COBALT SALTS. 35 



ening being quite slow at first. At 60 the limits of the band are X 4700 to 

 X 5600. At the higher temperatures the increase in the absorption through- 

 out the red becomes very great, and at 81 the absorption is practically- 

 complete. It is for this reason that the cobalt chloride solution becomes 

 blue. Bands appear at X 6310 and X 6440 at 72 and 81. 



Plate 13, B, gives the absorption spectra of a 0.315 normal concentra- 

 tion and a depth of layer of 10 mm. This solution does not change in color 

 and shows only an increased widening of the bands. The intense absorp- 

 tion in the red does not take place under these conditions of concentration 

 and temperature. 



A spectrogram showing the effect of rise in temperature was made for 

 an aqueous solution of cobalt chloride, using a 2.37 normal solution, and a 

 depth of cell of 3 mm. The length of exposure to the Nernst glower was 

 2 minutes, using 0.8 ampere current and a slit-width of 0.20 mm. The length 

 of time of exposure to the spark was 5 minutes. Starting from the num- 

 bered scale the temperatures were 0, 14, 28, 44, 58, and 73. 



The region of the spectrum beyond X 3000 is absorbed. The amount 

 of this absorption does not vary for the above changes in temperature. 

 Throughout the ultra-violet region of the spectrum there is a very consider- 

 able amount of general absorption of light. At there is a wide absorp- 

 tion band between X 4500 and X 5900. The ultra-violet edge of this band 

 is not affected by change in temperature ; the edge in the yellow, however, 

 widens out towards the longer wave-lengths with rise in temperature. 

 The boundaries of this edge are X 5900 at 0, X 5950 at 14, X 6000 at 28, 

 X 6050 at 44, and X 6100 at 58. Above 60 there is very little transmission 

 in the red end of the spectrum. 



At the higher temperatures as the transmission in the red is greatly 

 decreased, several cobalt bands appear. The bands at XX 6300 and 6450 

 are of about equal intensity and about 40 Angstrom units wide. A very 

 faint band appears at about X 6620. 



The Wratten and Wainwright films are sensitive to approximately 

 >l 7200 on short exposures. At cobalt chloride allows light to pass with 

 as long wave-lengths as can record themselves on the films. At the higher 

 temperatures, however, this is not the case. At 44 the light beyond X 7000 

 is absorbed, and at 60 all light beyond X 6800. 



A spectrogram showing the effect of rise in temperature was made for 

 an aqueous solution of cobalt chloride of 2.37 normal concentration and 

 1 mm. depth of cell. The length of exposure to the Nernst glower was 3 

 minutes, current 0.7 ampere, slit-width 0.20 mm. The exposure to the 

 spark was for 3 minutes. Starting with the solution next to the numbered 

 scale, the temperatures were 1, 12, 27, 45, 60, 70, and 85. 



The spectrum in the ultra-violet beyond X 3000 was completely ab- 

 sorbed by the cobalt chloride. The whole region between X 3000 and 

 X 5000 is a region of considerable absorption, possibly half of the light being 

 transmitted. Between X 5000 and X 5600 there is an absorption band with 

 diffuse edges. This absorption gradually widens with rise in temperature 

 until at 85 it extends from X 5000 to X 5800; the widening being slightly 

 unsymmetrical. 



