Bismuth Monosulphide, BiS

Bismuth Monosulphide, BiS, is stated to be formed when hydrogen sulphide acts upon bismuth monoxide, either directly or in a solution containing stannous compounds and tartaric acid; also by heating a mixture of bismuth hydroxide with an aqueous solution of potassium cyanide and thiocyanate. Crystals have been obtained by melting together bismuth and sulphur and cooling the melt quickly. These crystals are stated by some to be bismuth monosulphide and by others to be a mixture of trisulphide and metal.

When prepared in the dry way, the product is a slate-grey powder with a density of 7.6 to 7.8 at 20° C.; prepared in the wet way it is a black, dull powder, which can be obtained in the anhydrous form by drying over sulphuric acid. When dried over a water-bath some water is still retained.

The monosulphide is moderately stable in air, but it yields sulphur dioxide when heated in air. It is attacked by hydrochloric acid, bismuth trichloride being formed in solution and spongy metallic bismuth precipitated. It is decomposed into metal and trisulphide when heated to red heat in dry carbon dioxide.