256 HYDRATES IN AQUEOUS SOLUTION. 



Eye observations with the spectroscope confirmed qualitatively the above 

 results, and also brought out some additional facts relative to the red region 

 in the spectrum. For the mother-solution transmission began at 0.715/*, rose 

 to a maximum near 0.651/*, and then decreased to a very small value in the 

 neighborhood of 0.593/1. Transmission was extremely weak from 0.593/t to 

 0.520/(, i. e.,to the beginning of the ultra-violet region of complete absorption. 

 There appeared to be a slight minimum of transmission at 0.575/*, and a weak 

 maximum at 0.540/*. Red and orange were obviously the only colors appre- 

 ciably transmitted. The spectrum of the 4 per cent solution was very much 

 like that of the anhydrous solution. The spectra of both solutions agree in 

 having a relatively bright region of transmission in the red, followed by a 

 long, comparatively weak region in the direction of the shorter wave-lengths. 

 The maximum of transmission was near 0.640//, and complete extinction 

 commenced at about 0.490^. Green and blue were transmitted much more 

 strongly by the 4 per cent solution than by the mother-solution. The spec- 

 trum of the 8 per cent solution showed that the region of weak transmission 

 had left the green and comprised only the blue. There were no appreciable 

 contrasts in the transmitted regions of the spectra of the remaining solutions 

 in the series. As the percentage of water increased from zero to 52, the end 

 of the absorption band in the red receded gradually from about 0.715/* to 

 0.755/i. 



COPPER BROMIDE IN ETHYL ALCOHOL. [See plates 33 (a) and 34.] 



The concentration of the anhydrous mother-solution was 0.101. The per- 

 centages of water in the series were 36, 32,28,26,24,22,20, 18, 16, 14, 12, 10,8, 

 6, 4, and 0. Therefore, all the successive differences are equal to 2 per cent, 

 except the first two and the last one, and each of these is equal to 4 per 

 cent. Viewed in their bottles the solutions varied in color from bluish-green, 

 through the various shades of green and olive, to very dark brown as the 

 amount of water decreased from 36 to per cent. The mother-solution was 

 sensibly opaque except in very thin layers. The same succession of colors 

 was shown by the solutions when in the cell at a depth of 0.24 cm., with the 

 exception that the first four or five solutions appeared practically colorless. 



The photographic strips which correspond, respectively, to the solution 

 that contained the greatest amount of water, and to the one that was anhy- 

 drous, are adjacent to the numbered scale and to the comparison spectrum 

 of plate 34. The cell depth for both plates 33 and 34 was 0.24 cm. The 

 negative strip belonging to the 36 per cent solution recorded the faintest 

 trace of the cadmium line at 3261.2, but the continuous background became 

 very weak near 0.340 n. The spectrogram, taken as a whole, shows that the 

 locus of the limit of absorption of the region which included the ultra-violet, 

 was a smooth curve convex towards the region of shortest wave-lengths. 

 Also, the last six or seven photographic strips show that there was general 



