78 PROCEEDINGS OP THE AMERICAN ACADEMY. 



possibly to the slight solubility of silver iodide in ammonia. On account 

 of this newly discovered tendency of silver iodide, it seemed probable 

 that the results of the synthesis of silver iodide from known weights of 

 silver in the early part of this research were somewhat too low ; for 

 although the precipitations took place in ammoniacal solution and au 

 excess of iodine was employed, the fact that the solutions were always 

 very nearly as strong as tenth normal and that the amnionic iodide was 

 poured into the silver nitrate, made it probable that occlusion had taken 

 place at least to some extent even here. It is noteworthy that three of 

 these syntheses yielded results as high as 126.985. Similar conclusions 

 are to be drawn concerning the results of the titration of silver and 

 iodine, although in this case precipitation took place in the reverse 

 fashion, i. e., by adding the silver nitrate to the iodide. 



Accordingly experiments were carried out for the redetermination 

 of the ratios of silver to silver iodide and to iodine, as well as the 

 new one of iodine to silver iodide, with especial precautions to avoid 

 the error of occlusion by using very dilute solutions and no excess 

 of silver. After the iodine had been weighed, very nearly the exact 

 amount of silver to combine with the iodine was weighed out and 

 dissolved in nitric acid with the usual precautions to avoid spattering. 

 The quantity of iodine used in each analysis was between three and four 

 grams, and the amount of silver consequently about three grams. The 

 solutions of both silver and iodine were diluted to a volume of one liter 

 each, so that the solutions were about thirtieth normal, and then the 

 silver nitrate was added very slowly to the solution of hydriodic acid 

 with constant stirring. The flask in which precipitation was carried out 

 was then shaken for some time, and allowed to stand until the supernatant 

 liquid was clear. This liquid was tested for an excess of iodine or 

 silver in a nephelometer, # and if a deficiency of either was found, it was 

 made up and the solution again shaken, until the point was reached 

 where the extremely faint opalescence produced by both hydriodic acid 

 and silver nitrate was equal in both nephelometer tubes. The excess or 

 deficiency of silver was in no case over one tenth of a milligram, and in 

 most cases much less. 



Several samples of iodine were employed in these analyses, each one 

 of which had been three times distilled from an iodide as previously de- 

 scribed. Three different specimens of silver, purified by different methods, 

 were used. Sample A was a portion of the material used in the first 



* Richards and Wells, Amer. Chem. Jour., 31, 235. 



