LEAD. 131 



We have now nine ratios from which to compute : 



(i.) Per cent, of Pb in PbO, 92.8271, =b .0013 



(2.) Per cent of PbO in PbNPg, 67.4027, ± .0016 



(3.) Pb : PbSO^ : : lOO : 146.4262, ±1 .0023 



(4.) PbO : PbSO^ : : lOO : 135. S04, ± .0180 



(5.) PbSO^ : PbNjOg : : loo : 109.307, ± .0020 



(6.) Pb : PbNjOg : : loo : 159.9704, ±: .0010 



(7.) Pb : PbClj : : 100 : 134.191, ± .013 



(8.) PbCl2 : 2AgCl : : 100 : 103.21, zh .0745 



(9.) Agj : PbCIj : : lOO : 128.7266, ± .0130 



To reduce the.se ratios we must use the following data : 



S = 31.828, ± .0015 

 N = 13-935, ±.0021 

 AgCl = 142.287, dr. 0037 



For the molecular weight of lead oxide we now get three estimates : 



From (i) PbO = 221.375, zb .0403 



From (2) " = 221.796, ± .0132 



From (4) " =• 221.944, d= .1116 



General mean PbO = 221.757, ± .0125 



For lead chloride we have — 



From (8) PbClj = 275.723, d: . 1989 



From (9) " =275.753,^.0290 



General mean PbClj = 275.752, ± .0287 



Including these results, six values are calculable for the atomic weight 

 of lead : 



From molecular weight of PbO Pb = 205.878, d= .0126 



From molecular weight of PbClj 



From (3) 



From (5) 



From (6) 



From (7) 



= 205.394, rb .0302 

 = 205.367, ±.0051 

 = 203.352, ± .0479 

 = 205.341, ± .0068 

 = 205.779, ±.0831 



General mean Pb ^ 205.395, ± .0038 



If = 16, Pb = 206.960. If we reject the first, fourth, and sixth of 

 these values, which are untrustworthy, the remaining second, third, and 

 fifth give a general mean of Pb = 205.358, ± .0040. If O = 16, this 

 becomes Pb = 206.923. From Stas' ratios alone Stas calculates Pb = 

 206.918 to 206.934 ; Ostwald finds 206.911 ; Van der Plaats (A), 206.9089, 

 (B), 206.9308, and Thomsen 206.9042. The value adopted here repre- 

 sents mainly the work of Stas, and with H = 1 is 



Pb = 205.358, =h .0040. 



