IODINE. 63 



107.93 and CI = 35.457, giving 1 = 126.941 and 126.928. 

 The argentic iodide used was prepared from zinc iodide 

 which had been prepared from iodine in hirge crystals. 

 The argentic iodide was fused. {Annal. de Chim. et de 

 Phys., (3,) 55, 1859, 163.) 



J. S. Stas : 126.851. 



Stas ascertained the molecular weight of argentic iodide 

 as follows : 



In two complete analyses, a known weight of argentic 

 iodate was decomposed by heat in a current of pure, dry 

 nitrogen. The oxygen set free was caught by hot copper 

 and weighed, as well as the residual argentic iodide. In 

 one experiment argentic iodate was dissolved in ammonia, 

 precipitated by sulphuric acid, (to secure advantageous divi- 

 sion of the salt,) and reduced while in suspension by a slow 

 current of sulphurous acid. The mean molecular weight 

 reached was 234.779; extreme difference, 0.063. The sam- 

 ples of iodate employed were prepared : (1.) From argentic 

 sulphate and potassic iodate, mixed boiling, the latter in 

 excess, thorough washing and drying in air freed from 

 organic particles; (2.) By the reaction of potassic iodate on 

 argentic hyposulphite. The purity of the salt was carefully 

 tested. 



Stas ascertained the composition of argentic iodide as 

 follows : 



(1.) A known weight of argentic nitrate was precipitated 

 by hydro-iodic acid and the argentic iodide washed, dried, 

 and weighed in the same vessel. (2.) A known weight of 

 Ag was dissolved in nitric acid, converted into sulphate, 

 dissolved in very dilute sulphuric acid, and precipitated with 

 hydro-iodic acid. The precipitate was washed at tempera- 

 tures increasing up to 90°. (3.) A known weight of argen- 

 tic sulphate was allowed to react on a known and nearly 

 equivalent weight of iodine in an aqueous solution of sul- 

 phurous and sulphuric acids at 10°, and in the dark,till all 

 the iodine was taken up. The excess of iodine was titrated 

 with silver solution, and the iodide w^eighed. This method 

 was employed in two experiments. (4) differed from (3) 

 mainly in the conversion of the iodine into ammonium 

 iodide before bringing it into contact with argentic sul- 

 phate. Four experiments were made by the last method. 



The mean composition of the iodide, as derived from all 

 the experiments, is 100 Ag = 117.5343 iodine. From these 

 data Stas calculates the atomic weight of I at 126.857, and 



