SALTS OF NICKEL. 41 



were 1 and 3 minutes for the Nernst lamp and spark, respectively, the 

 width of the slit being 0.01 cm. 



The spectrogram shows exactly what might be expected from a study 

 of Plate 25. The extreme ultra-violet absorption disappears rapidly, as 

 does the absorption in the red. The band at A 3960, very wide at first, 

 narrows rapidly, becoming very faint in the most dilute solution. 



This plate, together with the similar one for cobalt chloride (Plate 

 39 B), shows at a glance what an insignificant role ions play in producing 

 the absorption of solutions of cobalt and nickel salts. 



NICKEL CHLORIDE IN WATER MOLECULES CONSTANT. (See Plate 26.) 



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, 2.18, 1.63, 1.22, 0.935, 0.750, and 0.610; the correspond- 

 ing depths of absorbing layer were 3, 4, 6, 9, 13, 18, and 24 mm. For set 

 B the concentrations were 0.800, 0.660, 0.493, 0.365, 0.280, 0.220, and 

 0.160; the depths of the cell were the same as for set A. The exposures 

 were 1 and 3 minutes, respectively, for the Nernst lamp and spark, the 

 slit having a width of 0.01 cm. 



The general ultra-violet absorption beyond the A 3960 band seems to 

 remain nearly constant in the five most concentrated solutions of set A, 

 then increases markedly in the sixth and seventh. The A 3960 band nar- 

 rows slightly from the first to the second strip (counting from the scale), 

 then begins to widen, slowly at first, but more rapidly from the fifth to 

 the seventh solutions. 



In B the general ultra-violet absorption may still be seen, and it in- 

 creases with dilution. The A 3960 band also widens regularly with dilution. 

 In the red the absorption increases regularly with dilution in both A and B. 



NICKEL CHLORIDE IN WATER WITH CALCIUM AND ALUMINIUM CHLORIDES. 



(See Plate 27.) 



The concentration of nickel chloride throughout was constant and 

 equal to 0.372. The concentrations of calcium chloride, beginning with 

 the solution whose spectrum is adjacent to the numbered scale, were 3.97, 

 3.40, 2.85, 2.30, 1.75, 1.20, 0.64, and 0.00. The corresponding concentra- 

 tions of aluminium chloride were 2.61, 2.25, 1.88, 1.52, 1.16, 0.79, 0.43, 

 and 0.00. 



A is the spectrogram made with the solutions containing calcium 

 chloride, while B was made with those containing the aluminium chloride. 

 The two spectrograms may conveniently be described together, as this will 

 facilitate comparisons. The strips will be referred to as first, second, 

 third, etc., the number giving the position of the strip with reference to 

 the numbered scale. 



In general it may be stated that the absorption in the violet and 

 ultra-violet is somewhat greater for the solutions containing aluminium 

 chloride than for the corresponding ones containing calcium chloride. 

 This is partly due to the greater absorption of the aluminium salt per 

 se for ultra-violet light. (See "Hydrates in Aqueous Solution," Plate 

 11 A.) The first strip of A shows that transmission in the violet ceases 



