SULPHIDE OF IRON. PROTOSULPHIDE OF IRON. SULPHURET OF IRON.

FeS.

This compound is occasionally met with in nature.

Preparation.-It may be prepared by the direct combination of iron and sulphur; this combination may even take place at the ordinary temperature; a mixture of sulphur and iron filings, if kept for some time in a moist state, become converted into sulphide of iron; such a mixture is sometimes called Lemery's volcano; the combination takes place with considerable evolution of heat, and if the mixture be buried in sand it forms a sort of mimic volcano.

The best method of preparing sulphide of iron, however, consists in projecting, by small portions at a time, into a redhot crucible, an intimate mixture of 30 parts of iron-filings with 21 parts of flowers of sulphur, always waiting till one portion has combined before adding another.

A hydrated (proto-) sulphide of iron is obtained when a solution of a protosalt of iron is mixed with an alkaline sulphide.

Properties.-(Proto-) Sulphide of iron is a dark gray substance, having a metallic appearance; it is easily oxidized when exposed to moist air, being converted into sulphate of the (prot-) oxide; when large masses of sulphide are oxidized in this way, sufficient heat is often evolved to set fire to the rest of the mass, and hence the dangerous fires in coal-mines where large quantities of this mineral exist.

When heated with free access of air, sulphurous acid is evolved, and the iron converted into magnetic oxide.

Sulphide of iron is perfectly insoluble in water, but dissolves in most acids, with evolution of sulphuretted hydrogen, and production of a proto-salt of iron :FeS+HO.SO, FeO.SO,+HS.

The hydrated sulphide of iron forms a black precipitate, which, when exposed to the air, is very rapidly converted into sulphate. It is somewhat soluble in alkaline sulphides, but is precipitated from the solutions by boiling; the hydrate dissolves very easily in most acids.

Uses.-Sulphide of iron is very largely used in the laboratory, for the evolution of sulphuretted hydrogen. The hydrated sulphide has been recommended as an antidote to corrosive sublimate and the salts of lead and copper; it is prepared for this purpose by precipitating solution of sulphate of iron with sulphide of ammonium, collecting on a cloth filter, and washing rapidly with hot water till the washings are no longer precipitated black by acetate of lead; the moist sulphide is then preserved in well-stoppered bottles.

SESQUISULPHIDE OF IRON, Fe,S,.

This sulphide is found in nature associated with the sulphide of copper, in copper-pyrites. It may be prepared by decomposing sesquioxide of iron by sulphuretted hydrogen at 212° F. (100° C.) It forms a grayish mass, which is decomposed when heated in close vessels, sulphur being evolved, and magnetic pyrites (Fe,S) left.

The sesquisulphide of iron is obtained as a black precipitate, when a solution. of sesquioxide of iron is added to an alkaline sulphide; if the experiment be reversed, a mixture of (proto-) sulphide of iron and sulphur is precipitated.

BISULPHIDE OF IRON. IRON PYRITES. MARTIAL PYRITES.

FeS,

The bisulphide of iron is found abundantly in nature in a crystallized state, often in well-defined cubes and dodecahedra. Its specific gravity is 4.98. It

has a fine brass-yellow color, and metallic lustre. It is generally unalterable in air at the ordinary temperature, but when roasted in air it disengages sulphurous acid, and is converted into sesquioxide of iron :—

When heated in close vessels, it gives up a part of its sulphur, and leaves magnetic pyrites.

Some varieties of iron pyrites are oxidized by exposure to moist air, being converted into sulphate of iron and sulphuric acid; this property is generally attributed to the presence of an inferior sulphide.

Bisulphide of iron is not affected by water or by hydrochloric acid. Nitric acid converts it into sulphate of sesquioxide of iron, with separation of sulphur, unless the acid be very concentrated. Boiling concentrated sulphuric acid also dissolves it, sulphurous acid being disengaged.

The bisulphide may be obtained artificially by heating the (proto-) sulphide with half its weight of sulphur, when it is left as a yellow powder.

Yellow octohedral crystals, resembling iron pyrites, may be obtained by heating a mixture of sesquioxide of iron, sulphur, and sal-ammoniac, in a sand-bath, to the temperature at which the latter is volatilized. It is also formed when the sesquioxide is acted on by sulphuretted hydrogen at a temperature exceeding 212° F.

Iron pyrites is employed as a source of sulphur; it is also, as before mentioned, turned to account in the preparation of alum and of various compounds of iron (green vitriol, &c.)

MAGNETIC PYRITES, Fe,S,=FeS,+6FeS Fe,S,,5 FeS.

This variety of pyrites, named from its magnetic properties, is found in nature in six-sided prisms of a bronze color. It is much more easily oxidized than the bisulphide, and evolves sulphuretted hydrogen when treated with sulphuric acid. It is always formed when either of the oxides of iron is strongly heated with an excess of sulphur, or when iron at a white heat is brought in contact with sulphur.

Another variety of magnetic pyrites, corresponding in composition to the magnetic oxide, is said to exist, its formula being Fe,S

The Tersulphide of Iron, FeS,, is not known in the separate state, but is said to be obtained in combination with sulphide of potassium when sulphuretted hydrogen is passed into a solution of ferrate of potassa in potassa; the tersulphide is decomposed, with separation of sulphur, when an attempt is made to isolate it.

SUBPHOSPHIDE OF IRON, Fe P.

This compound may be obtained by reducing the phosphate of (prot-) oxide of iron with charcoal at a high temperature; it is a gray, very hard, fusible substance. The presence of a very small quantity of this substance in a speci men of iron is capable of rendering it brittle, and hence unfit for the purposes of bar-iron.

IRON WITH CArbon.

§ 232. Only one carbide of iron of definite composition is known; this is obtained when ferrocyanide of potassium is calcined in close vessels, and the cyanide of potassium washed out of the residue with water; the black compound thus obtained has the composition, FeC,; when heated in contact with air, it is converted into sesquioxide of iron and carbonic acid.

When iron is heated in contact with carbon, it never takes up more than six per cent., which would cause the compound to approach to the formula Fe ̧C.

However, much smaller quantities of carbon are capable of giving rise to a notable alteration in the properties of the metal, a circumstance which will be further considered when we treat of the metallurgy of iron.

When iron containing carbon is dissolved in hydrochloric acid, a peculiar compound of carbon and hydrogen is evolved, which communicates a nauseous odor to the hydrogen thus produced.,

A boride of iron has been obtained by reducing the borate of iron by hydrogen. IRON WITH SILICON.-A compound of these elements may be obtained by strongly heating a mixture of iron filings, silicic acid, and carbon; the mass thus obtained has a metallic appearance, is malleable, and contains 9 or 10 per cent. of silicon. Most varieties of the iron of commerce contain 1 or 2 per cent. of silicon. When treated with acids, the silicide of iron is decomposed, leaving a residue of silica.

METALLURGY OF IRON.

§ 233. The following are the chief forms in which this metal is found in

nature.

Meteoric Iron, as its name implies, occurs in the metallic masses which occasionally fall upon the earth, and are known as aeroliths, or meteoric stones; in these, it is associated, in the metallic state, generally with cobalt, nickel, manganese, and some other metals, and with certain nonmetallic substances, as sulphur, carbon, phosphorus, and silicon.

Sesquioxide of iron, in the anhydrous state, is found in several minerals.

Oligist or specular iron (iron-glance), Fe,O,, occurs in rhombohedral crystals, which possess a certain metallic lustre, and spec. grav. 5.22. It usually contains a small quantity of the magnetic oxide. This mineral occurs chiefly in

Elba.

Micaceous iron consists also of sesquioxide; it is found in thin, hexagonal tables, with metallic lustre.

Red hæmatite (sometimes called blood-stone) is another form of the sesquioxide, occurring generally in reniform masses of a radiated fibrous structure; its spec. grav. is about 5, and its hardness very considerable; this latter property renders it useful for burnishing. Hæmatite has a brownish-red color, which changes, under some aspects, to steel-gray; its powder is red.

Brown hæmatite is a hydrated sesquioxide of iron: its form is similar to that of the red hæmatite.

Etite, kidney form clay-ironstone, or eagle-stone forms globular masses, consisting of hydrated sesquioxide of iron associated with clay.

Oolitic iron-ore has a similar composition, and is found in small round grains, aggregated together, like the milt of a fish, whence its name.

The ores known as morass-ore, swamp-ore, and meadow-ore, consist of hydrated sesquioxide of iron.

Magnetic iron-stone (Fe,O) is found chiefly in Sweden; its color is dark gray, and spec. grav. about 5.1

Iron-sand, which has a black color and metallic lustre, is composed chiefly of the magnetic oxide; it generally contains titanium.

The mineral termed umber, which is used as a pigment, consists of the hy drated oxides of iron and manganese.

Andrews has recently examined a specimen of this ore, in which part of the protoxide of iron was replaced by magnesia.

The two varieties of pyrites, viz. magnetic pyrites (Fe,S,), and common, or cubical pyrites (sometimes called radiated pyrites) have been already mentioned. (Proto-) Carbonate of iron occurs in two varieties; spathic (or sparry) iron-ore is sometimes found in amorphous masses, and sometimes crystallized in rhombs, octobedra, and dodecahedra. Its color varies between brown and yellow, and its spec. grav. from 3.6 to 3.8. It becomes dark when exposed to air, or when heated. Spathic iron-ore often contains a little manganese. The other variety, common clay-iron-stone (black-band) is yellow, or red-brown, and varies in spec. grav. from 2.9 to 3.5; it is generally, as its name imports, associated with clay. The above minerals, though containing iron in abundance, are not all made use of for the extraction of iron, and therefore should not, strictly speaking, be designated ores of that metal.

In this sense, the only true ores of iron are, the magnetic oxide, the anhydrous sesquioxide, the hydrated sesquioxide, and the (proto-) carbonate. The minerals containing sulphur and phosphorus are not employed, since they would yield an inferior product.

The manufacture of iron may conveniently be divided into 1. The preparation of the ores, 2. the extraction of the metal, and 3. its purification.

The preparation of the iron ores is very simple; the earthy ores are merely subjected to a species of rough levigation, by which the greater part of the clay is separated. Those ores which occur in rocks or large masses, clay iron-stone, for example, are roasted, by which the water and carbonic acid are expelled, and the ore is rendered more friable.

The extraction and purification of the iron, when the ore is very pure and rich, are sometimes effected in one process.

A large rectangular crucible is employed, the sides of which are formed of thick plates of cast-iron, and the bottom of very refractory stone; this crucible is furnished with a tuyère, or air-pipe, of copper, by which a rapid stream of air may be directed into the crucible. In order to charge the latter, a quantity of redhot charcoal is thrown into the bottom, and an iron-shovel is then held so as to divide the space above the charcoal into two compartments, one of which is charged with the previously roasted mineral, and the other with charcoal; the shovel is then withdrawn, and a gradually increasing current of air supplied by the tuyère, whilst the workman stirs the mass; in this manner, a spongy mass of metal is obtained, which is freed from the fused slag by hammering, and is then forged into bars. The explanation of this process is simple enough; the carbon is converted into carbonic acid at the expense of the air introduced into the crucible; this carbonic acid then coming in contact with a mass of redhot charcoal, is reduced to the state of carbonic oxide, which, in its turn, abstracts the oxygen from the iron-ore, thus reducing it to the state of metal, which is at first disseminated through the mass, and afterwards accumulated by the workman into a spongy state; the whole of the iron, however, is not reduced, for part of it, in the state of (prot-) oxide, combines with the silicic acid contained in the ore to form a fusible scoria or slag, which flows to the bottom of the crucible, whence it is drawn off from time to time.

The process lasts about six hours, and yields from 24 cwts. to 3 cwts. of marketable iron for every 94 cwts. of ore, with a consumption of about 10 cwts. of charcoal.

The process above described is very seldom employed, since it involves a considerable loss of metal, and can only be carried into operation with particular

ores.

We shall now proceed to consider the process generally used for smelting ironores, which consists in converting the iron into a fusible carbide, by exposing the oxide to a very high temperature in contact with carbon, and in a subsequent purification of the resulting product.

The extraction of the metal from the ore is effected in a blast-furnace, which has the form of two truncated cones joined together at their bases, and is lined with very refractory brick or stone.

Air is forced into this furnace, by means of a steam-engine, through two or three tuyère-pipes.

In order to obtain the compound of iron with carbon in a fused state, it is of course necessary that a fusible slag should be formed which contains all the impurities of the ore. These impurities (technically termed gangue) consist generally of silica and alumina (combined in the form of clay), and since these are very infusible, it is necessary to add some substance which shall form a liquid combination with them at the temperature of the furnace. For this purpose, carbonate of lime is employed, which produces with the clay a double silicate of alumina and lime, fusing with comparative readiness. Should the gangue consist of quartz only, the ore is mixed with an argillaceous iron-ore, and a quantity of limestone added. When the gangue consists of carbonate of lime, a proper quantity of clay, or of argillaceous ore is added. The substances thus added to promote the fusion of the slag are termed fluxes.

The carbonate of lime not only acts as a flux, but likewise prevents any loss of iron which would otherwise result from the production of a double silicate of alumina and oxide of iron, the latter base being replaced in the combination by an equivalent proportion of lime.

The operation is commenced by charging the furnace to a certain height with fuel, and, after this has fairly kindled, introducing a quantity of ore, mixed with flux, from the top of the furnace; the blast is increased gradually, and alternate layers of fuel and ore introduced from time to time. The fused combination of iron with carbon collects at the bottom of the furnace, and above it, a layer of slag; these are drawn off from time to time, through different apertures, the former being allowed to run into moulds of sand, in which it is cast into rough masses, sent into the market as pig-iron, or cast-iron. The process is not interrupted till the furnace is in want of repair.

The fuel employed in the blast-furnaces is either charcoal, wood, or coke; the latter is preferred where (as in England) coal can be obtained in abundance.

When charcoal is employed, the amount of lime present, in proportion to the clay, is so regulated that the most fusible slag shall be formed, and a lower temperature is required than when coke is employed; for, since this latter always contains more or less sulphur (as iron-pyrites), it is necessary to employ more limestone, in order to convert the sulphur into sulphide of calcium, and thus to prevent its passing into the pig-iron, the quality of which it would injure. The excess of limestone, however, renders the slag less fusible, and it becomes necessary to build the furnace higher, in order to raise the temperature to the required extent.

A considerable saving of fuel has been effected by feeding the furnace through the tuyères with air heated to 400° or 500° F., instead of with cold air, the air being raised to that temperature by the waste heat of the furnace. This is generally known as the hot-blast process.

The reactions which take place in the interior of the blast-furnace are easily followed, if we bear in mind the existence of an ascending column of atmospheric air and other gases, and of a descending column consisting of a mixture of ore, fuel, and slag. The air entering through the tuyères, at the lower part of the furnace, is at once deoxidized by the fuel, its oxygen being entirely converted into carbonic acid; the latter, coming in contact with another portion of heated fuel, is reduced to carbonic oxide, by which the reduction of the ore is chiefly

The most fusible slag is that in which the oxygen in the acid is double that in the two bases. The presence of manganese augments the fusibility of the slag.