296 PROCEEDINGS OF THE AMERICAN ACADEMY. 



principle ; or else, especially in the case of the rare metals, to the lack 

 of data affording room for intelligent difference of opinion. Among 

 the seventy-four atomic weights given in the table, only seven differ 

 enough from the values computed by Clarke to excite remaik. It seems 

 fitting to give a brief statement of the reasons for the differences in 

 these seven cases, leaving the details of reasoning about the other sixty- 

 seven elements unpublished. The elements mentioned are antimony, 

 cadmium, calcium, magnesium, platinum, tungsten, and uranium. 



It is not my purpose to enter at length into the discussion of the 

 antimony problem. Much of the voluminous work upon this subject 

 is now rejected by common consent. The work of Bongartz,* some- 

 times accepted as the best because it is the most recent, has the grave 

 faults inherent in all methods which involve the precipitation of baric 

 sulphate. Among all the published data Cooke's analyses of antimonious 

 bromide | (Sb = 119.92) seem to me the most satisfactory, because of the 

 admirable fitness of argentic bromide for quantitative work, and because 

 of the many precautions used in both preparation and analysis. Cooke's f 

 and Schneider's I work upon the sulphide (Sb = 120.5) are perhaps the 

 next in order; but Cooke's work upon this subject was far less satis- 

 factory than his work on the bromide. Accordingly, the value 120.0 is 

 given as the atomic weight of antimony in the accompanying table, 

 instead of 120.43, computed by Clarke. 



Although the atomic weight of cadmium has been the subject of 

 many investigations, it is still far from certainly established. Many 

 reasons combine to make me think that the highest of the published 

 values are the most accurate. Dumas's § work upou the chloride of cad- 

 mium led to the value 112.23 ; but his method of investigating chlorides 

 sometimes gave him too low results. 1| V. Hauer ^ and Partridge ** found 

 cadmium equal to less than 112 by heating cadmic sulphate in a stream 

 of hydric sulphide, but there is no proof that their initial substance was 

 thoroughly dried. On the other hand, Bucher's conversion of cadmic 

 sulphate into the oxide led to the value 112.36, which Bucher regards 



« ■ ■ — — ■ - ■ - — 



* Bongartz, Berichte d. d. chem Gesell., XVI. 1942. (1883.) 



i Cooke, Proo. Am. Acad., V. 13. (1877.) 



t Schneider, Pogg. Ann., XCVIII. 293 (1856) ; Journal prakt. Chem., (2), XXII. 

 131. (1880.) 



§ Dumas, Ann. Chem. Pharm., CXIII. 27. (I860.) 



II See these Proceedmgs, XXX. 371. Cases in point : barium, strontium, sodium, 

 and tin. 



TI Von Hauer, Journ. prakt. Chem., LXXII. 350. (1857.) 



** Partridge, Am. Journ. Sci., (3), XL. 377. (1890 ) 



