236 HYDRATES IN AQUEOUS SOLUTION. 



meant nothing more than an increase in the number of absorbing particles 

 per unit volume, and not a change in their effective mass, had to be taken 

 into account. The well-known theoretical formula involving the laws of Beer 

 and Lambert is 7 = I adc } where d symbolizes the thickness of absorbing 

 layer, and c denotes the concentration. The remaining symbols have obvious 

 definitions. 



Further details concerning the laws may be found in the third volume 

 of Kayser's " Handbuch der Spectroscopie," pp. 20, 25, and Chapter II, E. 

 Plates 3 (c) and 6 show conclusively the widening of the bands with increas- 

 ing concentration, in the case of aqueous solutions of copper bromide. The 

 data obtained from eye observations on the bands in the red confirm com- 

 pletely the spectrographic results. 



Plates 8, 9 (a), 9 (6), and 12 show that the bands in the ultra-violet and 

 green widen out as the amount of calcium chloride in the aqueous solutions 

 of cobalt chloride increased. It will be remembered that in these solutions 

 the mass of cobalt chloride was kept constant, while the quantity of the 

 dehydrating agent was varied. These facts agree perfectly with the theory, 

 since the calcium chloride has a much greater affinity for water particles than 

 the cobalt system. Therefore, as the concentration of the calcium chloride 

 increases, more and more water is taken away from the cobalt chloride, so 

 that the vibrations of the latter are less damped than before, and thus the 

 absorption bands cover a wider range of period. 



The same phenomenon is shown by plates 11 (b) and 12, for the solutions 

 containing variable amounts of aluminium chloride and a constant quantity 

 of cobalt chloride. 



The progress of the ultra-violet region of absorption, as the quantity of 

 calcium chloride in the solutions containing a constant amount of copper 

 chloride is increased, is very clearly shown by plate 13. 



Plate 17 brings out the same facts for the solutions having a constant mass 

 of copper chloride and a variable quantity of aluminium chloride. 



The absorption bands of solutions of copper bromide, which differ only 

 in the amounts of calcium bromide contained in the solutions, extend over 

 wider ranges of wave-lengths as the percentage of the dehydrating agent 

 increases. This is shown by plates 7 (b), 19 (a), and 19 (6). 



The results of the eye observations agree in detail with the facts derived 

 from the photographic negatives. [See especially figure 71 (a), (fe), (c), and 

 (d).] When to solutions containing constant amounts of cobalt chloride 

 or of copper chloride, varying quantities of calcium bromide are added, the 

 absorption phenomena are in general more complicated than in the cases 

 just discussed, because of the effective formations, respectively, of cobalt 

 bromide and of copper bromide. Similar conditions arise, of course, when 

 either calcium chloride or aluminium chloride is added to solutions containing 



