16 



FLUORESCENCE OF THE URANYL SALTS. 



For the determination of wave-lengths the eyepiece is provided with 

 a pointer in the focal plane and also with the usual slides for isolating 

 the region under observation. 



The collimator slits have micrometric adjustment, and to provide 

 for convenient comparison through the very great range of intensities 

 occurring in the study of fluorescence, the illumination of the com- 

 parison slit can be varied by moving the comparison light along a 

 photometer bar to any desired distance from the slit. The observing 

 telescope can be replaced by a camera whenever photographs of the 

 spectra are desired. With this instrument the wave-lengths of the 

 bands could be determined by setting the pointer to the region of 

 greatest brightness as estimated by the eye and the relative intensities 

 could be measured spectrophometrically. 



Tables 4 to 10 contain the resulting data for several salts; also the 

 frequencies corresponding to the wave-lengths and frequency intervals. 

 The measurements and computations were kindly made by Miss Wick, 

 who likewise determined the relative brightness of the bands in several 

 of the spectra. 



From the data in these tables some of the salient features of the 

 uranyl spectra may be deduced, viz: 



(1) The weakest bands are at the ends of the spectrum, i. e,, in the 

 red and the blue. 



(2) The brightest band is not in the center, being third from the 

 violet end and sixth from the red end when all 8 bands of the spectrum 

 are visible. 



(3) Taking the frequency intervals, instead of the differences of 

 wave-length, the bands, with the exception of the band of shortest 

 wave-length (band 8), are equidistant, at least within the rather large 



TABLE 4. Fluorescence bands of the nitrates. 



