Barium Sulphide, BaS

Barium Sulphide, BaS, may be formed by the action of sulphuretted hydrogen on the hydroxide at 85° C., with subsequent heating in hydrogen at 200° C., on barium carbonate at red heat, or, finally, on the sulphate at 1200° C., in all three cases cooling in hydrogen. It may also be obtained by the action of carbon disulphide on barium carbonate.

BaCO₃ + 2CS₂ = BaS + 3CO + 3S.

Polysulphides are always formed in this case, but may be reduced to the sulphide by heating in a current of hydrogen.

The method employed for the technical production of barium sulphide is the reduction of barytes by carbon or reducing gases. The sulphide thus formed is the starting-point for the production of all other commercial barium compounds. Laboratory tests indicate that a high temperature for a short time produces a more satisfactory yield than a low temperature with prolonged heating. Good results are obtained with 15-16 per cent, of carbon in muffles at 1000°-1100° C.

Barium sulphide as usually obtained is a greyish white amorphous powder, but after fusion in the electric furnace it forms cubic crystals of density 4.25. The heat of formation is 105.2 Cal.

On exposure to air it turns yellow. It is not reduced by hydrogen at 1200° C., but is readily attacked by halogens and is completely transformed into the sulphate by oxygen at high temperatures. It is attacked by gaseous acids in the cold. Carbon decomposes it at the temperature of the electric arc forming the carbide. Oxidising agents react with incandescence. When it is heated in water vapour, hydrogen and barium sulphate are formed. It is attacked by concentrated nitric acid with incandescence, and reacts with phosphorus trichloride forming barium chloride and phosphorus trisulphide. On heating with an equal quantity of barium chloride it forms an opaque red mass. In general, the crystallised sulphide is less readily attacked than the amorphous.

Barium sulphide is readily soluble in water with hydrolysis, forming the hydroxide and hydrosulphide. The heat of solution is 7.3 Cal. If the aqueous solution be concentrated in vacuo in the presence of free sulphur, a hydrated sulphide, BaS.6H₂O, crystallising in hexagonal plates, is obtained. When slowly heated it loses water between 100° and 300° C., and then sulphuretted hydrogen and sulphur.

It is insoluble in alcohol.

A dark red double barium nickel sulphide, BaS.4NiS has been obtained.

Barium sulphide, under the name of Bolognian phosphorus,11 was the first of the alkaline earth sulphides in which the property of phosphorescence was observed. The conditions affecting the phosphorescence of these sulphides have already been discussed under calcium sulphide.