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INDIANA UNIVEKSITY 



EXPERIMEN TAL MANIPULATION. 



Extraction of Metallic Selenium'^ Five hundred grams of Hue 

 dust was digested with two hundred grams of potassium cyanide 

 and six hundred cubic centimeters of distilled water. The sulphur 

 and selenium dissolved as potassium sulphocyanate (KCNS) and 

 potassium selenocyanate (KCNSe). ' Some of the tellurium formed 

 potassium telluride, which, however, readily decomposed by the 

 oxygen of the air with the precipitation of tellurium. To make 

 sure that the tellurium was completely eliminated, air was blown 

 through the filtrate. Upon the addition of hydrochloric acid, sele- 

 nocyanic acid (HCNSe) was formed, which, being unstable, broke 

 down into hydrocyanic acid and selenium, a red precipitate. 

 The sulphocyanic acid (HONS) is stable and remained un decom- 

 posed. The mixture was filtered and the residue of selenium 

 washed well with distilled water. The residue was heated about 

 three or four hours on the hot plate. The selenium was changed 

 to the stable modification and became black, hard and brittle, which 

 greatly facilitated filtration and washing. 



Preparation of Selenic Acid. The metallic selenium was tritu- 

 rated with distilled water until the last traces of hydrocyanic acid 

 were removed. After thus being thoroughly washed the selenium 

 was treated with concentrated nitric acid and heated on the water- 

 bath until it was completely dissolved. This solution was diluted 

 mth distilled water and filtered. The filtrate was treated with a 

 concentrated solution of potassium permanganate until it assumed 

 a permanent pink color, and then warmed on a water-bath for 

 twenty or thirty minutes. The permanganate oxidized the seleni- 

 ous acid to selenic acid with the precipitation of manganese diox- 

 ide. This managanese dioxide was removed by filtration. The 

 selenic acid thus formed was in the filtrate. The pink color caused 

 by the slight excess of permanganate was discharged by the addi- 

 tion of a few drops of hydrogen peroxide. 



Barium nitrate was then added to the above filtrate and the 

 mixture allowed to stand over night and filtered. The residue was 

 washed free from barium nitrate with distilled water. The barium 

 selenate thus formed was treated with a concentrated solution of 

 ''ammonium carbonate" and allowed to stand twenty-four hours, 

 with occasional stirring. Any sulphur which might not have been 

 eliminated by the potassium cyanide treatment would remain in 

 the residue as insoluble barium sulphate. The mixture was filtered 

 and the residue thoroughly washed with distilled water. The fil- 



0 Nilson, Benchte der Dcutschen Chemischen Oesellschaft, VII, 1719. 



