A REVISION OF THE ATOMIC \\TIGHT OF IODINE. 93 



chiefly in the formation of hydriodic acid and the precipitation of sulphur, 

 although a small quantity of sulphuric acid is always produced. Iodide of 

 cyanogen with hydrogen sulphide yields hydrocyanic acid, hydriodic acid, and 

 sulphur.^ The solution was first boiled for a short time until the sulphur had 

 clotted together, and the sulphur was removed by filtration. The clear solution 

 was then boiled for several hours in order to eliminate the hydrocyanic acid-^ 

 Finally the hydriodic acid was partially converted into iodine by distilling the 

 solution with a slight excess of potassium permanganate. This permanganate 

 must also have had the effect of oxidizing any organic impurities. Since in the 

 reaction three-eighths of the iodine remain in the form of iodides, the resulting 

 iodine was thus subjected to a second distillation from an iodide. The product 

 was again converted into hydriodic acid by means of hydrogen sulphide, and 

 this again into iodine by recrystallized potassium permanganate which was free 

 from even a trace of chlorine. Since in the case of bromine it has already been 

 shown that two distillations from a pure bromide are sufficient to free this ele- 

 ment from chlorine,^ three distillations of iodine from a solution of an iodide 

 should insure complete elimination of chlorine and bromine even if the original 

 substance were very impure. The purified iodine was again converted into hy- 

 driodic acid by hydrogen sulphide, and this into ammonium iodide by an excess 

 of freshly distilled ammonia. This material was used in the analyses made with 

 Sample I. 



It was suggested to me by Prof. T. W. Richards that an undiscovered element 

 resembling the halogens, but of a higher atomic weight, might exist, and an 

 attempt to detect the existence of such an element was carried out as follows: 

 One pound of iodine was purified as described above, but the process of convert- 

 ing the iodine into hydriodic acid by hydrogen sulphide, and the hydriodic acid 

 into iodine by potassic permanganate, was repeated four times. The iodine 

 obtained in the last distillation with permanganate, amounting in all to about 

 50 gm., was set free in 4 fractions by introducing the permanganate in portions 

 of about 2 gm. each. An element belonging to the halogen family, and of higher 

 atomic weight than iodine, should be more easily set free than iodine, hence the 

 first of the 4 fractions should have contained nearly all of such an element 

 which occurred in the pound of iodine. Each one of the fractions was once dis- 

 tilled ^vith pure water, and was then converted into ammonium iodide, as in the 

 case of Sample I. The first fraction was fraction i of Sample II, the fourth 

 was fraction 4 of Sample II. No difference in appearance between these samples 

 and Sample I or even the original crude iodine could be detected. 



All reagents used in the course of the purification or in the analyses were 

 carefully purified. Acids and ammonia were redistilled, usually with the use of 



* Dammer, Handb. d. anorg. Chem., II, i, 432. 



' Richards and Singer, Amer. Chem. Jour., 27, 205 (1902). 



* See page 60. 



