CUPRIC BROMIDE. 193 



fact that four of the five photographic strips of the negatives were blackened, 

 to a greater or less degree, as far as the end of the field of view of the camera; 

 while the fifth strip was very faint at this limit. 



On plate 3 (c) the penumbra mentioned above is clearly shown by the 

 third and fourth strips, counting from the sides of the spectrogram adjacent 

 to the numbered scale. Also the fifth strip shows no sign of this region of 

 weak transmission, as was also the case with the fifteenth strip in plate 6. 

 The shortest wave-length recorded on the negative plate 3 (c) for the most 

 concentrated solution was 0.541/j. 



The dependence of the limits of absorption upon thickness of layer for the 

 mother-solution of copper bromide was shown graphically by plate 7 (a). 

 The angle of the wedge-cell was 27.3' and the depth of solution varied linearly 

 from about zero to 0.25 mm. In the deeper portions of the cell the solution 

 appeared dull brown. The washed-out band in the blue-green was observed 

 with the eyepiece, and hence its presence on the spectrogram is not due to 

 the photographic film alone. As for the chloride of copper, so also for the 

 bromide, the absorption of the ultra-violet is very strong. The shortest 

 wave-length recorded on the negative for the least depth of liquid is 3250.5 

 A.U., and that for the greatest depth is about 0.43S. Plate 7 (a) shows the 

 boundary of the ultra-violet band sufficiently well to make further comment 

 on this region superfluous. The band in the green has its middle roughly at 

 0.518/<. The fact that the ends of the photographic strips resulting from the 

 three successive exposures, which ends are in the vicinity of 0.597/i, suggest 

 a straight line that slants with respect to the length of the spectrogram, 

 calls attention to the general absorption of the least refrangible portions of 

 the spectrum. 



The following facts were obtained by eye observations with the spectro- 

 scope, the cell having the same depth as above: The numbers recorded for 

 the limits of transmission in the red for the first, third, fifth, seventh, ninth, 

 eleventh, thirteenth, and fifteenth solutions named in the order of increas- 

 ing concentration were 0.750;*, 0.730/e, 0.725/*, 0.720/u, 0.712/<, 0.707;<, 0.690//, 

 and 0.680/(, respectively. Since the band in the red has a diffuse end in the 

 visible spectrum, the data just given are useful only in so far as they indicate 

 roughly the progressive increase of absorption with the like variation in 

 concentration, but they are not to be considered as very accurate. The 

 wave-lengths of the limits of absorption of the band which extends from the 

 ultra-violet into the visible spectrum, as obtained for the solutions mentioned 

 'in the above list, agree qualitatively with those derived from the spectro- 

 grams, and since the former are less reliable than the latter they will not be 

 given here. Special attention, however, was given to the solutions of concen- 

 tration 1.224 and 1.574, in order to find out whether there were any abrupt 

 changes in the absorption of the more concentrated solutions of the series, 



