114 RESEARCHES UPON ATOMIC WEIGHTS. 



tubing, which was attached to the reaction tube, was due to volatilized silver 

 halides, or to attacking of the glass by the hot halogens. At any rate, it is hard 

 to beheve that 1.5 meter of glass tubing subjected to the long-continued action 

 of mixed chlorine and iodine at 150° should not have altered its weight some- 

 what. Furthermore, Kothner himself showed that the tube in which the reac- 

 tion took place was slightly attacked by the fused silver chloride, but the nature 

 of the correction for this attacking of the glass is uncertain. Finally, although 

 the precaution was taken of fusing the silver iodide before the initial weighing, 

 so that the salt must have been free from moisture, it was not fused in an atmos- 

 phere of iodine. Hence it is possible that the iodide still contained traces of 

 occluded silver nitrate (or metallic silver). This deficiency in iodine, as well as 

 the possible gain in weight of the apparatus during the experiment, would have 

 lowered the atomic weight of iodine. 



As far as Kothner's syntheses of silver iodide from weighed amount of silver 

 are concerned, it need only be said that, even assuming that occlusion was 

 avoided in the synthesis in the wet way, and that in the synthesis in the dry 

 way a single precipitation of the iodine from solution in an iodide had completely 

 removed such impurities as chlorine and bromine, which would have accumulated 

 in the silver iodide during the experiment, the fact that Richards and Wells 

 have shown that silver fused in the air or with borax and saltpetre, according to 

 Stas, must contain oxygen, makes it certain that the results of Kothner's syn- 

 theses, 126.919 and 126.904, are too low. 



It is interesting to note, however, that Ladenburg's, Scott's, and Kothner 

 and Aeuer's work all afford confirmation that the atomic weight of iodine is 

 undoubtedly much higher than was formerly supposed from Stas's syntheses of 

 silver iodide. 



SUMMARY. 



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



1. The atomic weight of iodine is found to be 126.926(0 = 16.000 and Ag = 

 107.880). If silver is taken at 107.870, iodine becomes 126.914. 



2. The existence of an element of the halogen family of higher atomic weight 

 than iodine is shown to be improbable. 



3. The specific gravity of pure fused silver iodide is found to be 5.674 at 25° 

 referred to water at 4°. 



4. The observation by Kothner and Aeuer that under certain conditions sil- 

 ver iodide occludes silver nitrate, and that this occluded salt can not be removed 

 by washing with water, is confirmed. 



5. The value of Richards and Wells for the atomic weight of chlorine 

 35.457 (Ag = 107.880) and Baxter's for the atomic weight of bromine 79.916 

 are substantiated. 



