( 840 ) 



ZEEMAN-effect, the absorption spectra of which were fully described 

 at ordinary temperature by Lapraik ^). The so-called "blue" (dicliro- 

 itic red-blue) chromium-potassium oxalate \_Ci\Kf^ {C\0^)s -j- 6 //3OJ 

 mentioned in our first paper exhibited in liquid air a strong band 

 696,4—701,4 (cf. § 5), evidently still too broad to be taken into 

 account. This oxalate may Jiot be mistaken for the so-called *'red" 

 compound : 



Chromium- potassium oxahite [Ci\ K^ {C^O^)^ -{- x H^O ; different 

 authors consider .2? = 8, 10, 12]; this was obtained by Croft in 1842, 

 and its absorption-spectrum was investigated by Brewster '). Strongly 

 dichroïtic (claret liue bluish grey) probably monoclinic crystals. At 

 — 190° a number of fine bands and lines in the red are seen with 

 the spectrometer, the most striking of which are a rather strong 

 band 680,0, and a strong band 692,5 between the red ruby bands 

 7?, 1=691,8 and i^, = 693,2 (comp. §^ 7, 17). 



A plate, 1.5 ni.m. thick had to he examined with sunlight on 

 account of its strong absorption; for the same reason the crystallo- 

 graphic orientation could not be determined. At — 193^ line 692,5 

 had a width with field off of 0,14 mi with non-polarized light ; in a 

 field of 36,5 kgs. the widening amounted to about 0,05 f,j,u. 



Chromium-potassium malonate iCrJ{^{C^H^0^)^-\-QH^O], is evi- 

 dently homologous with the "blue" oxalate. This could only be 

 obtained as an interlaced dark crystal magma with irregular orien- 

 tation; dichroïtic (grass green-sky blue). In the red at — 193^ we 

 find a strong band, the middle of which 693,3 coincides pretty nearly 

 with the red ruby band A'i=693,2; and a broader rather faint band 

 698,3. A sample of a thickness of only 0,15 mm. exhibited band 

 693,3 with a width with field off of 0,8 ;<f* with unpolarized light; 

 moreover it appears to have shifted 0,8 n^i towards the red with 

 respect to the corresponding band of the oxalate above mentioned. 

 In a field of more than 40 kgs. the band became distinctly vaguer 

 and almost disappeared. We had no opportunity as yet to examine 

 a malonate homologous with the "red" oxalate; perhaps the phe- 

 nomenon would appear more clearly still in this case. 



§ 22. Fifth series. We have now made a closer examination 

 of some salts of the four metals Pr, Nd, Sm and Er, such as had 

 been used in 1899. 



Praseodymium sulphate [Pr^SOX- ^H,0]. Light green plate, 

 containing both optical axes, 0,6 mm. thick. Exhibits several not 



1) W. Lapraik, Journ. f. prakt. Chemie (2) 47 p. 307, 1893. 



2) A. Rosenheim, Zeitschr. f. anorg. Chemie 11 p. 196, 1896 ; and 28 p.337, 19Ü1. 



