CHAPTER VI. 



COPPER SALTS. 



Copper bromide. Copper nitrate. 



A fairly concentrated solution of copper chloride or bromide is greenish 

 brown, while dilute solutions are blue. The addition of aluminium or cal- 

 cium chloride to a blue dilute solution of copper chloride changes the color 

 to green. Uhler has investigated the effect of " dehydrating " agents, and 

 also dissolved the copper salts in different solvents. Jones and Anderson 

 have extended the investigations of Uhler. They consider that the ultra- 

 violet band must be due to the copper molecule rather than to the ion. 

 They consider from the way this band is affected by concentration that the 

 absorbing power of the molecule is greatly affected by its immediate sur- 

 roundings. The absorption band in the red, like the green cobalt band, 

 they consider to be due to the metallic atom. 



Copper Bromide. 



Two spectrograms were made of the absorption spectra of copper 

 bromide in water as affected by change in temperature. The first spectro- 

 gram (Plate 23, A) gives the absorption of a 2.06 normal solution of copper 

 bromide 1 mm. thick and the second (Plate 23, B) a 0.25 normal solution 

 8 mm. thick. The time of exposure to the Nernst glower was 2 minutes, 

 current 0.8 ampere and slit-width 0.20 mm. The time of exposure to the 

 spark was 6 minutes. Starting with the strip nearest the comparison 

 scale, the temperatures were 6, 17, 30, and 45 for the concentrated solu- 

 tion, and 6, 17, 31, 46, 59, 71, and 85 for the dilute solution. 



The effect of change in temperature on the absorption of light by 

 this salt is very great, especially for the concentrated solutions. Above 45 

 not enough light was transmitted to affect the photographic plate in any 

 part of the spectrum. At 6 a very faint transmission region runs from 

 X 5600 to X 6600 for the 2.06 normal solution. At 45 there is a very feeble 

 transmission about 200 Angstrom units wide at X 6400. 



The dilute solution shows apparently complete transmission at 6 be- 

 tween XX 3600 to 6800. As the temperature is raised this transmission band 

 widens, and at 85 it extends from X 4100 to X 6700. 



Copper Nitrate. 



Two spectrograms were made of aqueous solutions of copper nitrate, 

 the one (Plate 24, A) being 4.04 normal and having a depth of cell of 2 mm.; 

 and the second one (Plate 24, B) being 0.505 normal and a depth of layer 

 of 16 mm.; the amount of copper nitrate being the same in both cases. 

 For the first spectrogram the time of exposure to the Nernst filament was 

 2 minutes and for the second spectrogram 3 minutes, the current being 

 0.8 ampere and the slit-width 0.20 mm. Starting with the strip adjacent 

 to the comparison spectrum, the temperatures were 5, 15, 30, 45, 60, 



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