ATOMIC WEIGHTS 493 



LANTHANUM. 



If we leave out of account the work of Mosander, and some worthless 

 experiments of Choubine, our discussion of the atomic weight of lan- 

 thanum must begin with a single analysis by Banimelsborg ' published in 

 1842. From 0.700 gramme of lanthanum sulphate he obtained 0.883 of 

 barium sulphate. Hence 100 parts of BaSO^ are equivalent to 79.276 

 of La2(S0,)3, and La = 133.48. 



Marignac,^ working also with the sulphate of lanthanum, employed 

 two methods. First, the salt in solution was mixed with a slight excess 

 of barium chloride. The resulting barium sulpliate was filtered off and 

 weighed; but, as it contained some occluded lanthanum compounds, its 

 weight was too high. In the filtrate the excess of barium was estimated, 

 also as sulphate. This last weight of sulphate, deducted from the total 

 sulphate which the whole amount of barium chloride could form, gave 

 the sulphate actually proportional to the lanthanum compound. The 

 following weights are given: 



Hence we have the following quantities of Lao( 80^)3 proportional to 

 100 parts of BaSOi. Column A is deduced from the first BaSO^ and 

 column B from the second, after the manner above described: 



A. B. 



81.022 83.281 



80.934 83.662 



Mean, 80.978, ± .030 Mean, 83.471, ± .128 



From A La = 139.44 



From B " = 148.17 



A agrees best with other determinations, although, theoretically, it is 

 not so good as B. 



Marignac's second method, described in the same paper with the fore- 

 going experiments, consisted in mixing solutions of LaofSO,),. with solu- 

 tions of BaCL, titrating one with the other until equilibrium was 



^ Poggend. Annalen, 55, 65. 



2 Arch. Sci. Phys. Nat. (1), 11, 29. 1S49. Oeuvres Completes, 1, 230. 



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