252 HYDRATES IN AQUEOUS SOLUTION. 



negative strips corresponding, respectively, to the solution that contained the 

 greatest amount of water, and to the one that was anhydrous, gave the very 

 beginnings of transmission as 0.375/t and 0.480/i. The complete spectrogram 

 shows that the increments of absorption decreased gradually as the percent- 

 age of water decreased in arithmetical progression. 



The spectroscope revealed the existence of a one-sided region of absorption 

 in the red. The depth of cell used was 2.40 cm. The limit of visible trans- 

 mission moved towards the infra-red as the quantity of water in the solutions 

 increased. The approximate wave-lengths of this limit were 0.65/f and0.67/<, 

 respectively, for the mother-solution and for the solution that contained 40 

 per cent of water. 



COPPER CHLORIDE IN ETHYL ALCOHOL. [See plate 29.] 



The concentration of the mother-solution of copper chloride was 0.321. The 

 percentages of water in the solutions of the complete set were 56, 52, 48, 44, 

 40, 36, 32, 28, 24, 20, 16, 12, 8, 4, and 0. Each successive difference equals 

 4 per cent. The colors of the liquids when viewed in the cell varied from 

 blue, through greenish-blue, bluish-green, green, and yellowish-green, to olive, 

 as the percentage of water decreased from 56 to zero. The photographic strip 

 contiguous to the numbered scale belongs to the solution that contained 

 56 per cent of water. The next strip corresponds to the 52 per cent solution, 

 etc., until finally the strip adjacent to the comparison spectrum corresponds 

 to the anhydrous mother-solution. The depth of the cell was 2 cm. 

 The spectrogram shows a one-sided region of strong absorption in the ultra- 

 violet and violet, and suggests another like region in the yellow and orange. 

 The negative strip corresponding to the solution that contained the greatest 

 amount of water recorded faintly the strong cadmium doublet at 3467, but 

 the continuous background faded out at near 0.350,". Transmission began 

 weakly at 0.520^ for the mother-solution. The curve outlined by the ends 

 of the photographic strips appeared to be convex towards the ultra-violet 

 region of absorption throughout the greater part of its course, whereas in 

 general the curves obtained for copper chloride, whether in water alone or in 

 water which also contains some dehydrating agent, were concave towards 

 the left. 



The spectroscope showed that there was an absorption band in the infra- 

 red which extended into the visible spectrum. For the anhydrous mother- 

 solution transmission began at about 0.635/, and for the solution which 

 contained the greatest amount of water it commenced at 0.700/i. Eye obser- 

 vations on the spectra of the solutions in question showed that the limit 

 of absorption in the red receded to longer wave-lengths as the percentage of 

 water in the solutions increased. 



