RUBIDIUM. 87 



For lithium itself there are three values : 



From molecular weight LiCl Li :^ 6.9752, rh .0051 



From (3' " =6.9855, ±.0129 



From (4) " = 6.962S, zb .0077 



General mean Li r= 6.9729, ± .0040 



If = U\ Li r= 7.026. From Stas' ratios, Stas found Li = 7.022 ; Ost- 

 wald. 7.0303; Van der Plaats (A), 7.0273; (B), 7 0235; and Thomson, 

 7.0307. 



RUBIDIUM. 



Tlie atomic weight of ruhidium has l)een determined b}^ Bunsen, Pic- 

 card. Godeffro_v. and He3'cock from analyses of tlie chloride and bromide. 



Bunsen,''^ eniployino- ordinary gravimetric methods, estimated the ratio 

 between AgCl and R1)C]. His rubidium chloride was purified by frac- 

 tional 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 : 



One grm. RbCl gave I.1S73 grm, AgCl. S4.225 



I. 1873 " S4.225 



" I. 1850 " 84.38S 



" I. 1880 " 84.175 



Mean, 84.253, ± .031 



The work of Piccardf 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 : 



Mean, 84.290, zb -0105 



Godefi^roy, ;j; starting with material containing both rulndium and 



*Zeit. Anal. Chem., i, 136. Poggend. Anna!., 113, 339. iSSi. 



t Journ. fiir Prakt. Chem., 86, 4^4. 1S62. Zeit. Anal. Chem., i, 51S. 



tAun. Chem. Pharm., iSi, 1S5. 1S76. 



