Volume 4, Slice 1 Part 2 (2/2)

A certain amount of bis.m.u.th sulphate is always formed during the calcination; this is subsequently reduced to the sulphide and ultimately to the metal in the fusion. Calcination in reverberatory furnaces and a subsequent smelting in the same type of furnace with the addition of about 3% of coal, lime, soda and fluorspar, has been adopted for treating the Bolivian ores, which generally contain the sulphides of bis.m.u.th, copper, iron, antimony, lead and a little silver. The lowest layer of the molten ma.s.s is princ.i.p.ally metallic bis.m.u.th, the succeeding layers are a bis.m.u.th copper matte, which is subsequently worked up, and a slag. Ores containing the oxide and carbonate are treated either by smelting with carbon or by a wet process.

In the wet process the ores, in which the bis.m.u.th is present as oxide or carbonate, are dissolved out with hydrochloric acid, or, if the bis.m.u.th is to be extracted from a matte or alloy, the solvent employed is _aqua regia_ or strong sulphuric acid. The solution of metallic chlorides or sulphates so obtained is precipitated by iron, the metallic bis.m.u.th filtered, washed with water, pressed in canvas bags, and finally fused in graphite crucibles, the surface being protected by a layer of charcoal. Another process consists in adding water to the solution and so precipitating the bis.m.u.th as oxychloride, which is then converted into the metal.

The crude metal obtained by the preceding processes is generally contaminated by a.r.s.enic, sulphur, iron, nickel, cobalt and antimony, and sometimes with silver or gold. A dry method of purification consists in a liquation on a hearth of peculiar construction, which occasions the separation of the unreduced bis.m.u.th sulphide and the bulk of the other impurities. A better process is to remelt the metal in crucibles with the addition of certain refining agents. The details of this process vary very considerably, being conditioned by the composition of the impure metal and the practice of particular works.

The wet refining process is more tedious and expensive, and is only exceptionally employed, as in the case of preparing the pure metal or its salts for pharmaceutical or chemical purposes. The basic nitrate is the salt generally prepared, and, in general outline, the process consists in dissolving the metal in nitric acid, adding water to the solution, boiling the precipitated basic nitrate with an alkali to remove the a.r.s.enic and lead, dissolving the residue in nitric acid, and reprecipitating as basic nitrate with water. J.F.W. Hampe prepared chemically pure bis.m.u.th by fusing the metal with sodium carbonate and sulphur, dissolving the bis.m.u.th sulphide so formed in nitric acid, precipitating the bis.m.u.th as the basic nitrate, re-dissolving this salt in nitric acid, and then precipitating with ammonia. The bis.m.u.th hydroxide so obtained is finally reduced by hydrogen.

_Properties._--Bis.m.u.th is a very brittle metal with a white crystalline fracture and a characteristic reddish-white colour. It crystallizes in rhombohedra belonging to the hexagonal system, having interfacial angles of 87 40'. According to G.W.A. Kahlbaum, Roth and Siedler (_Ziet. Anorg. Chem. 29_, p. 294), its specific gravity is 9.78143; Roberts and Wrightson give the specific gravity of solid bis.m.u.th as 9.82, and of molten bis.m.u.th as 10.035. It therefore expands on solidification; and as it retains this property in a number of alloys, the metal receives extensive application in forming type-metals. Its melting-point is variously given as 268.3 (F.

Rudberg and A.D. von Riemsdijk) and 270.5 (C.C. Person); commercial bis.m.u.th melts at 260 (Ledebur), and electrolytic bis.m.u.th at 264 (Cla.s.sen). It vaporizes in a vacuum at 292, and its boiling-point, under atmospheric pressure, is between 1090 and 1450 (T. Carnelley and W.C. Williams). Regnault determined its specific heat between 0 and 100 to be 0.0308; Kahlbaum, Roth and Siedler (_loc. cit._) give the value 0.03055. Its thermal conductivity is the lowest of all metals, being 18 as compared with silver as 1000; its coefficient of expansion between 0 and 100 is 0.001341. Its electrical conductivity is approximately 1.2, silver at 0 being taken as 100; it is the most diamagnetic substance known, and its thermoelectric properties render it especially valuable for the construction of thermopiles.

The metal oxidizes very slowly in dry air at ordinary temperatures, but somewhat more rapidly in moist air or when heated. In the last case it becomes coated with a greyish-black layer of an oxide (dioxide (?)), at a red heat the layer consists of the trioxide (Bi2O3); and is yellow or green in the case of pure bis.m.u.th, and violet or blue if impure; at a bright red heat it burns with a bluish flame to the trioxide. Bis.m.u.th combines directly with the halogens, and the elements of the sulphur group. It readily dissolves in nitric acid, _aqua regia_ and hot sulphuric acid, but tardily in hot hydrochloric acid. It is precipitated as the metal from solutions of its salts by the metals of the alkalis and alkaline earths, zinc, iron, copper, &c.

In its chemical affinities it resembles a.r.s.enic and antimony; an important distinction is that it forms no hydrogen compound a.n.a.logous to arsine and stibine.

_Alloys_.--Bis.m.u.th readily forms alloys with other metals. Treated with sodammonium it yields a bluish-black ma.s.s, BiNa3, which takes fire in the air and decomposes water. A brittle pota.s.sium alloy of silver-white colour and lamellar fracture is obtained by calcining 20 parts of bis.m.u.th with 16 of cream of tartar at a strong red heat. When present in other metals, even in very small quant.i.ty, bis.m.u.th renders them brittle and impairs their electrical conductivity. With mercury it forms amalgams. Bis.m.u.th is a component of many ternary alloys characterized by their low fusibility and expansion in solidification; many of them are used in the arts (see FUSIBLE METAL).

_Compounds_.--Bis.m.u.th forms four oxides, of which the trioxide, Bi2O3, is the most important. This compound occurs in nature as bis.m.u.th ochre, and may be prepared artificially by oxidizing the metal at a red heat, or by heating the carbonate, nitrate or hydrate. Thus obtained it is a yellow powder, soluble in the mineral acids to form soluble salts, which are readily precipitated as basic salts when the solution is diluted. It melts to a reddish-brown liquid, which solidifies to a yellow crystalline ma.s.s on cooling. The Hydrate, Bi(OH)3, is obtained as a white powder by adding potash to a solution of a bis.m.u.th salt. Bis.m.u.th dioxide, BiO or Bi2O2, is said to be formed by the limited oxidation of the metal, and as a brown precipitate by adding mixed solutions of bis.m.u.th and stannous chlorides to a solution of caustic potash. Bis.m.u.th tetroxide, Bi2O4, sometimes termed bis.m.u.th bism.u.t.h.ate, is obtained by melting bis.m.u.th trioxide with potash, or by igniting bis.m.u.th trioxide with potash and pota.s.sium chlorate. It is also formed by oxidizing bis.m.u.th trioxide suspended in caustic potash with chlorine, the pentoxide being formed simultaneously; oxidation and pota.s.sium ferricyanide simply gives the tetroxide (Hauser and Vanino, _Zeit. Anorg. Chem_., 1904, 39, p. 381). The hydrate, Bi2O42H2O, is also known. Bis.m.u.th pentoxide, Bi2C5, is obtained by heating bis.m.u.thic acid, HBiO3, to 130C.; this acid (in the form of its salts) being the product of the continued oxidation of an alkaline solution of bis.m.u.th trioxide.

Bis.m.u.th forms two chlorides: BiCl2 and BiCl3. The dichloride, BiCl2, is obtained as a brown crystalline powder by fusing the metal with the trichloride, or in a current of chlorine, or by heating the metal with calomel to 250. Water decomposes it to metallic bis.m.u.th and the oxychloride, BiOCl. Bis.m.u.th trichloride, BiCl3, was obtained by Robert Boyle by heating the metal with corrosive sublimate. It is the final product of burning bis.m.u.th in an excess of chlorine. It is a white substance, melting at 225-230 and boiling at 435-441. With excess of water, it gives a white precipitate of the oxychloride, BiOCl.

Bis.m.u.th trichloride forms double compounds with hydrochloric acid, the chlorides of the alkaline metals, ammonia, nitric oxide and nitrosyl chloride. _Bis.m.u.th trifluoride_, BiF3, a white powder, _bis.m.u.th tribromide_, BiBr3, golden yellow crystals, _bis.m.u.th iodide_, BiI3, greyish-black crystals, are also known. These compounds closely resemble the trichloride in their methods of preparation and their properties, forming oxyhaloids with water, and double compounds with ammonia, &c.

_Carbonates_.--The basic carbonate, 2(BiO)2CO3H2O, obtained as a white precipitate when an alkaline carbonate is added to a solution of bis.m.u.th nitrate, is employed in medicine. Another basic carbonate, 3(BiO)2CO32Bi(OH)33H2O, const.i.tutes the mineral bis.m.u.t.i.te.

_Nitrates_.--The normal nitrate, Bi(NO3)35H2O, 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 const.i.tutes the ”magistery of bis.m.u.th” or ”subnitrate of bis.m.u.th” of pharmacy, and under the name of pearl white, _blanc d'Espagne_ or _blanc de fard_ has long been used as a cosmetic.

_Sulphides_.--Bis.m.u.th 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, Bi2S22H2O, is obtained by pa.s.sing sulphuretted hydrogen into a solution of bis.m.u.th nitrate and stannous chloride. Bis.m.u.th disulphide is a grey metallic substance, which is decomposed by hydrochloric acid with the separation of metallic bis.m.u.th and the formation of bis.m.u.th trichloride. Bis.m.u.th trisulphide, Bi2S3, const.i.tutes the mineral bis.m.u.thite, and may be prepared by direct union of its const.i.tuents, or as a brown precipitate by pa.s.sing sulphuretted hydrogen into a solution of a bis.m.u.th salt. It is easily soluble in nitric acid. When heated to 200 it a.s.sumes the crystalline form of bis.m.u.thite. Bis.m.u.th forms several oxysulphides: Bi4O3S const.i.tutes the mineral karelinite found at the Zavodinski mine in the Altai; Bi6O3S4 and Bi2O3S have been prepared artificially. Bis.m.u.th also forms the sulphohaloids, BiSCl, BiSBr, BiSI, a.n.a.logous to the oyxhaloids.

Bis.m.u.th 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.

Bis.m.u.th forms compounds similar to the trisulphide with the elements selenium and tellurium. The tritelluride const.i.tutes the mineral tetradymite, Bi2Te3.

_a.n.a.lysis_.--Traces of bis.m.u.th may be detected by treating the solution with excess of tartaric acid, potash and stannous chloride, a precipitate or dark coloration of bis.m.u.th oxide being formed even when only one part of bis.m.u.th is present in 20,000 of water. The blackish brown sulphide precipitated from bis.m.u.th 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 quant.i.tative 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 bis.m.u.th 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 bis.m.u.th 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.

BIs.m.u.tHITE, a somewhat rare mineral, consisting of bis.m.u.th 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 ma.s.ses 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. Bis.m.u.thite occurs at several localities in Cornwall and Bolivia, often in a.s.sociation with native bis.m.u.th and tin-ores. Other localities are known; for instance, Brandy Gill in Caldbeck Fells, c.u.mberland, where with molybdenite and apat.i.te it is embedded in white quartz. The mineral was known to A. Cronstedt in 1758, and was named bis.m.u.thine by F.S. Beudant in 1832. This name, which is also used in the forms bis.m.u.thite and bis.m.u.thinite, is rather unfortunate, since it is readily confused with bismite (bis.m.u.th oxide) and bis.m.u.t.i.te (basic bis.m.u.th carbonate), especially as the latter has also been used in the form bis.m.u.thite. The name bis.m.u.th-glance or bis.m.u.tholamprite for the species under consideration is free from this objection. (L. J. S.)

BISMYA, a group of ruin mounds, about 1 m. long and m. wide, consisting of a number of low ridges, nowhere exceeding 40 ft. in height, lying in the Jezireh, somewhat nearer to the Tigris than the Euphrates, about a day's journey to the south-east of Nippur, a little below 32 N. and about 45 40' E. Excavations conducted here for six months, from Christmas of 1903 to June 1904, for the university of Chicago, by Dr Edgar J. Banks, proved that these mounds covered the site of the ancient city of Adab (Ud-Nun), hitherto known only from a brief mention of its name in the introduction to the Khammurabi code (c. 2250 B.C.). The city was divided into two parts by a ca.n.a.l, on an island in which stood the temple, E-mach, with a _ziggurat_, or stage tower. It was evidently once a city of considerable importance, but deserted at a very early period, since the ruins found close to the surface of the mounds belong to Dungi and Ur Gur, kings of Ur in the earlier part of the third millennium B.C. Immediately below these, as at Nippur, were found the remains of Naram-Sin and Sar-gon, c. 3000 B.C. Below these there were still 35 ft. of stratified remains, const.i.tuting seven-eighths of the total depth of the ruins. Besides the remains of buildings, walls, graves, &c., Dr Banks discovered a large number of inscribed clay tablets of a very early period, bronze and stone tablets, bronze implements and the like. But the two most notable discoveries were a complete statue in white marble, apparently the most ancient yet found in Babylonia (now in the museum in Constantinople), bearing the inscription--”E-mach, King Da-udu, King of Ud-Nun”; and a temple refuse heap, consisting of great quant.i.ties of fragments of vases in marble, alabaster, onyx, porphyry and granite, some of which were inscribed, and others engraved and inlaid with ivory and precious stones.

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