CHAPTER IV. 



SALTS OF COPPER. 



A number of investigators have included salts of copper among those 

 whose absorption spectra they have studied. The results obtained with 

 copper salts are, however, neither as interesting nor apparently as impor- 

 tant as those furnished, for example, by cobalt. 



Hartley l in his elaborate investigations on absorption spectra included 

 the chloride and bromide of copper; and Miiller, 2 in his discussion of the 

 deviations from Beer's law, dealt with the salts of both copper and nickel. 

 Hartley explained the color changes in the case of copper chloride on 

 addition of water as due to the formation of the compounds CuCl,,H 2 O 

 and CuCl 2 ,2H 2 O from the compound CuCl 2 . 



Donnan and Bassett, 3 in their interesting paper in which they develop 

 the conception of complex ions as the cause of certain color changes in 

 solution, also include cupric chloride. 



Knoblauch 4 also studied the absorption spectra of copper sulphate. 



We have included in our work certain of the salts of copper, which 

 seemed to be most promising. 



COPPER CHLORIDE IN WATER BEER'S LAW. (See Plate 30.) 



The concentrations of the solutions used in making the negative for A, 

 beginning with the one whose spectrum is adjacent to the numbered scale, 

 were 4.5, 3.37, 2.25, 1.50, 1.038, 0.750, and 0.562; the corresponding depths 

 of absorbing layer were 3, 4, 6, 9, 13, 18, and 24 mm. For B the concentra- 

 tions were 1.5, 1.12, 0.75, 0.50, 0.37, 0.25, and 0.19; the depths of cell were 

 the same as in A. The concentrated solutions as viewed in their bottles 

 were green. With dilution the color changed through greenish-blue to a 

 rather light-blue. The exposures to the Nernst lamp and spark were, 

 respectively, 1J and 3 minutes, the slit having a width of 0.01 cm. 



The spectrogram show r s two regions of absorption, one in the blue, 

 violet, and ultra-violet, and the other in the red. The two are evidently 

 of quite different character, since the former narrows very rapidly with 

 decrease in concentration, the other only slightly. 



In A the first strip shows that transmission ends at A 4750, while for 

 the seventh strip the limit is at A 3750. The change in absorption is most 

 rapid from the second to the fifth strips, giving the edge of the band the 

 form of a compound curve. In B the band narrows most rapidly from the 

 first to the fourth strips, the corresponding limits of transmission being 

 /I 3950 and A 3400. In the seventh strip transmission ceases at A 3250. 



The edge of this ultra-violet band is fairly well-defined throughout, 

 differing in this respect from that of the red band, which is somewhat 

 hazy, although much less so than was the case with the red band of nickel. 



1 Trans. Roy. Dublin Soc. (2), 7, 253 (1900). 3 Journ. Chem. Soc., 81, 955 (1902). 

 'Ann. d. Phys., 12, 767 (1903). 4 Wied. Ann., 43, 738 (1891). 



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