32 



STUDIES IN LUMINESCENCE. 



ABSORPTION AND CONCENTRATION. 



The second set of experiments was undertaken to study the relation 

 between absorption and concentration and thus test the validity of Beer's 

 law for a fluorescent substance, i.e., "increasing the concentration of a 

 solution is equivalent to a like increase in thickness." 



The same method of observation was employed for this as for the pre- 

 ceding work, no changes in the apparatus being necessary. The coefficient 

 of absorption was found for different concentrations, the solution being 

 placed in a cell 2.05 cm. thick if dilute, and in cell 1.075 cm - thick if con- 

 centrated. This change of cell is permissible, since, according to the results 

 obtained above, Lambert's law of absorption applies to resorufin. The 

 absorption coefficient for different wave-lengths was thus obtained for 

 seven concentrations. 



Table 4. 

 Coefficient of absorption for corresponding wave-lengths in different concentrations. 



Figs. 27 and 28 give the results of these observations. It will be noticed 

 from these curves that the coefficient of absorption, in the case of dilute 

 solutions, increases in direct proportion to concentration. For concentrated 

 solutions this proportion fails, the concentration increasing more rapidly 

 than the absorption. This is true for all the wave-lengths; in every case 

 the curve starts out as a straight line for dilute solutions and bends down- 

 ward as higher concentrations are reached. 



Table 5. 



Coefficients of absorption computed from average of careful observations for 

 concentration ^ and average absorption concentration curve. (Fig. 28). 



