240 THE ATOMIC WEIGHTS. 



THE YTTRIUM GROUP. 



The atomic weights of the metals in this group can only 

 be said to have been determined approximately. Not only 

 do great difficulties attend the purification of the material 

 used for study and the separation of the earths from each 

 other, but there have been and still are grave doubts as to 

 the actual nature of some of the latter. The figures for 

 scandium, yttrium, and ytterbium seem to be tolerably 

 good ; those for decipium, philippium, thulium, erbium, and 

 terbium are little more than estimates ; for samarium we 

 have no data whatever. All the atomic weights in this 

 group are based upon analyses or sjaitheses of sulphates ; 

 and from analogy to the cerium metals all of these elements 

 are regarded as forming sesquioxides. 



SCANDIUM. 



Clevc,* who was the first to make accurate experiments 

 on the atomic weight of this metal, obtained the following 

 data. 1.451 grm. of sulphate, ignited, gave .5293 grm. of 

 ScoOg. .4479 grm. of ScjOg, converted into sulphate, 

 yielded 1.2255 grm. of the latter, which, upon ignition, 

 gave .4479 grm. of SC2O3. Hence, for the percentage of 

 SC2O3 in Sc2(S04)3 we have: 



36.478 

 36.556 

 36.556 



Mean, 36.530 



Hence, if SO 3 = 80, Sc = 45.044. 



Later and better results are those of Nilson,t who con- 

 verted scandium oxide into the sulphate. I give in a third 

 column the percentage of oxide in sulphate : 



* Compt. Rend., 89, 419. 

 f Compt. Rend., 91, 118. 



