A SPECTROPHOTOMETRY .STUDY OF FLUORESCENCE. 



tion. It will be seen that the maximum is shifted from 0.516 fx to 0.522 n, 

 and that while the two curves are nearly coincident on the side toward the 

 red the values on the other side of the curve fall off very rapidly as the 

 result of the increased absorption. The boundary of the fluorescence spec- 

 trum toward the violet in the one case would lie at about wave-length 0.505 11, 

 whereas in the thinner layer it would be visible to at least 0.490 y.. It is 

 obvious that the color of the fluorescence in the latter case will contain a 

 great excess of green. 



The effect of diluting the fluorescent solutionis similar to that of diminish- 

 ing the distance through which the light passes. The results of observa- 

 tion upon a solution of fluorescein, diluted until the intensity of the fluores- 

 cence spectrum was diminished as far as would permit of satisfactory 

 readings, are shown in Fig. 6. The curve A A represents the transmission 

 of the cell filled with the dilute solution and BB is the distribution curve 

 of its fluorescence spectrum. The dotted lines show the corresponding 



80 



60 



40 



20 



450." 60 



70 



80 90 .500" 10 



20 



30 40 



50 60 



70 



Fig. 6. Fluorescein. 



Effect of dilution upon the fluorescence spectrum. 



transmission curve and a portion of the fluorescence curve for the solution 

 before dilution. It will be noted that in this case, as in the case of the com- 

 parison of thick and thin layers of a given solution, the curves are coin- 

 cident toward the red, but that the dilute solution has its maximum shifted 

 toward the green, also that the ordinates on this side of the curve show 

 an increase indicative of the change of color, which, as is well known, is 

 always observed as the result of diluting the fluorescent solutions of this 

 substance. 



Although, as has been shown in Figs. 4 and 5, the modifications pro- 

 duced by absorption in the curves of the fluorescence spectrum may be 

 very marked, the effect of absorption diminishes rapidly with dilution of 

 the solution. For example, if we apply the correction for absorption to 

 the curve for the dilute solution in Fig. 6 we find, as is indicated in Fig. 7, 

 that the change is insignificant. In this figure C is the observed curve for 



