106 Browning, etc. — Tellurium, Arsenic, etc. 



Aim. X. — On the Qualitative Separation and Detection 

 (I) of Tellurium and Arsenic and (11) of Iron, Thallium, 

 Zirconium and Titanium • by Philip E. Browning, G. S. 

 Simpson and Lyman E. Porter. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — celxxviii. ] 



I. 



In a previous paper from this laboratory by one of us* it 

 was shown that an attempt to separate arsenic and tellurium by 

 the addition of magnesium chloride mixture to a solution of 

 ammonium arsenate and tellurite according to the method of 

 Noyes and Brayf often resulted in some confusion due to the 

 fact that a magnesium compound of tellurous acid was precipi- 

 tated which interfered with the test for arsenic and removed a 

 considerable part of the tellurium. 



The fact that the original hydrogen sulphide precipitate is 

 decomposed by hydrochloric acid and potassium chlorate, and 

 that this oxidation process would probably effect at least the 

 partial oxidation of the tellurium to telluric acid, suggested the 

 investigation of the formation of the telluric acid under these 

 conditions and its effect upon the method. A number of 

 experiments along this line seemed to show that after the treat- 

 ment of tellurium with hydrochloric acid and potassium chlor- 

 ate a mixture of tellurous and telluric acids resulted and that 

 the ammonium tellurate gave a precipitate with magnesium 

 chloride mixture as has been shown to be the case with ammo- 

 nium tellurite. From these results we conclude that any attempt 

 to remove tellurium from arsenic by this method is apt to yield 

 doubtful conclusions. We therefore recommend that the tel- 

 lurium be removed first by the method of Noyes and Bray, 

 viz. precipitation of elementary tellurium by sodium sulphite 

 in dilute hydrochloric acid solution in the presence of potas- 

 sium iodide. The filtrate from the tellurium should be boiled 

 to remove excess of sulphur dioxide, then treated with hydro- 

 gen dioxide, boiled to remove the greater part of the iodide 

 and then made alkaline with sodium hydroxide and treated 

 with more dioxide to oxidize the arsenic to arsenate. This 

 solution is then acidified to destroy sodium hydroxide and 

 made alkaline with ammonium hydroxide and treated with 

 magnesium chloride mixture which precipitates the arsenate. 

 The filtrate from the arsenate may be tested for molybdenum 

 by potassium sulphocyanide and zinc in hydrochloric acid solu- 

 tion according to Noyes and Bray. This modification of the 

 original method gave satisfactory results when used by a class 

 of about forty. 



* Browning, this Journal, xl, 349, 1915. 

 f Jour. Amer. Chem. Soc, xxix, 137. 





