368 UNIVERSITY OF VIRGINIA PUBLICATIONS 



hydroxide. The precipitate, after washing, was boiled with successive 

 portions of ammonium carbonate (about half hour each). The filtrate 

 was evaporated to dryness and heated gently, to drive off the excess of 

 ammonium carbonate. The ammonium vanadate thus obtained was 

 dissolved in water and transformed into sodium vanadate by the addition 

 of sodium hydroxide; the necessary quantity being calculated from the 

 known vanadium content of the ore used. This was evaporated until 

 sodium vanadate crystals began to appear, and then diluted to a con- 

 venient strength. The vanadium strength was determined by acidifying 

 with sulphuric acid, reducing with sulphur dioxide, and titrating with 

 potassium permanganate (Bull. U. S. Geological Survey, No. 176). 



EXPERIMENTAL DATA. 



The qualitative test for the presence of vanadium in all the following 

 experiments was the formation of ammonium sulpho-vanadate, the color 

 of a solution varying from pink to cherry-red according to the quantity 

 of vanadium present. In this test the solution is acidified with sulphuric 

 acid, made strongly alkaline with ammonia, and hydrogen sulphide gas 

 passed into it. 



The precipitatio7i of vanadium sulphide from water solutions of sodium vana- 

 date by hydrogen sulphide and soluble sulphides. 



' 1 . The reaction between hydrogen sadphide and sodium vanadate was 

 illustrated by diluting 5 cc. of the stock sodium vanadate solution to 50 cc, 

 and passing hydrogen sulphide into it. The solution turned yellow almost 

 immediately and became turbid in ten minutes. After passing the gas 

 for about an hour the precipitation was almost complete. A gelatinous, 

 dark brown precipitate settled out and the solution was colored cherry-red 

 through the secondary action between vana'dium sulphide and sodium 

 sulphide. The precipitate was found to contain 63.1 per cent sulphur 

 and 37.2 per cent vanadium, vanadium pentasulphide contains 61.1 per 

 cent S and 38.9 per cent V. 



2. The influence of carbon dioxide on the precipitation of vanadium, 

 sulphide. The influence of strong acids in bringing about the precipita- 

 tion of vanadium sulphide from solutions of sodium vanadate is known, 

 but it was necessary to determine the effect of carbon dioxide. The water 

 used to dilute the stock solution of sodium vanadate was saturated with 

 carbon dioxide and the experiment conducted as in (1) above. Except 

 that the reaction was a little quicker it was in all respects like that de- 

 scribed in (1). 



