226 HYDRATES IN AQUEOUS SOLUTION. 



The solution of concentration 3.157 changed from reddish-brown at room 

 temperature, to greenish-yellow in the neighborhood of its freezing-point. 

 Salts separated out at about 58 for the solution which had the concentra- 

 tion 3.608, and hence the freezing-point lowering could not be determined. 



COPPER BROMIDE AND CALCIUM BROMIDE. [See plates? (6), 19 (a), 19 (fc),20 (a), and 20 (6).] 



The concentrations of the mother-solutions of copper bromide and of 

 calcium bromide were, respectively, 2.186 and 4.236. The constant concen- 

 tration of the copper salt in all of the solutions was 0.219. The concen- 

 trations of the calcium bromide were 0.000, 0.254, 0.508, 0.762, 1.017, 1.271, 

 1.525, 1.779, 2.033, 2.287, 2.542, 2.796 ? 3.050, 3.304, 3.588, and 3.807. All of 

 the successive differences of concentration were equal to 0.2542, except the 

 last one, which had the value 0.249. 



The most pronounced colors of these solutions in the order of increasing 

 concentration of the dehydrating agent, were light-blue, bluish-green, green, 

 yellowish-green, brownish-green, and dull brown. 



The spectrogram of plate 7 (b) will be discussed first. The negatives 

 were taken on Cramer trichromatic plates. The photographic strip adja- 

 cent to the scales corresponds to the seventh solution of the series; that is, 

 to the solution which had the concentration 1.525. The depth of the cell 

 was 1.41 cm. Each exposure to light from the glower was 2.25 mm. in 

 length. A spark exposure of 1.5 mm. was given for each one of the strips 

 which pertained to the three most dilute solutions of the set. The negative 

 strip for the solution which did not contain any calcium bromide recorded 

 the beginning of taint transmission at 0.373. The strip pertaining to solu- 

 tion of concentration 1.107 showed that transmission began at 0.436/< and 

 continued to be weak to about 0.520/<. Transmission was strong from 0.520/t 

 to the end of the negative. 



The darkening of the next negative strip commenced very faintly at about 

 0.504/(, and became very gradually more intense. The strip associated with 

 the solution of concentration 1.525 showed extremely weak transmission from 

 0.546/t to the end of the plate, the maximum being at 5875 A. U. 



The facts presented by the negative of which plate 19 (6) is a reproduction 

 will now be considered. The first eight solutions of the complete series were 

 photographed. The depth of the cell was 0.06 cm., and, therefore, the solu- 

 tions when in the cell showed practically no color. The strips contiguous 

 to the numbered scale and to the comparison spectrum correspond, respec- 

 tively, to the solutions of concentration 0.000 and 1.779 of the dehydrating 

 agent. The times of exposure for the glower and spark were as usual. The 

 strip pertaining to the most dilute solution recorded the very faintest trace 

 of the air-line at 3007.0 A.U.; the continuous background, however, ceased 

 near 0.308/t. The negative strip corresponding to the 8th solution showed 

 that transmission began near 0.400/. When due allowance is made for the 



