SALTS OF CHROMIUM. 67 



The limits for the yellow band in the most concentrated solution are 

 A 5170 and A 6220, while for the most dilute they are ^ 5250 and X 6150, 

 showing considerable narrowing with decrease in concentration. 



It will be noticed that both the bands are somewhat nearer the region 

 of shorter wave-lengths in the nitrate than in the chloride, the centers of 

 the two bands for the latter being A 4175 and A 5925, while for the former 

 the corresponding figures are A 4065 and A 5700. The yellow band in the 

 nitrate is also much hazier on its violet side than was the case with the 

 chloride. This is not brought out by the reproduction, or even by the 

 negative made with the Seed film, on account of the fact that the edge of 

 the band falls so near the middle of the minimum in the sensibility curve 

 of the Seed emulsion. A negative made on a Wratten panchromatic plate, 

 giving both edges of the band, however, shows very clearly the difference 

 in the shading, this being nearly twice as great on the violet side as on 

 the red. 



The negative shows the band at X 6690 rather better than did those 

 made with the chloride solutions. The band is rather faint, but may be 

 seen well enough to enable one to determine its position and general char- 

 acter. It remains of constant width and intensity throughout. Its maxi- 

 mum of intensity falls very close to A 6690, from which position a gradual 

 shading extends to a distance of about 20 A.U. on both sides. Except for 

 this band, the solutions are almost perfectly transparent from A 6400 to 

 the end of the visible red. 



CHROMIUM NITRATE IN WATER MOLECULES CONSTANT. (See Plate 58 B.) 



The concentrations of the solutions, beginning with the one whose 

 spectrum is adjacent to the numbered scale, were 0.70, 0.55, 0.39, 0.28, 0.20, 

 0.15, and 0.12; the corresponding depths of cell were 3, 4, 6, 9, 13, 18, and 24 

 mm. The exposures and slit width were the same as used with Plate 58 A. 



The spectrogram shows the same bands as Plate 58 A, only here they 

 all widen somewhat with dilution, as was to be expected from their be- 

 havior when the conditions for Beer's law were fulfilled. 



