The Absorption Coefficient of Solution for Monochromatic Radiation. 67 



CHROMIUM SULPHATE IN WATER. 



Twelve solutions were prepared, varying in concentration from 

 c = 0.7 to c = 0.025. The general character of the absorption for the 

 sulphate is the same as that of the chromium-chloride solutions, and 

 therefore the absorption curves have not been plotted. The A c 

 curves for 704/iju, 724/x/z, and 744////, on the red edge of the green 

 absorption band show that in this region of the spectrum A is a 

 constant for all values of c. 



TABLE 28. Chromium Sulphate in Water (Fig. 25). 



POTASSIUM PERMANGANATE IN WATER 



Eleven solutions were prepared, varying in concentration from 

 c = 0.278 to c = 0.005. The absorption curves show the sharp edge 

 at about 800/z^i of the green absorption band, for which c = 0.25 shows 

 that this solution is nearly as transparent as pure water. 



In making up the mother solution of the potassium permanganate 

 care was taken to prepare the solution free from manganese dioxide. 

 The dilutions were then made, and the solutions in the bottles seemed 

 to keep well as long as they remained in the dark. During the course 

 of a measurement, however, the solution in the cells became rapidly 

 permeated with a black precipitate of manganese dioxide, which ap- 

 peared to be caused by the action of the light. Curve I, figure 25, 

 is for the fresh solution, for which c = 0.25; curves II, III, and 

 IV are plotted from measurements made at 30-minute intervals after 



