A SPECTROPHOTOMETRY STUDY OF FLUORESCENCE. 



EXCITING 



LIGHT *- 



FLUORESCENT 



SOLUTION 



spectrometer were removed, and in place of the latter a Nernst filament (N) 

 was mounted vertically. This filament afforded a nearly linear source of 

 light, giving a sufficiently powerful continuous spectrum. The filament was 

 attached to the arm carrying the collimator tube so as to move with the 

 latter and to remain in the vertical plane passing through its axis. The 

 observing telescope was clamped, and different portions of the spectrum 

 were brought into the field as desired by movements of the collimator tube. 

 The liquid, the fluorescence of which was to be studied, was placed in a rec- 

 tangular cell (C), upon one face of which a real image of the spectrum was 

 focused. This face of the cell was provided with a metal screen having a 

 vertical opening i mm. wide, through which the light used for exciting fluo- 

 rescence could pass. This opening (see Fig. 2) was so placed that the exciting 

 light entering the cell would be parallel to the adjacent face of the cell and as 

 near to the same as practicable. In adjusting the metal screen one edge 

 of the slit or opening was made to exactly cover the glass forming this face 

 of the cell, as shown in the figure. The fluorescence spectrum was observed 

 from a direction at right angles 

 to the path of the exciting beam, 



and in order to bring the brightest 

 fluorescence regions of the liquid 

 into the field the vertical plane of 

 the collimator of the spectropho- 

 tometer was adjusted so as to bring 

 into the field of view the layer of 

 liquid lying next to the face of the 

 cell through which the exciting 

 light entered. By this arrange- 

 ment the width of the opening 

 through which the light entered 

 the cell and the width of the slit 

 of the spectrophotometer each 

 being 1 mm., the average depth 

 of liquid within which fluores- 

 cence was produced was approximately 0.55 mm. and the average distance 

 which the fluorescence light passed through the liquid before leaving the 

 cell was also 0.55 mm. 



The source, A, of the comparison spectrum (Fig. 1) was an acetylene 

 flame, the light from which was reflected diffusely from the face of the 

 block of magnesium carbonate (M) mounted at an angle of 45 at the 

 end of the collimator slit. Measurements were made by varying the width 

 of the slit until the two regions of the spectrum under observation were 

 equally bright. 



The substances specified by Iyommel as belonging to his first class, in 

 which it is possible to excite fluorescence by means of light of wave-length 

 longer than that of a portion of the fluorescence spectrum, and in which 

 the distribution of intensities in the fluorescence spectrum is independent 

 of the character of the exciting light, are naphthalin-roth, eosin, and 

 chlorophyll. To this list Stenger added the substance fluorescein. The last- 

 named substance, on account of its intense fluorescence and the location 



2 



GLASS 



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Fig. 2. 



