CONTRIBUTIONS FKOM THE CHEMICAL LABORATORY OF 



HARVARD COLLEGE. 



A REVISION OF THE ATOMIC WEIGHT OF LEAD. 



PRELIMINARY PAPER. — THE ANALYSIS OF LEAD CHLORIDE. 

 By Gregory Paul Baxter and John Hunt Wilson. 



Presented November 13, 1907. Received October 18, 1907. 



Although lead is one of the most common elements, its atomic 

 weight has received comparatively Httle attention, the value at present 

 accepted being based almost wholly upon the work of Stas.^ Of the 

 earlier determinations of this constant those of Dobereiner ^ and Long- 

 champs ^ can hardly be considered as possessing other than historic 

 interest. The first results which can lay claim to accuracy are those 

 of Berzelius,* who obtained values ranging from 206.7 to 207.3 by re- 

 duction of litharge in a current of hydrogen. Berzelius also synthe- 

 sized the sulphate from metalHc lead with the result 207.0.^ Shortly 

 after. Turner ^ criticized the first method employed by Berzelius and 

 attributed the irregularity of his results to the action of lead oxide on 

 the silicious matter of the tube at the temperature employed in the 

 reduction. By the conversion of both the metal and the oxide into 

 sulphate Turner in a painstaking research deduced the values 207.0 



^ Earlier work on the atomic weight of lead has been carefully summarized 

 by Clarke. Smithsonian Miscellaneous Collections, Constants of Nature, "A 

 Recalculation of the Atomic Weights," 1897. 



In recalculating the data of earlier determinations the following atomic 

 weights have been used in this paper : 



0=16.000; Ag= 107.88; CI = 35.46; N= 14.01; S = 32.07 

 Richards and Wells, Pub. Car. Inst., No. 28 (1905) ; Richards and Forbes, Ibid., 

 No. 69, p. 47 (1907) ; Richards and Jones, Ibid., No. 69, p. 69; Report of Inter- 

 national Committee on Atomic Weights, Jour. Amer. Chem. Soc, 29, 110 

 (1907). 



2 Schweig. Jour., 17, 241 (1816). 



3 Ann. Chim. Phys., 34, 105 (1827). 

 * Pogg. Ann.. 19, 314 (1830). 



5 Lehrbuch, 5th ed., 3. 1187 (1845). 



6 Phil. Trans., 527 (1833). 



