( 587 ) 



on the red side, which with decrease of temperature first becomes 

 more distinct, but then vanishes at still lower temperature. Also for 

 this double nitrate the crystalline foam exhibited more sharply defined 

 bands at — Id'S"^ ■ the 5 bands in the green from 500— 525 parti- 

 cularly the first and the fourth were broadened in the field. 



Neodipniuui. honix, obtained by melting together about 5 — lO'/o 

 neodymium oxide with anhydrous borax; pink amorphous mass. 



With decrease of temperature the spectrum is also subjected to 

 important modifications, but displays in general wider bands than 

 the preceding one. Analogous in this respect are : 



Neodymium glass, prepared for us by the firm of Schott & Co. at 

 Jena (V.S. 5255 and 5256), with 15 7,, a-nd 20 7o cerite; it contains 

 so much neodymium that it has a pink colour, and exhibits strong 

 selective absorption. 



§ 10. Erhiain nitrate [Er;;N03)3. GH^O]. By evaporation of the 

 solution this, too, may be obtained as an amorphous transparent 

 mass, which has an absorption spectrum rich in narrow bands, 

 which, however, has not yet been further examined. 



Erbium nuKjnesium nitrate [2 Er(N03)3. ^Mg(N03),. 24 H,0]. 



Treated just as the neodymium salt; yellow transparent mass; 

 readily absorbs water of crystallisation and becomes crystalline and 

 opaque. 



Like the preceding salt it shows a very complex spectrum, of 

 which the following groups, measured for a sample of about 10 

 m.m. thickness, are particularly noteworthy : 



At 18": 514.5 — 527.3 group of bands, consisting of three intense 

 bands, at 516.9-517.2; 517.7—519.5; 520.5—521.7. At —193° 

 this becomes as follows: 513.7 — 521.8 grouj) of bands, consisting 

 of: 513.8—514.0 bands; 514.8-514.9 intense band; 515.1-515.7 

 band; 516.3— 517.2 intense band; 517.7—519.3 intense band ; 520.1 

 faint band; 521.0 — 521.8 intense band. 



At — - 193^ a number of double lines in the red are of impor- 

 tance, the principal of which lie at 641.4 and 642.6; 643.7 and 

 645.6; 647.7 and 649.4. At 18^ these lines have entirely vanished. 



The whole visible spectrum of this salt contams about 40 baiids 

 and lines, partly very faint, which vanish for a thinner layer. 



Erbium borax obtained by melting together 15 — 20 7o erbium 

 oxide with anhydrous borax; yellow, amorphous, transparent. 



Here decrease of temperature has not so impoi'tant an inÜtience. 



The most remarkable group of bands, extending at 18° from 



