436 PROCEEDINGS OF THE AMERICAN ACADEMY. 



thermore Ladenburg did not fuse tlio silver iodide before weighing it. 

 Although Stas states that silver iodide may be completely dried without 

 fusion, his experiments show a loss in vveiglit on fusion of two thousandths 

 of a per cent, while the average loss on fusion as given on page 427 is 

 about four thousandths of a per cent. Moreover, Ladenburg's method 

 of purifying silver iodide, by washing the precipitated salt with ammonia, 

 could hardly be expected to remove last traces of silver chloride and silver 

 cyanide "included" by the precipitate. These errors are all so small 

 that they would not affect the second place of decimals. However, 

 Ladenburg's, Scott's,* and Kothner and Aeuer's work all afford confirma- 

 tion that the atomic weight of iodine is undoubtedly much higher than 

 has been usually supposed. 



The results of the research are, then, as follows : 



1. The atomic weight of iodine is found to be 126.975 (O = 16.000). 



2. Richards and Wells's value for the atomic weight of chlorine, 

 35.467, is confirmed. 



3. The existence of an element of the halogen family of higher atomic 

 weight than iodine is shown to be improbable. 



4. The specific gravity of pure fused silver iodide is found to be 5.674 

 at 25° referred to water at 4°. 



I am indebted to the Cyrus M. Warren Fund for Research in Hafrvard 

 University for platinum vessels, quartz crucibles, and balance, all indis- 

 pensable in the research. 



Chemical Laboratory of Harvard College, 

 Cambriuge, Mass., August 6, 1904. 



* Proc. Chem. Soc, 18, 112. 



