Carbonates.—The basic carbonate, 2(BiO)2CO3·H2O, obtained as a white precipitate when an alkaline carbonate is added to a solution of bismuth nitrate, is employed in medicine. Another basic carbonate, 3(BiO)2CO3·2Bi(OH)3·3H2O, constitutes the mineral bismutite.
Nitrates.—The normal nitrate, Bi(NO3)3·5H2O, is obtained in large transparent asymmetric prisms by evaporating a solution of the metal in nitric acid. The action of water on this solution produces a crystalline precipitate of basic nitrate, probably Bi(OH)2NO3, though it varies with the amount of water employed. This precipitate constitutes the “magistery of bismuth” or “subnitrate of bismuth” of pharmacy, and under the name of pearl white, blanc d’Espagne or blanc de fard has long been used as a cosmetic.
Sulphides.—Bismuth combines directly with sulphur to form a, disulphide, Bi2S2, and a trisulphide, Bi2S3, the latter compound being formed when the sulphur is in excess. A hydrated disulphide, Bi2S2·2H2O, is obtained by passing sulphuretted hydrogen into a solution of bismuth nitrate and stannous chloride. Bismuth disulphide is a grey metallic substance, which is decomposed by hydrochloric acid with the separation of metallic bismuth and the formation of bismuth trichloride. Bismuth trisulphide, Bi2S3, constitutes the mineral bismuthite, and may be prepared by direct union of its constituents, or as a brown precipitate by passing sulphuretted hydrogen into a solution of a bismuth salt. It is easily soluble in nitric acid. When heated to 200° it assumes the crystalline form of bismuthite. Bismuth forms several oxysulphides: Bi4O3S constitutes the mineral karelinite found at the Zavodinski mine in the Altai; Bi6O3S4 and Bi2O3S have been prepared artificially. Bismuth also forms the sulphohaloids, BiSCl, BiSBr, BiSI, analogous to the oyxhaloids.
Bismuth sulphate, Bi2(SO4)3, is obtained as a white powder by dissolving the metal or sulphide in concentrated sulphuric acid. Water decomposes it, giving a basic salt, Bi2(SO4)(OH)4, which on heating gives (BiO)2SO4. Other basic salts are known.
Bismuth forms compounds similar to the trisulphide with the elements selenium and tellurium. The tritelluride constitutes the mineral tetradymite, Bi2Te3.
Analysis.—Traces of bismuth may be detected by treating the solution with excess of tartaric acid, potash and stannous chloride, a precipitate or dark coloration of bismuth oxide being formed even when only one part of bismuth is present in 20,000 of water. The blackish brown sulphide precipitated from bismuth salts by sulphuretted hydrogen is insoluble in ammonium sulphide, but is readily dissolved by nitric acid. The metal can be reduced by magnesium, zinc, cadmium, iron, tin, copper and substances like hypophosphorous acid from acid solutions or from alkaline ones by formaldehyde. In quantitative estimations it is generally weighed as oxide, after precipitation as sulphide or carbonate, or in the metallic form, reduced as above.
Pharmacology.—The salts of bismuth are feebly antiseptic. Taken internally the subnitrate, coming into contact with water, tends to decompose, gradually liberating nitric acid, one of the most powerful antiseptics. The physical properties of the powder also give it a mild astringent action. There are no remote actions.
Therapeutics.—The subnitrate of bismuth is invaluable in certain cases of dyspepsia, and still more notably so in diarrhoea. It owes its value to the decomposition described above, by means of which a powerful antiseptic action is safely and continuously exerted. There is hardly a safer drug. It may be given in drachm doses with impunity. It colours the faeces black owing to the formation of sulphide.
BISMUTHITE, a somewhat rare mineral, consisting of bismuth trisulphide, Bi2S3. It crystallizes in the orthorhombic system and is isomorphous with stibnite (Sb2S3), which it closely resembles in appearance. It forms loose interlacing aggregates of acicular crystals without terminal faces (only in a single instance has a terminated crystal been observed), or as masses with a foliated or fibrous structure. An important character is the perfect cleavage in one direction parallel to the length of the needles. The colour is lead-grey inclining to tin-white and often with a yellowish or iridescent tarnish. The hardness is 2; specific gravity 6.4-6.5. Bismuthite occurs at several localities in Cornwall and Bolivia, often in association with native bismuth and tin-ores. Other localities are known; for instance, Brandy Gill in Caldbeck Fells, Cumberland, where with molybdenite and apatite it is embedded in white quartz. The mineral was known to A. Cronstedt in 1758, and was named bismuthine by F.S. Beudant in 1832. This name, which is also used in the forms bismuthite and bismuthinite, is rather unfortunate, since it is readily confused with bismite (bismuth oxide) and bismutite (basic bismuth carbonate), especially as the latter has also been used in the form bismuthite. The name bismuth-glance or bismutholamprite for the species under consideration is free from this objection.