344 THE ATOMIC WEIGHTS. 



LANTHANUM. 



Leavino- out of account the work of INFosauder. and the valueless ex- 

 periments of Choubine, we may consider the estimates of the atomic 

 weight of lanthanum which are due to Hermann, Rammelsberg, INIarig- 

 nac, Czudnowicz, Holzmaun, Zschiesche, Erk, Cleve, Brauner, Bauer, 

 and Bettendorff. 



From Rammelsberg* we have but one analysis. .700 grm. of lantha-' 

 num sulphate gave .883 grm. of barium sulphate. Hence 100 parts of 

 BaSO^ are equivalent to 79.276 of La2(SO^)3. 



Marignac.f working ^^^al so with the sulphate of lanthanum, employed 

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

 of barium chloride. The r(?feulting barium sulphate 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 i'rom 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 La,,(SOJ.j i)roportional to 

 100 parts of BaSO^. 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, zb .030 Mean, 83.471, ± .128 



From A La = 138.47 



From B "=147-13 



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

 not so good as B. 



Marignac's second method, described in the same pa[)er with the forego- 

 ing experiments, consisted in mixing solutions of La./SO^v^ with solutions 

 of BaCl.^, titrating one with the other until equilibrium was established. 

 The method has already been described under cerium. The weighings 



* Poggend. Annalen, 55, 65. 



t Arch. Sci. Phy.s. el Nat. (1), 11, 29. 1849. 



