24 ABSORPTION SPECTRA OF SOLUTIONS. 



shorter wave-length than X 2800 are absorbed. In addition an absorption 

 band having its center at X 3010 makes its appearance, and increases rap- 

 idly in intensity and width with the increase in the amount of calcium 

 bromide. In the solution corresponding to the eleventh strip, this band 

 and the band in the extreme ultra-violet have run together, causing all 

 light of wave-length shorter than X 3140 to be absorbed. 



The question whether all the absorption in the ultra-violet is due to 

 the presence of calcium bromide as such, or whether it is due to some 

 action of this salt on the cobalt bromide in the solution may be answered 

 by referring to Plate 11 A, in "Hydrates in Aqueous Solution," and to 

 the description of it given on page 208, as well as to Plate 10, which shows 

 the effect on the absorption of cobalt chloride produced by adding cal- 

 cium bromide of various concentrations. A concentrated solution of 

 calcium bromide 4.236 normal, in a depth of layer of 1.41 cm., still trans- 

 mits some light of wave-length shorter than X 2800, although it exerts 

 some absorption as far as X 3100. Plate 10, "Hydrates in Aqueous Solu- 

 tion," shows that a solution of cobalt chloride containing calcium bromide 

 in such concentrations as 0.7 normal, still transmits light of a wave-length 

 as short as X 2500 when the layer is 1.41 cm. deep, without any sign of 

 absorption in the region X 3010. We may accordingly conclude that the 

 widening of the extreme ultra-violet band in Plate 12 is due to the absorb- 

 ing action of calcium bromide, but that the band at X 3010 is to be ascribed 

 to the joint action of this salt and cobalt bromide. 



The band in the green widens regularly and symmetrically with the 

 addition of calcium bromide. Measurements on the negatives give the 

 following results: For the strip pertaining to the solution containing no 

 dehydrating agent, the limits of transmission are X 5020 and X 5300, center 

 at X 5160. For the strip corresponding to the solution containing the 

 greatest amount of calcium bromide the limits were X 4770 and X 5560, 

 center at X 5165. 



In the red the solutions containing the greatest amount of the dehy- 

 drating agent show a set of four absorption bands having their centers 

 at X 6400, X 6650, X 6950; the center of the fourth band lies in the extreme 

 red, beyond the region of sensibility of the photographic plate used. Its 

 presence is shown by the cutting off of the extreme red end of the strips 

 nearest the numbered scale. The band at X 6400 is rather narrow, the 

 others moderately wide, the one at X 6650 being the most intense and also 

 persisting the longest with decrease in the amount of the calcium salt. 

 A comparison of this spectrum with the diagram shown on page 197 of 

 "Hydrates in Aqueous Solution," which shows the position and relative 

 intensity of the red bands of cobalt chloride brought out by adding large 

 quantities of calcium chloride, reveals some notable differences. The posi- 

 tions of the bands are sensibly the same, but in calcium chloride the band 

 at X 6950 is stronger than the one at X 6650, whereas the reverse is true 

 for the bromide. Also, the chloride shows a weak band at X 6400 with 

 stronger ones at X 6240, and X 6095, while the bromide has an intense band 

 at X 6400, and none at all in the other positions. The bands with the 

 chloride were the same whether calcium chloride, calcium bromide, or 



