230 THE ATOMIC WEIGHTS. 



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 result- 

 ing 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 esti- 

 mated, also as sulphate. This last weight of sulphate, de- 

 ducted from the total sulphate which the whole amount of 

 barium chloride could form, gave the sulphate actually pro- 

 portional to the lanthanum compound. The following 

 weights are given : 



La^{S0^)3. BaCl^. jst BaSO^. 2d BaSO^. 



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



4-733 " 5-178 " 5-848 " .147 " 



Hence we have the following quantities of La2{S04)3 pro- 

 portional 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, dr .030 Mean, 83.471. dr .128 



From A La =: 138.776 



B " =147.474 



A agrees best with other determinations, although, theo- 

 retically, it is not so good as B. 



Marignac's second method, described in the same paper 

 with the foregoing experiments, consisted in mixing solu- 

 tions of La2(S04)3 with solutions of BaCL, , titrating one 

 with the other until equilibrium was established. The 

 method has already been described under cerium. The 

 weighings give maxima and minima for BaCL,. In another 

 column I give La. (SO J 3 proportional to 100 parts of BaCL,, 

 mean weights being taken for the latter : 



* Archives des Sci Phys. et Naturelles, (i,) ii, 29. 1849. 



