88 THE ATOMIC WEIGHTS. 



Cfesium, separated the two metals b}^ fractional cr3^stallization of their 

 alums, and obtained salts of each spectroscopicall}^ pure. The nitric 

 acid employed was tested for chlorine and found to be free from that 

 impurity, and the weights used were especially verified. In two of his 

 analj^ses of RbCl the AgCl was handled by the ordinary process of filtra- 

 tion. In the other two it was washed by decantation, dried, and weighed 

 in a glass dish. The usual ratio is appended in the third column : 



1.4055 grm. RbCl gave 1.6665 &'■"• '^gCl. 84.33S 



1.8096 " 2.1461 " 84 320 



2.2473 " 2.665 " 84.326 



2.273 " 2.6946 " 84.354 



Mean, 84.3345, ±.0051 



Combining the three series, we get the following result : 



Bunsen 84.253, rfc .031 Rb = 84. 702 



Piccard 84.290, ±.0105 " ^84.754 



Godeffroy 84.3345,4^.0051 " =84.817 



General mean 84.324, ± .0045 



Heycock'"^ worked by two methods, l)ut unfortunately his results are 

 given only in abstract, without details. First, silver solution was added 

 in slight deficiency to a solution of rubidium chloride, and the excess 

 of the latter was measured by titration. The mean of seven experiments 

 gave — 



Ag : RbCl : : 107.93 = 120.801 



Hence Rb = 84.702. 



Two similar experiments with the l>romide gave — 



Ag : RbBr : : 107.93 : 165.437 

 Ag : RbBr : : 107.93 = 165.342 



Mean, 165.3S95, d: .0320 

 There are now three ratios for the metal rul)idium, as follows : 



(l.) AgCI : RbCl : : 100 : 84. 324, dr .0045 



(2.) Ag : RbCl : : 107.95 : 120.S01 



(3.) Ag : RbBr : : 107.93 = 165.3S95, ± .0320 



To reduce these ratios we have — 



Ag = 107.108, it .0031 

 Br = 79.344, ± .0062 

 CI = 35-179, ± -0048 



AgCl = 142. 2S7, zh .0037 

 * British Association Report, 1SS2, p. 499. 



