Ytterbium occurrence

The atomic volumes of the lanthanides, as calculated from their room-temperature lattice parameters, are shown in fig. 3. Basically this is the same plot as given by Klemm and Bommer where the lanthanide contraction is evident, and also the anomalous valence states for cerium (slightly greater than three) and europium and ytterbium (both divalent). Anomalies due to divalency are also evident in many of the physical properties and these will be duly noted throughout the chapter. The occurrence of divalency in europium and ytterbium is a striking confirmation of Hund s rule that half-filled (in the case of divalent europium with a 4f con-... 

Since the printing of these Essays I became acquainted with an investigation by Dauvillier concerning the X-ray spectra of some rare earths. From this it appears that the element with atomic number 72 is to be identified with the material Celtium whose existence had already been conjectured earlier by Urbain. The occurrence of this element in a fraction which contains the materials Ytterbium and Lutetium, would demand that the classification given in Fig. 5 is to be changed... 

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