38 A STUDY OF THE ABSORPTION SPECTRA. 



Cobalt Sulphate. 



A spectrogram (Plate 16, A) of the absorption spectra of a normal 

 aqueous solution of cobalt sulphate was made for the different temperatures, 

 6, 19, 36, 49, 64, and 80; the strip representing the lowest temperature 

 being nearest the comparison spectrum. The depth of cell was 3 mm., the 

 length of exposure to the Nernst glower 2 minutes, to the spark 6 minutes. 

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



The absorption spectrum of cobalt sulphate under these conditions 

 consists at 6 of a band in the yellow from X 4900 to X 5250. At 80 this 

 band has widened almost symmetrically and extends from X 4800 to X 5400. 

 Except the change in this band rise in temperature produced no appre- 

 ciable effect. 



Cobalt Acetate. 



Two spectrograms were made of cobalt acetate in water; the first 

 (Plate 17, A) being of normal concentration and 3 mm. depth of cell, and 

 the second being 0.125 normal concentration and 24 mm. depth of cell. 

 Starting with the strip nearest the comparison spectrum, the temperatures 

 were 4, 18, 32, 49, 64, and 79 for the concentrated solution, and 7, 27, 

 47, 61, 73, and 81 for the more dilute solution. The time of exposure 

 for each concentration was 6 minutes to the spark and 2 minutes to the 

 Nernst glower, current being 0.8 ampere and slit-width 0.20 mm. 



At the lowest temperature there was transmission in the ultra-violet 

 out to X 2400. This transmission decreased with rise in temperature, and 

 at 80 extended to X 2600 for both concentrations. For the yellow-green 

 band, however, the effect of temperature was much greater in the case of 

 the concentrated solution. For the more concentrated solution at 4 the 

 yellow-green band extended from X 4900 to X 5400. As the temperature 

 was raised it increased in width until at 64 it extended from X 4600 to X 5700. 

 The widening produced by heating the solution to 79 from 64 is unsym- 

 metrical, the band now extending from X 4550 to X 6000. For the dilute 

 solution at 70 the yellow-green band extends from X 4900 to X 5300, and 

 at 81 from approximately X 4650 to X 5600. This yellow-green band has 

 very diffuse edges and there is usually a slight general transmission through- 

 out the whole extent of the band. 



Cobalt Chloride and Calcium Chloride. 



A spectrogram (Plate 18, ^4) was made to show the effect of rise in 

 temperature on a mixture of cobalt chloride and calcium chloride in water. 

 The concentration of the cobalt chloride was 0.237 normal and of the cal- 

 cium chloride 4.14 normal. The length of layer was 2 mm. The exposure 

 to the Nernst glower was for 3 minutes; the current being 0.7 ampere and 

 the slit-width 0.20 mm. The length of exposure to the spark was 3 min- 

 utes. Starting with the strip nearest the comparison scale, the temperatures 

 were 2, 15, 30, 42, 60, 75, and 85. 



Throughout the whole ultra-violet region there was strong absorption, 

 but this did not indicate the existence of any banded structure. The only 

 portion of the spectrum showing any change due to temperature was at 

 the red end of the spectrum. The increase of absorption in this region will 



