gular mass at the bottom of the hearth. The earthy matters at the same time separate as slag. Fresh supplies of ore and fuel are added from time to time, and in about three hours a mass, weighing 300 lbs., termed 66 a bloom," is lifted and held before the twyers for a few minutes, then carried to the hammer and shingled. It is then reheated and fashioned into bars. Sir L. Bell says that such a process can only be conducted where high prices, fostered by protective duties, prevail, and where it would be inexpedient to incur the large outlay involved in the erection of modern ironworks.

The Chenot process was introduced about the year 1855, and was considered a great metallurgical discovery, but after a few years working it was abandoned, except in one locality in Spain, where its continuance depended on the possession of a quantity of charcoal screenings. which would otherwise have been wasted.

The furnaces are rectangular retorts built in pairs4 feet 6 inches long, 1 foot 8 inches wide, and 33 feet high. Beneath each retort is a rectangular tube of the same section, into which the metallic sponge is discharged. The total height of retort and tube is 50 feet. At the junction of the two parts are arranged four fireplaces, the flames from which circulate round both furnaces by a series of channels, which unite near the top and pass into a common flue. This mode of heating is very imperfect, as more heat is lost outside than passes into the retort. Four tons of fuel are required for the production of 1 ton of merchant-bars, and about 45 per cent. of the iron is lost. The retorts are charged with ore, broken small, and mixed with charcoal. The reduction extends over three days, producing a spongy mass of metallic iron, which requires three days to cool out of contact with air, to prevent rapid oxidation. sponge obtained is made into steel by melting in crucibles with carbon; or balled in a charcoal hearth,

The

F

4

Fig. 6.

then hammered, piled, re-heated, and rolled into bars of wrought iron.

Blair's process. In 1873 Mr. Blair in America introduced the Chenot process on an improved plan, but the furnace was irregular in its action, and the production small compared with that of the blast-furnace. The retorts are cylinders 3 to 4 feet in diameter, and 40 feet high. The great difficulty was to cause the heat to penetrate successfully to the centre. In order to effect this, Blair placed in the top of each retort a concentric cylinder, and through its axis a double blowpipe, by means of which a current of gas and air was forced in, producing by its combustion sufficient heat to make the ore and charcoal, charged into the annular space round the cylinder, red-hot.

Fig. 6 represents in section and plan one of a group of three furnaces. A is the retort, C the cylinder, D the gaspipe, E the air-pipe, F the chargingspace, G the annular space for combustion of the gas, K the gas-main, which introduces the gas at two different levels. This gas was originally obtained from the reduction of the ore, but its amount being found insufficient, a special gas-producer was afterwards provided. The cylinder L beneath the reduction. chamber receives the sponge of iron, and is kept hermetically closed while the iron cools, as in the Chenot furnace. The wrought iron walls are double, in order to allow a current of water to circulate through them.

Siemens' direct process.-This is one of the most recent attempts to extract iron in an economical manner from the ore in one operation, but it suffers under the disadvantages of all direct methods, as explained on page 43.

The furnace (Fig. 7) consists of a cylindrical rotating

chamber, 8 feet in diameter and about 9 feet long, and rests on four anti-friction rollers. The inside is lined with bauxite, which consists of alumina, ferric oxide, water, and a little silica. From this substance, when mixed with 3 per cent. clay and 6 per cent. plumbago, bricks are made. The working door is at one end, and beneath this is a tap-hole for slag. The furnace is heated with gas supplied from a gas-producer, the air being heated by passing through one of a pair of regenerators. Ore, in small pieces, is charged into the hot furnace with lime, and the cylinder rotated. When red-hot, about 20 per cent. of small coal is added as the reducing agent, and the velocity increased. The carbon and hydrogen of the coal, together with the carbonic oxide of the gas, react on the oxide of iron, removing its oxygen and liberating metallic iron, the particles of which gradually

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cohere to form a spongy mass, called a bloom. The lime and the basic lining of the furnace unite with the siliceous matters to form a slag, which, in consequence of its basic character, is highly favourable to the taking up of any phosphorus that may be present in the ore. When the reduction is complete, the slag is tapped off; then a quick rotation is imparted to collect the iron into three or more balls, which is effected by means of ribs projecting from the lining. The balls are then shingled, re-heated, and finished in the usual way. If steel is desired, 10 per cent. of spiegel-eisen is added after tapping off the slag. The charge is then melted and cast into moulds. In some cases the balls are treated for steel in the open-hearth furnace. The advantages claimed for this method are-economy of time, saving of fuel, and purity of the iron, since the metal is not brought in contact with solid fuel, as in the blast-furnace, except the coal added as a reducing agent.

In a newer form of the rotator the length is 10 feet 6 inches, and the same in diameter. At the back of the rotating chamber is fixed a water-jacket to keep the ring at the back cool. In order to maintain the circulation of water, and also to turn the charges over as the vessel revolves, four water pipes pass beneath the lining from back to front of the rotator, connected alternately with a valve at the front end, and the water-jacket at the back. Each pipe has two bends or knees, the lining on which stands above the general level of the furnace-lining. These knees serve to divide the bloom of iron at the conclusion into three balls.

QUESTIONS.

1. What is meant by the term "malleable iron"? State its chief physical properties.

2. How may iron be protected from rust? Describe the method invented by Professor Barff.

3. What do you understand by the "direct" method of extracting malleable-iron?

4. Under what disadvantages do all direct methods suffer with regard to economy of production?

5. Very pure iron may be obtained by direct methods; would the iron be equally pure if obtained from a coke blastfurnace and afterwards treated by puddling? Give reasons for your answer.

6. How would you extract the iron from a rich ore in a fine state of division?

7. When an ore consisting wholly of ferrous carbonate is heated to strong redness in a vessel from which atmospheric air is excluded, and the substance of which has no action on the ore, what chemical change occurs?

8. When iron is extracted in the malleable state from phosphoric ore in the Catalan forge, what becomes of the phosphorus?

9. What difficulties are met with in attempts to reduce iron ore by gas alone, without the admixture of solid fuel?

10. Describe Siemens' direct process of producing malleable iron, and roughly sketch the furnace employed.

11. Describe the production of iron in the American bloomery.

Pig- or cast-iron. In the indirect method of producing malleable iron, a crude product consisting of iron, carbon, silicon, phosphorus, sulphur, manganese, and very frequently other elements, such as copper, arsenic, titanium, chromium, etc., is first obtained; it is termed "pig-iron," and is D-shaped in section, being 3 or 4 inches square and about 3 feet long. Pig-iron is arranged into a variety of classes, according to the colour, texture, size of the crystalline plates, and general char