,goS.] NEODYMIUM AND PRASEODYMIUM. 289 



towards the red from the first to the fourth strips, the wave lengths 

 of its center for the two strips being, respectively, A 4287 and A 4292. 

 Accompanying this shift is a change in its character which may be 

 gathered from the following statements: In the first strip it has 

 the appearance of an unsymmetrical band, the maximum intensity 

 being nearer the violet ; in the third strip it extends from A 4280 to 

 A 4295 and has about the same intensity throughout ; in the fourth 

 strip the intensity of its violet edge has decreased, while that of 

 the red edge has increased considerably, giving it the appearance 

 of an unsymmetrical band with the maximum intensity towards the 

 red. In the fifth strip the violet shading from A 4280 to about 

 A 4284 has disappeared, leaving a band very nearly symmetrical 

 about A 4290. It appears, therefore, that we are really dealing with 

 two unresolved bands, one having its center at about A 4285, and the 

 other at A 4292. 



The band at A 4275, due to the aqueous solution, decreases in in- 

 tensity throughout, but more rapidly from the third to the sixth 

 strips than at first. Its position remains the same throughout. As 

 near as the eye can judge, this band has had its intensity reduced 

 to about half-value when the fourth strip is reached, corresponding 

 to 8 per cent, of water in the solution. The alcohol band at 

 A 4292 also has about 50 per cent, of its final intensity in the same 

 solution. 



The band at A 4760 shows the same kind of a change that we 

 described in some detail above, only the change is much more gradual 

 and easy to follow here. It also shows about equal intensity for the 

 two sets of bands when the amount of water is 8 per cent, of the 

 whole. 



The green and yellow bands are not sufficiently resolved in a 

 to allow the change in the individual bands to be followed, and 

 hence these apparently show only a gradual shift towards the red 

 with decrease in the amount of water. In h, however, they are 

 sufficiently resolved to enable us to follow the change in each 

 individual band, which, although a little difficult, on account of 

 their large number and the incompleteness of their separation in 

 some cases, may still be done. The change is in every respect the 

 same as we have found for the other bands ; namely, those due 



