SILVER, POTASSIUM, ETC. 49 



Mean, 153.6994, ± .0178 



The .synthesis of silver iodide has been effected by both Marignac and 

 Stas. Marignac, in the paper above cited, gives these weighings. In the 

 last column I add the ratio between iodine and 100 parts of silver: 



15.000 grm. Ag gave 31.625 Agl. I17.500 



14.790 " 32.^170 " 1 17-512 



18.545 " 40.339 " 117-519 



Mean, corrected for weighing in air, 1 17.5335, ± -0036 



Stas* in his experiments worked after two methods, which gave, how- 

 ever, results concordant with each other and with those of Marignac. 



In the first series of experiments Stas converted a known weight of 

 silver into nitrate, and then precipitated with pure hydriodicacid. The 

 iodide thus thrown down was washed, dried, and weighed without trans- 

 fer. By this method 100 parts of silver were found to require of iodine : 



117.529 

 117-536 



Mean, 117.5325, =h .0024 



In the second series a complete synthesis of silver iodide from known 

 weights of iodine and metal was performed. The iodine was dissolved 

 in a solution of ammonium sulphite, and thus converted into ammonium 

 iodide. The silver was transformed into sulphate and the two solutions 

 were mixed. When the precipitate of silver iodide was completely de- 

 posited the supernatant liquid was titrated for the trifling excess of iodine 

 which it always contained. As the two elements were weighed out in the 

 ratio of 127 to 108, while the atomic weight of iodine is probably a little 

 under 127, this excess is easily explained. From these experiments two 

 sets of values were deduced ; one from the weights of silver and iodine 

 actually employed, the other from the quantity of iodide of silver col- 

 lected. From the first set we have of iodine for 100 parts of silver : 



117-5390 

 117-5380 

 ii7-53'8 

 117-5430 

 117.5420 

 117.5300 



Mean, 117-5373, ± -0015 

 * Aronstein's translation, pp. 136, 152. 



