90 THE ATOMIC WEIGHTS. 



RUBIDIUM. 



The atomic weight of rubidium has been determined by 

 Bunsen, Piccard, and Godcffroy ; but only from analyses of 

 the chloride. 



Bunsen,* employing ordinary gravimetric methods, esti- 

 mated the ratio between AgCl and RbCl. His rubidium 

 chloride was purified by fractional crystallization of the 

 chloroplatinate. He obtained the following results, to which, 

 in a third column, I add the ratio between RbCl and 100 

 parts of AgCl : 



Mean, 84.253, dz .031 



The work of Piccardt was similar to that of Bunsen. In 

 weighing, the crucible containing the silver chloride was 

 balanced by a precisely similar crucible, in order to avoid 

 the correction for displacement of air. The filter was 

 burned separately from the AgCl, as usual ; but the small 

 amount of material adhering to the ash was reckoned as 

 metallic silver. The rubidium chloride was purified by 

 Bunsen's method. The results, expressed according to the 

 foregoing standard, are as follows : 



.0105 



GodefFroy,t starting with material containing both ru- 

 bidium and caesium, separated the two metals by fractional 



*Zeit. Anal. Chem., I, 136. Poggend. Annal., 113, 339. 1861. 



f Journ. fur Prakt. Chem., 86, 454. 1862. Zeit. Anal. Chem., i. 51S. 



J Ann. Chem. Pharm., 181, 185. 1876. 



