o 



COBALT SALTS. 39 



be given for each temperature. At 2 there was transmission to X 7100, 

 below which the film was but slightly sensitive; at 15 the limit of trans- 

 mission being X 6900; at 30 X 6700, while at the same time the cobalt bands 

 appear; at 42 the whole region from X 6050 to X 6500 is very weak and shows 

 the cobalt bands at XX 6105, 6240, and 6415; at 60 the limit of transmission 

 is at X 6000; at 75 X 5900, and at 85 X 5800. 



Cobalt Chloride and Aluminium Chloride. 



A spectrogram (Plate 18, B) was made showing the effect of rise in 

 temperature on the absorption spectra of an aqueous solution of 0.161 

 normal cobalt chloride and 2.75 normal aluminium chloride. The depth 

 of layer was 2 mm. The length of exposure to the Nernst glower was 3 

 minutes, current 0.7 ampere, and slit-width 0.20 mm. Starting with the 

 strip nearest the numbered scale, the temperatures were 1.5, 13, 31, 

 45, 60, 72, and 87. 



As no spark was used there is of course no impression on the photo- 

 graphic film in the ultra-violet. The only region of absorption is in the 

 red and this increases very rapidly with rise in temperature. The cobalt 

 bands appear at 1. At 1 the transmission extends to X 6900; at 13 

 to X 6800; at 31 there is almost complete absorption to X 6100. The co- 

 balt bands do appear approximately at XX 6100, 6150 and 6420; at 45 the 

 absorption extends to X 6050; at 60 to X 5950; at 72 to X 6900, and at 87 

 to X 5850. 



A spectrogram (Plate 19, A) was made to test the effect of rise in 

 temperature on the change in the absorption spectra of a dilute solution of 

 cobalt chloride (0.00316 normal) in a concentrated (3.06 normal) solution of 

 aluminium chloride in water. The length of layer was 150 mm. The time 

 of exposure was 2 minutes to the Nernst glower and 4 minutes to the spark. 

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

 Starting with the strip adjacent to the comparison scale, the temperatures 

 were 1, 18, 41, 55, 68, and 85. 



The effect of rise in temperature in this case was greater than in that 

 of a more concentrated solution of cobalt chloride. There is absorption in 

 the whole violet region, so that the spectrum at 1 consists simply of a 

 transmission from X 4000 to X 6500. The transmission is weak from X 6100 

 to X 6500 and shows the cobalt bands at XX 6100, 6350 (about 100 Angstrom 

 units wide), and 6420. At 18 the transmission band runs from X 4000 to 

 X 6050. With rise in temperature the transmission band narrows and at 85 

 extends only from X 4300 to X 6750. Weak bands about 100 Angstrom 

 units wide appear at XX 5050 and 5300. These are considerably broader at 

 the lower temperatures. 



A spectrogram (Plate 19, B) was made to show the effect of rise in 

 temperature on the absorption spectra of a 0.0095 normal cobalt chloride 

 and 4.6 normal calcium chloride solution in water. The depth of the layer 

 was 50 mm., the length of exposure to the Nernst glower 3 minutes, the 

 current 0.7 ampere and the slit-width 0.20 mm. The length of exposure 

 to the spark was 5 minutes. The temperatures, starting with the strip 

 adjacent to the comparison scale, were - 1.5, 20, 30, 45, 57, 74, and 88. 



