LEAD. 77 



We have now seven ratios upon which to base our com- 

 putations : 



(l.) Per cent, of Pb in PbO, 92.8271, rfc .0013 



(2.) Per cent, of PbO in PbNjOg, 67.4016, zt .0014 



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



(4.) PbO : PbSO^ : : loo : 135.804, ± .018 



(5.) PbSO^ : PbN^Og : : lOO : 109.307, ± .002 



(6. ) Pb : PbN^Og : : lOO : 159.9704, ± .OOIO 



(7.) Al,^ : PbCI.^ : : lOO : 128.7266, ± .OI3 



Discussing these separately, we get an equal number of 

 values for the atomic weight of lead : 



From (i) Pb :-- 206.587, ± .059 



" (2) " = 207.046, zt .041 



" (3) " = 206.435, ± .041 



" (4) '• = 207.131, zfc .118 



" (5) "=204.803,^.329 



" (6) " = 206.454, ± .037 



" (7) " = 206.473, d= .042 



General mean " = 206.604, ± -019 



If = 16, this becomes Pb = 207.079. 



In the above discussion are included several values which 

 ■diverge widely from this general mean, and which, for 

 other reasons, are probably erroneous. Although but one of 

 these carries much weight, it is as well to exclude them, and 

 to base our computations upon the others. If, now, we 

 reject the second, fourth, and fifth values, we get for the 

 atomic weight of lead, Pb = 206.471, ± .021. If = 16, 

 this becomes Pb = 206.946. 



From the synthesis of the nitrate Stas found 206.918, and 

 from the sulphate, 206.934. The agreement of these values 

 with our own general mean is certainly very close. 



