SALTS OF NEODYMIUM. PRASEODYMIUM, AND ERBIUM. 97 



ERBIUM CHLORIDE IN WATER BEER'S LAW. (See Plate 80.) 



The concentrations of the solutions used in making the negative for A, 

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

 were 1.4, 1.18, 0.98, 0.80, 0.66, 0.56, and 0.47. The concentrations for B 

 were 0.80, 0.67, 0.56, 0.46, 0.38, 0.32, and 0.27, the corresponding depths 

 of absorbing layer being 8, 9.5, 11.5, 14, 17, and 24 mm. 



The concentrations here given were obtained by assuming the atomic 

 weight of the metallic atom as 166, that is, assuming that the solution was 

 one of pure erbium chloride. As the salt contained very large quantities 

 of yttrium and other related elements, the figures given for the concentra- 

 tion can have no meaning in the absolute sense. They merely indicate the 

 relative amounts of erbium chloride in the different solutions employed. 



For these solutions of the chloride Beer's law holds pretty accurately, 

 excepting for the absorption in the extreme ultra-violet, where the limits 

 of transmission for the most concentrated and most dilute solutions of A 

 are A 2870 and A 2760. For B the corresponding figures are A 2760 and 

 A 2650. 



The positions of the chief bands are as follows: A 3240, A 3500, A 3635, 

 and A 3785 in the region covered by the spark spectrum; A 4150, A 4210, 

 A 4415, A 4495 moderately strong, A 4515 fairly intense, A 4670 very faint, 

 A 4845, A 4865 intense, A 4905, A 5185 faint, A 5205 fairly intense, A 5230 

 intense, A 5365, A 5415, A 5435, A 5490 faint, A 6410 faint, A 6490 faint, A 6535 

 fairly intense, and A 6680 rather faint. 



ERBIUM NITRATE IN WATER BEER'S LAW. (See Plate 81.) 



The concentrations of the solutions used in making the negative for A, 

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

 were 1.4, 1.05, 0.88, 0.70, 0.56, 0.44, and 0.35. For B the concentrations 

 were 0.70, 0.52, 0.44, 0.35, 0.28, 0.22, and 0.17, the depths of absorbing 

 layer being in both cases 6, 7.5, 9.5, 12, 15, 19, and 24 mm. 



What was said about the significance of the figures given for the con- 

 centrations under erbium chloride, applies equally well in this case, since 

 the same material was used. Here the ultra-violet is limited by the N0 3 

 band at about A 3300 as usual. 



The more concentrated solutions give a spectrum which is somewhat 

 different from that produced by the chloride solutions. The bands are as 

 a rule wider and hazier, and their intensity maxima sometimes fall in slightly 

 different positions. With dilution the character of the bands changes con- 

 siderably, becoming more and more like the bands given by the chloride 

 solution. Here, again, then, we find a state of affairs very like the one we 

 discussed at some length under neodymium nitrate Beer's law. 



Judging from the negatives made with the solutions of erbium salts, 

 it appears that the absorption spectrum of erbium would make fully as 

 interesting a study as that of neodymium, and it is to be hoped that in 

 the continuation of this work some preparation richer in erbium than the 

 one we employed will be available. 



