COBALT CHLORIDE AND CALCIUM CHLORIDE. 195 



The strip corresponding to the solution that contained no calcium chloride 

 appears next to the numbered scale, while the strip associated with the solu- 

 tion which had the greatest concentration in calcium chloride lies closest to 

 the comparison spectrum. The depth of the cell was 1.41 cm. The line 

 of separation for the half-films lies between the fifth and sixth photographic 

 strips. 



These regions of absorption are shown by the spectrogram. One of these 

 is in the extreme ultra-violet, another is in the green, and a third is in the 

 orange and red. The solution of cobalt chloride alone was unusually trans- 

 parent to short waves of light, transmitting the spark line at 2265.1. The 

 negative showed no shorter wave-lengths. The band in the ultra-violet 

 gradually extended to longer waves, as the concentration of calcium chloride 

 increased. For example, the ninth solution transmitted the line of wave- 

 length 2258.0, but nothing more refrangible, and the continuous background 

 did not persist quite as far as to the spark line last mentioned. The line 

 spectrum of the strip adjacent to the spark scale is not comparable with the 

 other strips, because the Leyden jar brokedown in the course of the exposure. 

 This accident had no influence, of course, on that part of the tenth strip, 

 which was obtained by the use of the Nernst filament. The marked lack of 

 intensity of the comparison spectrum was due to the same break. The band 

 in the green extended from about 0.505/t to 0.530 /( , as shown by the negative 

 for the solution containing no calcium chloride. This band widened out 

 more and more as the concentration of the calcium chloride increased. At 

 the same time, general absorption was present on the orange side of the band, 

 and not on the blue side. This fact, together with the one to be discussed 

 below in connection with the eye observations, namely, that there were bands 

 of continually increasing width in the red, accounts for the change in the 

 resultant color from red to blue when the calcium chloride was added to the 

 solution of cobalt chloride. 



Plate 9 (6) shows the variation of the absorption of solutions of cobalt 

 chloride and calcium chloride, when the successive increments of concentra- 

 tion were all equal. The electrical conductivities of these solutions were also 

 measured, as will be seen later. The constant concentration of the cobalt salt 

 was 0.271, and the concentrations of the calcium chloride were 0.000, 0.325, 

 0.650,0.974, 1.299, 1.624, 1.950. The common difference used in the calculation 

 was 0.3248. The concentrations of mother-solutions of cobalt and of calcium 

 chloride were, respectively, 2.71 and 4.06 normal. The solution which con- 

 tained the greatest amount of calcium chloride has its photographic strip 

 adjacent to the comparison spectrum. The depth of the cell was the same 

 as for plate 8. 



The region of absorption in the ultra-violet widened out from 2194.7 to 

 about 0.245ju, when the extreme strips were measured. The limits of the 



