SALTS OF NEODYMIUM, PRASEODYMIUM, AND ERBIUM. 95 



The limits of transmission in the ultra-violet, for the most concentrated 

 and most dilute solutions of A, are, respectively, X 2720 and X 2650. The 

 edge is fairly sharp, indicating the presence of a rather intense band. 

 This is also indicated by B, where the spectrum ends abruptly at X 2630, 

 the limit being the same for all of the solutions. 



The absorption bands shown in A are as follows: X 4380 to X 4480, 

 strong band with red edge somewhat shaded; X 4640 to X 4710, sharp on 

 red side, quite diffuse towards the violet; X 4800 to X 4830, sharply defined 

 on both sides; A 5860 to X 5950, both edges diffuse; X 5985, fairly narrow 

 band with diffuse edges. The region between this band and the principal 

 yellow one shows very strong absorption. 



B shows the following: X 4410 to X 4465, both edges a little diffuse; 

 X 4685, fairly narrow band, still more diffuse towards the violet, although 

 somewhat shaded also towards the red; X 4815, narrow band, with edges 

 slightly shaded; X 5900, wide hazy band; absorption not complete, even 

 at its middle; X 5985, rather faint, hazy band. 



The greenish tinge of the solutions would suggest that there is con- 

 siderable general absorption in the red, because the absorption in the 

 yellow is not sufficient to impart any marked color to the solution, and 

 the bands in the violet and blue could only give it a yellow tint. The nega- 

 tive for A does, in fact, show pretty strong general absorption from X 7100 

 to the end of the red, but no doubt a spectrophotometric study of the 

 solutions would show general absorption much farther down into the red. 

 The negative for B shows no sign of this absorption, for very obvious reasons. 



PRASEODYMIUM CHLORIDE IN MIXTURES OF THE ALCOHOLS AND WATER. 



(See Plate 78.) 



The concentration of the praseodymium chloride was constant through- 

 out and equal to 0.5 normal. The percentages of water in the solutions, 

 beginning with the one whose spectrum is adjacent to the numbered scale, 

 were 0, 2.3, 5.6, 8, 10.6, 13.3, and 16. The depth of absorbing layer was 

 1.0 cm. Methyl alcohol was the chief solvent in the solutions pertaining 

 to A, while ethyl alcohol was employed in the solutions used in making 

 the negative for B. The two spectrograms are identical, except for a little 

 greater general absorption in the ultra-violet with the ethyl alcohol. The 

 most striking feature of the spectrograms is the appearance of the intense 

 absorption band near X 3000 as the percentage of water is gradually 

 decreased. Only a faint trace of this band is visible with 16 per cent of 

 water in the solution, and the band is comparatively weak even with only 

 8 per cent of water. From this point it increases very rapidly in width 

 and intensity with decrease in the amount of water, until in the pure 

 alcohol solutions its limits (transmission) are X 2970 and X 3230, being by 

 far the most intense band in the whole spectrum. 



The bands in the violet and blue apparently shift somewhat towards 

 the red, this being, however, due to the fact that the alcohol bands are a 

 little nearer the red end of the spectrum, and that when the percentage 

 of water changes from 16 to 0, the two sets of bands coexist, but are far 

 from being separated. The change is exactly the same in character as the 



