Separation of Selenium from Tellurium. 183 



The Drexel bottle and bulbs contained a solution of potassium 

 iodide. A current of carbon dioxide was passed slowly 

 through the apparatus to secure quiet ebullition and to aid in 

 the transfer of the distillate to the receiver. Upon applying 

 heat to the first flask, V 1 , the solution boiled quietly and with- 

 out change until the volume of liquid had decreased to about 

 30 cm 3 , when traces of red selenium began to deposit in the 

 tube joining the first and second flasks. When the volume had 

 further diminished to about 25 cm 3 the liquid began to take on 

 color, darkened rapidly, and evolved bromine, which at once 

 attacked the selenium previously deposited. The greater part 

 of the bromine was absorbed in the second flask, V 2 , but a 

 trace found its way to the Drexel bottle, in which it set free a 

 slight amount of iodine from the iodide, as was afterward 

 proved by the effect upon starch. As the operation progressed, 

 an orange-yellow crystalline solid, presumably selenium tetra- 

 bromide for the most part, appeared in the tube where the 

 selenium had been, while a dark oily liquid, consisting largely, 

 no doubt, of the monobromide, condensed in drops upon the 

 walls of the flask and returned to form a floating layer upon 

 the hot liquid. Finally, when the volume had diminished to 

 15 cm 3 , the liquid had become perfectly clear and colorless, 

 white fumes of hydrobromic acid were evolved, and the tube 

 between the two flasks had been cleared. At this point the 

 operation was stopped and the apparatus allowed to cool. The 

 addition of potassium iodide to the contents of the first flask 

 neither liberated iodine nor precipitated selenium, and to 

 proved that no reducible compound of selenium still remained 

 in that flask. The amount of selenium which had been volati- 

 lized we determined directly by means of a method worked 

 out in this laboratory and to which reference has already been 

 made.* We introduced into the second flask, V 2 , which now 

 contained (beside a trace of selenium corresponding to the 

 slight amount of bromine which had escaped to the Drexel 

 bottle) the colorless selenious acid regenerated by the action of 

 the water and free bromine upon the mixed bromides which 

 had distilled, 1 grm. of potassium iodide and 5 cm 3 of hydro- 

 chloric acid and, after removing the first flask, V 1 , and connect- 

 ing the carbon dioxide generator with the inlet tube of V 2 , 

 boiled the solution ten minutes while a current of carbon 

 dioxide passed through this apparatus. At the end of this 

 time the iodine set free by the action of the iodide had been 

 almost completely removed to the Drexel bottle, leaving a 

 nearly colorless solution containing particles of dense, crystal- 

 line selenium. The iodine in the receiver, including of course 

 the small amount set free by the bromine which reached the 



. *GrOOch and Reynolds, this Journal, 1, 254. 



