54 ABSORPTION SPECTRA OF SOLUTIONS. 



sorption is very slight, the limit of transmission as shown by A being at 

 A 7200 and A 7250, respectively, for the most concentrated and most dilute 

 solution. The solutions of B transmitted perfectly to beyond A 7400; 

 hence no absorption is registered on the photographic plate. 



Compared with the solutions in methyl alcohol, these solutions of 

 copper bromide in ethyl alcohol show very much stronger absorption in 

 the region of shorter wave-lengths. In the red the absorption in the two 

 solvents is not very different, if the differences in concentration are taken 

 into account in making the comparison. 



COPPER BROMIDE IN METHYL ALCOHOL WITH WATER. (See Plate 42.) 



The concentration of the copper salt was constant throughout, and 

 equal to 0.05 normal. The percentages of water in the solutions, beginning 

 with the one whose spectrum is adjacent to the numbered scale, were 0, 4, 

 8, 10, 12, 14, 16, 18, 20, 24, 28, 32, 36, 40, 44, and 50. The depth of the 

 absorbing layer was constant and equal to 2.0 cm. 



The solution containing no water was brown, and practically opaque 

 in deep layers. With addition of water the color changed rapidly to yellow- 

 ish-green, and finally became bluish-green in the solutions containing the 

 greatest amount of water. 



The time of exposure to the light of the Nernst lamp and spark was, 

 respectively, 1 and 3 minutes, the slit having, as usual, a width of 0.01 cm. 



The limits of transmission for the first eight solutions, beginning with 

 the one containing no water, were A 5450, A 4900, A 4625, X 4520, A 4450, 

 A 4330, A 4270, and A 4220. Leaving out the first two, where there was 

 considerable general absorption, the limits fall almost exactly on a straight 

 line. The solution containing 50 per cent of water transmitted as far down 

 as X 3700. 



In the red the absorption band also narrows and quite regularly with 

 addition of water, the bromide behaving in this respect quite differently 

 from the chloride. The extreme limit of transmission for the solution 

 containing no water was A 6850, there being considerable absorption from 

 A 6600 on. For the solution containing the largest percentage of water the 

 limit was A 7250, with considerable shading from A 6650 on. The edge of 

 the band hence becomes more hazy with addition of water here also, as 

 it did in the case of the chloride. 



A comparison of this spectrogram with the one of the chloride in methyl 

 alcohol (Plate 35) shows not only that the absorption of the bromide in the 

 ultra-violet is stronger, but also that it decreases much more rapidly on 

 addition of water. This is undoubtedly due to the much smaller concen- 

 tration of the bromide, which would make the ratio of water to colored 

 salt very much greater than it was for the chloride. In the red the absorp- 

 tion is about what we should expect from the concentration of the solutions. 



COPPER BROMIDE IN ETHYL ALCOHOL WITH WATER. (See Plate 43.) 



The concentration of the copper bromide was constant throughout, 

 and equal to 0.06 normal. The percentages of water in the solutions, 

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



