COPPER BROMIDE AND CALCIUM BROMIDE. 227 



known disturbing influences, the eight strips of plate 19 (6) seem to shew 

 that the end of the ultra-violet absorption band shifted directly propor- 

 tional to the increments of concentration of the calcium bromide. 



It is now desirable to give the most salient points relative to plate 19 (a). 

 The negative of the spectrogram in question was made with a Cramer tri- 

 chromatic plate. The 7th to the llth solutions, inclusive, had their spectra 

 recorded by this plate. The strips pertaining to the solutions of concentration 

 1.525 and 2.542 are, respectively, nearest to the outside edge of plate 19 (a) 

 and to the scale. The depth of the cell was 0.06 cm. The duration of each 

 exposure to the radiation of the filament was 2.25 mm. Hence, the 7th and 

 Sth solutions of the complete series have their absorption spectra given by 

 both plates 19 (a) and 19 (6). The negative strip, corresponding to solu- 

 tion of concentration 1.525, showed that transmission began at 0.383/1. 

 The third strip, counting from the outer edge of plate 19 (a), recorded 0.417/t 

 for the beginning of transmission, and 0.500, for the middle of the region of 

 rather weak transmission. The fourth strip showed very weak transmission 

 from 0.436, to 0.484/<, then apparent absorption from 0.484/t to about 0.530//, 

 and finally stronger transmission from 0.530/< to the end of the spectrogram. 

 The negative strip pertaining to the solution of concentration 2.542 recorded 

 very weak transmission from 0.555/^ to the end of the plate. 



The most concentrated solution of the set was so opaque to light, that its 

 absorption spectrum could only be satisfactorily recorded by the aid of the 

 wedge-cell. For plate 20 (b) the angle of the liquid wedge was about 11.7', 

 and the depth of the absorbing layer increased linearly from zero mm. to 

 0.11 mm. In the cell the solution appeared to be deep red. The absorption 

 band in the blue-green could be distinctly seen with the aid of the eyepiece. 

 The edges of this band are very diffuse and poorly defined. The exposures 

 were as usual. Obviously the edge of the negative closest to the comparison 

 spectrum was produced by the light that passed through the least depth 

 of the solution, i, e., nearest to the refractive edge of the liquid prism. Even 

 for the thinnest layers the continuous background was completely absorbed 

 from 0.200 to about 0.240/. The negative showed that the absorption 

 began to decrease in the vicinity of 0.335/e, and continued to do so, according 

 to a curve of gentle slope, until it reached a minimum at 0.455/. From this 

 point on the absorption increased to a maximum near 0.517/(, and then dimin- 

 ished again at the less refrangible side of the absorption band. 



Except in so far as the wave-length of the middle of the absorption band in 

 the green is concerned, plate 20 (a), whose negative was taken with a Cramer 

 trichromatic plate, fully confirms the facts as recorded by the spectrogram 

 of plate 20 (6). The angle of the wedge was only 7.8', and since the least 

 depth was zero, the greatest depth of absorbing layer was about 0.08 cm. 

 The three successive exposures to the light from the glower were each given 



