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INDIANA UNIVERSITY 



6. The Preparation of Ammonium Selenate : A New Method.^ 

 By Frank C. Mathers and Roy S. Bonsib. 



Introductory Statement. Owing to the ease with which am- 

 monium selenate will react with the higher metallic oxides, it is one 

 of the most convenient starting materials for the preparation of the 

 corresponding salts of selenic acid. For example : 



(NHJ.SeO, + CnO CuSeO, + 2NII, + H.O. 



This reaction shows the desirability of a quick and convenient 

 method for the preparation of ammonium selenate. 



The only method^, described for the preparation of ammonium 

 selenate is the saturation of selenic acid with ammonia. This 

 method is undesirable because the selenic acid, itself, is difficult to 

 prepare. 



Ammonium selenate may be much more easily prepared by treat- 

 ing barium or lead selenate with a strong solution of ammonium car- 

 bonate. The barium or lead selenate is changed into insoluble 

 barium or lead carbonate and soluble ammonium selenate. Evapo- 

 ration of the filtrate from this mixture completely volatilizes the 

 excess of ammonium carbonate and precipitates the small amounts 

 of barium and lead selenates which are dissolved. Pure ammonium 

 selenate may be obtained from this filtrate by crystallization. 



The barium and lead salts of selenic acid were selected as start- 

 ing materials on account of the ease ^xith which they may be ob- 

 tained in a pure condition. Pure selenic acid is not necessarily re- 

 quired for the preparation of the barium or lead salt, for selenic 

 acid solutions containing the by-products of its formation may be 

 used. The barium or lead selenate thus formed is purified by wash- 

 ing thoroughly \wth distilled water. The solubility of lead selenate 

 was determined in order to find the loss caused by this washing. 

 Four closely agreeing determinations showed the solubility to be 

 0.006 gram in 100 cc. of water at-23° C. 



The selenic acid solution mentioned above may be easily ob- 

 tained by several well-known methods. For example: Treating a 

 nitric acid solution of selenium dioxide with an excess of potassium 

 permanganate or by adding selenium dioxide to fused sodium perox- 

 ide or sodium nitrate. 



1 From a thesis to be submitted to the Faculty of Indiana University, for the 

 degree of Master of Arts, by Roy S. Bonsib, 1011. 



' Gmelin-Kraut, Hondduch (old edition); Dammor, TIamlhuch ; Ladenbnrg. 

 Handivorlerl)ncli der Ghemie. 



