99 



339-983, 



=b . 04 1 I 



The lack of sharp concordance in these data and the consequently 

 high probable errors seem to indicate a distinct sui)eriority of the purely 

 chemical method of determination over that adopted by the j^hysicist. 

 The eight distinct series now combine as follows : 



Richards, first series corrected 339.408, ± .or 14 



Richards, second series ... 339.404, zh .0046 



Richards, CuBrj series . 339.392, ± .0108 



Rayleigli and Sidgewick 340.561, ± .0935 



Gray, with large plates 340.935, d= .1072 



Gray, with small plates 339-953, =t .0521 



Shaw 339-983, ± .041 1 



Vanni 340.406, zb .0520 



General mean 339-41 '> =b .0039 



If we combine Richards' three series into a general mean separately, 

 we get 339.402, dz .0040. Hence the other determinations, liaving high 

 probable errors, practically vanish from the result, and it is a matter of 

 indifference whether they are retained or rejected. 



We now have the following ratios from which to compute the atomic 

 weight of copper : 



(l.) Percentage of Cu in CuO 79.8355, zb .0010 



(2.) " of Cu in CuSO^ 39.795, zfc .0036 



{3.) " of Cu in CuSO^, 5H2O. . 25.451, d= .0011 



(4.) " of CuO in CUSO4. . . . . . 49.816, zh .0017 



(5.) Cu : NajCOg : : lOO : 166.838, zt .0035 



(6.) Cu : Na2S0^ : : loo : 223.525, zb .0098 



(7.) BaSO, : Cu : : 93.2S9 : 25.448. 



(8.) 2AgHr : Cu : : 100 : 16.924, d= .0007 



(9.) Cu : Ag2 : : lOO : 339.411, zb .0039 



