228 HYDRATES IN AQUEOUS SOLUTION. 



2.25 minutes. The negative was somewhat under-developed. It gave for 

 the first maximum of transmission the wave-length 0.454;<. The maximum* 

 of absorption in the green was recorded as 0.500/i. The spectrogram of plate 

 19 (a) gives a more correct graphical representation of the band in the blue- 

 green than dot-s that of plate 19 (6). The asymmetry of this band, and its 

 greater width of penumbra on the less refrangible side, was confirmed 

 directly by observations. 



The results obtained by a rather extended series of eye observations on 

 the solutions that contained copper bromide and calcium bromide will now 

 be given in some detail. 



The solutions were first studied in pairs by the aid of the double-compart- 

 ment cell. The length of each absorbing column was, therefore, 2.5 cm. 

 As the solutions became more and more concentrated, the band in the red 

 gradually shifted its visible boundary to shorter wave-lengths. The incre- 

 ments of absorption in the violet and blue appeared to become greater and 

 greater as the more and more concentrated solutions were studied. The 

 solution of concentration 1.107 of calcium bromide absorbed the blue-green 

 and blue almost completely, and also dimmed the entire region of trans- 

 mission appreciably more than the next less concentrated solution. In like 

 manner the solution of concentration 1.271 showed throughout weaker 

 transmission than the next lower member of the series, and it absorbed 

 completely all colors more refrangible than the green. In addition, this 

 co or was greatly weakened in intensity. The last two solutions just men- 

 tioned showed at the more refrangible side of the green a fairly long region 

 of transmission, which was so extremely faint that the eye could not detect 

 any color as such, but only an indefinite gray. The spectrum of the solution 

 whose concentration was 0.254 was compared with that of distilled water. 

 Very weak transmission of the same intensity began at 0.665, and 0.770/<, 

 respectively, for the solution and for the pure water. The solution also 

 absorbed the extreme violet quite noticeably. 



In order to study with the spectroscope the solutions of greater concentra- 

 tion than 1.525, as well as to obtain checks on the data obtained photograph- 

 ically, the cell sketched in fig. 66 was adjusted to a depth of 0.06 cm. and 

 arranged so as to be used with its axis of figure horizontally. The following 

 facts were then observed and noted: In this cell the solution of concentra- 

 tion 2.033 had a light, yellowish-brown color. The spectrum extended from 

 about 0.747/t to 0.425/*. The weakening of transmission in the blue-green 

 was very delicate. 



The^spectrum transmitted by the solution of concentration 2.287 began 

 about 0.740/x,and continued to be uniformly bright to, say, 0.540/t. At this 

 wave-length the penumbra of the absorption band in the blue-green com- 



* Not the center of the band in the green. 



