ATOMIC WEIGHTS 



199 



LEAD. 



For the atomic weight of lead we have to consider experiments made 

 upon the oxide, chloride, nitrate and sulphate. The researches of Ber- 

 zelius upon the carbonate and various organic salts need not now be 

 considered, nor is it worth while to take into account any work of his 

 done before the year 1818. The results obtained by Dobereiner ^ and 

 by Longchamp " are also without special present value. 



For the exact composition of lead oxide we have to depend upon the 

 researches of Berzeliiis. His experiments were made at different times 

 through quite a number of years; but were finally summed up in the 

 last edition of his famous "Lehrbuch."^ In general terms his method 

 of experiment was very simple. Perfectly pure lead oxide was heated 

 in a current of hydrogen, and the reduced metal weighed. From his 

 weighings I have calculated the percentages of lead thus found and 

 given them in a third column : 



Earlier Results. 



Mean, 92.8271, ± .001c 



Hence Pb = 207.062. 



For the synthesis of lead sulphate we have data by Berzelius, Turner 

 and Stas. Berzelius,* whose experiments were intended rather to fix 

 the atomic weight of sulphur, dissolved in each estimation ten grammes 

 of pure lead in nitric acid, then treated the resulting nitrate with sul- 

 phuric acid, brought the sulphate thus formed to dryness, and weighed. 

 One hundred parts of metal yield of PbSO^ : 



iSchweig. Journ., 17, 241. 1S16. 

 2 Ann. Chim. Phys., 34, 105. 1827. 

 3Bd. 3, s. 121S. 

 *Lehrbuch, 5th ed., 3, 11S7. 



