76 ABSOLUTE ATOMIC WEIGHT. 



I have just revised the calculation once more, before 

 going to press; the result is exactly as stated. 



Simple inspection shows : 



Atomic Ratio, . 0.83 521 Hinrichs, 1901. 



Analytical Ratio, . 0.83 517 Berzelius, 1817. 



or, in our parlance, . . u 4. low " only in the fifth place! 



Now since our " change is 6 high " corresponding to o.i, 

 the atomic weight corresponding to the two determinations 

 of Berzelius, made in 1817, is or % of o.i low, that is 0.06 

 low. Accordingly Pb = 206.94. 



That is, the experimental determinations of Berzelius, 

 taken to be absolutely exact, would correspond to the atomic 

 weight of lead being 0.06 less than the standard 207; that is 

 Pb = 206.94. 



But Berzelius himself would never assume absolute 

 accuracy for his work. We see then, that his oldest deter- 

 minations of the carbonate on record agree within the errors 

 of experiment -with the standard atomic iveight of lead^ 2Of. 



And these errors of experiment we have found to be not 

 in excess of 0.06. 



Contrast herewith " the most recent work" tabulated by 

 Clarke in his edition of 1897, for all determinations of lead, 

 ranging 2.5 units, instead of 0.06, or forty times the uncer- 

 tainty of the work of Berzelius done in 1817! 



B. Lead Oxide, Wet Way. 



In the earliest determinations on the conversion of lead 

 into lead oxide, Berzelius generally started with ten grammes 

 of lead, dissolved the same in a glass matrass with long neck 

 by nitric acid, and converted the resulting nitrate by igni- 

 tion into the oxide in the same matrass. Special variations 

 in the general process we need not refer to here. 



The formula of this process is 



Pb O : Pb = 223 : 207 =. i .07 730. 



A rise of o.i in the atomic weight of lead causes a rise of 

 6 units in the fifth place of this ratio; that is, gives 6 high. 



Berzelius found ten grammes of lead to gain 77.5 centi- 

 grammes when evaporated in the same glass vessel, and 78 



