Separation of Selenium from Tellurium. 



185 



dioxide was passed through, and the solution in V 1 was boiled. 

 The phenomena of each individual set of experiments with the 

 selenious and tellurous acids occurred now together — the color- 

 ing of the liquid, the evolution of bromine, the distillation of 

 the selenium bromides, the crystallization of the tellurium 

 tetrabromide, the disappearance of the selenium compounds 

 from the connecting tube, and the final stopping of the distil- 

 lation when the volume of the residue has diminished to 15 cm 3 . 

 After cooling, the first flask V 1 was removed, 1 grm. of potas- 

 sium iodide and 5 cm 3 of hydrochloric acid were added to the 

 contents of the second flask, V 2 , the current of carbon dioxide 

 was again started through the apparatus, the mixture was boiled 

 ten minutes, and the iodine in the flask, receiver and trap was 

 determined by titration with sodium thiosulphate and taken as 

 the measure of the selenium dioxide. In some preliminary 

 experiments trouble was experienced in removing the last 

 traces of the selenium bromides held back mechanically by the 

 oily tellurium compound which collected upon the walls of the 

 distillation flask and in the connecting tube ; but the difficulty 

 was satisfactorily overcome by cloaking the flask with a mantle 

 of asbestos board and flaming the connecting tube gently 

 toward the close of the process of distillation. The results 

 obtained are gathered in the following table : 



TeO a 

 taken. 



KBr 



taken. 



H 3 P0 4 



(Sp.gr. 1-70) 



taken. 



Final 

 volume. 



Se0 2 

 taken. 



Se0 2 



found. 



Error. 



grm. 



grm. 



cm 3 . 



cm 3 . 



grm. 



grm. 



grm. 



O'l 



1 



20 



15 



0-0733 



0-0735 



0-0002 4- 



a 



a 



a 



a. 



0-0997 



0-0995 



0-0002 — 



a 



tc 



a 



a 



0-1004 



0-1003 



o-oooi — 



a 



a 



a 



a 



0*0916 



0-0914 



0-0002 — 



a 



a 



it 



a 



0-0997 



0-0995 



0-0002 — 



a 



a 



tt 



a 



0-1010 



0-1014 



0-0004 + 



a 



it 



a 



a 



0-1015 



0-1008 



0-0007 — 



a 



a 



a 



a 



0-1019 



0-1022 



0-0003 + 



a 



a 



a 



a 



o-ioio 



0-1012 



00002 + 



et 



a 



a 



a 



0-1002 



o-iooo 



0-0002 — 



a 



a 



(C 



a 



0-1006 



0-1004 



0-0002 — 



a 



a 



a 



a 



0-1006 



0-1001 



0-0005 — 



Obviously the error of the process, when carefully conducted 

 and applied to the amounts of material which we have 

 employed, is very small. 



