igoS.] NEODYMIUM AND PRASEODYMIUM. 281 



several of them are shown in the process of breaking up into sim- 

 pler bands. The bands in the ultra-violet have disappeared except- 

 ing the one at A 3435-A 3595, which is still intense, and a trace of 

 the one at A 3220-A 3330. Transmission in this region now extends 

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

 seen. 



The A 3435-A 3595 band now has the limits A 3450-A 3580, and 

 shows a weak transmission at A 3485, which increases somewhat 

 with dilution, thus dividing the band into two. 



The band at A 4180 is weak throughout b, plate i. 



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

 praseodymium, in a, plate i, 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 equal to 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 praseody- 

 mium may also be seen throughout the entire series under consid- 

 eration. 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 has a band nearly coin- 

 cident 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, this nearly coinciding with the rather nar- 

 row, strong neodymium band whose position is A 4695. 



The band which under a, plate i, was recorded as having the 

 limits A 4580-A 4650, shows in & as a hazy band with its center at 

 4615, together with a narrow faint line at A 4645. 



The band which in the table is recorded as A 474C)-A 4770 has 

 in b, plate i, become a slightly hazy band having its middle at 

 A 4760. Its intensity is intermediate between that of the bands at 

 A 4695 and A 4825. 



The band which in a, plate i, has the limits A 5000-A 5330, breaks 

 up into a rather complicated series of bands on dilution, some idea 

 of which may perhaps be gained from the following: b, plate i, 

 shows some absorption throughout the region given, but with a 

 deep, narrow band at A 5090, and faint transmission at A 5100 and 

 in the region A5150-A5180. Absorption is complete from A 5105 



