PAPERS OX CHEMISTRY AND PHYSICS 229 



acidity of the mother liquor; likewise; that this factor 

 for a bromide system is 2.6 while for a chloride system 

 it is about 1.6. Eeasoiiiiig from the familiar relation- 

 ships sho"v\^i in the periodic table, it might readily be 

 concluded that if a bromide system was more efficient 

 than a chloride system the fractional crystallization of 

 the iodides would be considerably more efficient than 

 either the chloride or the bromide. With this view point 

 in mind a series of experiments are now being conducted 

 to determine the practicability of an iodide system of 

 radium concentration. 



Before this experiment could be carried out success- 

 fully, it was necessary to determine the best method of 

 preparing the iodide solution. Several methods were 

 tried such as: (1) Superheated steam was passed over 

 the sulfide, converting it to the hydroxide, which was 

 then heated to a dull red in a stream of hydriodic acid 

 gas; (2) the sulfide was transformed to the iodide by 

 boiling with an alcoholic solution of iodjne; (3) the sul- 

 fide was added to a boiling solution which contained 

 sightly more than the calculated amount of ferrous io- 

 dide; (5) the sulfide was boiled with hydriodic acid solu- 

 tion and a small amount of iodine in hydriodic acid was 

 added. Of these methods, the last proved to be the most 

 satisfactory, so it was employed. 



To test out the efficiency of the halide fractionation 

 system, three samples of radium-barium sulfate, -each 

 weighing 100 grams, were reduced with charcoal and the 

 resulting sulfides were treated with hydrochloric, hydro- 

 bromic and hydriodic acids respectively. After the ac- 

 tion had ceased they were boiled to expel hydrogen sul- 

 fide, filtered and the residue washed thoroly. The fil- 

 trates were evaporated to diyness, taken up with a small 

 quantity of water to which was added a little of the free 

 acid, and the fractional crystallization begun, by evapor- 

 ating on a steam bath until the solutions were completely 

 saturated. Then the dishes were cooled in ice water, the 

 ciystals filtered out, redissolved in pure water and re- 

 crvstallized. 



C. E. Scholl. Jour. Am. Chem. Soc. i2, S89 (1920). 



