224 HYDRATES IN AQUEOUS SOLUTION. 



COPPER BROMIDE AND CALCIUM CHLORIDE. [See plates 18 (a) and IS (6).] 



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

 chloride were, respectively, 2.186 and 4.51. The concentrations of the 

 chloride in the solutions, whose absorption spectra are given by the plates 

 designated above, were 0.000, 0.451, 0.902, 1.353, 1.804, 2.255, 2.706, 

 3.157, 3.608, and 4.059. The successive differences in concentration were 

 all equal to 0.451. The concentration of the copper bromide in all the solu- 

 tions had the constant value 0.219. By transmitted daylight the solutions 

 in columns 2.5 cm. long had colors that varied from greenish-blue through 

 various shades of green and brownish-green to dark reddish-brown. The 

 photographic strip nearest to the number scale of plate 18(6) corresponds to 

 the solution that contained only the one salt. The remaining strips succeed 

 one another in the order of increasing amounts of calcium chloride in the 

 solutions, so that the strip adjacent to the comparison spectrum pertains to 

 the solution of concentration 4.059. The depth of the cell was 1.41 cm. 



Of the various facts brought out by the negative for plate 18 (6), the 

 following are the most striking: In the most dilute solution, transmission 

 began at 0.377/t; the second photographic strip began at 0.3S2/<. On 

 the negative the fourth and fifth strips commenced at about, respectively, 

 0.419/1 and 0.499/t. Consequently, when the concentration of the calcium 

 chloride was changed from 0.000 to 0.451, the end of the absorption band in 

 the ultra-violet and violet was displaced towards the red by 50 A.U. Again, 

 when the concentration of the dehydrating agent varied from 1.353 to 

 1.S04, the above-mentioned end of the absorption band was displaced by 

 300 A. U. in the same direction. Therefore, as is easily seen from the spec- 

 trogram, up to a certain concentration the end of the band encroached more 

 rapidly on the region of longer waves as the concentration of calcium chloride 

 increased. In all the cases discussed in the preceding pages, the successive 

 increments of absorption decreased steadily as the concentration of the dehy- 

 drating agent increased in arithmetical progression. As just noted, the 

 change is exactly the reverse for the solutions of copper bromide and calcium 

 chloride. With the sixth photographic strip the end of the absorption band 

 altered somewhat its nature. The negative showed that very weak trans- 

 mission began at about 0.478/<, and extended over a relatively wide range of 

 wave-lengths. In fact, comparatively intense transmission began only near 

 0.528/1. The negative strip corresponding to the most concentrated solution 

 showed that transmission was weak and began in the neighborhood of 0.522/*. 

 The negative of which plate 18 (a) is a reproduction was taken with a 

 Cramer trichromatic plate. The photographic strip adjacent to the scales 

 corresponds to the most concentrated solution of the set, and the strip at 

 the opposite side of the spectrogram corresponds to the solution of concen- 

 tration 2.55. The depth of the cell was 1.41 cm. Each exposure to the light 



