attempts have been made in recent years to revive the ancient principle of direct extraction, but the blast-furnace has been brought to such a pitch of excellence as regards economy of materials, and perfection of its reducing action, as to outstrip all rivals.

In reducing the ore directly, two things have to be taken. into account: 1st, the easy oxidation of iron by carbonic acid and water, at the temperature at which ferrous oxide is reduced to the metallic state by carbon, carbonic oxide, or hydrogen; 2nd, the facility with which iron at a redheat combines with carbon. Now if gaseous fuel be employed as a source of heat and reducing energy, carbonic acid and water will be produced, and a large excess of unburnt gas would be required to neutralise the oxidising tendency of these bodies, and this excess would require to be increased with the temperature. Sir L. Bell states that at a temperature near whiteness, iron will be oxidised, if carbonic acid and carbonic oxide are present in equal proportions, and that when the volume of carbonic acid CO2, to carbonic oxide CO, is as 11 to 100, the reduction of protoxide of iron is no longer possible. In other words, gas ceases to be useful as a reducing agent, when it contains one tenth its volume of burnt gas. This enormous volume of unburnt gas not only represents a great waste of fuel, but also a great quantity of heat is absorbed in raising it to the requisite temperature, which can only be done by strongly heating the whole of the gas previous to its partial combustion. In the blastfurnace the combustion of solid carbon to carbonic oxide produces the requisite temperature, without producing an oxidising atmosphere, which makes that furnace unequalled for reducing energy.

With regard to the second difficulty, viz., the readiness with which iron combines with carbon at a red-heat. If solid carbon be employed to reduce oxide of iron, then only the exact quantity of carbon for such reduction must be added, in order to avoid carbonisation of the iron,

and the operation must be performed in a closed vessel, heated from the outside. But for this purpose the ore must be broken small, the flux and fuel well mixed with it, and the temperature maintained for a long time, with a considerable expenditure of fuel.

In all direct processes malleable iron can only be produced, by sacrificing a considerable portion of the iron, which passes into the slag, and this loss is in inverse ratio to the amount of carbon taken up by the iron. On the other hand, the blast-furnace allows of the most perfect utilisation of the fuel, and the slags produced therein are practically free from iron. Moreover, the pig-iron produced can be converted into malleable iron or steel in the Bessemer-converter, without an additional expenditure of

fuel.

Catalan process.-This primitive method of making iron is now practically obsolete, only being retained in remote districts where there is an abundant supply of wood fuel and rich ores, as in the Pyrenees. It consists

Fig. 4.

of a hearth made of sandstone, and lined with charcoal Fig. 4. The back and opposite walls are faced with iron, and of the remaining sides, one is of rough masonry, and the other, which forms the working side of the furnace, consists of two iron plates, the lower one having a hole for tapping the slag. The top of this plate serves as a fulcrum for the workman's tools. The twyer is made of sheet copper, and generally inclines at an angle of from 30 to 40 degrees, according to the degree of carbonisation desired. The blast is supplied by a blowing apparatus called a trompe Fig. 5. The water falling down the pipe A, drags air through the inclined openings BB. This mixture of air and water falling into the cistern is divided into two streams, the air rising and passing forward into the twyer, the water running out of the cistern at C.

Hæmatites are smelted directly, but carbonates are first

calcined. The ore in small

a

pieces is charged in with charcoal, several lumps of charcoal being placed near the twyer. The heat is gradually raised until pasty mass is formed, which is then pushed towards the twyer. After two hours the full blast is turned on and the slag tapped off. The slag is fluid and formed at the expense of the iron; it is a silicate of iron 2FeO, SiO2, containing lime, magnesia, and oxide of manganese, which composition is favourable for the trans-1 ference into the slag of any phosphorus that may be present. When the whole of the ore is reduced, the blast is stopped, and the spongy masses of iron worked into a lump or Fig. 5. bloom with iron tools; it is then carried to the shingling hammer and shingled, in order to squeeze out the slag and consolidate the porous mass of iron. It is then re-heated in a similar fire and the iron finished under the hammer. If the operation is prolonged by arranging the twyer at a less inclination than in the above case the iron combines with carbon and forms steel. The conditions governing the formation of slag in this hearth are similar to those of the puddlingfurnace, and different to those in the blast-furnace; the former being oxidising in its action, the latter reducing.

The chemical changes occurring in the Catalan process may be briefly stated thus-The air introduced by the twyers, being brought in contact with red-hot charcoal, causes a brisk combustion, with the formation of carbonic acid CO. This gas on ascending through other highlyheated charcoal is reduced to carbonic oxide CO. The latter being a reducing agent acts on the ferric oxide Fe2O3, which is partly reduced to the metallic state, and partly to ferrous oxide FeO, which unites with silica and other foreign matters to form the fusible slag mentioned above.

American bloomery, Jersey-, and Champlain forge. This simple method, largely employed in the United States and Canada, is a modified form of the Catalan-process, and is conducted in much the same manner, except that the ore is in a finer state of division, and the furnace is worked continuously.

The furnaces are built in rows on either side of a wall, each measuring about 28 by 30 inches in area by 25 feet in height above the twyers, and 14 inches below them. The sides are formed with cast-iron plates, and the bottom of beaten earth or cinders. In some cases a hollow iron bottom, cooled by water, is used. A water-box 12 inches by 8 inches is let into the twyer plate, and the water, after cooling the twyer, passes through the bottom plate. The twyers are arranged so that the blast strikes the middle of the hearth. In front of the forge, at 16 inches above the bottom, is a flat iron hearth 18 inches wide, and in the side plate beneath it is a tap-hole for withdrawing the slag. The blast is used at a pressure of 1 to 12 lbs. per square inch, and heated to 300° C. by passing through cast-iron pipes in chambers fixed above the hearth.

The fire being made up, the forge is heaped up with charcoal, and crushed ore is scattered over the fuel. The ore is gradually reduced, without melting, as it descends, and the reduced grains collect into an irre