208 HYDRATES IN AQUEOUS SOLUTION. 



water; in other words, the zinc line at 2024.2 was recorded. The calcium 

 chloride transmitted a trace of the strong cadmium line at 2265.1. This 

 solution absorbed practically all of the continuous background between 0.280;* 

 and 0.202/1. The mother-solution of aluminium chloride transmitted pre- 

 cisely the same lines as did the solution of calcium chloride, but the former 

 absorbed and weakened the continuous background a good deal more than 

 the latter. When the concentrations of these two solutions are taken into 

 account, the relatively great absorbing power of the aluminium salt for the 

 very short waves becomes evident at once. The strong emission line at 

 2748.7 was weakly transmitted by the solution of calcium bromide, but the 

 continuous background was almost completely absorbed beyond 0.313/*. 

 Since the concentration of the calcium bromide solution was somewhat less 

 than that of the calcium chloride, the second and fourth photographic strips 

 show conclusively how very much stronger the absorption of the bromide 

 is than that of the chloride for the short light waves. For the depth used 

 in the visible region, the three solutions in question exerted no appreciable 

 absorption. 



In the light of what has just been explained, a comparison of the spectro- 

 grams of plates 2, 9 (a), 9 (6), 10, 11 (a), and 11 (6) leads to the conclusion that, 

 in general, the absorption of the ultra-violet light by the cobalt chloride is 

 masked to some extent by the superposition of the greater absorption of the 

 dehydrating agent in a given solution. Therefore, the absorption bands in 

 the visible spectrum are better criteria for the behavior of the cobalt salt 

 in the presence of some one of the dehydrating agents than the regions of 

 absorption in the ultra-violet. It does not seem necessary to enter into 

 minute details relative to the general principles just stated. 



Eye observations on the absorption spectra of the solutions which con- 

 tained the chlorides of cobalt and aluminium led to practically the same 

 results as were obtained with the other two dehydrating agents under 

 investigation. The chief characteristics of these spectra are shown by the 

 four curves of fig. 71. The depth of column used was 2.5 cm. The solutions 

 of concentration 1.118 and 1.394, in the aluminium salt, did not show even 

 the faintest traces of discrete bands in the red. The entire set of five bands 

 could barely be distinguished with the solution of concentration 1.676. The 

 solution of concentration 1.781 has its systems of bands represented fairly 

 well by fig. 71 (a), except that the band at 6405 was hard to see. The bands 

 at 6405, 6245, and 6095 were relatively intense, but not very clear-cut and 

 well-defined for the solution of concentration 1.887. Figure 71 (c) gives an 

 idea of the regions of transmission and absorption for the solution of con- 

 centration 2.100. For this solution the bands at 0.697/< and 0.661/c had 

 coalesced and the resultant region extended from 0.713/t to 0.653;<. A deep 



