202 JONES-STRONG— THE ABSORPTION SPECTRA [April 24, 



As the absorption edge recedes from the uranyl bands, the general 

 transmission is so great as almost to entirely obscure them. 



A, Plate I, represents the absorption spectra of an aqueous 

 solution of uranyl nitrate of different depths of layer. The narrow 

 and rather weak bands shown here are the uranyl bands. Twelve 

 of these bands have been photographed. Starting at the band of 

 longest wave-length they shall be designated by the letters a, h, c, d, 

 etc. On account of the irregularity of the distribution of light in 

 the spark spectrum and the small intensity of the uranyl bands, the 

 Nernst glower was used as the source of light in the ultra-violet, 

 and long exposures were made. A screen was used that cut out 

 all wave-lengths greater than A 4200. A represents a typical 

 spectrogram of this kind. Starting with the spectrum strip at the 

 top, the concentrations were 1.5 N, 1.1255 N, 0.75 N, 0.5 N, 0.375 

 N, 0.25 N, and 0.1875 N. The slit width was 0.08 mm. and the 

 current through the Nernst glower 0.8 amperes. The spectra of 

 wave-lengths greater than A 4300 represent the absorption of a 

 depth of layer of 15 mm.; the spectra of shorter wave-lengths rep- 

 resent the absorption of a depth of layer of 3 mm. The upper 

 spectrum strip represents then the absorption spectrum of a 1.5 

 normal solution of uranyl chloride 15 mm. thick, exposure being 

 made i min. to the Nernst glower. It will be seen that the uranyl 

 a band comes out very strongly. The screen was then placed in 

 the path of light and exposure of 5 minutes made to the violet and 

 ultra-violet beyond A 4300; a solution of uranyl nitrate of 1.5 

 normal concentration and 3 mm. depth of cell being in the path 

 of the beam of light. This amount of uranyl nitrate absorbed 

 practically all the light in this region. A very short exposure was 

 afterwards made to the spark in the region A 2600, in order to get 

 a comparison spark spectrum in this region, so that the wave- 

 lengths of the uranyl bands could be measured. 



Throughout this work a comparison spark spectrum usually 

 containing the very strong line A 2478.8 was photographed on each 

 spectrum strip. In measuring the uranyl bands all measurements 

 were made from this line as a standard, and although the absolute 

 wave-lengths of the uranyl bands may not be correct to within 20 



