100 A STUDY OF THE ABSORPTION SPECTRA. 



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 X 4200. A represents a typical spectro- 

 gram of this kind. Starting with the spectrum-strip at the top, the con- 

 centrations were 1.5, 1.1255, 0.75, 0.5, 0.375, 0.25, and 0.1875 normal. 

 The slit-width was 0.08 mm. and the current through the Nernst glower 

 0.8 ampere. The spectra of wave-lengths greater than X 4300 represent 

 the absorption of a depth of layer of 15 mm.; the spectra of shorter wave- 

 lengths represent 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 to the Nernst glower 

 having been 1 minute. It will be seen that the uranyl band a comes out 

 very strongly. The screen was then placed in the path of light and expo- 

 sure of 5 minutes made to the violet and ultra-violet beyond X 4300; a solu- 

 tion of uranyl nitrate of 1.5 normal concentration and 3 mm. deep 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 after- 

 wards made to the spark in the region X 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 contain- 

 ing the very strong line X 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 Angstrdm units, yet relatively 

 they are probably correct to within less than 10 Angstrom units for the 

 finer bands. 



The second spectrum-strip from the top represents in the long wave- 

 length end of the spectrum, the absorption of a 15 mm. layer of a 1.125 

 normal solution of uranyl nitrate exposed 1 minute to the Nernst glower. 

 The a band appears, although not nearly as intense as in the spectrum- 

 strip above. The region of shorter wave-lengths beyond X 4300 represents 

 the absorption of a 3 mm. layer of a 1.125 normal solution exposed 5 min- 

 utes to the Nernst glower. A very faint transmission is shown in the 

 region X 3700. The ultra-violet line X 2478.8 is shown in the comparison 

 spark-spectrum. The other spectrum-strips were made in a similar manner, 

 with the concentrations given above. 



By this method of exposing, two new bands were detected in the ultra- 

 violet. In aqueous solutions the intensities of the bands are much the same. 

 In other solvents, however, and for other uranyl salts, the relative intensi- 

 ties of the bands change very greatly. For uranyl nitrate crystals the 

 bands are even more closely related to each other than in aqueous solu- 

 tions. The longer the wave-length of the band the more intense and wider 

 it is as a rule. The position of the long wave-length bands in the ortho- 

 rhombic uranyl nitrate crystals, U0 2 (N0 3 ) 2 6H 2 0, is the same as the posi- 

 tion of the bands for an aqueous solution. The wave-lengths of the bands 

 are as follows: 



