1101 



and 5, may lead to ihe suspicion, that the atomic vohüurs of the 



2,000 

 1.975 

 1,950 

 1,925 

 1,500 

 1.875 

 I,8S0 

 1.825 

 1,800 

 1,775 

 1,750 



C/2 



Yt. 



Ficj.4 



NYb 



Thu/' 



Ce 



I: Eu - ■•* 



;'; SfTL- ■ 



;i Nd ■ 



.J 

 La 



Oy^' 



Ep-? 



80 85 90 35 100 105 110 115 120 ]25 130 135 HO 145 150 155 160 165 170 175 180 



Atomic woiffhts. 



mntuallj substituting elements in these salts, can no longer be con- 

 sidered as gradually increasing with the increase of the atomic weights 

 within this series of elements, if no better proof of this view is 

 brought forward than has been done up to this date. Possibly more 

 detailed accurate research witli spectroscopically pure materials, and 

 extended over all terms of this remarkable group of elements, would 

 prove with full e\'idence, that the atomic-volume-curve of Lothar 

 Meykr and Mendelejeff possesses also a single or double periodicity 

 within the group of the rare earth-metals. 



That this fact was not shown previously in any clear way, may 

 be caused by the extreme difficulty of getting these elements in an 

 absolutely pure state. For they will form within the whole series 

 solid solutions with each other in all proportions; and as is well- 

 known from Retgeks' investigations, the specific volume of such 

 mixed crystals will be in general continuously variable with their 

 chemical composition, and will be calculable in most cases from a 

 linear function of this composition and the specific volumes of the 

 pure components. 



{Bruvais) as "unit" of the space-lattice, from the relations: 



i Z — 



2 sin 60° 



and «t = 



sin 60 



o ' 



