COPPER BROMIDE IN METHYL ALCOHOL. 255 



COPPER BROMIDE IN METHYL ALCOHOL. [See plates 32 and 33 (6).] 



The concentration of the mother-solution of copper bromide in methyl 

 alcohol was 0.112. The percentages of water in the solutions of the series 

 were 52, 44, 40, 36, 32, 28, 24, 20, 18, 16, 14, 12, 10, 8, 4, and 0.* There- 

 fore, the successive differences in percentage were 8, 4, 4, 4, 4, 4, 4, 2, 2, 2, 2, 

 2, 2, 4, and 4. In the cell which was at a depth of 0.76 cm., the first four 

 solutions were practically colorless, the next three were of an extremely pale 

 brownish-yellow, and the last two dull brown. For the spectrogram of plate 

 32 the strips corresponding, respectively, to the solution that contained 

 the greatest amount of water, and to the anhydrous solution, are adjacent 

 to the numbered scale and to the comparison spectrum. The negative strip 

 corresponding to the 52 per cent solution recorded faintly the zinc line at 

 3282.4, but the continuous background hardly extended as far as 0.334/. 

 The strip pertaining to the 8 per cent solution showed that weak general 

 absorption had set in beyond the limit of the intense ultra-violet region of 

 absorption. In other words, transmission began at about 0.453^, and con- 

 tinued to be relatively weak as far as 0.527/<. Of course the maxima and 

 minima of photographic sensibility exaggerated the phenomenon in question. 

 The strip corresponding to the 4 per cent solution showed very faint trans- 

 mission from 0.482/i to about 0.530/*. 



The strip pertaining to the mother-solution recorded extremely faint 

 transmission from 0.543 n towards the red. The last three strips showed the 

 existence of general absorption in the orange. Due allowance being made 

 for the values of successive differences in the amounts of water in the solu- 

 tions, as well as for variations in photographic sensibility, the complete 

 spectrogram shows that the curve for the limit of ultra-violet absorption was 

 convex towards the region of shortest waves, at least throughout the greater 

 part of its course. 



The negative for plate 33 (6) was taken with a Cramer trichromatic plate. 

 It gave the spectra of the five solutions of the set in question, which contained 

 the smallest percentages of water, including no water at all. The cell depth 

 was as above, 0.76 cm. Each exposure to the light from the glower was two 

 minutes long. The negative strip corresponding to the 8 per cent solution 

 showed that transmission began at about 0.453;*, and remained relatively 

 weak as far as 0.503,u. The strip pertaining to the solution that contained 

 4 per cent of water gave 0.498/z as the wave-length of the very beginning 

 of faint transmission. The strip belonging to the anhydrous mother-solution 

 showed an extremely faint transmission from about 0.530ju to the end of the 

 spectrogram. 



* The solutions of this set, instead of being made up in the usual way, were prepared 

 by measuring the volume of the mother-solution, and adding water to the mark on the 

 measuring flask. 



