182 



Gooch and Peirce — Method for the 



halogens, and the further continuance of the treatment results 

 in the more or less complete removal of the selenium com- 

 pounds to the distillate. From the mixture containing the 

 phosphoric acid, selenious acid, and sodium chloride we have 

 been able to secure only a partial volatilization of the selenium 

 chloride. The transfer of the selenium bromide, however, 

 from the mixture of the acids and potassium bromide is rapid 

 and complete, and this fact points out a possible method for 

 the separation of selenium from substances which do not form 

 volatile products under similar conditions of treatment. Tel- 

 lurium proves to be such a substance, and the work to be 

 detailed has to do with a process for the separation of selenium 

 from tellurium, based upon the volatility of selenium tetra- 

 bromide and the non-volatility of tellurium tetrabromide under 

 definite conditions. 



The selenious acid which we used was made by dissolving 

 in water a known weight of the white, crystalline, anhydrous 

 dioxide prepared from pure selenium by oxidation with nitric 

 acid, treatment in solution with barium hydroxide to remove 

 selenic acid, and repeated sublimation in a current of oxygen. 

 The tellurium was obtained in solution in its lower condition 

 of oxidation by dissolving in potassium hydroxide a known 

 weight of tellurium dioxide (made by oxidizing presumably 

 pure tellurium by nitric acid and igniting the product at a low 

 red heat), neutralizing with phosphoric acid, and redissolving 

 in a sufficient excess of that acid the precipitate formed in the 

 process of neutralization. 



In our preliminary experiments we made use of a form of 

 apparatus previously employed for similar purposes and 

 described in former articles from the laboratory, viz : a Yoit 

 flask, serving as the retort, sealed to the inlet tube of a Drexel 

 wash-bottle, used as a receiver, the outlet tube of which was 

 trapped by sealing on Will and Varrentrapp absorbtion bulbs. 

 Later the apparatus was changed to the form shown in the 

 accompanying figure by introducing a second Yoit flask, in 



order that the selenium might be 

 estimated in the distillate more con- 

 veniently. 

 v* 41 y 1 k ^ nt0 tne nrs ^ ^oit flask, V 1 , were 



^^jrffc^ Qk ^t P llt measured amounts of the solu- 

 tion of selenious acid with 20 cm* 

 of syrupy phosphoric acid (sp. gr. 

 1*70), 1 grm. of potassium bromide, 

 and water enough to make the entire 

 volume of liquid 50 cm 3 . The 

 second flask, Y 2 , contained about 

 15 cm 3 of water, and was kept cool by immersion in water. 



