ATOMIC WEIGHTS 527 



Secondly, for the percentage of SboO. in the hydrous sulphate, giving, 

 arbitrarily, the single determinations of Marignac and Brauner the same 

 weight as in the anhydrous series : 



Marignac 47.502, ± .0199 



Brauner 47.629, ± .0199 



Urbain and Lacombe 47.590, ± .0026 



General mean 47.589, ± .0025 



The value of these combinations is perhaps questionable. The earlier 

 work on the atomic weight of samarium is affected by the discovery 

 of europium, which was made by Demargay/ According to this chemist, 

 the original samaria contained admixtures of europia, which tended to 

 raise its apparent molecular weight. For samarium itself, by the sul- 

 phate method, he found Sa = 147.2 to 148, and for europium, Eu=151. 

 The material studied by Urbain and Lacombe, how^ever, was free from 

 europium, and still gave a higher percentage of oxide in sulphate than 

 the substances examined by the earlier investigators. Their material, 

 therefore, was either free from europium, or else contained compensating 

 impurities. At all events, the general means are close to Urbain and 

 Lacombe's figures, and may be allowed to stand unchanged. 



Still another metliod for measuring the atomic weight of samarium has 

 been proposed by Matignon,'' who found that the normal sulphate, heated 

 to between 500° and 1000°, yielded a stahle basic salt, SaoSOc- In one 

 determination, 0.7325 gramme Sa„ (804)3 gave 0.5335 of SaoSOg- 

 Hence Sa = 150.67. 



There are also the determinations by Feit and Przibylla,' with their 

 special volumetric method, as follows: 



Sa.Os. 0. Atomic weight. 



.5576 .07668 150.522 



.6576 .07670 150.477 



.5583 .07684 150.378 



.5633 .07747 150.514 



Mean, 150.473, ± .0221 

 In all, there are five ratios relative to the atomic weight of samarium : 



(1). Sa,(SOj3.8H,O:Sa,(SOJ,::100:80.338, ± .0048 

 ( 2 ) . Sa, ( SO J ,.8H„0 : Sa,0, : : 100 : 47.589. ± .0025 

 (3). Sa,(S0J.,:Sa^03: : 100: 59.2074, ± .0018 

 (4). Sa,(SO,),:Sa,SOe::100:72.883 

 (5). 0:Sa: 116:150.473, ± .0221 



' (ompt. l?eml., 122. 728. 1900. Jbid.. l-Sn, 1185, 1469. 19(>0. Ibid., 132, 14S4. 



^ Oompt. Rtnd., 141, 1230. 



^•Zeitsch. aiiorg. Chem., 50, 2.59. IJK'G. 



