ATOMIC WEIGHTS 



163 



silver is thrown down, and the weights of the two metals were in equiv- 

 alent proportions. In the first paper the following results were obtained. 

 The third column gives the value of x in the ratio Cu : 2Ao:: : 100 : x. 



Mean, 339.475, ± .0114 



In the second paper Bichards states that the silver of the fifth experi- 

 ment, which had been dried at 150°, as were also the others, still retained 

 water, to the extent of four-tenths milligramme in two grammes. If we 

 assume this correction to be fairly uniform, as the concordance of the 

 series indicates, and apply it throughout, the mean value for the ratio 

 then becomes 339.408, ±.0114. This procedure, however, leaves the 

 ratio in some uncertainty, and accordingly some new determinations 

 were made, in which the silver, collected in a Gooch crucible, was heated 

 to incipient redness before final weighing. Copper from two distinct 

 sources was taken, and three experiments were carried out upon one 

 sample to two with the other. Treating both sets as one series, the 

 results were as follows : 



Mean, 339.404, ± .0046 



a value practically identical with the corrected mean of the previous 

 determinations, and with that found in the later experiments upon copper 

 bromide. Hence Cu = 63.570. 



In various electrical investigations the same ratio, the electrochemical 

 equivalent of copper, has been repeatedly measured, and the later results 

 of Lord Eayleigh and Mrs. Sidgewick,' Gray,'' Shaw,^ and Vanni * may 

 properly be included in this discussion. As the data are somewhat dif- 

 ferently stated, I have reduced them all to the common standard adopted 



1 Phil. Trans., 175, 458. 



2 Phil. Mag. (5), 22, 389. 



^British Assoc. Report, 1886. Abstract in Phil. Ma?. (5), 23, 138. 

 ■• Ann. der Phys. (Wiedemann's) (2), 44, 214. 



