COBALT CHLORIDE AND ALUMINIUM CHLORIDE. 207 



green is a little more intense for the solutions which contain calcium chloride 

 than for the solutions of the other set. That this difference, however, is not 

 very appreciable is readily seen from plate 12. Due to the presence of a 

 small quantity of some impurity, the mother-solution of aluminium chloride 

 had a very slight color in layers of 5 cm. or more in thickness. The facts 

 brought out by the spectrogram of the mother-solution of aluminium chloride 

 are given below. Two strips were photographed, the one corresponding to a 

 depth of 15.1 cm. and the other to a depth of 1.41 cm. The Nernst filament 

 was given an exposure each time of two minutes, and the spark was run for 

 1.5 minutes. The negative shows complete absorption of all the ultra-violet 

 and violet as far as 0.415^ for the deeper layer, and the entire strip is relatively 

 faint and under-exposed. In fact, the photographic impression fades away 

 about 230 A. U. farther from the longer wave-length end of the negative for 

 the deeper layer than for the shallower one. The faintest trace of the spark 

 line at 2558 was transmitted by the shallow layer of solution; also the line 

 at 2748.7 was barely recorded on the negative. The continuous background 

 began at about 0.288/*, and did not attain its full intensity for wave-lengths 

 shorter than 0.325 fi. 



Eye observations have completely confirmed photographic results in 

 the visible region, especially with regard to appreciable absorption of the 

 violet even for a depth of 5.3 cm., and marked general absorption through 

 the entire spectrum for a depth of 15.1 cm. It was, therefore, evident that 

 the mother-solution of aluminium chloride possessed both selective and 

 general absorption, which were certainly not negligible for long columns of 

 solution, and perhaps not inappreciable for such short columns as 1.41 cm. 

 Consequently, the differences in ultra-violet absorption shown by plate 12 

 for the successive pairs of solutions, may be due to the strong absorption 

 in this region of the aluminium chloride, and not to the presence of the 

 cobalt chloride, even alone or as influenced by the dehydrating agent. 



Before giving the facts obtained by eye observations and by freezing- 

 point and conductivity measurements, with the solutions containing the 

 chlorides of cobalt and of aluminium, it may not be out of place to present 

 the salient points brought out by the photographic comparison of the rela- 

 tive intensities and extents of absorption exerted by the mother-solution 

 of calcium chloride, calcium bromide, and aluminium bromide. The spectra 

 are shown by plate 11 (a). The concentration of the calcium chloride solu- 

 tion was 4.51, that of the bromide was 4.236, and that of the aluminium 

 salt was 2.75. The strip nearest to the numbered scale corresponds to 

 distilled water. The next strip pertains to the solution of calcium chloride, 

 the third strip is due to the aluminium chloride, and the strip adjacent to 

 the comparison spectrum is that of calcium bromide. The depth of the cell 

 was 1.41cm. The negative indicated no absorption at all for the distilled 



