CHAPTER III. 



SALTS OF NICKEL. 



Among the more important investigations on the absorption spectra 

 of nickel salts are the following : 



Brewster, 1 in his early work on absorption, included the nitrate of 

 nickel, and Emsmann 2 also studied the same salt. 



Vogel 3 studied not only cobalt chloride but also the chloride of nickel, 

 in connection with its power to absorb light. 



The work of Soret 4 in 1878 also had to do with the chloride of nickel. 



The splendid investigations of Hartley 5 on absorption spectra included 

 also certain salts of nickel. 



The work of Miiller 6 in connection with salts of nickel calls for special 

 comment. He tested Beer's law for certain salts of nickel and copper, 

 and found that it holds for the sulphate and nitrate of nickel. The chlo- 

 ride and bromide of nickel showed deviations from the law. The deviations 

 from Beer's law he thinks are to be explained on the basis of dissociation. 



In a subsequent paper Miiller 7 tests the above suggestion, and comes 

 to the conclusion that dissociation alone can not account for all the devia- 

 tions from Beer's law. If the law does not hold, rise in temperature would 

 produce a change in the absorption, and rise in temperature would be 

 expected to produce a result similar to increase in concentration. 



The fact is that rise in temperature produces a different effect on absorp- 

 tion from increase in concentration, which shows that more than one factor 

 must be taken into account in dealing w T ith the causes of the deviation 

 from Beer's law. 



Miiller thinks that both hydration and molecular complexes come into 

 play. 



NICKEL CHLORIDE IN WATEB BEER'S LAW. (See Plate 25.) 



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 2.66, 2.00, 1.33, 0.89, 0.61, 0.44, and 0.33, the corresponding 

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

 tions were 0.44, 0.33, 0.22, 0.15, 0.101, 0.073, and 0.055; the depths of 

 layer were the same as for A. 



The solutions were green; the more dilute ones tending towards a 

 light yellowish-green. The exposures to the Nernst lamp and spark were 

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



1 Phil. Mag. (4), 24, 441 (1862). 



2 Pogg. Ann. Erganzb., 6, 334 (1875). 



3 Ber. d. deutsch. chem. Gesell., 8, 1533 (1875). 



4 Archiv. d. Sci. Phys. et Nat., 61, 322 (1878). 



5 Trans. Roy. Dub. Soc. (2), 7, 253 (1900). Journ. Chem. Soc., 83, 221 (1903). 



6 Ann. d. Phys., 12, 767 (1903). 



7 Ibid., 21, 515 (1906). 



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