COBALT SALTS. 37 



At the lower temperatures the effect of rise in temperature was the 

 same for both solutions. In the case of the concentrated solution all light 

 was practically absorbed at 70, a narrow transmission band in the blue 

 being the only light not absorbed. At about 50 the bands in the red appear. 

 Their wave-lengths are approximately XX 6100 and 6250. 



A spectrogram was made of a 2.52 normal concentration of cobalt 

 chloride in water and having a depth of cell of 1.3 mm. This spectrogram 

 showed an extremely diffuse band between about X 4600 and X 5500. Rise 

 in temperature had very little effect on absorption, except in the red region, 

 where the general absorption was greatly increased. At 38 the cobalt 

 bands appear and increase in intensity with rise in temperature. Their 

 positions are about XX 6100 and 6250 the same positions as on the pre- 

 vious plate. 



A spectrogram (Plate 14, A) was made showing the effect of rise in 

 temperature on a 0.0394 normal concentration of cobalt chloride in water. 

 At 5 the cobalt band extended from X 4400 to X 5600. At 75 it had wid- 

 ened out to X 4300 and X 5750. For a dilute solution it will be seen that 

 rise in temperature produces only a small change in the absorption spectra. 



Cobalt Nitrate. 



A spectrogram (Plate 14, B) was made showing the absorption spectra 

 of a 2.3 normal aqueous solution of cobalt chloride of 2 mm. depth. The 

 exposures to the Nernst glower were for 3 minutes, current 0.7 ampere and 

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

 scale, the temperatures were 2, 14, 30, 45, 60, 75, and 85. 



The effect of rise in temperature on the absorption spectrum of 

 cobalt nitrate was not great. The wide band in the yellow extended from 

 X 4600 to X 5500 at 2. The band gradually widened with rise in tempera- 

 ture, and at 85 extended from X 4450 to approximately X 5650. 



It will be noticed that the effect of rise in temperature on the absorption 

 spectra of cobalt nitrate is very small compared with that of cobalt chloride. 

 Hartley considered that salts crystallizing with the largest amounts of 

 water usually showed the greatest change in their absorption spectra when 

 heated. These two cobalt salts, however, both crystallize from aqueous 

 solutions with 6 molecules of water. 



A spectrogram (Plate 15, B) was made of cobalt nitrate in water, of 

 0.287 normal concentration and a 3 mm. length of cell. The length of 

 exposure to the Nernst glower was 2 minutes and to the spark 3 minutes. 

 The current in the glower was 0.8 ampere and the slit-width 0.20 mm. The 

 temperatures, starting with the strip nearest the comparison spectrum 

 were 13, 27, 42, 61, 73, and 85. 



At ordinary temperatures cobalt nitrate crystallizes out with 6 mole- 

 cules of water. The effect of rise in temperature on the absorption spectra 

 of cobalt nitrate at this concentration was very small. The N0 3 ultra- 

 violet band extended to about X 3300. It did not appear to be affected 

 in the least by the change in temperature. A weak band from X 5000 to 

 X 5200 appears at the higher temperatures, increasing in intensity slightly 

 with rise in temperature. 



