SALTS OF NEODYMIUM, PRASEODYMIUM, AND ERBIUM. 91 



thus far been observed in the study of the absorption spectra of neodym- 

 ium salts. That it also suffices for salts of the other rare earths studied 

 will appear in what follows. 



NEODYMIUM NITRATE IN WATER MOLECULES CONSTANT. (See Plate 72 A.) 



The concentrations of the solutions, beginning with the one whose 

 spectrum is adjacent to the numbered scale, were 1.34, 1.08, 0.79, 0.58, 

 0.43, 0.34, and 0.27; the corresponding depths of absorbing layer being 

 3, 4, 6, 9, 13, 18, and 24 mm. 



As a rule the bands all widen and become somewhat more intense with 

 increasing dilution, as might be expected from the spectrograms showing 

 the behavior of the spectrum when the conditions for Beer's law obtain. 

 The band at X 4275, however, shows here the same change qualitatively 

 as it did in the series for Beer's law; that is, the violet edge increases 

 markedly in intensity. The red edge, however, remains of about the same 

 intensity throughout, indicating that it owes its origin to the undissociated 

 nitrate molecules. 



The A 4330 band, though rather faint, shows a considerable increase in 

 intensity with dilution, again indicating that it is due to the same absorber 

 that gives the violet edge of the A 4275 band. 



NEODYMIUM NITRATE IN METHYL ALCOHOL BEER'S LAW. (See Plate 73.) 



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 0.80, 0.64, 0.50, 0.40, 0.32, 0.25, and 0.20; and for B they were 0.32, 

 0.25, 0.20, 0.16, 0.13, 0.10, and 0.08; the corresponding depths of absorb- 

 ing layer were 6, 7.5, 9.5, 12, 15, 19, and 24 mm. in both cases. 



On account of the NO 3 band the spectrum terminates at A 3250 in the 

 ultra-violet for A, and at about A 3200 for B. 



The absorption near A 3500 resembles that shown by aqueous solutions 

 much more nearly than was the case with the chloride. Only two bands 

 show, their positions being A 3465 and A 3545, respectively. The general 

 shading extends from about A 3450 to A 3570. 



The bands in the blue and violet are not as intense as the correspond- 

 ing bands in the alcoholic solution of the chloride. Their positions and 

 general character are much more nearly the same as those shown by con- 

 centrated solutions of the nitrate in water. There is a band at A 4280, 

 about 10 A.U. wide and not specially intense. At A 4430 is a wide, faint 

 band, and there is a similar one at A 4600. Three faint bands show at 

 A 4690, A 4735, and A 4825, resembling very much the three corresponding bands 

 in concentrated aqueous solution. The intensity here is, however, much less. 



In the aqueous solution we found bands at A 5205, A 5225, and A 5235, 

 of which the first one was evidently due to the cation, the second one due 

 partly to the cation and partly to the molecule, while the one at A 5235 

 was apparently due only to the nitrate molecule. In the methyl alcohol 

 solution, we find only a weak shade in the region A 5200, while at A 5225 

 and A 5240 there are two rather narrow, intense bands. There is consider- 

 able shading to both sides of these bands. 



