igoS.] NEODYMIUM AND PRASEODYMIUM. 291 



Praseodymium Chloride in Water — Beer's Law. 

 (See plate 5.) 



The concentrations of the solutions used in making the nega- 

 tive for a, beginning with the one whose spectrum is adjacent to 

 the numbered scale were 2.56, 1.92, 1.25, 0.85, 0.60, 0.42 and 0.32. 

 For b the concentrations were 0.85, 0.63, 0.42, 0.28, 0.20, 0.14 and 

 o.ii ; the depths of absorbing layer being, respectively, 3, 4, 6, 9, 13, 

 18 and 24 mm. 



The solutions of praseodymium chloride are all green or yellow- 

 ish green, only the intensity of the color changing with change in 

 the concentration. 



For these solutions Beer's Law holds very exactly, excepting 

 for the extreme ultra-violet absorption in a, and the yellow bands in 

 the two or three most concentrated solutions of a. 



The limits of transmission in the ultra-violet for the most con- 

 centrated and most dilute solutions of a are, respectively, A. 2720 

 and A 2650. The edge is fairly sharp, indicating the presence of 

 a rather intense band. This is also indicated by b, where the spec- 

 trum ends abruptly at A 2630, the limit being the same for all the 

 solutions. 



The absorption bands shown in a are as follows : A 4380 to 

 A 4480, strong band with red edge somewhat shaded ; A 4640 to 

 A 4710, sharp on red side, quite diffuse towards the violet; A 4800 

 to A 4830, sharply defined on both sides ; A 5860 to A 5950, both 

 edges diffuse; A 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 : A 4410 to A 4465, both edges a little dif- 

 fuse ; A 4685, fairly narrow band, still more diffuse towards the vio- 

 let, although somewhat shaded also towards the red; A 4815, narrow 

 band with edges slightly shaded ; A 5900, wide hazy band ; absorp- 

 tion not complete even at its middle ; A 5985, rather faint, hazy band. 



The greenish tinge of the solutions would suggest that there is 

 considerable general absorption in the red, because the absorption 

 in the yellow is not sufficient to impart any marked color to the solu- 

 tion, and the bands in the violet and blue could only give it a yellow 



