A REVISION OF THE ATOMIC WEIGHT OF ARSENIC 



THE ANALYSIS OF SILVER ARSENATE. 



INTRODUCTION. 



Below is a summary of the previous work upon the atomic weight of arsenic,* 

 the results obtained by the several investigators having been recalculated with 

 the use of the most recent ^ atomic weights: 



A glance at this rather discordant series of results shows the necessity for a 

 redetermination of the atomic weight of arsenic. Even in the more recent in- 

 vestigations of Hibbs and Ebaugh there exists an extreme variation of nearly 

 0.2 unit in the averages of the five series. 



In this research silver arsenate was chosen for analysis, first, because the 

 compound is unchanged by moderate heating, and hence may be dried at a 

 temperature high enough to expel all but a very small amount of moisture. 

 In the second place, silver compounds may be analyzed with great ease as well 

 as accuracy by precipitation of the silver as silver halogen compounds. Fur- 

 thermore, preliminary experiments confirmed the statement by Ebaugh that 



* Clarke: A recalculation of the atomic weights, Smith. Misc. Coll., Constants of Nature, 

 Part V (1910). For an excellent critical discussion by Brauner of previous work, see 

 Abegg's Handbuch der anorganischen Cketnie, 3, (2), 491 (1907). 



* O = 16.00; Na = 22.98; S = 32.07; CI = 35.46; K = 39-10; Cr = 52.01; Br =■ 

 79.92; Ag = 107.88; Pb = 207.09. 



73 



