ABSORBING POWER AND FLUORESCENCE OF RESORUFIN. 



37 



too 



" corrected" curve, C, has for ordinates the value of / computed from the 

 formula (page 34) and shows the relative intensity of actual fluorescence in 

 different concentrations. 



The following method of obtaining the corrected fluorescence curves 

 was used as a check upon the first, the final results being obtained by a 

 graphical rather than a mathematical procedure. 



The apparatus was set up as before, except that the light exciting fluo- 

 rescence, instead of striking the whole face of the glass, was allowed to 

 strike only a vertical section 1 mm. in width. The side of the cell next to 

 the exciting light S' was covered with a black paper screen having a vertical 

 opening 1 mm. wide, through which light was admitted. This opening 

 was set at different distances from the end of the cell and the fluorescence 

 intensity was measured for three or four different positions. In order 

 to make possible accurate measurements of the distance from the edge 

 of the glass, a scale was etched 

 upon the face of the cell just above 150 

 the level of the collimator slit 



The effect of absorption upon 

 the position of the maximum of 

 the fluorescence spectrum is well 

 shown in Fig. 34, in which the 

 three curves were taken with the 

 opening at different distances 

 from the face of the cell. 



In order to correct for absorp- 

 tion, curves similar to those 

 shown in Figs. 35 and 36 were 

 plotted for each solution. These 

 curves show the variation in the 

 intensity of the fluorescent light 

 with the thickness of the liquid 

 through which the light passes. 

 From the intercept of one of these 

 curves upon the y axis the intensity 

 of fluorescence can be found when 

 the thickness becomes zero. In 



such a case there is no absorption. The error of extrapolation was reduced 

 to a minimum by taking one point very close to the edge of the glass. 



The corrected values of fluorescence intensity thus obtained were used 

 in plotting the accompanying fluorescence curve in Fig. 36. The same 

 procedure was followed in the case of each solution. 



The observations and results obtained by this graphical method are 

 given in Table 10. The corrected fluorescence spectra obtained in this 

 way are plotted together in Fig. 37, the vertical scale being such that 

 values for wave-length 0.589 n are the same as the values for the corre- 

 sponding concentration in Fig. 32. 



A comparison of the curves of Figs. 32 and 37 shows that the results 

 obtained by the two methods are the same. The typical fluorescence 

 curves are all similar in form and the position of maximum fluorescence 



Fig- 34- 



Observed fluorescence produced by light from i mm. 

 section oassing through different thicknesses of solu- 

 tion. Thickness of D\ = i mm.; of Di=i cm.; of 



Us =2 cm. 



