Tungsten trisulphide

Ammonium sulphide solution no precipitate, but if the solution is afterwards acidified with dilute hydrochloric acid, a brown precipitate of tungsten trisulphide, WS3, is produced. The precipitate dissolves in ammonium sulphide solution forming a thiotungstate ion, WS4. ... 

Solutions of tungstates containing ammonium sulphide yield with hydrochloric acid a brown j recipitate of tungsten trisulphide. The addition of zinc chloride to a tungstate solution produces a yellow precipitate which becomes blue on warming with dilute hydrochloric or sulphuric acid. When excess of hydrochloric acid is added to a solution of alkali tungstate and the mixture reduced by means of zinc, brilliant colours, from red to blue, are produced if phosphoric acid is used, a fine blue precqntate results. 

Colloidal Tungsten Trisulphide.—It W as obser% ed by Berzelius that when the freshly precipitated trisulphide is washed with water, it dissolves to a slight extent, forming a yellow solution. If the precipitate is boiled with pure water it dissolves in considerable quantity, yielding a brownish-yellow solution. Winssinger obtained a dark brown solution of tungsten trisulphide by adding to a solution of sodium thiosulphate a little more dilute hydrochloric acid than was... 

The compounds are generally yellow to yellowisli brown in colour and yield well-defined crystals which are soluble in water. The solution, on additioir of an acid, deposits tungsten trisulphide. 

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