Bismuth Thiochloride, BiSCl

Bismuth Thiochloride, BiSCl, was first obtained by Schneider by heating bismuth ammonium chloride either with sulphur or in a current of hydrogen sulphide. It has also been obtained by heating bismuth trichloride with sulphur, by the action of hydrogen sulphide on bismuth trichloride at the ordinary temperature, or at temperatures below red heat,

BiCl₃ + H₂S = BiSCl + 2HCl

and by the action of chlorine on bismuth trisulphide at temperatures below red heat:

Bi₂S₃ + 6Cl = BiSCl + BiCl₃ + S₂Cl₂

The thiochloride crystallises in dark grey, metallic needles, which appear ruby-coloured under the microscope. It is decomposed on heating in air, bismuth trichloride and sulphur dioxide volatilising, leaving a residue of oxychloride and basic sulphate; on heating in a current of carbon dioxide, bismuth trichloride volatilises, leaving a residue of bismuth trisulphide; in a current of hydrogen, bismuth trichloride, hydrogen chloride and hydrogen sulphide are volatilised, leaving bismuth contaminated with a little chlorine and sulphur. By strongly heating in a current of hydrogen sulphide it is converted into bismuth trisulphide. It is not attacked by water or dilute mineral acids, even on boiling; but it is decomposed by concentrated acids, hydrogen sulphide being liberated by hydrochloric acid, and sulphur by nitric acid. Potassium hydroxide (and weaker bases more slowly), decomposes it with liberation of chlorine.