344 THE ATOMIC WEIGHTS. 



LANTHANUM. 



Leaving out of account the work of Mosander. and the valueless ex- 

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

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

 nac, Czudnowicz, Holzmann, 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 

 BaS0 4 are equivalent to 79.276 of La 2 (S0 4 ) 3 . 



Marignac.f 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 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 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 : 



, BaCl r ist BaSO,. 2 d BaSO,. 



4.346 grm. 4.758 grm. 5.364 grm. .115 grm. 



4-733 " 5.178 " 5-848 " .147 " 



Hence we have the following quantities of La,,(S0 4 ) 3 proportional to 

 100 parts of BaS0 4 . Column A is deduced from the first BaS0 4 and 

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



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 forego- 

 ing experiments, consisted in mixing solutions of La.,(S0 4 \. 5 with solutions 

 of BaCl. 2 , 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. Phys. et Nat. (i), n, 29. 1849. 



