88 THE ATOMIC WEIGHTS. 



caesium, separated the two metals by fractional crystallization of their 

 alums, and obtained salts of each spectroscopicalty 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 

 analyses of RbCl the AgCl was handled by the ordinary process of nitra- 

 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 g rm - AgCl. 84.338 



1.8096 " 2.1461 84320 



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, .031 Rb = 84.7O2 



Piccard ................. 84.290, .0105 " 1=84.754 



Godeffroy ............... 84.3345, dz .0051 " =84.817 



General mean 84.324, =fc .0045 



Heycock* worked by two methods, but 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 bromide gave 



Ag : RbBr : : 107.93 : 165.437 

 Ag : RbBr : : 107.93 : 1 ^>S'34- 2 



Mean, 165.3895, .0320 



There are now three ratios for the metal rubidium, as follows : 



(i.) AgCl : RbCl : : loo : 84.324, .0045 



(2.) Ag : RbCl : : 107.93 : 120.801 



(3.) Ag : RbBr : : 107.93 ' l6 5-3 8 95> -3 2 



To reduce these ratios we have 



Ag = 107.108, zb .0031 

 Br = 79.344, .0062 

 C1 = 35- T 79, -0048 

 AgCl = 142.287, zh .0037 



* British Association Report, 1882, p. 499. 



