CHAPTER VIII. 



ERBIUM SALTS. 



Introduction. Erbium chloride in glycerol. Erbium chloride in water as affected by rise 

 in temperature. Erbium nitrate and other salts. 



Of all compounds known those of erbium probably show the most 

 characteristic absorption spectra in the solid state and in solution. The 

 first to make a detailed study of the erbium spectrum was H. Becquerel. 1 

 One of the minerals that he studied was xenotine or hussakite, a uniaxial 

 crystalline compound consisting mainly of the phosphates of yttrium and 

 erbium. The wave-lengths of the ordinary and extraordinary spectrum 

 bands are given. The absorption spectrum observed in any direction 

 through the crystal Becquerel found to be made up by the superposition of 

 two series of bands, one corresponding to vibrations normal to the axis 

 of the crystal and the other to vibrations parallel to this axis. 



Schulz 2 has worked on the effect of a magnetic field on the absorption 

 spectrum (obtained by reflection) of erbium oxide. He finds that the bands 

 vU 4482.2, 4491.3, 4510.5, 4541.9, 4554.1, 4562.6, 4571.8, 4579.1, 4606.5, 

 4625.9, 5197.0, 5205.5, 5242.2, 5261.0, 5387.7, 6430.0, 6476, 6496, 6524, 

 6538, 6546, 6562, 6581, 6598, 6617, and 6652 broaden when the magnetic 

 field is turned on; A 4482.2 is shifted to the red, while A 4510.5 and X 4562.6 

 are shifted towards the violet. 



Bois and Elias 3 have made a very thorough study of the absorption 

 of hussakite, erbium yttrium sulphate, erbium nitrate and erbium mag- 

 nesium nitrate at 18 and at 190 and also found the Zeeman effect at 

 these temperatures. As the results are all collected in the above reference 

 no detailed account will here be given. In general, the bands show a Zee- 

 man effect. Doublets and triplets are quite common. 



A very extended investigation on the effect of low temperatures and 

 magnetic fields on the absorption spectra of erbium has been made by 

 J. Becquerel. As the papers of Becquerel are somewhat scattered, a rather 

 full account of them will be given here. The first work * of Becquerel was 

 upon the effect of a magnetic field on the absorption spectra of xenotine 

 and tysonite at ordinary temperatures. In the following table + will 

 signify a strong band and + + a very strong band. Field will always refer 

 to the magnetic field which in this work is usually 14,100 c.g.s. units. Units 

 of wave-length are stated in Angstrom units. 



When the optic axis is parallel to the beam of light a crystal behaves 

 like an isotropic body. When placed in a magnetic field, however, a recti- 

 linear vibration is transformed into an elliptical one. This is Becquerel's 

 magnetic double-refraction. The effect of the magnetic field on vibrations 

 normal to the field is different from the effect on vibrations parallel to 



1 Ann. Chim. Phys. (6), 14, 194 (1888). 



2 Astrophys. Journ., 30, 383 (1909). 



3 Ann. Phys., 27, 279 (1908). 



*Compt. rend., Mar. 26, Apr. 21, May 21, Nov. 19, Dec. 3, Dec. 10, Dec. 24 (1906); 

 Jan. 21 (1907). Le Radium, Feb. (1907). 



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