188 H. L. Wells — Quantitative Determination of Cmium. 



After standing several hours the precipitates were collected on 

 asbestus filters in porcelain Gooch crucibles, washed with dilute 

 hydrochloric acid saturated with chlorine, dried at 100° and 

 weighed. 



A B 



Cs 2 PbCl 6 and Rb a PbCl fi found, 0-5621 0'4538 



The precipitates were treated on the filters with hot water, the 

 resulting solutions were evaporated with sulphuric acid, the 

 lead sulphate was removed by filtration, the filtrates were 

 evaporated and finally ignited in an ammoniacal atmosphere 

 and the mixed sulphates were weighed. 



A B 



Cs a S0 4 and Rb a S0 4 found, 0-2826 0*2164 



For calculating the results, the following formulae were used : 



(P = weight of Cs 2 PbCl 6 + Rb 2 PbCl B ) 

 (S = weight of Cs 2 S0 4 + Rb 2 S0 4 ) 

 Weight of Cs = 5*095S — 2*30lP 

 Weight of Rb = 2*006P — 3*80lS 



A B 



Caesium taken 0*1381 0*0599 



Caesium found 0*1464 0*0584 



Error in caesium 0*0083+ 0*0015 — 



Rubidium taken 0*0823 0*1186 



Rubidium precipitated .. 00534 0*0876 



The results show that approximate determinations of caesium 

 can be made by this method when all the alkali-metals are 

 present. The process leaves a part of the rubidium with the 

 potassium, and these two metals can be precipitated as platinic 

 chlorides and their amounts determined indirectly. 



The method which has been described is useful for the ex- 

 traction of caesium and rubidium from their natural sources. 

 The following method of procedure may be suggested, suppos- 

 ing all the alkali-metals to be present as chlorides in a concen- 

 trated aqueous solution : 



At least an equal volume of concentrated hydrochloric acid 

 is added, and any precipitated sodium and potassium chlorides 

 are removed. The solution is diluted somewhat to avoid a 

 subsequent precipitation of these chlorides, a solution of lead 

 chloride, made by boiling lead oxide with a large excess of 

 hydrochloric acid, is gradually added while chlorine is passed 

 into the solution until it is cold and until fresh additions of 

 lead chloride fail to produce a yellow precipitate. According 

 to my solubility determinations, this precipitation leaves less 

 than l g of rubidium and a much smaller quantity of caesium in 

 each liter of the solution. The precipitate is usually almost 



