BAXTER A REVISION OP THE ATOMIC WEIGHT OF IODINE. 431 



THE ATOMIC WEIGHT OF IODINE. 

 Ag:I. 



the true value of the atomic weight of iodine. 

 tigatioD was not allowed to rest at this point. 



Nevertheless, the inves- 



PART III. 



The Ratio of Silver Iodide to Silver Chloride. 



In any atomic weight investigation it is extremely desirable to obtain 

 the value sought by reference to as many different well-known atomic 

 weights as possible. The method of heating silver iodide in a current of 

 chlorine, which has already been used by Berzelius and Dumas as well 

 as by Ladenb^urg, furnishes the ratio between iodine and chlorine, and 

 seemed capable of yielding trustworthy results ; for since the silver 

 halides fuse at a comparatively low temperature, there is no possibility 

 of inclusion of silver iodide by the silver chloride formed in the reaction, 

 and hence there is certainty that the reaction will be complete. 



First, silver iodide was prepared by precipitating an ammoniacal solu- 

 tion of the purest ammonium iodide (Sample I) with a solution of recrys- 

 tallized silver nitrate. In this operation a slight excess of ammonium 

 iodide was used.- The precipitate was well washed with one per cent 

 nitric acid, rinsed with water, and was collected on a Gooch crucible with 

 the use of a disk of filter paper instead of an asbestos mat. In this way 

 contamination of the precipitate with asbestos shreds was avoided. The 

 silver iodide was finally dried in an air-bath at about 100° C for at 

 least eight hours. After removal of the filter paper, those portions of 

 the precipitate which had come in contact with the filter paper were cut 

 away with a clean knife. Next the substance was fused in a weighed 



