86 



ABSOLUTE ATOMIC WEIGHT. 



the standard atomic weight of each of these compounds by 

 summing the standard atomic weights of the symbols speci- 

 fied in the formula; third, we give the atomic ratio by divid- 

 ing the second into the first, carrying out this division 

 uniformly to five decimals. Lastly we add the change which 

 this ratio undergoes if we raise the atomic weight of lead to 

 207.1. 



The reason why we carry out the division to Jive places 

 has already been stated, but may be repeated here. By an 

 extended critical examination of all the atomic weight deter- 

 minations we have found this number of decimals practi- 

 cally the limit of accuracy or precision attained. 



The unit in the last or Jifth place represents the one 

 hundred thousandth part, by weight, of the amount of sub- 

 stance operated upon. This is the limit of precision 

 attained in the best work. 



Atomic Ratios for Reactions Used. 



1. PbO 



2. Pb 



3. PbO 



4. PbChS 

 5- PbO 



6. PbO 4 S 



7. Pb(OsN) 2 



8. PbCh 



9. Pb(OaN)2 



10. PbCh 



11. 2AgCl 



PbOsC 



PbO 



Pb 



PbO 



Pb(O3N): 



Pb 



Pb 



Pb 



Pb04S 

 2Ag 



PbCh 



The change is the number of units in fifth place changed 

 in the direction stated by raising the atomic weight o.i or 

 207.1. 



The first three reactions here tabulated have been fully 

 considered in preceding sections. 



The fourth reaction represents the synthesis of lead sul- 

 phate from the oxide and sulphuric acid, driving off the 

 excess of acid by heat. It is evidently a reaction that cannot 

 admit of a high degree of precision. 



