134 



RESEARCHES UPON ATOMIC WEIGHTS. 



iodide. Kothner and Aeuer ^ and Baxter have shown that silver iodide formed in 

 ammoniacal solution is freer from occluded matter than when formed in acid 

 solution. This experiment was a failure, for silver was reduced to the metallic 

 state owing to the slight excess of hydrazine. 



The question of adsorption of silver nitrate by the precipitate was further 

 tested in several instances by evaporating the wash-waters of the silver iodide 

 separately from the filtrate. In every such case only a mere trace of silver could 

 be detected, even when the precipitate was allowed to stand in contact with 

 the wash- waters for several hours. 



No experiments were performed to test for complete reduction of the iodic 

 acid to hydriodic acid, since evidence upon this point is already available. 

 Sammet ^ has recently determined the equilibrium constant for the reaction of 

 iodides upon iodates in acid solution to be as follows: 



(H+)«.(I03-).(I-)' _ 



(l2)^ 



2.8 . lO' 



,—47 



i. e., 10 f = 



(Id' 



m+ni-y 



.2 .8 . IO-" 



Since after reduction by the hydrazine the concentration of the free iodine ap- 

 proximates zero, and since the concentrations of the hydrogen and iodide ions 

 are fairly large, and since the constant itself is extremely small, it is evident 

 that the concentration of residual iodate must have been vanishingly small. 



A few analyses which met with known accidents are omitted from the fol- 

 lowing table : 



The Ratio of Silver to Iodine Pentoxide. 



Series II. By G. P. Baxter. 



• Loc. cit. 



^ Zeit. physik. Chem., 53, 640 (1905). 



» AgBr. 



