1902 Encyclopedia > Bismuth

Bismuth




BISMUTH. This metal appears to have been unknown notices. to the older metallurgical writers, it having been first noticed by Agricola, who speaks of it as a form of lead, and describes the method of separating it from its associ-ated minerals by liquation. Mathesius in his Bergpostilla, written between 1553-1562, describes it as white like pyrites, and occasionally cubical like marcasite, easily over-come by the fire when melted, and running together with the tin, which thereby is rendered brittle and unsound,— the last remark referring to its occurrence with tin ores in Saxony. It was considered by the miners as a hopeful indication of silver, and even in certain cases is said to have been transformed gradually into that metal, as por-tions of the ore which had lain for some time exposed were found afterwards to be partly or wholly changed into silver. This remark is interesting, as the same belief seems to have come up again in our own time. The name Wismuth is a miner's term, whose origin is completely lost; but Mathesius assigns it a fanciful derivation from Wisse = Wiese, a meadow, because in the mine it is found covered with flowers or incrustations of various colours, resembling a meadow covered with brilliantly coloured flowers,—an obvious confusion with the minerals known as nickel and cobalt bloom, derived from the oxidation of arsenides of nickel and cobalt, with which native bismuth is commonly associated in Saxony. It is to this association with cobalt and arsenic that must be ascribed the statements that its principal use was to produce a blue colour, and that it gave off a very poisonous furnace smoke. The chief use of the metal at that time seems to have been by pewterers, who added it to their alloy in small proportions for the purpose of rendering their wares hard and sonorous when struck.

The principal minerals containing bismuth are:—1. Ores. Native bismuth, essentially the pure metal, having all the properties described below. This, the most important ore, occurs in connection with nickel and cobalt ores at Schnee-berg, Saxony, at Wheal Sparnon in Cornwall, similarly associated, and with tin ores in the mines of the St Just district. It is also found in some quantity in Bolivia. 2. Tetradymite, or telluric bismuth, a compound in variable proportions with the isomorphous element tellurium. This contains from 60 to 80 per cent, of bismuth, 15 to 35 per cent, of tellurium, and from 3 to 5 per cent, of sulphur. It occurs usually in association with gold ores; the principal localities are Schemnitz and Retzbanya in Hungary, the gold mining district of Virginia and North Carolina, California, and other western states of America. It was also found at the Merionethshire gold mines as a rarity. 3. Bismuth silver, found at Schapbach in Baden, and near Copiapo in Chili. The mineral from the former locality contains 27 of bismuth to 15 of silver, with some lead and sulphur, and a little iron; and that from the latter 60 of silver to 10 of bismuth, the remainder being copper and arsenic. 4. Bismuthine, or bismuth glance, a sulphide of bismuth, of the composition Bi2S3, containing 81'6 per cent, bismuth and 18-4 per cent, sulphur, crystallizing in acicular rhombic prisms isomorphous with antimony glance. It occurs with tin ore at Botallack and other mines near St Just in Cornwall, and in the Saxon localities given above. 5. Bismuth ochre, an earthy oxide of bismuth, containing 90 per cent, bismuth and 10 per cent, oxygen, which is derived from the oxidation both of the native metal and of the sulphide. 6. Bismutite, a hydrated car-bonate of bismuth, containing 90 per cent, bismuth oxide, 6-56 per cent, carbonic acid, and 3-44 per cent, water, an-other product of atmospheric action upon native bismuth. It is found principally in Saxony and South Carolina. Besides the above there is also a silicate described, but this is an exceedingly rare mineral, as is also Hypochlorite, a hydrated silicate mixed with phosphate of alumina. Practi-cally the only ore is the native metal, and of late years, from the supply not keeping pace with the demand, the price has risen very considerably. The bismuth of commerce usually contains both gold and silver, often in considerable quantity, which circumstance has probably given rise to the story current about its transmutation into these metals.

Bismuth may he readily obtained in crystals by pouring it when properties, melted into a heated iron ladle, and cooling it until a crust is formed on the surface, which must then be pierced by a red-hot iron rod, and the liquid metal poured off. The solidified portion adhering to the ladle is found to be covered with hopper-shaped crystals, which are usually beautifully irised, owing to the formation of a thin film of oxide on the surface, showing the colours of thin plates. This colouring is only obtained when the metal is quite free from arsenic. It may be purified by melting with about 10 per cent, of nitre, and keeping it constantly stirred at a temperature not much above its melting point, whereby the more oxidizable metals are removed, and form a slag at the surface. Another method of purifying it from arsenic is by fusing it with from 3 to 5 per cent, of zinc, covering the surface with charcoal to prevent oxidation of the zinc, which takes off the whole of the arsenic, and is subsequently removed by treatment with hydrochloric acid, the purified bismuth remaining insoluble. When prepared by any of these processes, Bismuth is a hard, brittle metal, and the fracture is highly crystal-line and white, with a perceptible red tinge by reflected light. The crystalline form is rhombohedral, the angle of the primary rhom-bohedron being 87° 40', or very close to a cube. The specific gravity is 9'83, but when subjected to great pressure the density is reduced to 9-6. The melting point is 264° C. (507° Fahr.) (Eudberg), or 268°-3 (515°) (Eiemsdijk). Like water it may be cooled 6° or 7° C. below its freezing point; but when solidification sets in the tempera-ture rises to 480 Fahr., and continues until the mass is completely solidified. Like ice it expands about TV of its volume in solidifi-cation, a property which is communicated to its alloys, rendering them valuable for taking casts of incised or relief surfaces for reproduction, as printing-blocks by electrotype or other processes. It may be distilled by heating to a higher temperature in hydrogen. Despretz volatilized it by subjecting it to the current from 600 Bunsen elements. The spectrum of the vapour in the voltaic arc shows numerous brilliant green lines, one strong and one fainter line on the red, and a faint line on the orange field (Masson). The coefficient of expansion by heat is o801341, calorific eonducti-bility 61,' silver being 1000 (Calvert and Johnson), and specific heat 0-0305 (Kopp). The electric conductivity is 119 at 14° C, silver being 100 at 0° (Matthiesen). According to Matteuci the conductivity varies in the crystals according to the direction of the cleavages. It is the most strongly diamagnetic of all metals. Chemical The atomic weight is 208 (Schneider) or 210 (Dumas). Like properties, phosphorus and arsenic it is both triatomic and pentatomic, the latter state being represented only by a very unstable acid ; there are also several diatomic compounds, including BiBr2, BiCl3, and Bil2. The triatomic compounds are the most numerous and stable. Unlike the elements chemically similar,—phosphorus, tellurium, arsenic, antimony, &c,—it does not form a gaseous compound with hydrogen. Bismuth does not change in dry air, but in moist air it oxidizes superficially, and by long exposure may be converted into carbonate. When melted at a red heat it oxidizes, and the oxide (whose formula is Bi203), by a higher temperature, melts to a glassy substance, in which property it resembles lead, the oxide, like litharge, exerting a very corrosive action upon earthern crucibles, or substances containing silica, at a red heat. At a red-white heat it slowly decomposes water with the production of oxide. The higher oxide Bi2Oe corresponds to arsenic acid ; it is a very unstable compound, and of no practical value. An intermediate oxide is known which is generally regarded as a compound of the other two, Bi203, Bi206. Bismuth unites directly with chlorine, bromine, and iodine, and when fused with sulphur forms a sulphide of the form Bi2S3, corresponding to bismuth glance, and isomorphous with the corresponding sulphide of antimony. The same sulphide is produced when sulphuretted hydrogen is passed through a solution containing bismuth.

Salts. Bismuth is but slightly acted upon by hydrochloric or sul-
phuric acids in the cold ; but the latter dissolves it more readily when heated. The best solvent is nitric acid, which attacks it readily, producing a nitrate which crystallizes from the concentrated solution in colourless transparent crystals belonging to the triatomic system, whose composition is Bi. 3N03. 5H,0. These crystals are soluble in nitric acid, but, like all neutral salts of the metal, are decomposed by water, with the formation of.an insoluble basic nitrate and an acid liquor. These basic salts are very numerous and complex in constitution, the most important one being that represented by the formula Bi.N03.H20, which is known as pearl-white, blanc de fard. This, which is largely used as a medicine, is prepared by adding to a concentrated solution of bismuth dissolved in nitric acid from 40 to 50 times its weight of water, which precipi-tates a considerable proportion in the form of a white powder; the remainder, which is retained by the acid liquor, may be separated by neutralizing the excess of acid with ammonia, when a rather more acid salt than the first precipitate Is obtained. Under the name of pearl-white the sub-nitrate is used as a cosmetic, but it has the disadvantage of being readily blackened by sulphuretted hydrogen.

Bismuth unitei readily with other metals, the alloys being remark- Alloys, able for their ready fusibility, and by their property of expanding on solidification. An alloy with potassium is obtained by calcining 20 parts of bismuth with 16 parts of cream of tartar in a crucible, and heating the mixture to a very strong red heat. On cooling, a button of metal is found, of a silvery white colour and lamellar fracture, which fuses easily, and remains for a long time in a pasty condition before solidification ; it is brittle, can be easily powdered, and is readily decomposed by water. The alloy with sodium is obtained in a similar manner, with a sodic tartrate. With silver, gold, and metals of the platinum group, bismuth forms brittle alloys. With mercury it forms a liquid amalgam; but when equal weights of the two metals are heated together, there is a separation on cooling of octahedral crystals, which may be a solid amalgam. The copper alloy is brittle, and of a pale red colour. The ternary alloys of lead, tin, and bismuth, are the most interesting of these compounds, from their low fusibility, which is much below that of any of the components taken separately. This property was known to Sir Isaac Newton ; the alloy named after him, Newton's fusible metal, melts at 94°-5 C. (202° Fahr.) ; it contains 8 parts of bismuth, 5 of lead, and 3 of tin. Darcet's fusible metal, containing 2 of bismuth, 1 of lead, and 1 of tin, melts at 93° (199°'4 Fahr.) Another, with 5 of bismuth, 2 of tin, and 3 of lead, melts at 91°'6 (197° Fahr.) Eose's fusible metal, containing 420 parts of bismuth, 236 of lead, and 207 of tin, a composition corresponding to the formula Bi2Sn2Pb, fuses below 100° (212°), and remains pasty for a con-siderable range of temperature below that point. The expansion of this alloy by heat proceeds regularly from 0 to 35° C, but by further heating it contracts up to 55 , from which point up to 80° the rate of expansion is more rapid than at the lower temperatures. Above 80° the normal rate is resumed. The fusibility of these alloys is increased by an addition of cadmium. Thus Wood's fusible metal, containing 1 to 2 parts of cadmium, 2 of tin, 2 of lead, and 7 to 8 of bismuth, melts between 66° and 71° C. Another, described by Lipowitz, containing 8 parts of lead, 15 of bismuth, 4 of tin, and 3 of cadmium, is silvery white, and has a specific gravity of 9" 4. It softens at about 55°, and is completely liquid at a little above 60°.

Fusible alloys containing bismuth are used to some extent as safety plugs for steam boilers, as an accessory to the safety-valve,—a hole in the boiler being plugged by a disc of the metal, which in the event of the temperature of the water rising through excessive pressure is melted, and the steam passes through the aperture in the same manner as through an opened safety-valve. It is found, however, that this method is not trustworthy, owing to the liqua-tion of the more fusible components of the mass, when subjected to continued heating near but below the melting point, leaving a more refractory alloy behind. The alloy known as Britannia metal, con-sisting chiefly of tin, antimony, and copper, often contains a little bismuth.

In analysis bismuth is usually separated from solution as car- Analysis bonate by precipitation with carbonate of ammonia, which is then and separa-converted into oxide by calcination at a gentle heat, in which form tion. it is weighed and estimated. The oxide Bi203 contains 89-74 per cent, of bismuth. It is readily precipitated as sulphide by passing sulphuretted hydrogen through an acid solution, but the precipitate cannot be weighed, as it usually contains an excess of sulphur, and cannot be completely freed from water below 200°, so that it must be redissolved in nitric acid and precipitated as carbonate as above described. It may be precipitated in the metallic state by zinc, cadmium, copper, iron, or tin. A plate of copper introduced into a boiling solution of a bismuth salt, even when very weak, is readily covered with a coating of the reduced metal of a steel-gray colour.

Bismuth may be employed instead of lead for the assay of gold and silver by cupellation, as the melted oxide is absorbed by bone ash in exactly the same manner as litharge.

The separation of bismuth from solutions in which it is associated with silver, copper, mercury, cadmium, and lead, may be effected by cyanide of potassium ; by digesting the solution with an excess of this reagent the cyanides of bismuth and lead remain in the insoluble portion, while those of the other metals are contained in the filtrate. On redissolving, the lead may be precipitated as sul-phate, or by hydrochloric acid and alcohol, which renders the chloride of lead insoluble. The bismuth is finally precipitated from the filtrate by sulphuretted hydrogen. From copper it is readily separated by carbonate of ammonia, bismuth being precipitated, and copper re-maining in solution. Another method is by heating in a current of chlorine, when chloride of bismuth is volatilized.

The metallurgical processes for the extraction of bismuth are very Metallurgy, simple, being mainly comprised in liquation out of contact with the air, and subsequent fusion of the liquated product of the first operation. At Schneeberg, in Saxony, the liquation is effected in cast-iron tubes placed transversely over a fire-grate which runs the whole length of the furnace. The tubes are inclined, the higher end being open for charging, and the lower stopped, with the excep-tion of a small hole for the passage of the separated metal, which is received in a cast-iron pot placed in front and heated with charcoal. The charge, about half a cwt. of ore, broken into pieces about half inch cube, occupies about half of the length and rather more than half the area of each tube. When all the tubes are charged the upper ends are stopped by sheet-iron doors, and heat is applied by means of a wood tire upon the grate. The liquid metal soon commences to flow, and is received in the pots in front. If the flow ceases through any obstruction the passage is cleared by an iron rod introduced through the aperture at the lower end. When the operation, which usually lasts about an hour, has terminated, the residues in the tubes are removed and thrown into a water trough placed behind the furnace on the charging side, and a fresh supply of ore is introduced. The bismuth collected in the pots is ladled out and cast into ingots of from 25 to 50 lb weight. In a furnace containing 11 tubes about 20 cwts. of ore may be heated daily with a consumption of 63 cubic feet of wood. In Plattner's modification the furnace is of the reverberatory form, the tubes being placed with their inclined axes in the direction of the flame, an arrangement which allows the use of a smaller fire-grate and a proportionate saving of fuel. At Joachimsthal, ores containing from 10 to 30 per cent, of bismuth are heated in a finely-ground state with scrap-iron, carbonate of soda, and a little lime and fluor-spar in earthen crucibles, which are heated until the mixture is completely fused, when the contents are poured into iron moulds of a sugar-loaf form. The bismuth collects in the point of the mould, and is covered with a cake of speiss, containing all the nickel and cobalt of the ore with about 2 per cent, of bismuth, which is reserved for further treat-ment ; the slag filling the upper part of the mould is thrown away. If the bismuth is sufficiently rich in silver it is cupelled, and the oxide formed is subsequently reduced or revived by fusion with carbon. When argentiferous lead containing bismuth is subjected to cupellation the former metal is oxidized more rapidly than the latter, which accumulates to such an extent that it may often form a notable proportion of the litharge produced towards the end of the process, although not existing in sufficient amount to be appreci-able by the ordinary processes of analysis in the original lead. This property has recently been utilized to recover a small quantity of bismuth existing in the silver ores smelted at Freiberg. The last portion of the litharge, and the hearth or test bottom from the silver refining furnace, are heated in quantities of 80 or 100 lb in earthen-ware pots with hydrochloric acid until complete solution of the bismuth oxide takes place, the proportion of acid and water being regulated to prevent the formation of insoluble salts. When the liquid is clear it is siphoned off to the precipitating tubs, where it is thrown down as an insoluble oxyehloride by the addition of a large quantity of water. By redissolving and reprecipitating, a purer material is obtained, which is then dried and reduced by fusion in iron crucibles with carbonate of soda and charcoal. The production of bismuth annually in Saxony is about 22 tons, and in Austria about 17 cwt.

The principal properties and reactions of bismuth and its com-
pounds were described in 1739 by Pott, who gave a summary of
the information contained in the earlier writers. Our more exact
knowledge of the subject is due to Neumann, Hellot, Geoffrey
(1753), John Davy (1812), Lagerhjelm (1815), Stromeyer, and,
more recently, Schneider and Nickles. (H. B.)







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