i9o8.] NEODYMIUM AND PRASEODYMIUM. 293 



A 4660 to A 4700, A 4800 to A 4825. In the solution in pure alcohol 

 they are A 4410 to A 4480, A 4690 to A 4715, A 4810 to A 4840. Hence 

 it appears that the .two most refragible bands have a slightly greater 

 width in the aqueous solution, while the A 4815 band is more intense 

 in the alcoholic solutions. 



The bands in the yellow show very well, indeed ; the fact that 

 here as in the spectrum of neodymium chloride we have the coex- 

 istence of two sets of bands when the water content of a one-half 

 normal solution is in the neighborhood of 8 per cent. The band 

 in the yellow has already been described under Beer's Law, but as 

 the concentration and depth of layer is different here, the following 

 will serve to indicate what the spectrum of the 16 per cent, aqueous 

 solution shows. 



Absorption begins at A 5850 and rises to a maximum at about 

 A 5900, then decreases to a minimum at A 5950, from which it again 

 rises to a' maximum at about A 5980, falling off to zero at A 6000. 

 The solution in pure alcohol shows the following : Weak absorption 

 begins at A 5800, and continues without material change up to 

 A 5880, where it falls almost to nothing. At A 5900 it begins to 

 increase and reaches a strong maximum at A 5955, falling off gradu- 

 ally to zero at A 6000. The intermediate solutions show the gradual 

 disappearance of the bands characteristic of the aqueous solution, 

 and the increase in intensity of those belonging to the alcoholic 

 solution as the percentage of water is gradually decreased. The 

 maximum change takes place from the fifth to the third strips, 

 counting from the numbered scale, indicating here as with neody- 

 mium chloride that the two sets have about half their normal in- 

 tensity when the water content of the solution is about 8 per cent., 

 or when the solution contains about ten molecules of water per 

 molecule of the dissolved substance. 



Discussion of the Results. 



The results established by these plates may be briefly summar- 

 ized as follows : 



1. The absorption spectra of a salt in dift'erent solvents are, in 

 general, different. 



2. When a salt is dissolved in mixtures of two solvents the 



