igo8.] NEODYMIUM AND PRASEODYMIUM. 287 



alcoholic solution is double and answers the following description : 

 Very faint absorption begins at A 4753 and rises to a faint maxi- 

 mum at about A 4757, becoming again zero at A 4760. It begins 

 again at A 4772, rises rapidly to a strong maximum at A 4780 and 

 falls to zero at A 4790. The component whose center is at A 4757 

 is very faint compared with the main band. 



In the first and second strips we have nothing but the band 

 corresponding to the aqueous solution. In the third strip the red 

 side of the band has increased slightly in intensity, making it appear 

 much more nearly symmetrical. This change increases in the fourth 

 and fifth strips, the band at the same time widening considerably. 

 In the sixth strip its appearance is as follows : Absorption begins at 

 A 4748 and rises to a maximum just to the violet side of A 4760, 

 then decreases slightly towards A 4770, after which it increases 

 somewhat to A 4778, then falls off to zero at A 4787. 



It is very evident from a study of the change in this band that 

 the two bands characteristic of the aqueous and alcoholic solutions 

 coexist, and that the band appearing in our photographic strips is the 

 sum of the two taken in different proportions. The proportion of 

 the alcohol band being, however, very much smaller than the pro- 

 portion of alcohol in the corresponding solution. A similar de- 

 scription might be given for any one of the other bands, but this is 

 not necessary as the changes are of exactly the same nature as those 

 we have already indicated. In every case where the alcoholic solu- 

 tion has a strong band, which differs somewhat in position from 

 any band in the aqueous solution, we begin to see traces of this 

 band when the proportion of alcohol in the mixture reaches 50 per 

 cent., but the band remains comparatively faint even when the pro- 

 portion is as high as 83y per cent. 



In order to study the change which takes place between the sixth 

 and seventh strips of the spectrograms of plate 3, more carefully, a 

 series of alcohol solutions were prepared containing the following 

 percentages of water, o, 2|, 5*, 8, io|, 13^ and 16. The concen- 

 tration of the neodymium chloride was constant and equal to 0.5 

 normal. Two spectrograms were made, one with a depth of absorb- 

 ing layer of 1.5 cm., in order to show the fainter bands, and the 

 other with the depth of the cell only 5 mm. in order to show as 



