H. L. Wells — Quantitative Determination of 'Caesium. 187 



These results indicate greater errors than were expected from 

 the previous solubility determinations. It is suspected that a 

 little of the precipitate was dissolved by washing, and the use 

 of hydrochloric acid containing lead chloride as well as chlorine 

 would probably diminish the error. The last experiment shows 

 that the presence of a considerable amount of potassium has no 

 influence upon the result. 



The determination of caesium by this method can be simpli- 

 fied by weighing the precipitated ceesium-plumbic chloride 

 directly. The salt is perfectly stable at 100°. The following 

 table gives the details of a number of determinations made in 

 this way. The precipitates were all thoroughly washed with 

 hydrochloric acid containing chlorine and dried on an asbestus 

 filter at 100°. 



Cs 2 PbCl 6 PbCl, KC1 Volume Cs 2 PhCl 6 Cs. 2 PbCl 6 





taken. 



taken. 



taken. 



HC1. 



found. 



lost. 



A 



•2761? 



0-25 = 



... 



28 cc 1 : 1 



•2650? 



•0111 



B 



•0878 



1-0 



0'5? 



52 1:1 



•0833 



•0035 



C 



•1202 



1-0 







52 1:1 



•1071 



•0131 



D 



'7558 



o-i 







28 cone. 



•7369 



•0189 



E 



•2483 



o-i 







20 cone. 



•2359 



•0124 



The results show considerable losses in caesium, which appa- 

 rently do not entirely depend upon the volume in which the 

 precipitation is made. It is believed that the losses occur 

 chiefly in washing, for large quantities usually show a larger 

 total loss than small ones. 



AY hen caesium and rubidium are together, the precipitation 

 of caesium plumbic chloride is accompanied by a partial pre- 

 cipitation of the rubidium, unless the quantity of the latter is 

 small. It is possible, however, to make an indirect determina- 

 tion of the caesium in such a precipitate by weighing it and 

 afterwards determining the weight of the caesium and rubidium 

 sulphates. Two experiments have been made on this plan, 

 where not only rubidium, but also potassium, sodium and 

 lithium were present. 



A B 



Cs 2 PhCl 6 taken, 0*3561? 0*1545? 



Rb 2 PbCl B taken, 0.2845 0'4101 



To each of these were added about (H5 g each of potassium 

 and sodium chlorides, 0*25 g of lithium carbonate and 0*1? of 

 lead chloride. The substances were dissolved by boiling with 

 dilute hydrochloric acid, about an equal volume of concen- 

 trated acid was added, and chlorine was passed until the solu- 

 tions became cold. 



A B 



Volume of solution, 30 cc 50 cc 



