COPPER CHLORIDE AND ALUMINIUM CHLORIDE. 221 



COPPER CHLORIDE AND ALUMINIUM CHLORIDE. [See plate 17.] 



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

 salts were, respectively, 3.976 and 2.75. The several solutions of the series 

 had the following concentrations of aluminium chloride: 0.000, 0.165, 0.330, 

 0.495, 0.660, 0.825, 0.990. 1.155, 1.320, 1.485, 1.650, 1.815, 1.980, 2.145, 

 2.310, 2.482. The successive differences in concentration were all equal to 

 0.165, except the last, which equaled 0.172. The solutions varied in color 

 from pure blue, through various intermediate shades of greenish-blue, bluish- 

 green, and dear green, to greenish-yellow. The photographic strip next to 

 the numbered scale corresponds to the solution which contained only copper 

 chloride, and the successive strips, of course, became shorter and shorter as 

 the amount of dehydrating agent in the corresponding solutions increased. 

 The depth of the cell was 1.41 cm. 



The half-films were not developed simultaneously. The last two strips 

 corresponding to the most concentrated solutions are not quite comparable 

 with the first fourteen, as is shown by the fact that they extend a little too 

 far out towards the red end of the spectrum. This was due to opening the 

 slit of the spectrograph a little too wide as the result of an accidental blow 

 to the micrometer head, and the failure to produce exactly the original 

 adjustment. 



The negative for the first strip recorded very faintly the intense cadmium 

 line of wave-length 3403.7 A. U., but nothing more refrangible. The con- 

 tinuous background, however, barely extended to 0.347 '/*. According to the 

 negative, the most concentrated solution began to transmit at 0.504,. 



Since the concentrations of the aluminium chloride are in arithmetical 

 progression, the spectrogram shows at a glance the fundamental relation 

 between the limit of absorption of the shorter waves and the concentration 

 of the solution. That the curve of absorption advanced rapidly along the 

 wave-lengths at first, and then changed by smaller steps, is shown by the 

 fact that about 150 A. U. lie between the more refrangible ends of the third 

 and fourth photographic strips, whereas only 50 such units are comprised 

 in the corresponding interval between the fifteenth and sixteenth strips. 



The solutions were studied in pairs, with the aid of the spectrograph and 

 double-compartment cell. The data obtained visually, for the limits of 

 absorption in the violet and blue, agree completely with the photographic 

 results, and, therefore, they will not be repeated. Each solution absorbed 

 the red a little more than the one immediately preceding, and hence the less 

 concentrated member of the set. 



The dispersion of the spectroscope was not great enough in this region to 

 enable the observer to obtain quantitative result for consecutive solutions. 

 The most dilute solution began to transmit red at about 0.644//, and the most 

 concentrated had approximately the same intensity of transmission at 0.629/t. 



