244 HYDRATES IN AQUEOUS SOLUTION. 



SOLUTIONS. 



The solutions were made up as follows: A chosen volume of pure water 

 was run out of a burette into a measuring flask. Then some of the mother- 

 solution of one of the colored salts was run into the flasks, and thoroughly 

 mixed with the water until the volume of the resulting homogeneous solution 

 was exactly equal to the calibrated capacity of the flask. In the following 

 account of the work, the amount of water in a given solution will be expressed 

 in per cent of the total volume of the solution. For example, if occ.of water 

 were made up to 200 cc. of solution, the amount of water would be given as 

 2.5 per cent, or simply 2.5. The colored salts used were cobalt chloride, 

 copper chloride, and copper bromide. The solvents employed were methyl 

 alcohol, ethyl alcohol, and acetone. Special precautions were taken to have 

 both the colored salts and the solvents as free from water as possible. 



COBALT CHLORIDE IN METHYL ALCOHOL. [See plate 23.] 



The concentration of the mother-solution was 0.099. The percentages 

 of water in the solutions were 12. GO, 9.50, 7.00, 6. CO, 5.00, 4.00, 3.50, 3.CO, 

 2.00, 1.50, 1.26, 1.01,0.50, 0.00. The successive differences in per cent were 

 2.50, 2.50, 1.00, 1.00, 1.00, 0.50, 0.50, 1.00, 0.50, 0.24, 0.25, 0.51, 0.50. As 

 the quantity of water increased, the color of the solution gradually changed 

 from the purple of the mother-solution to a pale pink, passing through the 

 intermediate tints. Photographic strips corresponding to the solutions that 

 contained the greatest and least amount of water are adjacent, respectively, 

 to the numbered scale and to the comparison or spark spectrum. The depth 

 of cell was 2 cm. The first seven strips were taken on one half the photo- 

 graphic film, and the remaining seven on the other half. 



The spectrogram shows a region of absorption in the ultra-violet and violet, 

 and a band in the green. The air-line at 3007 was very faintly recorded by 

 the strip corresponding to the solution that contained the greatest amount 

 of water, but the continuous background did not extend beyond about 0.314/'.. 

 The middle of the band in the green was 0.517/. As shown by the corre- 

 sponding strip, transmission began near 0.373, for the mother-solution of 

 cobalt chloride in the methyl alcohol. The middle of the band in the green 

 was at 0.525 n. Therefore, one effect of the addition of water is to shift this 

 band towards the blue. It is interesting to note in this connection that the 

 center of the absorption band in the green was displaced towards the red by 

 about 100 A. U. when the solvent was changed from water alone to methyl 

 alcohol. This absorption band widened very gradually as the amount of 

 water in the successive solutions decreased. In fact, for the mother-solution 

 the negative strip indicated that transmission began near 0.505/1 and 0.540/< 

 at the sides of this absorption band. The band was very weak for the solu- 

 tion containing the greatest amount of water. It must, however, be remem- 



