153 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 54 



C2ESIUM. 



The atomic weight of csesium, like that of rubidium;, has been com- 

 puted from analyses of the chloride and bromide, and also from experi- 

 ments upon the nitrate. The earliest determination, by Bunsen,' was 

 incorrect, because of impurity in the material studied. The first trust- 

 worthy determinations were published by Johnson and Allen ^ in 1863. 

 Their material was extracted from the lepidolite of Hebron, Maine, and 

 the cfesium was separated from the rubidium as bitartrate. From the 

 pure cffisium bitartrate csesium chloride was prepared, and in this the 

 chlorine was estimated as silver chloride by the usual gravimetric method. 

 Reducing their results to the convenient standard adopted in preceding 

 chapters, we have, in a third column, the quantities of CsCl equivalent 

 to 100 parts of AgCl: 



1.8371 grm. CsCl gave 1.5634 grm. AgCl. 117.507 



2.1295 " 1.8111 " 117.580 



2.7018 " 2.2992 " 117.511 



1.56165 " 1.3302 " 117.399 



Mean, 117.499, ± .025 



Hence Cs = 132.963. 



Shortly after the results of Johnson and Allen appeared a new series 

 of estimations was published by Bunsen.' His caesium chloride was 

 purified by repeated crystallizations of the chloroplatinate, and the ordi- 

 nary gravimetric process was employed. The following results represent, 

 respectively, material thrice, four times and five times purified : 



1.3835 grm. CsCl gave 1.1781 grm. AgCl. Ratio, 117.435 

 1.3682 " 1.1644 " " 117.503 



1.2478 " 1.0623 " " 117.462 



Mean, 117.467, ± .013 



Hence Cs = 132.917. 



Godeffroy's work" was, in its details of manipulation, sufficiently 

 described under rubidium. In three of the experiments upon caesium 

 the silver chloride was washed by decantation, and in one it was col- 

 lected upon a filter. The results are subjoined : 



1 Zeitsch. Anal. Chem., 1, 137. 



- Amer. Journ. Sci. (2), 35, 94. 



3 Poggend. Annalen, 119, 1. 1863. 



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



