SALTS OF COPPER. 53 



spending depths of absorbing layer being 6, 7.5, 9.5, 12, 15, 19, and 24 mm. 

 For B the concentrations were 0.028, 0.022, 0.018, 0.014, 0.011, 0.009, and 

 0.007; the depths of cell were the same as for A. 



The more concentrated solutions were reddish-brown, from which the 

 color changed on dilution to a pale greenish-yellow. 



The exposure to the light of the Nernst lamp was 1| minutes with a 

 width of slit of 0.015 cm. for A, and 50 seconds with a slit width of 0.012 

 cm. for B. No exposures to the light from the spark were made, as a 

 preliminary test showed that even the most dilute solution was opaque 

 in the ultra-violet. 



In the region of short wave-lengths, the limits of transmission, corre- 

 sponding to the most concentrated and most dilute solutions of A, are 

 A 4800 and A 4550, while for B the corresponding limits are at ^ 4320 and 

 /t 4170, respectively. The line formed by the edge of the absorption band 

 is very nearly a straight line in both cases. 



In the red the absorption is slight. The limits of transmission for the 

 most concentrated and most dilute solutions of A are X 7150 and X 7200, 

 respectively. In B the edge of the band is sensibly straight, and at right 

 angles to the length of the spectrum strips, its limit being at A 7350. This 

 is, however, so near the limit of sensibility of the plates used that there 

 was, perhaps, transmission to some little distance beyond this. Comparing 

 this spectrogram with that of copper chloride in methyl alcohol (Plate 32), 

 it is seen that the ultra-violet absorption in the two cases is nearly iden- 

 tical, notwithstanding the fact that the concentration of the chloride was 

 about nine times as great as that of the bromide. This shows at once 

 the great power of the bromide for absorbing light of short wave-lengths, 

 when dissolved in methyl alcohol. The absorption for red light is perhaps 

 not very different for the two salts. A comparison is not possible, owing 

 to the great difference in concentration. 



COPPER BROMIDE IN ETHYL ALCOHOL BEER'S LAW. (See Plate 41.) 



The concentrations of the solutions used in making the negative for 

 A, beginning with the one whose spectrum is adjacent to the numbered 

 scale, were 0.0447, 0.036, 0.028, 0.022, 0.018, 0.014, and 0.011; the corre- 

 sponding depths of absorbing layer were 6, 7.5, 9.5, 12, 15, 19, and 24 mm. 

 For B the concentrations were 0.014, 0.011, 0.0088, 0.0070, 0.0056, 0.0044, 

 and 0.0035; the depths of cell were the same as in A. 



The more concentrated solutions were deep brownish-red, opaque in 

 layers of any considerable depth, from which the color changed on dilu- 

 tion to a light clear-yellow. 



The exposures to the light of the Nernst lamp were 1^ minutes with a 

 slit 0.02 cm. wide for A, and 50 seconds with a slit 0.012 cm. wide for B. 

 No exposure to the light of the spark was made, since all the solutions 

 were opaque in the ultra-violet. 



Towards the ultra-violet the first solution of A transmitted faintly as 

 far as X 5500; the seventh solution as far as X 5050. The corresponding 

 limits for B are X 4500 and X 4300, respectively. The edge of the band in 

 either case forms very approximately a straight line. In the red the ab- 



