1103 



thulium, neoytterbium and lutetium. On the otlier side however, 

 lanthanium is diamagnetie, while praseodymium possesses a greater 

 valne for ft than neodymium. Tluis the curve, showing (he dependence 

 of fi upon the atomic weight, must possess two maxima -. one in 

 the Genitm-^vou\), and the second, much steeper maximum, in the 

 yttrium-^voyx^. 



There also exists such a periodicity in the basic properties of these 

 oxides; these seem to decrease from laiitkanium to terhium, then to increase 

 with Jwlmium {yttrium) and erbium, and again to decrease to the side 

 of neoytterbium; the elements are arranged in order of increasing 

 solubility of their ethjlsulphates : 



— La p^ Nd Sm {Cerium-gronp), 



and: Eu Gd 21) Dys Ho Yt Er Tim N-Yb {Yttrium-gvon\)) 



An analagous periodicity seems to exist also for the solubility of 

 other salts of these metals, e.g. for the oxalates, etc. 



Finally all these facts may persuade us to some extent, that it 

 is really not at all justitiable, to deny the possibility of such a 

 periodicity a priori, even with respect to the relation between atomic 

 weight and volume, without accurate and extended investigations 

 with absolutely ])ure material ; on the contrary : the facts here published 

 can be used as strong arguments in favour of the view of the 

 existence of such a periodical relationship. ^) 



§ 7. Now some more data about analogous investigations with 

 scandium-, beryllium- and iiidium-ssdts may find a place here. Originally 

 tentatives were made, to reach our scope also by means of the stud}- 

 of the ethylsulphates. We succeeded in obtaining from scandium-, 

 and i?idium-oxide, the corresponding ethylsulphates in the form of 



1) In connection with this I may remark once more, that an aaalogous abnor- 

 mality in the molecular volumes of the double nitrates of these same oxides of 

 Urbain, was found a short time ago by Jantsgh : Zeits. f- anorg. Chemie 76, 303, 

 (1914)), with the salts oï praseodymium and neodymium: the last compounds 

 always possess the greater molecular volume. 



Moreover another argumentation for such a periodicity of properties within this 

 group of elements, can be derived from the available data of me/^ingrpomfe of these 

 metals or of their analogous compounds. For Muthmann and Weiss (Lieb. Ann. 

 331. 1. (1904)) stated, that the mcltingpoint of La is: 810° C; of Ge: 623° G. ; 

 of Pr: 940^ C. ; of Nd: 840^ C. In the same way Boukion (Ann. de Chim. et 

 Phys. (8) 20. 547, ("1910), showed, that the meltingpoints of the chlorides are: 

 of LaClr^: 890° G. ; of CeCk: 848° G ; of PrCl.,: 810° G. ; of NdCl.: 784° C. ; 

 of SmCl;^: 68G° G.; of GdC^: Ü28° G.; of TljCl-i: 588° G., but on the contiary, 

 for DysCl^: 68u° C., — being thus about 100^ higher. 



72 

 Proceedings Royal Acad. Amsterdam. Vol X\'I. 



