196 HYDRATES IN AQUEOUS SOLUTION. 



band in the green increased linearly with the like change in the concentration 

 of the calcium chloride. Also the center of this band remained at the same 

 wave-length 0.518/ for the seven solutions under consideration. 



Plate 9 (a) gives the absorption spectra of another set of solutions contain- 

 ing the chlorides of cobalt and of calcium. These solutions were made up 

 of such concentrations as to contain the same number of chlorine atoms as 

 the corresponding solutions of a set in which aluminium chloride was the 

 dehydrating agent, instead of calcium chloride. The reasons for this will be 

 discussed later when the facts about the spectra of aluminium chloride are 

 given. Plate 9 (a) supplements plate 9 (6) from the standpoint of concen- 

 tration, and also because of the circumstance that the solutions of both of 

 these spectrograms have their conductivity data collected in one table and 

 in a single curve in a later section. The concentration of the cobalt chloride 

 was 0.271, as before, and the concentrations of the calcium chloride were 

 0.000, 1.676, 2.091, 2.515, 2.671,2.830, 3.143, 3.555. Therefore, the differ- 

 ences of first order were 1.676, 0.415, 0.524, 0.156, 0.159, 0.313, 0.412. The 

 depth of the absorbing layer, the times of exposure, and the relative posi- 

 tions of the photographic strips are the same for plate 9 (&) as for plate 9 (a). 

 The negative for 9 (a) shows a faint trace of the spark line at 2194.7 A. U. 

 and 2573.1 A. U. for the strips associated, respectively, with the solutions of 

 least and greatest concentration in the calcium salt. The continuous back- 

 ground does not extend quite as far as the wave-lengths just given, especially 

 in the case of the most concentrated solution. The general absorption in 

 the yellow and orange is brought out clearly by the eighth strip. 



The question as to how much of the absorption in any given mixture of 

 solutions is to be ascribed to the colored salt, and how much is due to the 

 dehydrating agent, will be taken up immediately after the other matters 

 pertaining to the solutions containing cobalt chloride, together with either 

 calcium chloride, or calcium bromide, or aluminium bromide, shall have 

 been discussed. 



The most important facts brought out by the observations of the bands 

 in the orange and red were -the following. It is not necessary to give here the 

 data relative to the band in the green, since they confirm in detail the results 

 obtained photographically, and the latter as shown by the spectrograms. 



The solutions studied with the spectroscope were the ones which accom- 

 pany plate 8. The depth of cell used was 2.5 cm. With distilled water in the 

 cell, the red end of the spectrum appeared to begin at about 0.775/i. The 

 solution containing only cobalt chloride, as well as the one having the 

 concentration 1.676, showed no absorption in the red. For the solution of 

 concentration 2.514 of the calcium salt, two very faint {lutings of intensity 

 showed their maxima of absorption at 0.697^ and 0.661/1. By moving the 



