SALTS OF NEODYMIUM, PRASEODYMIUM, AND ERBIUM. 87 



It will be remembered that the very concentrated solutions of the 

 chloride showed some slight deviations from Beer's law, the absorption 

 to the red side of the narrow band at A 4275 being described in some detail. 

 The deviations from Beer's law are smaller in the bromide solutions, per- 

 haps on account of the concentrations being less. No shading or fine ab- 

 sorption line between A 4275 and A 4290 is to be seen in the spectra of even 

 the most concentrated solutions used in making the negative for A of 

 Plate 69. The shading on the red side of the yellow band narrows some- 

 what with increasing dilution, but not quite as rapidly as was the case 

 with the chloride. 



Some neodymium bromide was dehydrated in a current of hydrobromic 

 acid and dissolved in methyl alcohol, and also in mixtures of methyl alcohol 

 and water. The solution in methyl alcohol was stable, and showed the 

 same spectrum as a solution of the chloride in the same solvent. On add- 

 ing water, precipitates were formed, indicating some chemical change. 

 These were filtered out, and a spectrogram made to see whether the same 

 changes take place in this case that we observed with the chloride. This 

 spectrogram is not reproduced, but it indicated that the changes which 

 took place were quantitatively as well as qualitatively the same as those 

 which we discussed under Plates 65 and 66. 



NEODYMIUM NITRATE IN WATER BEER'S LAW. (See Plates 70 and 71.) 



The concentrations of the solutions used in making the negative for 



A, Plate 70, beginning with the one whose spectrum is adjacent to the 

 numbered scale, were 2.96, 2.22, 1.48, 0.99, 0.69, 0.50, and 0.38. For B 

 the concentrations were 1.48, 1.11, 0.74, 0.50, 0.35, 0.25, and 0.19. For A, 

 Plate 71, they were 0.74, 0.55, 0.37, 0.25, 0.175, 0.125, and 0.095; and for 



B, 0.37, 0.275, 0.185, 0.125, 0.092, 0.062, and 0.048. The depths of absorb- 

 ing layer were in each case 3, 4, 6, 9, 13, 18, and 24 mm. 



The nitrate solutions are much less yellow than the chloride solutions, 

 having when concentrated a decided pinkish tint, indicating greater trans- 

 parency in the violet region of the spectrum. 



The spectrum of the nitrate solutions, especially when the concentra- 

 tion is considerable, differs quite a little from that of the chloride. It is 

 true that at first glance they seem identical, for wherever there is a band 

 in the spectrum of the chloride solution a band is found when the nitrate 

 solution is examined; but, at least in concentrated solutions, the bands 

 have a very different appearance. The general difference is that the nitrate 

 bands are much broader and hazier than those observed with the chloride. 

 With dilution the spectrum of the nitrate changes very much more than 

 that of the chloride, which we found practically unaltered when the concen- 

 trations were changed from about 1.5 normal nearly to zero. The spectrum 

 of the nitrate solutions changes somewhat, even in B, Plate 71, where the 

 concentration ranges from 0.37 to 0.048 normal. 



Instead of giving a detailed description of the spectrum of the nitrate, 

 we will limit ourselves to a description of the changes that take place in 

 a few of the bands, which differ most from the corresponding bands in the 

 spectrum of the chloride solution. 



