombined con- 

 dition or the same depth of water in the solution in question is the more 

 transparent. 



The data obtained by dividing the deflections produced by the deeper 

 solutions by those for the shallower, and, similarly, by those for water, are 

 also given in tables 6 to 10. These are the data from which the accom- 

 panying curves were plotted. 



The substances studied were chosen from the standpoint of their power to 

 solvate or to combine with the solvent in which they were dissolved. In all 

 of the work recorded in this paper the solvent used was water. We were 

 practically limited, in this phase of the work, to those substances which 

 themselves have little or no power to absorb light, and which are both color- 

 less in the visible part of the spectrum, and have little or no absorption in 

 the regions in which the absorption bands of water occur. 



