TITANIUM-TITANIO ACID. 391 292. TITANIUM, which stands in close chemical relationship to tin, used to be described as a very rare metal, but it has lately been found to exist in considerable quantity in iron ores and clays, although no very important practical application has hitherto been found for it. The form in which it is generally found is titanic acid (TiO2), which occurs uncombined in the minerals rutile, anatase, and brookite, the first of which is isomorphous with tin-stone, and is extremely hard like that mineral. In combination with oxide of iron, titanic acid is found in iron-sand, iserine, or menachanite (found originally at Menachan in Cornwall), which resembles gunpowder in appearance, and is now imported in abundance from Nova Scotia and New Zealand. Some specimens of this mineral contain 40 per cent. of titanic acid, combined with protoxide of iron. To extract titanic acid from it, the finely ground mineral is fused with three parts of carbonate of potash, when carbonic acid is expelled and titanate of potash formed; on washing the mass with hot water, this salt is decomposed, a part of its alkali being removed by the water, and an acid titanate of potash left, mixed with the oxide of iron. This is dissolved in hydrochloric acid, and the solution evaporated to dryness, when the titanic acid, and any silicic acid which may be present, are converted into the insoluble modifications, and are left on digesting the residue again with dilute hydrochloric acid; the residue is washed with water (by decantation, for titanic acid easily passes through the filter), dried, and fused at a gentle heat with bisulphate of potash. The sulphuric acid forms a soluble compound with the titanic acid (TiO2. SO3), which may be extracted by cold water, leaving the silicic acid undissolved. The solution containing the titanic acid is mixed with about twenty times its volume of water, and boiled for some time, when the titanic acid is separated as a white precipitate, exhibiting a great disposition to cling as a film to the surface of the flask in which the solution is boiled, and giving it the appearance of being corroded. The titanic acid becomes yellow when strongly heated, and white again on cooling; it does not dissolve in solution of potash like silica, but when fused with potash it forms a titanate, which is decomposed by water; the acid titanate of potash which is left may be dissolved in hydrochloric acid, and if the solution be neutralised with carbonate of ammonia, hydrated titanic acid is precipitated, very much resembling alumina in appearance. By dissolving the gelatinous hydrate in cold hydrochloric acid, and dialysing, a solution of titanic acid in water is obtained, which is liable to gelatinise spontaneously if it contain more than one per cent. of the acid. Titanic acid is employed in the manufacture of artificial teeth, and for imparting a straw-yellow tint to the glaze of porcelain. If a mixture of titanic acid and charcoal be heated to redness in a porcelain tube, through which dry chlorine is passed, bichloride of titanium (TiCl) is obtained as a colourless volatile liquid, very similar to bichloride of tin. By passing the vapour of the bichloride of titanium over heated sodium, the metallic titanium is obtained in prismatic crystals resembling specular iron ore in appearance. Like tin, it is said to dissolve in hydrochloric acid with liberation of hydrogen. The most remarkable chemical feature of titanium is its direct attraction for nitrogen, with which it combines when strongly heated in air. By passing ammonia gas over titanic acid heated to redness, a violet powder is formed, which is a nitride of titanium (TIN). Beautiful cubes of a copper colour and great hardness, formerly believed to be metallic titanium, are found adhering to the slags of blast-furnaces in which titaniferous iron ores are smelted; these contain about 77 per cent. of titanium, 18 of nitrogen, and rather less than 4 of carbon, and are believed to consist of a compound of cyanide with nitride of titanium, TiCy, 3Ti,N. A similar compound is obtained by passing nitrogen over a mixture of titanic acid and charcoal heated to whiteness. Violet-coloured crystals of sesquichloride of titanium (Ti2Cl) are obtained by passing hydrogen charged with vapour of bichloride of titanium through a red-hot porcelain tube; it forms a violet solution in water, which resembles stannous chloride in its reducing properties. When a solution of titanic acid (or acid titanate of potash) in hydrochloric acid is acted on by zinc, a violet solution is formed, which deposits, after a time, a blue (or green) precipitate, which appears to be a sesquioxide of titanium (Ti2O3), and rapidly absorbs oxygen from the air, being converted into titanic acid. A protoxide of titanium (TiO) is said to be obtained as a black powder when titanic acid is strongly heated in a crucible lined with charcoal. Bisulphide of titanium is not precipitated, like bisulphide of tin, when hydrosulphuric acid acts upon the bichloride; but if a mixture of the vapour of bichloride 392 TUNGSTEN-TUNGSTIC ACID. of titanium with hydrosulphuric acid is passed through a red-hot tube, greenishyellow scales of the bisulphide, resembling mosaic gold, are deposited. Titanium, like tin, is classed among the tetratomic elements; its equivalent is 25, and its atomic weight 50. 293. TUNGSTEN is chiefly found in the mineral wolfram, which occurs, often associated with tin-stone, in large brown shining prismatic crystals, which are even heavier than tin-stone (sp. gr. 7-3), from which circumstance the metal derives its name, tungsten, in Swedish, meaning heavy stone. The symbol (W) used for tungsten is derived from the Latin name wolframium. Wolfram contains the tungstates of iron and manganese in somewhat variable proportions, but its general composition is expressed by the formula MnO. WO, 3(FeO. WO3). Scheelite, tungstate of lime (CaO. WO,), is another mineral in which tungsten is found. Tungstate of soda is employed by calico-printers as a mordant, and is sometimes applied to muslin, in order to render it inflammable. It is obtained by fusing wolfram with carbonate of soda, an operation to which tin ores containing this mineral in large quantity are sometimes submitted previously to smelting them. Water extracts the tungstate of soda, which may be crystallised in rhomboidal plates having the composition NaO. WO3, 2Aq. When a solution of this salt is mixed with an excess of hydrochloric acid, white hydrated tungstic acid (HO. WO, + Aq.) is precipitated; but if dilute hydrochloric acid be carefully added to a 5 per cent. solution of tungstate of soda, in sufficient proportion to neutralise the alkali, and the solution be then dialysed (p. 104), the chloride of sodium passes through, and a pure aqueous solution of tungstic acid is left in the dialyser. This solution is unchanged by boiling, and when evaporated to dryness, it forms vitreous scales, like gelatine, which adhere very strongly to the dish. It redissolves in one-fourth of its weight of water, forming a solution of the very high specific gravity 3-2, which is, therefore, able to float glass. The solution has a bitter and astringent taste, and decomposes carbonate of soda with effervescence. It becomes green when exposed to air, from the deoxidising action of organic dust. When the hydrated tungstic acid is heated, it loses water, and becomes of a straw-yellow colour and insoluble in acids. There are at least two modifications of tungstic acid, which bear to each other a relation similar to that between stannic and metastannic acids. The most characteristic property of tungstic acid is that of yielding a blue oxide (WO2, WO) when placed in contact with hydrochloric acid and metallic zinc. A very remarkable compound containing tungstic acid and soda is obtained when bitungstate of soda (NaO.2WO3.4HO) is fused with tin. If the fused mass be treated with strong potash, to remove free tungstic acid, washed with water, and treated with hydrochloric acid, yellow lustrous cubical crystals are obtained, which are remarkable, among sodium compounds, for their resistance to the action of water, of alkalies, and of all acids except hydrofluoric. The composition of these crystals appears to be NaO. WO2.2WO3. The binoxide of tungsten (WO2) appears to be an indifferent oxide, and is obtained by reducing tungstic acid with hydrogen at a low red heat, when it forms a brown powder which is dissolved by boiling in solution of potash, hydrogen being evolved, and tungstate of potash formed. Metallic tungsten is obtained by reducing tungstic acid with charcoal at a white heat, as an iron-grey infusible metal of sp. gr. 176, very hard, not affected by hydrochloric or diluted sulphuric acid, but converted into tungstic acid by the action of nitric acid. When tungsten is dissolved in about ten times its weight of fused steel, it forms an extremely hard alloy. When tungsten is heated in chlorine, the terchloride of tungsten (WC13) sublimes in bronze coloured needles, which are decomposed by water. When gently heated in hydrogen, it is converted into the bichloride (WC1), but if its vapour be mixed with hydrogen and passed through a glass tube heated to redness, metallic tungsten is obtained in a form in which it is not dissolved even by aqua regia, though it may be converted into tungstate of potash by hypochlorite of potash mixed with potash in excess. Bisulphide of tungsten (WS) is a black crystalline substance resembling plumbago, obtained by heating a mixture of bitungstate of potash with sulphur, and washing with hot water. Tersulphide of tungsten (WS) is a sulphur-acid, obtainable as a brown precipitate by dissolving tungstic acid in an alkaline sulphide, and precipitating by an acid, 294. MOLYBDENUM derives its name from oλúßdara, lead, on account of the resemblance of its chief ore, molybdena, to black lead. Molybdena is the bisulphide of molybdenum (MOS), and is found chiefly in Bohemia and Sweden; it may be recog MOLYBDENUM-VANADIUM. 893 nised by its remarkable similarity to plumbago, and by its giving a blue solution when boiled with strong sulphuric acid. It is chiefly employed for the preparation of molybdate of ammonia, which is used in testing for phosphoric acid. For this purpose the bisulphide of molybdenum is roasted in air at a dull red heat, when sulphurous acid is evolved, and molybdic acid (MoO1) mixed with oxide of iron is left. The residue is digested with strong ammonia, which dissolves the molybdic acid in the form of molybdate of ammonia, obtainable in prismatic crystals on evaporation. When a solution of molybdate of ammonia is added to a phosphate dissolved in diluted nitric acid, a yellow precipitate of phosphomolybdate of ammonia is produced, which contains molybdic and phosphoric acids combined with ammonia, by the formation of which very minute quantities of phosphoric acid can be detected. If hydrochloric acid be added in small quantity to a strong solution of molybdate of ammonia, the molybdic acid is precipitated, but it is dissolved by an excess of hydrochloric acid, and if the solution be dialysed, the molybdic acid is obtained in the form of an aqueous solution which reddens blue litmus, has an astringent taste, and leaves a soluble gum-like residue when evaporated. Molybdic acid fuses at a red heat to a yellow glass, and may be sublimed in a current of air in shining needles. In contact with diluted hydrochloric acid and metallic zinc, it is converted into a blue compound of molybdic acid with binoxide of molybdenum (MoO,. 4MoO,) which is soluble in water, but is precipitated on adding a saline solution. Molybdate of lead (PbO. MoO3) is found as a yellow crystalline mineral. The binoxide of molybdenum (MoO) is basic, and forms dark red-brown salts. Protoxide of molybdenum (MoO) is obtained by adding an alkali to the solution resulting from the prolonged action of zinc upon a hydrochloric solution of molybdic acid. It is a basic oxide which absorbs oxygen from the air. Metallic molybdenum is obtained by reducing molybdic acid with charcoal at a white heat, as a white metal, fusible with difficulty, unacted upon by hydrochloric and diluted sulphuric acids, but converted into molybdic acid by boiling with nitric acid. It is rather a light metal, its specific gravity being 8-62. When heated in chlorine it yields bichloride of molybdenum (MoCl2), which forms a red vapour, and condenses in crystals resembling iodine, soluble in water. A protochloride (MoCl) is also known. The tersulphide (MoS,) and tetrasulphide (MoS,) of molybdenum are sulphur-acids. In addition to the natural sources of molybdenum above mentioned, there may be noticed molybdic ochre (an impure molybdic acid), and the difficultly fusible masses called bear, from the copper works in Saxony, which contain a large amount of molybdenum combined with iron, copper, cobalt, and nickel. 295. VANADIUM (Vanadis, a Scandinavian deity) was originally obtained from certain Swedish iron ores, but its chief ore is the vanadiate of lead, which is found in Scotland, Mexico, and Chile. Vanadic acid has also been found in some clays, and in the cupriferous sandstone at Perm in Russia. By treating the vanadiate of lead with nitric acid, expelling the excess of acid by evaporation, and washing out the nitrate of lead with water, impure vanadic acid (VO) is obtained, which may be purified by dissolving in ammonia, crystallising the vanadiate of ammonia, and decomposing it by heat, when vanadic acid is left as a reddish-yellow fusible solid, which crystallises on cooling, and dissolves sparingly in water, giving a yellow solution. It dissolves in hydrochloric acid, and if the solution be treated with a reducing agent (such as hydrosulphuric acid) it assumes a fine blue colour, from the production of bichloride of vanadium (VCl2). If a solution of vanadiate of ammonia be mixed with tincture of galls, it gives an intensely black fluid, which forms an excellent ink, for it is not bleached by acids, alkalies, or chlorine. By heating vanadic acid with potassium, metallic vanadium is obtained as a white metallic powder, which is not attacked by sulphuric or hydrochloric acid, but dissolves in nitric acid, forming a blue solution of nitrate of binoxide of vanadium, The protoride of vanadium (VO) appears to be an indifferent oxide. Terchloride of vanadium (VCl2) is a volatile yellow fuming liquid. Bisulphide of vanadium (VS) is obtained as a black precipitate by the action of an alkaline sulphide upon the bichloride of vanadium; it appears to be a sulphur-acid, for it dissolves in an excess of the alkaline sulphide, fuming a purple solution. 296. Niobium (formerly called columbium) has been obtained from a rare dark grey hard crystalline mineral known as columbite, occurring in Massachusetts. This mineral contains niobic acid (NbO2) combined with the oxides of iron and manganese. The niobic acid is extracted by a laborious process, and forms a white powder 394 METALLURGY OF PLATINUM. sparingly soluble in hydrochloric acid. Niobium itself has been obtained as a black powder insoluble in nitric acid and in aqua regia, but dissolved by a mixture of nitric and hydrofluoric acids. Tantalum, formerly believed to be identical with niobium, occurs in the tantalite and yttrotantalite of Sweden, which contain tantalic acid (TaO2)* resembling niobic acid. Niobium and tantalum have recently been found to the amount of 2 or 3 per cent. in the tin ore of Montebras. PLATINUM. 297. Platinum (platina, Spanish diminutive of silver) is always found in the metallic state, distributed in flattened grains through alluvial deposits similar to those in which gold is found; indeed, these grains are generally accompanied by grains of gold, and of a group of very rare metals only found in platinum ores, viz., palladium, iridium, osmium, rhodium, and ruthenium. Russia furnishes the largest supply of platinum from the Ural Mountains, but smaller quantities are obtained from Brazil, Peru, Borneo, Australia, and California. The process for obtaining the platinum in a marketable form is rather a chemical than a metallurgic operation. The ore containing the grains of platinum and the associated metals is heated with a dilute mixture of hydrochloric and nitric acids, by which the platinum is converted into bichloride of platinum (PtCl) and dissolved, whilst the iridium and osmium are left in the residue. The solution is then mixed with some chloride of ammonium, which combines with the bichloride of platinum to form a yellow insoluble salt (ammonio-chloride of platinum, NH,. HCl. PtC1). This precipitate is collected, washed, and heated to redness, when all its constituents, except the platinum, are expelled in the form of gas, that metal being left in the peculiar porous condition in which it is known as spongy platinum. To convert this into compact platinum is by no means an easy task, on account of the infusibility of the metal, for it remains solid at the very highest temperatures of our furnaces. The spongy platinum is finely powdered in a wooden mortar (as it would cohere into metallic spangles in one of a harder material) and rubbed to a paste with water; this paste is then rubbed through a sieve to render it perfectly smooth and uniform, and introduced into a cylinder of brass, in which it is subjected to pressure so as to squeeze out the water and cause the minute particles of platinum to cohere into a somewhat compact disk; this disk is then heated to whiteness and beaten into a compact metallic ingot by a heavy hammer; it is then ready for forging. A more modern process for obtaining platinum from its ores is based upon the tendency of this metal to dissolve in melted lead. The platinum ore is fused in a small reverberatory furnace, with an equal weight of sulphide of lead and the same quantity of oxide of lead, when the sulphur and oxygen escape as sulphurous acid, and the reduced lead dissolves the platinum, leaving undissolved a very heavy alloy of osmium and iridium which sinks to the bottom. The upper part of the alloy of lead and platinum is then ladled out and cupelled (page 353), when the latter metal is left in a spongy condition, the lead being removed in the form of oxide. The platinum is then fused by the aid of the oxyhydrogen blowpipe in a furnace made of lime (fig. 259), whence it is poured into an TaO, according to more recent experiments. PROPERTIES OF PLATINUM. 395 ingot mould made of gas-carbon. The melted platinum absorbs oxygen. mechanically like melted silver, and evolves it again on cooling (see page 354). Platinum articles are now frequently made from the fused metal, instead of from that which has been welded. Its resistance to the action of high temperatures and of most chemical agents, renders platinum of the greatest service in chemical operations. It will be remembered that platinum stills Fig. 259. are employed, even on the large scale, for the concentration of sulphuric acid. In the form of basins, small crucibles, foil, and wire, this metal is indispensable to the analytical chemist. Unfortunately, it is softer than silver, and therefore ill adapted for wear, and is so heavy (sp. gr. 21.5) that even small vessels must be made very thin in order not to be too heavy for a delicate balance. Since it expands less than any other metal when heated, wires of platinum may be sealed into glass without danger of splitting it by unequal expansion. Its malleability and ductility are very considerable, so that it is easily rolled into thin foil and drawn into fine wires; in ductility it is surpassed only by gold and silver, and it has been drawn, by an ingenious contrivance of Wollaston's, into wire of only both of an inch in diameter, a mile of which (notwithstanding the high specific gravity of the metal) would only weigh a single grain. This remarkable extension of the metal was effected by casting a cylinder of silver around a very thin platinum wire obtained by the ordinary process of wire-drawing. When the cylinder of silver, with the platinum wire in its centre, was itself drawn out into an extremely thin wire, of course the platinum core would have become inconceivably thin, and when the silver casing was dissolved off by nitric acid, this minute filament of platinum was left. Platinum is sometimes employed for the touch-holes of fowling-pieces on account of its resistance to corrosion. A little iridium is sometimes added to platinum in order to increase its elasticity. The remarkable power possessed by platinum, of inducing chemical combination between oxygen and other gases, has already been noticed. Even the compact metal possesses this property, as may be seen by heating a piece of platinum foil to redness in the flame of a gauze gas-burner, rapidly extinguishing the gas, and turning it on again, when the cold stream of gas will still maintain the metal at a red heat, in consequence of the combination with atmospheric oxygen at the surface of the platinum. A similar experiment may be made by suspending a coil of platinum wire in the flame of a spirit-lamp (fig. 260), and suddenly blowing out the flame when the metal is intensely heated; the wire will continue to glow by inducing the combination of the spirit vapour with oxygen on its surface. By substituting a little ball of spongy platinum for the coil of platinum wire, and mixing some fragrant essential oil with the spirit, an elegant perfuming lamp has been contrived. Upon the same principle an instantaneous light apparatus has been made, in which a jet of hydrogen gas is kindled by falling upon a fragment of cold spongy platinum, which at once ignites it by inducing its combination with the Fig. 260. |