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Bismuth Trisulphide, Bi2S3

Bismuth Trisulphide, or Bismuth Sesquisulphide, Bi2S3, is found free in nature as bismuthinite, or bismuth glance. It may be made artificially in a variety of ways, such as by melting together bismuth and sulphur, by subjecting a mixture of bismuth and sulphur in powder form to high pressure, by precipitation from a solution of a bismuth salt by hydrogen sulphide or alkali sulphide, by the action of sodium thiosulphate on a neutral solution of a bismuth salt, or by heating bismuth trioxide with potassium thiocyanate. In addition, it may be prepared from bismuth halides. It may be obtained in the crystalline form by the interaction of the vapour of bismuth trichloride with hydrogen sulphide.

Bismuth trisulphide crystallises in the rhombic system, although other crystal forms have been described. The crystal elements of the mineral bismuthinite are:

a:b:c = 0.9862:1:1.0493

By X-ray examination it is deduced that the unit cell contains four molecules. The parameters have been determined to be:

a = 11.13 A., b = 11.27 A., c = 3.97 A.

giving as axial ratios:

a:b:c = 0.9876:1:0.3523

As usually prepared the sulphide is a grey or black powder, which can be converted into a microcrystalline mass by heat, by pressure, or by heating in a solution of alkali sulphide. It has a density of 7.00 to 7.81; that of bismuthinite is 7.4 at 20° C.

The melting point is 718° C. By heating strongly in an atmosphere of carbon dioxide it can be volatilised in small quantities without decomposition.

The compressibility of bismuthinite has been measured. The heat capacity is 0.06 gram-calorie per gram. When examined with light from an electric arc, bismuth trisulphide shows very great photoconductivity (i.e. an alteration in electrical conductivity on exposure to light).

Bismuth trisulphide is only very slightly soluble in water, the solubility, measured by a conductivity method, being 0.35×10-6 mole per litre. It is slightly soluble in dilute hydrochloric acid, the solubility increasing rapidly with rise of temperature. With dilute acid hydrogen sulphide is evolved at about 70° C., but the temperature of evolution is dependent on the concentration of the acid. The trisulphide is readily soluble in concentrated hydrochloric acid. It is readily attacked by dilute nitric acid, sulphur being precipitated. It is decomposed by heating with sulphuric acid, sulphur dioxide being evolved. It is slightly soluble in sulphurous acid, but insoluble in an aqueous solution of sodium sulphite. It is insoluble in aqueous solutions of alkali hydroxides, but is soluble in solutions of alkali sulphides, the solubility increasing rapidly with increase in concentration of the alkali sulphide. From the accompanying table it will be seen that this solubility is increased by the presence of alkali hydroxides. Bismuth trisulphide is, however, insoluble in alkali hydrosulphides; this is demonstrated by the fact that when a solution of the trisulphide in a solution of alkali sulphide is saturated with hydrogen sulphide, the trisulphide is completely reprecipitated. The trisulphide is also insoluble in solutions of ammonium sulphide. In addition, the solubility in solutions of sodium disulphide is very much less than in corresponding solutions of sodium monosulphide. It is probable, therefore, that the solubility of bismuth trisulphide in solutions of alkali sulphides is due to the formation of complex anions with the sulphide ion, S-2, and that complex anions with either the hydrosulphide ion, SH-, or the hydroxyl ion, OH-, are not formed.

Bismuth does not appear to form a hydrosulphide.

Solubility of Bismuth trisulphide in aqueous solution of alkali sulphides at 25° C

Concentration of Aqueous Solutions used as Solvents (Moles per litre)Solubility of Bismuth Trisulphide (Grams per 100 c.c. Solution).
Sodium Monosulphide.Sodium Hydroxide.Potassium Monosulphide.Potassium Hydroxide.
0.5. . .. . .. . .0.0040
1.0. . .. . .. . .0.0238
1.5. . .. . .. . .0.1023
0.51.0. . .. . .0.0185
1.01.0. . .. . .0.0838
. . .. . .0.5. . .0.0042
. . .. . .1.0. . .0.0337
. . .. . .1.5. . .0.0639
. . .. . .
. . .. . .
. . .. . .

Bismuth trisulphide is stable in air at temperatures up to 100° C.; above that temperature it begins to lose weight; sulphur is removed on melting, and on cooling crystals of bismuth can be detected in the mass; it is completely desulphurised by heating in the electric furnace. It is very slowly reduced by heating in a current of hydrogen, and the conditions of equilibrium between bismuth trisulphide and hydrogen have been studied between 400° and 1000° C. The effect of the presence of alkaline earth sulphides upon the equilibrium

Bi2S3 + 3H2 ⇔ 2Bi + 3H2S

has also been studied. Calcium sulphide appears to be without effect, but the presence of sulphides of strontium and barium retards the decomposition of bismuth trisulphide.

The trisulphide is oxidised when heated in air or oxygen; it is difficult, however, to eliminate all the sulphur unless the heating is carried out in vacuo. The presence of excess of bismuth trioxide also facilitates the removal of sulphur. The calculated heat of oxidation of bismuth trisulphide is:

Bi2S3 + 4.5O2 = Bi2O3 + 3SO2 + 278,500 calories

The trisulphide, when red hot, will decompose steam; the products of the reaction are bismuth, bismuth trioxide and hydrogen sulphide. No reaction occurs on heating with ammonium chloride. The trisulphide is reduced by phosphine to metallic bismuth; phosphorus and hydrogen sulphide are also formed by this reaction.

Reduction to the metal occurs by heating on a charcoal block, the reduction being accelerated by the presence of sodium carbonate. On passing a mixture of air and carbon tetrachloride over heated bismuth trisulphide, bismuth trichloride volatilises.

When heated with sulphur dioxide, bismuth sulphate and metallic bismuth are formed.

The sulphide does not react with a solution of potassium cyanide, but it is completely reduced to metal when heated in the dry state with that salt.

Freshly precipitated bismuth trisulphide reacts when boiled with an aqueous solution of cuprous chloride and sodium chloride to form bismuth trichloride and cuprous sulphide; the trichloride is subsequently hydrolysed. When boiled with a dilute aqueous solution of cupric chloride, cupric sulphide and bismuth trichloride are formed in a similar manner. In each case the bismuth trichloride may be partially hydrolysed. An investigation into the action of solutions of various metallic salts upon various metallic sulphides - including bismuth trisulphide - indicated that the affinity of bismuth for sulphur is greater than that of any other element in the fifth group of the Periodic Classification, and is also greater than that of lead.

By treatment of bismuth trisulphide with a cold, saturated, ammoniacal solution of mercuric cyanide, bismuth cyanide and mercuric sulphide are formed; the latter is volatilised on heating, and the former decomposed, the resultant bismuth metal being oxidised to trioxide by heating in air.

The trisulphide reacts with ferric chloride in a sealed tube; bismuth trichloride and ferrous chloride are formed and some sulphur is set free. With ferric sulphate a reaction takes place according to the equation

Bi2S3 + 3Fe2(SO4)3 = Bi2(SO4)3 + 6FeSO4 + 3S

The ferrous sulphate thus formed can be estimated by titration with potassium permanganate and the method used for the volumetric estimation of the trisulphide.

The following heats of formation from solid bismuth and sulphur vapour, and from solid bismuth and solid (rhombic) sulphur, have been calculated:

2Bi (solid) + 1½S2 (vapour) = Bi2S3 + 111,540 calories

2Bi (solid) + 3S(rhombic) = Bi2S3 + 67,200 calories

Colloidal bismuth trisulphide may be obtained by passing hydrogen sulphide through a very weak solution of bismuth nitrate, acidified with acetic acid, and dialysing.


Several compounds of bismuth trisulphide with other metallic sulphides have been described, and certain minerals which contain bismuth sulphide in association with sulphides of copper, silver or lead are stated to be complex compounds of this type; some of these have been made artificially. By melting together metallic bismuth, sulphur and alkali carbonate, Schneider claimed to have produced complex sulphides with alkalis, but attempts to repeat this preparation proved unsuccessful. On the other hand, reactions have been described between bismuth trisulphide and sulphides of the alkaline earth metals which have resulted in the formation of the thiobismuthites SrBi2S4 and BaBi2S4. The corresponding compound of calcium has not been obtained. The calculated heat of formation of the strontium compound is 4173 gram-calories, that of the barium compound being 13,380 gram-calories per mole.

Freezing Point Curves of Bi, S, Sb, Te, Ag, Se
Freezing Point Curves of the Systems Bi2S3-Sb2S3, Bi2S3-Bi2Te3, Bi2S3-Ag2Se
Thermal examinations of binary systems of bismuth trisulphide with other metallic compounds have been made, including the system with antimony trisulphide, bismuth telluride and silver selenide. The results are summarised in fig.

The ternary system bismuth-sulphur-tellurium has also been investigated, the results pointing to the existence of one ternary compound only, Bi4S3Te3 or Bi2S3.Bi2Te3. Several minerals are known containing bismuth, sulphur and tellurium, but their constitution is unknown. Oruetite, to which the formula Bi8S4Te has been ascribed, is revealed as a mixture (or solid solution) when examined by X-rays.

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