70 ATOMIC WEIGHT DETERMINATIONS. 



C. Erk : 135.39 (0 = 16). 



Determined by analysis of the sulphate by the method 

 employed by llolzmann. The bases were separated by the 

 methods which Hermann used. Yttrium w^as also elimi- 

 nated. Fresenius in his Zeitschrift, 10, 509, objects to the 

 details of the Erk's manipulation of barium sulphate. 

 {Kopjy's Jahresberichi, 1870, 319 ; Jena Zeitschr. fur Med. und 

 Nat, 6, 1870, 299.) 



D. Mendelejeff : 180 (0 = 16). 



As La forms but one oxide, the salts of which are not, 

 according to Marignac, isomorphous with those of the 

 lower oxide of didymium, Mendelejefi' concludes that it 

 belongs to the same group, but that its oxide is a binoxide, 

 and its atomic weight 180. {Liebig's Ann., SuppL, 8, 1871, 

 190.) 



C. Marignac : 138.75 (0 = 16). 



By heating the sulphate till all acid was expelled, Marig- 

 nac, in two experiments, determined La (bivalent) at 92.52 

 and 92.56 ; by precipitation with ammonia and heating at 

 92.24 and 92.48. The sulphate was purified by a great num- 

 ber of partial rccrystallizations, and showed only doubtful 

 traces of didymium in the spectroscope. CS ^= 16. {AnnaL 

 de Chim. et de Fhys., (4,) 30, 1873, 67.) 



P. T. Cleve: 139.15 (0 = 16). 



Determined by the conversion of lanthanium oxide into 

 sulphate. The number is the mean ; extreme difference 

 0.55. The oxide was purified from didymium by repeated 

 partial precipitation from nitric acid solution with ammonia, 

 basic didymium nitrate going down. The lanthanium 

 was finally precipitated with oxalic acid. The oxide was 

 found to be spectroscopically pure by Thalen. {Kojxp's Jah- 

 resberichi, 1874, 257; Paris Bull, de la Soc. Chim., 31, 196, 

 246, 344.) 



LEAD. 



Regnault, Kopp and others have determined the specific 

 heat of lead. It answers to an atomic weight of about 207. 

 {Gmelin- Kraut, I. c.) 



