3G A STUDY OF THE ABSORPTION SPECTRA. 



The cobalt bands XX 6315 and 6440 appear in the spectrum strip taken 

 at 85. At this temperature there is a very large amount of general absorp- 

 tion from X 5800 on to X 6800. Beyond X 6800 the absorption is complete. 

 The faint band at X 6620 also appears at this temperature. The bands 

 XX 6315 and 6440 appear at lower temperatures, but the transmission is so 

 great for the long exposures necessary for the other regions of the spectrum 

 that the bands are almost obliterated. 



A spectrogram (Plate 15, A) showing the effect of rise in temperature 

 was made for an aqueous solution of cobalt chloride 0.125 normal concen- 

 tration and a layer 12 mm. long. Exposures of 4 minutes were made to 

 the Nernst glower, current 0.8 ampere, slit-width 0.20 mm. The time of 

 exposure to the spark was 6 minutes. Starting with the strip next to the 

 numbered scale, the temperatures were 5, 18, 38, 52, 64, and 83. 



The absorption spectrum of cobalt is characterized by two wide bands 

 in the visible spectrum and an ultra-violet band. At 5 the ultra-violet 

 band extends to X 2700. As the temperature rises this band widens slightly, 

 its edge falling at about X 2800 at 83. The edge of this absorption band is 

 quite sharp. The violet band extends from about X 4000 to X 4400 at 5. 

 This band is very diffuse, there being considerable transmission throughout 

 the whole extent of the band. The yellow band extends from X 5500 to 

 X 6100 at 5, there being slight general transmission also throughout the 

 whole extent of this band. Both these bands gradually broaden with rise 

 in temperature, and at 83 the limits of the violet band are XX 4000 and 

 4600; of the yellow band XX 5500 and 6400. It will be seen that these 

 bands widen unsymmetrically, the short wave-length edges remaining 

 nearly stationary, while the long wave-length edges recede towards the red. 

 The amount of transmitted light in the red region from X 6400 to X 7000 

 is much less at the higher temperatures. 



A spectrogram (Plate 13, B) was made of an aqueous solution of cobalt 

 chloride of 0.315 normal concentration and 10.4 mm. depth of cell. The 

 exposures were 3 minutes to the Nernst glower; the current being 0.7 

 ampere and the slit-width 0.20 mm. Starting with the strip adjacent to the 

 comparison scale, the temperatures were 2, 14, 30, 44, 60, 75, and 81. 



The most noticeable effect of rise in temperature on the absorption 

 spectra of cobalt chloride is to widen the band in the green. At 1 this 

 band extended from >l 4900 to X 5300, at 45 from X 4800 to X 5400. Above 

 this temperature the band widens quite rapidly, and at 83 it extends 

 from X 4500 to X 5700. The widening is approximately symmetrical. 



A spectrogram similar to the one described above was made with a 

 cobalt chloride solution of 0.315 normal concentration and a depth of laj^er 

 of 24 mm. No exposure was made to the spark at all. At the lowest tem- 

 perature, 4, the whole of the short wave-length spectrum was absorbed 

 up to X 5700. No trace of the cobalt bands in the red was noticeable. 



A spectrogram was made to compare with the one described immedi- 

 ately above. These two spectrograms were taken under the same condi- 

 tions, and with the same amount of cobalt chloride in the path of the 

 beam of light. In the solution used for the spectrogram now being 

 described, the concentration was 2.52 normal and the length of cell 3 mm. 



