SILVER

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SILVER ; a metal which appears to have been known almost as early as gold, and, without doubt, for the same reason, be cause it occurs T~°ry frequently in a state of purity in the earth, and requires but an ordinary heat for its fusion. Mention id made of silver in the book of Job, which is considered the oldest of the books contained in the Old Testament. The ores of silver are somewhat numerous; and we shall defer our account of them to the conclusion of the present article, commencing with the chemical history of this metal. Pure silver is of a fine white color, with a shade of yellow, without either taste or smell, and, in brilliancy is inferi except polished steel. It is softer than copper, but harder than gold. When melted, its specific gravity is 10.47; when hammered, 10.510. It is next in malleability to gold, having been beaten out into leaves only r"o oyoTroth °^' an nicn m thickness. Its ductility is no less remarkable. It may be drawn out into a wire much finer than a human hair; so fine, "ndeed, that a single grain of silver may be extended about 400 feet in length. Its tenacity is such, that a wire of silver 0.078 of an inch in diameter is capable of supporting a weight of 187.13 pounds avoirdupois without breaking. Silver melts when heated completely redhot; and, while in the melted state, its brilliancy is greatly augmented. If the heat be increased after the silver is melted, the liquid metal boils, and may be volatilized; but a very strong and longcontinued heat is necessary. Gasto Claveas kept an ounce of silver melted in a glasshouse furnace for two months, and found, by weighing it, that it had sustained a loss oof one twelfth of its weight. When heated upon charcoal under the flame of the compound blowpipe, however, the silver is volatilized with rapidity, passing off in a visible smoke. When cooled slowly, its surface exhibits the appearance of crystals ; and, if the liquid part of the metal be poured out as soon as the surface congeals, pretty large crystals of silver may be obtained. Silver is not oxidized by exposure to the air: it gradually, indeed, loses its lustre, and becomes tarnished; but this is owing to a different cause. Neither is it altered by being kept under water. But, if it be kept for a long time melted in an open vessel, it gradually attracts oxygen from the atmosphere, and is converted into an oxide. When silver is dissolved in nitric acid, and an alkali dropped into the solution, a browncolored precipitate falls in flocks, which, when washed and dried, constitutes the oxide of silver. Its color becomes a dark brown when dried. Its specific gravity is 7.14. When exposed to the direct rays of the sun, it gives out oxygen gas, and is converted into a black powder, the nature of which has not been examined. The oxide of silver is a compound of 93.1 silver and 6.8 oxygen. When oxide of silver is dissolved in ammonia, and the solution left exposed to the air, it is soon covered with a brilliant pellicle, which is a suboxide of silver. A superoxide of silver appears to ins formed, when a platina wire battery is plunged into a weak solution of nitrate of SILVER, the compound in question accumulating in ironblack octahedrons upon the wire. Silver does not burn in chlorine gas, even when heated ; but it gradually absorbs the gas, and is converted into the wellknown compound formerly called horn SILVER, and afterwards muriate of SILVER, though now with more propriety denominated chloride of silver. This chloride, however, is more easily obtained by dissolving silver in nitric acid, and mixing the solution with a solution of common salt. A copious curdy precipitate falls. When this precipitate is washed and dried, it constitutes pure chloride of silver. Its specific gravity is 5.129. It is one of the most insoluble substances known, requiring no less than 3072 parts of water for its solution. When exposed to the air, it changes from white to a purple or blackish color. It melts at 500° Fahr., and assumes, on cooling, the form of a graycolored, semitransparent mass, having some resemblance to horn, and for that reason called lima cornea. A strong heat sublimes it. When heated strongly in an earthen crucible, it passes through altogether, and is lost in the fire; but when mixed with about, four times its weight of fixed alkali formed into a ball, with a little water, and melted rapidly in a crucible well lined with alkali, the silver is reduced, and obtained in a state of purity. Chloride of silver is composed of silver 13.75, and chlorine 4.50. A b?*omide and an iodide of silver may be formed simply by adding in the one case, a solution of a hydrobromate to one of nitrate of silver, and, in the other, a solution of a hydriodate. If one ounce of silver, one ounce of phosphoric glass, and two drachms of charcoal, be mixed together, and heated in a crucible, pkosphuret of silver is formed. It is of a white color, and crystalline in its texture. It is composed of four parts of silver and one of phosphorus. Heat decomposes it by separating the phosphorus. When thin plates of silver and sulphur are laid alternately above each other in a crucible, they melt readily in a low red heat, and form sidphurei of silver, Its color is black, and it crystallizes in small needles. It is capable of being cut with a knife, and is more easily fused than silver. It is well known that when silver is long exposed to the air, especially in frequented places, as churches, theatres, &c, it acquires a covering of a vio ret of silver. Selenium appears to enter into combination with silver in two different proportions, forming seleniets. Arsenic forms an alloy with silver in the proportion of sixteen of the former to one hundred of the latter; it is steelgray, brittle, and fine granular. Silver may be alloyed with antimony by fusion. Silver and iron unite readily: the alloy has the color of silver, but it is harder, very ductile, and attracted by the magnet. When 500 parts of good Indian steel are fused along with one part of silver, the compound is greatly improved for the purposes of cuttin g instruments. Melted lead dissolves a great quantity of silver at a slightly red heat; the alloy is brittle and leadcolored. Silver is easily alloyed with copper by fusion: the compound is harder, and more sonorous than silver, and retains its white color, even when the proportion of copper exceeds one half: the hardness is at its maximum when the copper amounts to one fifth of the silver. The alloy of silver and tin is very brittle and hard. That of silver and mercury is formed by throwing pieces of red hot silver into mercury heated till it begins to smoke: it forms clendritical crystals, which contain eight parts of mercury, and one of silver. The most important combination among those of the acids and silver (the nitrate of silver) has been alluded to above, in the description of the oxide of silver. Nitric acid is the proper solvent of this metal, from which solution the other salts of silver are obtained: it dissolves more than half its weight of the metal, the solution being attended with effervescence: if the silver and the acid are pure, the solution is limpid and colorless, exceedingly heavy and caustic: it stains the skin, and all animal substances, of an indelible black color; hence it is often used to dye hair, &c.: when evaporated till a pellicle begins to form on its surface, it deposits, on cooling, transparent crystals of nitrate of silver, in the form of sixsided, foursided, or threesided, thin plates; but, by slow evaporation, the salt may be obtained in short, right rhombic prisms of 129° 31/: its taste is intensely bitter and metallic, and it is usually employed as a corrosive substance, Under the name of lunar caustic: it is soluble in its own weight of cold, and in half its weight of hot, water. From the solution, the silver is thrown down in a metallic state by a great number of bodies ; for example, hydrogen, sulphurous acid, sulVOL. xi. 35of the metals. The specific gravity of lunar caustic is 3.52. When heated, it readily melts, swells up, and then remains liquid: in this state it is cast into small cylindrical moulds by apothecaries, to be employed by surgeons for the purpose of opening ulcers and destroying fungous excrescences: as an escharotic, its action is powerful, and it is greatly preferred to caustic potash also, in consequence of its not being liable to deliquesce and spread. Both the crystals and the fused salt are anhydrous, consisting of 118 parts oxide of silver, and 54 nitric acid : it detonates, when heated with combustible bodies, and with phosphorus it detonates on percussion. Sulphate of silver is obtained with ease by mingling together solutions of nitrate of silver and sulphate of soda: it falls in the state of a white powder, which may be dissolved in water, and crystallized: the crystals are white and brilliant, and have the form of very fine prisms: it has the peculiarly disagreeable taste of the nitrate; is anhydrous, and composed of sulphuric acid 5, and oxide of silver 14.75. Sulphite cf silver is obtained by mixing the solutions of sulphite of ammonia and nitrate of silver. It assumes the form of small, shining, white grains: when exposed to the light, it assumes a brown color. Phosphate of silver is insoluble in water, and is hence precipitated when a solution of phosphate of soda is added to a solution of nitrate of silver. The salts of silver are decomposed by the alkalies and the earths. Prussiate of potash, when dropped into a solution of a salt of silver, occasions a white precipitate: hydrosulphuret of potash produces a black precipitate; and an infusion of nutgalJs gives a yellowish brown precipitate. A fulminating preparation of silver, similar to that of gold, but more energetic, is prepared by dissolving silver in nitrous acid, diluted with three parts of water: to the solution limewater is added as long as any precipitation is occasioned ; the precipitate is washed and dried; it is then allowed to remain for several hours in liquid ammonia, when it becomes a black powder; the liquor is decanted, and it is allowed to dry in the air: when completely diy, such is its tendency to explosion, that it cannot be touched, the slightest agitatior* causing it to detonate ; and so violent is the detonation, that the experiment can not be made with safety on more than a grain. The theory of its detonation ra considered as s\ filar to that of fulminating gold : it prubably consists of oxide of silver and ammonia, the elements being united by affinities so nicely balanced, that, the slightest external, force subverts them, and causes new combinations: the oxygen of the oxide unites with the hydrogen of the ammonia, and forms watery vapor ; the nitrogen must assume the elastic form, and the augmentation of elasticity in these products, by the caloric suddenly extricated, may be the cause of the detonation. A fulminating silver totally different from that above described, is frequently sold as an object of amusement : it is enclosed between the folds of a card cut in two lengthwise, the powder being placed at one end, and the other being notched, that it may be distinguished : if it be taken by the notched end, and the other be held over the flame of a candle, it soon detonates with a sharp sound and violent flame; the card is torn and changed brown, and the part in contact with the composition is covered with a slight metallic coating of a grayishwhite color. This compound is formed in the following manner: Into a pint tumbler, or other glass vessel, is introduced 100 grains of dry nitrate of silver, over which is poured one ounce of alcohol, and the same quantity of smoking nitric acid. The mixture of the alcohol and nitric acid occasions much heat and effervescence in the liquid: if this is so violent as to overflow the vessel, cold alcohol is added in small portions to abate the ebullition : in a few minutes the liquor becomes turbid, and a very heavy, white, crystalline powder falls down, which is separated by the filter, and thoroughly washed with tepid water: before being fully dry, it should be separated into parcels of ten or twenty grains, which portions, when thoroughly dried at a distance from the fire, present the following properties: The substance is white and crystalline; the light changes its color to a dark brown; when heated, it explodes with great violence. It explodes also by percussion and friction, and the contact of sulphuric acid. When put into dry chlorine gas, it explodes with a loud report. So powerful is this powder in its explosions, that no persons but chemists should venture upon its manufacture, or presume to experiment with it. The most painful accidents have repeatedly occurred with it, in the hands of the inexperienced and the careless. It is composed of oxide of silver 14.75, and of a peculiar acid, called the fulminic, 5.25. (For some ac count of fulminic acid, see Prussin Acid.) Silver Ores.There are five important ores of silver, viz.1. Native silver; % vitreous silver (or silver glance); 3. black silver; 4. red silver; 5. horn silver.JV<xtive silver is occasionally found crystallized in the following shapes, viz.the cube, octahedron, tetrahedron, rhombic dodecahedron, trapezohedron, and sixsided tables. The cube is the primitive form; but it more often occurs in dentiform, filiform, and capillary shapes ; also reticulated, arborescent, and in plates; likewise in plates, formed in fissures, and in superficial coatings; cleavage none, fracture hackly ; lustre metallic; color silverwhite, more or less subject to tarnish ; streak shining; ductile; hardness between gypsum and calcareous spar; specific gravity, 10.47. Native silver has been distinguished into common and auriferous native silver: the former consists of silver alloyed with a small proportion of antimony, arsenic, iron, &c.; the latter frequently contains fifty per cent, of gold. Native silver occurs principally in veins, traversing gneiss, clayslate, and other primitive and transition rocks.. There are but few countries in which it is found in any considerable quantity. Among these are the mining districts of Saxony and Bohemia, also Norway and Siberia, but particularly Mexico and Peru. Vitreous silver presents itself crystallized in cubes, octahedrons, and rhombic dodecahedrons. Its primitive form is the cube. It also occurs in reticulated, arborescent, dentiform and capillary shapes; also massive and impalpable; fracture imperfect, and small conchoidal, uneven ; lustre metallic, subject to tarnish; color blackish leadgray; streak shining; malleable ; hardness about that of gypsum; specific gravity 7.19. It consists of silver 85.0, sulphur 15.0. It is easily fusible before the blowpipe, and intumesces ; but it gives a globule of silver by a continuation of the blast. It has been hitherto found almost exclusively in veins, along with ores of lead, antimony and zinc. It occurs in Saxony, Bohemia, Hungary, Mexico and Peru. It is an important species for the extraction of silver. Black silver has for its primitive form a right rhombic prism of 100° 0'. The crystals, however, are not often observed; but it is more frequently in granular masses; fracture imperfect conchoidal, uneven; lustre metallic; color ironblack; streak unchanged ; sectile; hardness about that of gypsum ; specific gravity 6.2. It consists of Iron, .Vy. ......... ... 5.00 Sulphur, . ,............12.00 Copper and arsenic, ........50 §aoo Before the blowpipe, upon charcoal, it yields a darkcolored metallic globule, which may be reduced with saltpetre. It is found in silver veins along with other ores of silver. It occurs chiefly in Saxony, Bohemia and Hungary, in Mexico and Peru. It is a valuable ore for the extraction of silver.Red silver. The primitive form of this species is an obtuse rhomboid of 109° 28'. Its secondary forms are sixsided prisms, variously truncated and acuminated, and an equiangular double sixsided pyramid; cleavage parallel with the sides of the primitive form, pretty distinct; fracture conchoidal; lustre adamantine ; color ironblack to cochinealred; semitransparent to opaque ; sectile ; hardness about that of gypsum ; specific gravity 5.84. The crystals are very liable to occur twinshaped. Red silver is often found massive, granular, and even impalpable. It consists of Silver,...............58.949 Antimony,............22.846 Sulphur,.............16.609It decrepitates before the blowpipe upon charcoal, mdlts, and emits fumes of sulphur and antimony, after which it yields a irlobule of silver. Red silver is confined to a small number of localities, and occurs in veins along with other ores of silver, galena and blende. It is found in the metallic veins near Freiberg, also at Marienberg, Annaberg, Schneeberg, and Johanngeorgenstadt in Saxony; likewise in Bohemia, Hungary, Dauphiny, and Norway; but is much more abundant in Mexico and Peru. It is a valuable ore for silver.Horn silver lias the cube for its primitive form, in which shape it frequently occurs, as also in acicular fibres; cleavage none; fracture more or less perfect conchoidal; lustre resinous, passing into adamantine ; color pearlgray, passing into lavenderblue, and some shade of green; the color becomes brown on being exposed to light; streak shining; translucent ; sectile ; hardness about that of talc ; specific gravity 5.5. It occurs also in crusts and granular masses. It consists of silver 76.0, oxygen 7.6, and muriatic acid 16.4. It is fusible in the flame of a candle, and emits fumes of muriatic acid. Horn silver is most frequently along with other ores of silver, or with ironochre. It is not abundant in European countries, but occurs in large masses in Mexico and Peru. It is used for extracting silver.Such are the ores of silver which are properly so called, and from which silver is chiefly extracted. Besides these, however, argentiferous sulphuretsof lead and copper are sometimes smelted for the small proportion of this precious metal which they contain. We have now to allude to the methods em , ployed in obtaining the silver from its various ores. These are two in number, smelting and amalgamation. The former is founded on the great affinity of silver for lead, which, when fused with silver, acts as a solvent, and extracts it from its union with baser metals. The silver is afterwards separated from the lead by the wellknown process of cupellation, which consists in exposing the alloy to a stream of atmospheric air, by which the lead is converted into an oxide or litharge, while the silver remains untouched. The latter method depends upon the property of mercury to dissolve silver without the aid of heat. The first is called the dry, the last, the wet way of treating silver ores. One or the other process is employed, according to the nature of the ores. The ores which are treated in the wet way are usually those which consist principally of argentiferous sulphuret of lead. The first thing to be done, by this method, is to pulverize and roast the ore in & furnace, to expel the sulphur. When the well or crucible is full of metal, it is tapped and run off. It is now ready for the process of refining, or cupellation. For this purpose, a reverberatory furnace is employed, the lower part of which is covered with wood ashes and clay, so as to form a cupel. On one side of the furnace there is a hole for the exit of the litharge; and on the opposite side is another for the admission of air to the surface of the metal, which is introduced through an aperture above, to which a cover is adapted. After the lead is melted and brought to a red heat, the blast of air is admitted, and the scoria, as h collects, is removed. When the litharge is formed, the heat is increased, and the quantity becomes greater, and is withdrawn through the opening in the furnace. At the same time, some lead is volatilized. Towards the end of the process, the litharge which comes off contains a small quantity of silver, and is therefore kept separate from the rest. After the whole of the litharge is removed, and the surface of the metal in the furnace becomes bright, a quantity of water is poured on it, to keep it from spirting, which it is apt to do when congealing. The metal thus obtained is subjected to a similar operation for about five hours, in a smaller furnace, and at a higher temperature, by which it is completely freed from the lead. With respect to the other method of reduction or separationamalgamationthe following is an outline of the more important steps, of which it consists. The ores best adapted to this process are native silver and vitreous silver. The first operation that requires description is the selection of the ores to form a proper mixture, with reference to the quantity of silver and sulphur they contain. It has been observed that the amalgamation process succeeds best when the silver produce is about seventyfive ounces to the ton of ore; at the same time, regard being had to the quantity of sulphur present, which is ascertained from the quantity of sulphuret in the ore, previously learned by an assay in the crucible. The sulphur is got rid of, by adding to the mixture of raw ore ten per cent, of common salt, by which, during the furnace operation, the sulphur becomes acidified, and the acid thus formed, uniting with the base of the salt, forms sulphate of soda; whilst the muriatic acid, thus set free, combines with the silver in the ore, that was not ii? the metallic state, and forms muriate of silver. In this state, the ore is subjected to various mechanical operations, with riddles, mills and sieves, until it is reduced to an impalpable powder. It is then submitted to the action of mercury. This operation is performed in barrels, which are arranged so as to revolve on their axes. The mixture or charge in each barrel consists of sifted calcined ore, mercury, metallic iron, and water, in certain proportions. The ore is composed of sulphate of soda, muriate of silver, and other metals and earthy matters. By the process of amalgamation, the barrels being made to revolve during a period of sixteen or eighteen hours, the muriate of silver becomes decomposed by the action of the iron on its acid; and the silver, thus reduced to the metallic state, combines with the mercury, forming what is termed amalgam, whilst the sulphate of soda, the muriate of iron, and other salts, become dissolved in the water. The silver combined with mercury is then filtered, by which the surplus metal is separated, and a compound remains in the sack, consisting of six parts of mercury and one of silver This amalgam is subjected to the action of heat in a distilling furnace, by which the mercury is sublimated, and the silver remains. Silver is also sometimes separated from copper by the process of eliquation. The eliquation is effected by means of lead, which, possessing a greater affinity for silver than for copper, combines with the former, when brought into fusion with the alloy, and forms a new metallic compound. The argentiferous lead, thus obtained, is subjected to the usual processes of cupellation, and the coarse copper, from which the silver has been separated, is refined.We shall now take notice of the mines of silver in different parts of the world, which furnish the silver of commerce. Those of Mexico and South America are incomparably more important than those of all the rest of the world. Mexico alone has above three thousand mines, or excavations for silver ores, which produced annually during the last ten years o£ the seventeenth century, about $4,000,000. The mines of Guanaxuato yielded nearly on© quarter of this amount; while the single mine of Valenciana, situated in the same district, has afforded, for years together during the last thirty .years, between one and two million dollars. Nor are the ores of Mexico, for the most part, rich in silver; but the rich produce of that country has depended upon their abundance, and the facility with which they have been explored. In Peru, the annual produce of this metal was formerly as great as $2,000,000; the major part of which was furnished by the mines of Tasco, of Chota, and of Huantajaya. Chile affords $150,000 per annum. Buenos Ayres contains the celebrated mines of Potosi. discovered in 1545, and which have pro duced, according to the estimate of Humboldt, from the time of their discovery* the enormous amount of $1,150,000,000. These mines have diminished in value of late, though they still rank next to those of Guanaxuato. The celebrated mines of Kongsberg, in Norway, once so rich in native silver, have now become in a great measure exhausted. They are estimated to have produced above $20,000,000 since they were opened in 1623. The most important silver mines of Europe at present, are those of Saxony, Hungary, and the Hartz. The annual produce of Saxony is about $250,000; while those of the Hartz and of Hungary are each about the same. Within the last sixteen years there has been .a great increase in the produce of silver from the Russian mines. According to a communication from baron Humboldt, made since his return from Asia, to the editor of Poffendorf's Annalen, it appears that the annual produce of the mines of precious metals of Europe and Asiatic Russia amounts to 25,500 marcs of gold, and 292.000 marcs of silver; of which 76,500 of silver and 22,000 of gold are supplied from the Russian empire. The value of all this silver is about $2,353,000. The present annual produce of all the silver mines in the world is probably within $20,000,000. SILVER FISH. (See Gold Fish.) SILVER TREE (leucadendron argenteum); so called from the appearance of the leaves, which are lanceolate and silky. It is a large evergreen shrub, with handsome foliage, a native of the cape of Good Hope, together with the other species of the genus, and is a favorite in greenhouses. It belongs to the protectees, the most remarkable family of plants in the southern hemisphere, and one which contributes largely to give peculiar features to the vegetation of that portion of the globe. More than four hundred species of these plants are known, which are arranged in numerous genera. They are usually shrubs or small trees, but some attain large dimensions: the leaves are simple, entire or serrated, in most species hat, but sometimes cylindrical or threadSnap^d; the flowers are sometimes district, upon solitary footstalks, or in clusters, spikes, or corymbs, with bractea at the base; sometimes they are sessile, situated upon a common receptacle, surrounded with a manyleaved involucre, or are disposed in scaly cones; the color is green, yellow, or rt,d: in short, the remarkable differences in the habit, foliage and flowers of these plants have given rise to the name of the order. The greater proportion of these planu inhabit New Holland, where they adorn laige tracts of country; they are numerous, likewise, at the cape of Good Hope, but a few species only are found in the southern pails of South America. They are generally favorite greenhouse plants, and are not delicate with respect to cold; but their culture, in other respects, requires many precautions.