merce usually contains both gold and silver, often in con siderable quantity, which circumstance has probably given rise to the story current about its transmutation into
these metals.
Bismuth ma} be readily obtained in crystals by pouring it when 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 l>y 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 S3, but when subjected to great pressure the density is reduced to 9-6. The melting point is 264 C. (507 Fahr.) (Paulberg), or 268 - 3 (515) (Riemsdijk). 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 -^ 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 (JIasson). The coefficient of expansion by heat is 001341, calorific conducti- bility 61, silver being 1000 (Calvert and Johnson), and specific heat 0-0305 (Kopp). The electric conductivity is T19 at 14 C., silver being 100 at (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.
The atomic weight is 208 (Schneider) or 210 (Dumas). Like 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 BiBr 2 , BiCl 2 , and Bil.,. 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 Bi 3 3 ), 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 Bi 2 5 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, BijO-j, Bi 2 5 . Bismuth unites directly with chlorine, bromine, and iodine, and when fused with sulphur forms a sulphide of the form Bi 2 S 3 , 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.
Bismuth is but slightly acted upon by hydrochloric or sulphuric 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 . 3N0 3 . 5H 2 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.N0 3 .H. 2 0, which is known as pearl- white, blanc defard. 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 unites readily with other metals, the alloys being remarkable 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 so dium 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 com ponents 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.) Kose s fusible metal, containing 420 parts of bismuth, 236 of k-ad, and 207 of tin, a composition corresponding to the formula Bi 2 Sn.,Pb, 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 J 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 3 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 CO". 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 carbouate by precipitation with carbonate of ammonia, which is then converted into oxide by calcination at a gentle heat, in which form tion. it is weighed and estimated. The oxide Bi 2 3 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, mercuiy, 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 in soluble 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 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
