CHAMBERS'S INFORMATION FOR THE PEOPLE. 



formation. But such as are rich in the metal, or 

 from which it can be extracted with comparative 

 ease and profit, are only plentiful in certain dis- 

 tricts ; and in some countries where they do occur, 

 the localities are so inconveniently situated for 

 cheap carriage, that ores, even of the richest kind, 

 cannot be profitably mined. The leading kinds of 

 iron ore are : I. Magnetic or black oxide of iron ; 

 2. Haematite, or red oxide of iron ; 3. Brown 

 haematite, or hydrated sesquioxide of iron ; 4. 

 Spathic carbonate of iron ; 5. Clay, or earthy car- 

 bonate of iron, including the black-band variety. 



I. Magnetic oxide of iron is the richest ore, 

 containing, when pure, nearly 73 per cent, of iron. 

 It was formerly called loadstone, and has been 

 long worked in Norway, Sweden, Russia, India, 

 Canada, and the United States, where, as in 

 other countries, it is found in igneous and meta- 

 morphic rocks. It is usually smelted with charcoal, 

 and the ore having few impurities, a high-class 

 iron is thus produced. 2. Hematite, or sesqui- 

 oxide of iron, is nearly as rich in iron as the last, 

 containing, when pure, 70 per cent. Chemically, 

 it is the same thing as iron-rust. When crystal- 

 lised, it is called specular iron ore. It often 

 occurs in compact reniform pieces, called ' kidney 

 ore.' A good deal of haematite is, however, found 

 as a loose, soft, earthy powder. This fine ore 

 occurs largely in England at Whitehaven and 

 Ulverstone, where it fills up hollows in the moun- 

 tain-limestone. More usually, it takes the form 

 of a regular dike or vein. Fully 2,200,000 tons 

 of it were raised in England in 1871. 3. Brown 

 hcematite, or hydrated sesquioxide of iron, con- 

 tains, when pure, 60 per cent, of iron. It is 

 not so rich, therefore, as red haematite, and 

 also differs from it in containing about 14 per 

 cent, of water. Brown is easily distinguished 

 from red haematite by its brown streak, that of the 

 latter being red. Under the name brown haematite 

 are included not only the compact kinds, often 

 botryoidal, mammillated, and fibrous, but also bog- 

 iron ore and other earthy varieties. In England, 

 this ore is found most largely in the Forest of Dean, 

 and in the Oolite of Northamptonshire, where 

 it occurs in an earthy form, and in superficial 

 deposits. In 1871, 2,000,000 tons were raised. 

 Earthy brown haematite is the chief ore worked 

 in France and Belgium. 4. Sparry carbonate 

 of iron, spathose or spathic iron ore. This 

 ore is, as its name denotes, a sparry marble-like 

 substance. When pure, it contains 48 per cent, 

 but it is usually mixed to a considerable extent 

 with manganese, and also with a little magnesia. 

 It occurs abundantly in Prussia, and the iron 

 made there from spathic ore is highly prized for 

 making steel. In England, spathose ore is 

 worked in the Brendon Hills and at Exmoor, 

 and has also been noticed at one or two places 

 in Scotland. 5. Clay and black-band ironstones, 

 earthy carbonates of iron. These are the ores 

 from which most of the iron made in Great 

 Britain is smelted. They are found as balls 

 or nodules in the shales, or form continuous beds 

 of themselves in the strata of the coal-measures. 

 Ore of this kind also occurs over an extensive 

 area of the Lias formation in Yorkshire, as well as 

 to some extent m the Wealden and Tertiary of the 

 south of England. Being dull, earthy, slaty, or 

 stone-like substances, their value has, in some 

 instances, only been discovered in recent years. 



406 ' 



and occasionally after large quantities of valuable 

 material had been rejected as worthless. 



The following analysis will give a good idea of 

 the composition of three leading varieties of 

 British argillaceous iron ores. No. I, by J. Spiller, 

 is from the coal-measures, Lowmoor, Yorkshire ; 

 No. 3, by Dr Murray Thomson, is Scotch black- 

 band from the same formation ; and No. 2, by A. 

 Dick, is from the Lias (Cleveland) district of 

 Yorkshire : 



It will be seen that these are far from being 

 pure ores. Manganese, calcium, and magnesium 

 carbonates, clay, phosphoric acid, sulphur, and 

 potash, are the foreign substances most frequently 

 present in them, and of these, sulphur and phos- 

 phorus are the most deleterious. All argillaceous 

 ores undergo a preliminary roasting before being 

 smelted. Clay iron-stones lose from 25 to 30 

 per cent, and black-band ores from 40 to 50 per 

 cent, of their weight by calcination. The loss is 

 chiefly carbonic acid and water, and there is left 

 oxide of iron, and earthy or clayey matter. 



Except in savage or semi-civilised countries, 

 where more primitive methods are in use, iron 

 ore is now always smelted in a blast-furnace. 

 This is a circular tower of massive brickwork 

 hooped round with strong iron rings, or it is wholly 

 cased with malleable iron plates, in which case 

 the brickwork is not so thick. Until lately, blast- 

 furnaces were seldom built more than 60 feet 

 high ; but many recently built ones are as high 

 as 80 and even 100 feet, as it is found that a saving 

 of fuel is obtained by the additional height. Inter- 

 nally they vary much in form, but perhaps the 

 barrel shape is the most prevalent. They are, 

 of course, lined with fire-brick: Fig. 2 is a dia- 

 grammatic section shewing a blast-furnace and 

 blowing-engine. There is an arrangement for 

 heating a coil of pipes in connection with the 

 blowing-engine, by which a powerful ' blast ' of 

 air heated to from 600 to 1000 F. is made to 

 enter the lower part of the furnace at several 

 points by nozzles called tuyeres. This is what 

 is called the 'hot-blast ;' but the old 'cold-blast' 

 is still used to a small extent, and is considered 

 to produce a superior iron. The materials put into 

 the blast-furnace, technically termed the ' charge,' 

 are calcined ore, coal or coke, and limestone to 

 act as a flux. Taking the simplest view of matters, 

 what takes place during the operation of smelting 

 is this : The metallic iron is reduced from the 



