74 ABSORPTION SPECTRA OF SOLUTIONS. 



The limits of transmission for the yellow band, as shown by the spec- 

 trum of the most concentrated solution, are A 5660 and A 5950; hence the 

 narrowing of its red side amounts to 20 A.U. 



B, Plate 59, starts at the same concentration as A, but the effective 

 depth of absorbing layer is only one-fourth of that used in A. Hence this 

 spectrogram represents the spectrum of a solution of neodymium chloride 

 24 mm. deep and having a concentration of 0.43 normal. The absorption 

 bands are all much narrower, and several of them are shown in the process 

 of breaking up into simpler bands. The bands in the ultra-violet have dis- 

 appeared, excepting the one at A 3435 and A 3595, which is still intense, and 

 a trace of the one at A 3220 to A 3330. Transmission in this region now ex- 

 tends faintly to A 2460. No new absorption bands beyond A 2800 can be seen. 



The A 3435 to A 3595 band now has the limits A 3450 to A 3580, and shows a 

 weak transmission at A 3485, which increases somewhat with dilution, thus 

 dividing the band into two. In A, Plate 60, this has broken up further into 

 bands having their centers at A 3465, A 3500, A 3540, and A 3560, the bands at 

 A 3465 and A 3540 being the narrowest and most intense. In B, Plate 60, 

 A 3465 and A 3540 are both narrow, intense bands, while A 3500 is faint and 

 wide; A 3560 disappeared entirely as a band. In B, Plate 72, the only things 

 that remain of the group are the two narrow lines at A 3465 and A 3540. 



The band at A 4180 is weak throughout B, Plate 59, and may be said 

 to have disappeared in A, Plate 60. The narrow band at A 4275 is very 

 persistent, showing as a fine black line even in B, Plate 72. Its width 

 remains about the same as that shown by the negative for B, Plate 59, 

 throughout the range of concentrations studied. The band at A 4330 be- 

 haves exactly like the one at A 4180, practically disappearing in A, Plate 60. 



The band having its middle at A 4445, which is perhaps entirely due to 

 the praseodymium present as an impurity, may be seen even in B, Plate 

 72, although it is weak and very diffuse there. In A, Plate 59, it has about 

 the same intensity as it shows in a solution of praseodymium chloride 

 having a concentration of 0.85 and a depth of absorbing layer of 3 mm. 

 This indicates that the percentage of praseodymium in the neodymium 

 salts used was about 6 per cent. The band at A 4825, partly due to prase- 

 odymium, may also be seen throughout the entire series under considera- 

 tion, the wave-length of the praseodymium band being A 4815, while that 

 of the band showing in all the neodymium spectra has the position A 4825, 

 showing that neodymium had a band nearly coincident with that given by 

 praseodymium, but lying a little closer to the red end of the spectrum. 



The remaining praseodymium band has the position A 4685, thus 

 nearly coinciding with the rather narrow, strong neodymium band whose 

 position is A 4695. This neodymium band shows with considerable inten- 

 sity even in Plate 72 B, while the praseodymium band at A 4685 is so much 

 fainter than the A 4445 band due to the same substance that we should 

 hardly expect it to show here. 



The band which under A, Plate 59, was recorded as having the limits 

 A 4580 to A 4650 shows in B as a hazy band with its center at A 4615, to- 

 gether with a narrow, faint line at A 4645. The band is visible in A, Plate 

 60, but has practically disappeared from view in B, of the same plate. 

 The narrow line at A 4645 does not show beyond B, Plate 59. 



