EXTRACTION OF IRON IN THE LABORATORY. 321 the ancients, and the slag left from old iron-works does not indicate the use of any flux. Some works of this description are still in operation in the Pyrenees, where the Catalan process is employed. The crucible is lined at the sides with thick iron plates, and at the bottom with a refractory stone. A quantity of red-hot charcoal is thrown into it, and the space above this is temporarily divided into two compartments by a shovel. The compartment nearest to the pipe through which the blast enters is charged with charcoal, and the other compartment with the calcined ore in small pieces. The shovel is then withdrawn, and a gradually increasing current of air supplied, fresh ore and fuel being added as they sink down. One part of the oxide of iron is reduced to the metallic state by the carbonic oxide, and the rest combines with the silica present in the ore to form a slag. After about five hours the spongy masses of bar-iron are collected into a ball upon the end of an iron rod, and hammered into a compact mass like the metal obtained in the puddling furnace. The blowing machine employed in the Pyrenees is one in which the fall of water from a cistern down a long wooden pipe, sucks in, through lateral apertures, a supply of air which it carries down with it into a box, from which the pressure of the column of water projects it with some force through the blast-pipe, the water escaping from the box through another aperture. In the North American bloomery forges a modernised form of the same process is adopted. The wrought-iron produced by this process always contains a larger proportion of carbon than puddled iron, and is therefore somewhat steely in character. 217. Extraction of iron on the small scale.-In the laboratory, iron may be extracted from hæmatite in the following manner:-A fire-clay crucible (A, fig. 237), about 3 inches high, is filled with damp charcoal powder, rammed down in successive layers; a smooth conical cavity is scooped in the charcoal, and a mixture of 100 grs. red hæmatite, 25 grs. chalk, and 25 grs. pipe-clay, is introduced into it; the mixture is covered with a layer of charcoal, and a lid placed on the crucible, which is heated in a Sefström blast furnace, fed with coke in small pieces, for about half an hour. On breaking the cold crucible, a button of cast-iron will be obtained. Chemically pure iron may be prepared by fusing the best wire-iron with about one-fifth of its weight of pure peroxide of iron, to oxidise the carbon and silicon which it contains. Some powdered green glass, perfectly free from lead, must be employed as a flux, and the crucible (with its cover well cemented on with fire-clay) exposed for an hour to a very high temperature. A silvery button of pure iron will then be obtained. Fig. 237.-Sefström furnace. 218. Chemical properties of iron.-In its ordinary condition, iron is unaffected by perfectly dry air, but in the presence of moisture it is gradually converted into hydrated sesquioxide of iron (2Fe2O3. 3HO), or rust. This conversion takes place more rapidly when carbonic acid is present, water being then decomposed, and carbonate of iron formed (Fe+ HO+ CO2 = FeO. CO2 + H); this is dissolved by the carbonic *This very useful furnace, shown in section in fig. 237, consists of two iron cylinders with a space (B) between them, into which air is forced through the tube C by a doubleaction bellows. The inner cylinder has a fire clay lining (D), through which four or six copper tubes (E) admit the blast into the fuel. X 322 FERROUS AND FERRIC OXIDES. acid present, and the solution rapidly absorbs oxygen from the air, depositing the sesquioxide of iron in a hydrated state 2(FeO.CO2) + 0 = Fe20, + 2CO2. When iron nails are driven into a new oaken fence, a black streak will soon be observed descending from each nail, caused by the formation of tannate of iron (ink) by the action of the tannic acid in the wood upon the solution of carbonate of iron formed from the nails. The diffusion of iron-mould stains through the fibre of wet linen by contact with a nail is also caused by the formation of solution of carbonate of iron. The iron in chalybeate waters is also generally present in the form of carbonate dissolved in carbonic acid, and hence the rusty deposit which is formed when they are exposed to the air. Iron does not rust in water containing a free alkali, or alkaline earth, or an alkaline carbonate. Concentrated sulphuric and nitric acids do not act upon iron at the ordinary temperature, though they dissolve it rapidly when diluted. Even when boiling, strong sulphuric acid acts upon it but slowly. When iron has been immersed in strong nitric acid (sp. gr. 1.45), it is found to be unacted upon when subsequently placed in diluted nitric acid, unless previously wiped; it is then said to have assumed the passive state. If iron wire be placed in nitric acid of sp. gr. 1.35, it is acted upon immediately, but if a piece of gold or platinum be made to touch it beneath the acid, the iron assumes the passive state, and the action ceases at once. A state similar to this, the cause of which has not yet been satisfactorily explained, is sometimes assumed by other metals, though in a less marked degree. 219. Oxides of iron.-Three compounds of iron with oxygen are known in the separate state, and one is believed to exist in certain compounds Protoxide of iron, or ferrous oxide, Sesquioxide or peroxide of iron, or ferric oxide, Magnetic oxide, or ferroso-ferric oxide, Ferric acid (?), FeO 3 FeO3. The protoxide of iron is little known in the separate state on account of the readiness with which it absorbs oxygen and forms sesquioxide of iron. If a little potash or ammonia be added to a solution of the green sulphate of iron (FeO. SO,), a whitish precipitate of hydrated protoxide of iron is formed, which immediately absorbs oxygen, and is converted into the dingy green hydrate of the magnetic oxide; on exposing this to the air, it absorbs more oxygen and becomes brown hydrated peroxide. This disposition of the hydrated protoxide to absorb oxygen is turned to advantage when a mixture of sulphate of iron with lime or potash is employed for converting blue into white indigo. The protoxide of iron is a strong base. Peroxide or red oxide of iron has been already noticed among the ores of iron, and has also been referred to as occurring in commerce under the names of colcothar, jeweller's rouge, and Venetian red, which are obtained by the calcination of the green sulphate of iron- Fe203 + SO, + SO,. 2 The hydrated peroxide (2Fe,O,. 3HO), obtained by decomposing a solution of perchloride of iron with an alkali, forms a brown gelatinous precipitate, which is easily dissolved by acids; but if it be dried and heated to dull redness it exhibits a sudden glow, and is converted into a modification which is dissolved with great difficulty by acids, although it has the same composition as the soluble form which has not been strongly heated. When the peroxide of iron is heated to whiteness it loses oxygen, and is converted into magnetic oxide of iron Existing as it does in all soils, sesquioxide of iron is believed to fulfil the purpose of oxidising the organic matter in the soil, and converting its carbon into carbonic acid, to be absorbed by the plant; the sesquioxide being thus reduced to protoxide, which is oxidised by the air, and fitted to perform again the same office. The sesquioxide of iron, like alumina, is a weak base, and even exhibits some tendency to play the part of an acid towards strong bases, though not in so marked a degree as alumina. Magnetic or black oxide of iron is generally regarded as a compound of the protoxide with the sesquioxide of iron (FeO. Fe,O), a view which is confirmed by the occurrence of a number of minerals having the same crystalline form as the native magnetic oxide of iron, in which the iron, or part of it, is displaced by other metals. Thus, spinelle is MgO. A10, ; Franklinite, ZnO. Fe,O,; chrome-iron ore, FeO. Cr2O,. The natural magnetic oxide was mentioned among the ores of iron, and this oxide has been seen to be the result of the action of air or steam upon iron at a high temperature. The hydrated magnetic oxide of iron (Fe,O,. HO) is obtained as a black crystalline powder by mixing one equivalent of protosulphate with one equivalent of persulphate of iron, and pouring the mixture into a slight excess of solution of ammonia, which is afterwards boiled with it. Magnetic oxide of iron, when acted upon by acids, yields mixtures of protosalts and persalts of iron, so that it is not an independent basic oxide. Ferric acid is only known in combination with bases as ferrates. When iron filings are strongly heated with nitre, and the mass treated with a little water, a fine purple solution of ferrate of potash is obtained. A better method of preparing this salt consists in suspending 1 part of freshly precipitated sesquioxide of iron in 50 parts of water, adding 30 parts of solid hydrate of potash, and saturating the mixture with chlorine (Fe2O3 + Cl2 + 5KO = 3KC1 + 2(KO. FeO3); the ferrate of potash forms a black precipitate, being insoluble in the strongly alkaline solution, though it dissolves in pure water to form a purple solution, which is decomposed even by dilution, oxygen escaping, and hydrated peroxide of iron being precipitated; 2(KO. FeO3) = 2KO + Fe2O, +03. A similar decomposition takes place on boiling a strong solution, or on adding an acid with a view to liberate the ferric acid. The ferrates of baryta, strontia, and lime are obtained as fine red precipitates when solutions of their salts are mixed with ferrate of potash. 220. Protosulphate of iron, copperas, green vitriol, or ferrous sulphate, is easily obtained by heating 1 part of iron wire with 1 parts of strong sulphuric acid, mixed with 4 times its weight of water, until the whole of the metal is dissolved, when the solution is allowed to crystallise. Its manufacture on the large scale by the oxidation of iron pyrites has been already referred to. It forms fine green rhomboidal crystals, having the composition FeO. SO. HO + 6Aq. The colour of the crystals varies somewhat, from the occasional presence of small quantities of the sulphate of sesquioxide of iron (Fe,O,. 3SO,). It dissolves very easily in twice its weight of cold water, yielding a pale green solution. When the commercial sulphate of iron is boiled with water, it 824 EQUIVALENT AND ATOMIC WEIGHTS OF IRON. yields a brown muddy solution, in consequence of the decomposition of the sulphate of sesquioxide of iron contained in it, with precipitation of a basic sulphate. The sulphate of iron has a great tendency to absorb oxygen, and to become converted into the sulphate of sesquioxide. Thus, the ordinary crystals when exposed to air gradually become brown, and are converted into a mixture of the neutral and basic sulphates of the sesquioxide of iron 10(FeO.SO) + 05 = 3(FeO. 3SO) + 2FeO3. SO ̧ . This disposition to absorb oxygen renders the sulphate of iron useful as a reducing agent; thus, it is employed for precipitating gold in the metallic state from its solutions. But its chief use is for the manufacture of ink and black dyes, by its action upon vegetable infusions containing tannic acid, such as that of nut-galls. This application will be more particularly noticed hereafter. Sulphate of sesquioxide of iron, or persulphate of iron, or ferric sulphate, is found in Chile as a white silky crystalline mineral, coquimbite, having the composition, Fe,О ̧. 3SO, + 9Aq. 3 The phosphates of protoxide and sesquioxide of iron are found associated in the mineral known as vivianite or native Prussian blue. 221. Sesquichloride, or perchloride of iron or ferric chloride (Fe,Cl), is obtained in beautiful dark green crystalline scales when iron wire is heated in a glass tube through which a current of dry chlorine is passed, the sesquichloride passing off in vapour, and condensing in the cool part of the tube. The crystals almost instantly become wet when exposed to air, on account of their great attraction for water. The perchloride of iron may be obtained in solution by dissolving iron in hydrochloric acid, and converting the protochloride of iron (FeCl) thus formed into perchloride by the action of nitric and hydrochloric acids (p. 167). The solution of perchloride of iron has been recommended in some cases as a disinfectant, being easily reduced to protochloride, and thus affording chlorine to unstable organic matters in contact with it (p. 146). A solution of perchloride of iron in alcohol is used in medicine under the name of tincture of iron. 222. Equivalent and atomic weights of iron.-When iron is dissolved in hydrochloric acid, 28 parts by weight of iron combine with 1 eq. (35.5 parts) of chlorine, displacing 1 part of hydrogen; hence 28 is the equivalent weight of iron. The specific heat of iron and its isomorphism with magnesium, zine, and cadmium, show that its atomic weight must be represented by double the equivalent, or 56, so that iron is a diatomic or biequivalent element. The atomic formula of the oxides and chlorides of iron would then be written thus (Fe = 56)— Ferrous oxide, Fee Ferric oxide, Fe„Ð ̧ Ferrous chloride, FeCl The molecular formula of ferric chloride has been confirmed by the determination of the specific gravity of its vapour, which has been found to be 165 times that of hydrogen. If, therefore, one volume (or one atom) of hydrogen be represented as having a weight 1, two volumes (or one molecule) of ferric chloride vapour would weigh (165 × 2) 330, = PEROXIDE OF MANGANESE. 325 a number nearly agreeing with the sum of two atoms of iron (112) and six atoms of chlorine (2130). It will be remarked that iron possesses a different atomicity accordingly as it exists in ferrous or ferric compounds. Thus, in ferrous oxide (FeO) and ferrous chloride (FeCl), it occupies the place of two atoms of hydrogen, and is diatomic; but in ferric oxide (Fe,O,) and ferrie chloride (Fe,Cl) each atom of iron occupies the place of three atoms of hydrogen, and is triatomic. Some chemists designate the diatomic iron existing in ferrous compounds by the name ferrosum (Fe"), and the triatomic iron of the ferric compounds by ferricum (Fe""). MANGANESE. 223. Manganese much resembles iron in several particulars relating both to its physical and chemical characters, and is often found in nature, associated, in small quantities, with the compounds of that metal. The metal itself has not been applied to any useful purpose. It is obtained by reducing carbonate of manganese (MnO. CO) with charcoal, at a very high temperature, when a fused mass, composed of manganese combined with a little carbon (corresponding to cast-iron), is obtained, which is freed from carbon by a second fusion in contact with carbonate of manganese. Metallic manganese is darker in colour than (wrought) iron, and very much harder; it is brittle, and only feebly attracted by the magnet. It is somewhat more easily oxidised than iron. 224. Oxides of manganese.-Three distinct compounds of manganese with oxygen have been obtained in the separate state, and two others are believed to exist in combination, but have not been satisfactorily made out in the anhydrous state The binoxide of manganese is the chief form in which this metal is found in nature, and is the source from which all other compounds of manganese are obtained. Its chief mineral form is pyrolusite, which forms steel-grey prismatic crystals; but it is also found amorphous, as psilomelane, and in the hydrated state as wad. In commerce pyrolusite is known as black manganese, or simply manganese, and is largely imported from Germany, Spain, &c., for the use of the manufacturer of bleaching-powder, the glassmaker, &c. It is also used as a cheap source of oxygen, which it evolves when heated to redness, leaving the red oxide of manganese, MnO̟. The binoxide of manganese is an indifferent oxide, and does not combine with acids; when heated with strong sulphuric acid, it loses half its oxygen, and forms the protoxide of manganese, which is a powerful base, and combines with the sulphuric acid to form sulphate of manganese-MnO2+ HO. SO, MnO. SO, + но Since the natural binoxide contains peroxide of iron, some persulphate of iron is formed at the same time; but if the mixture be dried and heated to redness, the iron-salt is decomposed, evolving sulphuric acid, and leaving = + 0. |