48 THE ABSORPTION SPECTRA OF SOLUTIONS. 



The fact that this one band should appear of a different wave-length in 

 ethyl alcohol, as compared with water, while the other dysprosium bands appear 

 to be the same for both solvents, might be taken to indicate that this band 

 was not due to dj'sprosium. A difference of this kind might lead to a possible 

 method of ascertaining the presence of the salts of two different elements in 

 solution. In the case of neodymium salts it was found, in general, that if one 

 solvent had one characteristic band, all the solvent bands were more or less 

 characteristic. On the other hand, it must be remembered that in the case 

 of the uranyl bands the differences for different solvents were usually much 

 greater for the longer wave-length bands. So, in the above case of dysprosium 

 chloride in ethyl alcohol, we may assume that the band X 5380 may not be 

 due to dysprosium. It may be possible that the difference in the action of 

 acids on the bands of the spectra of a given salt, or the difference of the spectra 

 as obtained with the same salt in different solvents, may be useful in separating 

 the different elements. 



Dysprosium Acetate in Water. 



The absorption spectrum of dysprosium acetate (0.4 normal) in water is 

 given in A, plate 31. The depths of cell were 4, 16, 25 and 34 mm. The spec- 

 trum is very similar to that of the aqueous solution of the chloride. The bands 

 are, however, somewhat more diffuse. The wave-lengths of the bands, while 

 comparatively weak, appear to be the same for the chloride and the acetate. 

 The acetate bands widen more to the red, so that when the bands are 

 quite wide, the acetate bands appear to be relatively shifted towards the 

 red. The addition of- concentrated nitric acid produces little effect on the 

 wave-length, or the appearance of the dysprosium acetate bands in water. 



THE ABSORPTION SPECTRUM OF SAMARIUM. 



The absorption spectrum of samarium has been studied much more exten- 

 sively than that of gadolinium and dysprosium. On the following page is a 

 table giving the wave-lengths of some of the bands as determined by various 

 observers. 



In general appearance the absorption spectra of samarium salts are very 

 similar to those of the dysprosium salts, the strong bands of the spectrum 

 being located in approximately the same violet and ultra-violet part of the 

 spectrum. The general appearance of the individual bands is very similar 

 to that of the dysprosium bands, the samarium bands being, however, some- 

 what narrower and having sharper edges. 



Samarium Chloride in Water. 



The absorption spectrum of samarium chloride in water is shown in A, 

 plate 32. The concentration is 1.31 normal and the depths of cell, starting 

 from the lowest strip, are 2, 6, 12, 16, 20, and 100 mm. 



From the spectrogram it is seen that for the aqueous solution the ultra- 

 violet absorption is very small indeed. A weak and apparently quite wide 

 band appears at about X 3050. For the 6 mm. depth of cell, second strip, bands 

 appear at XX 3200, 3320, 3510, 3630, 3910, etc. The other bands are quite 

 weak and will be given for the 20 mm. layer. Of the above bands, the X 3910 

 is by far the strongest of all the samarium bands^ For the 20 mm. layer the 

 following bands appear : X 3420 (diffuse, about 20 Angstrom units wide), X 3470 



