109' 



sulpliales, wliicli differ, like mosi other sails, in (hoii- coiilc^nt of watci- 

 of' (MTStallisalion with the successive elements of the series ; etc. 

 Thus my clioice was finall}- fixed on the ethyisulpiiates ; of' these 

 only the salts of tJinlkmi and of y/(^6'-//^/f^^/7;m;;/. were somewliat difficult 

 to obtain in a measurable form, because of their iiigh solubility and 

 their tendency to form supersaturated solutions. However dually also 

 these salts were obtained in a well developed form. 



From the b(MTOvved salts (double nitrates, oxalates, bromates, etc.) 

 first the pure oxides were prepared, then the sul|)hates, and these 

 finally decomposed \\\ aqueous solution by jneans of bariumethylsulphate 

 at a low temperature. To avoid any strong- elevation of temperature 

 as much as possible, the solution was evaporated in \acuo or at a 

 strongly diminished pressure on the waterbath, at temperatures of 

 22° till 'i^° 0; first the solution must stand for a long time to make 

 the finely divided bariumsulphate precipitate, and to separate it from 

 the mothei'-liquor by decanting and filtration. Only in this way it 

 was possible, to avoid an admixture of sulphate to the etliylsulphates, 

 formed by hydrolysis of these. 



§ 4. The specific weights of the crystallized salts were determined 

 with the utmost care ; 1 gratefully wish to remember here the xaluable 

 assistance of Mr. M. J. Smit, cand. chem., in this tedious work. As well 

 by the pycnometrical method, with orthochlorotoluene as an immersion- 

 liquid, as also by means of heavy liquids (floating-method), we obtained 

 data, which were in full accordance with each other ; it need hardly 

 be said, that this was no easy task, regarding the very small quan- 

 tities of the salts at our disposal. 



During this work we found, how far even the purest products 

 of the rare earths, sold in commerce (de Haën, Dr. Drossbach) for 

 scientific purposes, are still removed from the spectroscopical purity 

 of Urbain's preparations and those of the other mentioned scientists. 

 The following determinations of the specific weight may give an 

 impression of this : 



Element: Specific weight of Spec.weightof thebest 



the pure salts: products in commerce: 



1,801 

 1,839 

 1,848 

 1,866 

 1,884 

 1,905 

 1,857 



