254 HYDRATES IN AQUEOUS SOLUTION. 



For the sake of comparison, the spectra of the solutions of copper chloride 

 in the four pure solvents were recorded side by side photographically. [See 

 plates 31 (a) and 31 (fr).] The concentrations of the solutions in water, in 

 methyl alcohol, in ethyl alcohol, and in acetone as solvents were, respectively, 

 0.795, 0.283, 0.321, 0.022. The depth of cell used was 1.50cm. for both 

 plates. In the cell the aqueous solution was blue, the solution in methyl 

 alcohol was yellowish-green, the solution in ethyl alcohol was very dark 

 green, and the solution in acetone was brownish-yellow. The negative strips 

 corresponding, respectively, to the solutions in water and in acetone are 

 adjacent to the numbered scale and to the comparison spectrum. The strip 

 nearest to the one that pertains to the aqueous solution, corresponds to the 

 solution in methyl alcohol. The negative of plate 31 (6) showed that the 

 extreme limits of transmission for the aqueous solution were 0.397/< and 

 0.59S, . Only the more refrangible limit of the region of visible transmission 

 could be recorded by the Seed film for the solution in methyl alcohol. This 

 limit was given as 0.472/!. The limits of faint transmission for the solution in 

 ethyl alcohol were recorded as 0.523.". and 0.598.".. The negative strip corre- 

 sponding to the solution in acetone as solvent showed that transmission 

 began at about 0.519,". and extended beyond the region of sensibility of the 

 photographic emulsion . 



The negative for plate 31 (a) was taken with a Cramer trichromatic 

 plate. The concentrations of the non-aqueous solutions were the same as 

 for plate 31 (b). The concentration of the aqueous solution of copper chloride 

 was 1.590, i.e., twice as great as formerly. This solution was green, with a 

 bluish tinge. The length of the exposure for the Nernst glower was two min- 

 utes. The photographic strips succeed one another in exactly the same order 

 for plate 31 (a) and for plate 31 (b}. However, the strip corresponding to the 

 solution in acetone is adjacent to both scales, w r hile the one pertaining to the 

 aqueous solution is nearest to plate 31 (b). The extreme limits of transmis- 

 sion were shown by the negative to be 0.431/t and 0.591/< for the aqueous 

 solution. The strip corresponding to the solution in methyl alcohol showed 

 that transmission began near 0.462/<, and only became weakened to a very 

 slight extent at the very end of the plate. The strip pertaining to the solu- 

 tion in ethyl alcohol gave the limits of transmission as 0.512/t and 0.608/<. 

 The acetone solution began to transmit at about 0.507/t and continued to do 

 so beyond the field of view of the spectrograph. The results of eye observa- 

 tions, combined with the data obtained photographically, show that as the 

 solvent for copper chloride was, successively, water, ethyl alcohol, methyl 

 alcohol, and acetone, the middle of the region of transmission in the visible 

 spectrum moved to longer and longer wave-lengths. 



