METALS-METALLURGY. 



Oxide partly by the incandescent carbon of the fuel, 

 but more largely by carbonic oxide gas, which 

 is formed in large quantity in the furnace. But 

 as both the ore and the fuel contain such ingre- 

 dients as clay and sand, these must be converted 

 into a fusible slag with lime, in order to separate 

 them from the metal, otherwise the siliceous 

 matter would form a slag of silicate of iron, or, 



in other words, the slag would in that case abstract 

 the iron to the less of the smelter. The action 

 of the furnace is continuous that is, ore, fuel, and 

 flux are regularly thrown in at the top, and towards 

 the bottom of the furnace melted iron is always 

 trickling down and accumulating on the hearth. 

 The slag, which floats on the top of the liquid 

 metal, flows out over what is called the dam, and 



Fig. 2. Hot-blast Furnace. 



A, body of furnace ; B, hearth ; C, tuyere, by which hot air enters ; D, belt and cone for closing mouth of furnace ; F, blowing-engine ; 

 G, blowing-cylinder; H, receiver; I, oven for heating blast-pipes. 



in France by Aubutot as far back as 1811, and 

 that, moreover, this iron-master appears to have 

 clearly foreseen its value. In England and Scot- 

 land it is scarcely more than twenty years since 

 the saving of the 'waste gases,' as they are termed, 

 was seriously attempted. For reasons which we 

 have not room to state here, nearly all the early 

 attempts to utilise advantageously the gases in 

 question decidedly failed. Yet the prize awaiting 

 even moderate success was great, and the waste of 

 fuel going on almost culpable. Take the Cleve- 

 land district of Yorkshire, for example, where not 

 a single furnace existed till the middle of this cen- 

 tury, but which now sends annually 1,000,000 tons 

 of iron into the market There the waste gases 

 are successfully collected and consumed, saving, 

 according to one of the leading iron-masters in the 

 district, 000,000 tons of coal per annum. In that 

 part of the country, too, nothing but coke is used 

 for smelting, so that in Scotland, and in those 

 parts of England where bituminous coal is used, 

 the coal-gas generated in the furnace is also to 

 be considered. 



In those iron-works where the waste gases are 

 consumed for heating purposes, the most common 

 method of preventing their escape is this : The 

 mouth of the furnace is closed by what is called 

 a cup and cone valve, which only requires to 

 be opened at intervals to admit of the furnace 

 being fed. When shut, the gaseous products, of 

 which the carbonic oxide is the most useful 

 portion, are forced along a large pipe or pipes to 

 the steam-boilers and heaters, where, by a suitable 

 arrangement, they are burned in lieu of coal. 

 Formidable difficulties, however, attend this plan 

 when raw coal is used, and this has led Mr Ferrie, 



by means of a tapping-hole, the molten cast-iron 

 is run off twice or thrice in twenty-four hours. It 

 is run out into parallel rows of open moulds formed 

 in the sand ; the pieces so made are termed pigs, 

 hence the name pig-iron. 



We shall now take a glance at the successive 

 improvements which have been introduced in the 

 manufacture of cast-iron ; and as these relate 

 mainly to reducing the cost of production by 

 economising fuel, they are especially interesting 

 at the present time. Previous to 1618, when Lord 

 Dudley introduced coal, the only fuel used for 

 smelting was charcoal ; but the iron-masters of 

 that day did not like the change, and so charcoal 

 continued to be used till Abraham Darby tried 

 coal again at Coalbrook-dale in 1713. The make 

 of English iron, however, fell off greatly with the 

 innovation, and did not rally till the introduction 

 of coke about 1750. This at once gave a great 

 impetus to the manufacture ; and not long after, 

 namely, in 1770, came Watt's steam-engine, which 

 changed the scale on which not only this, but 

 every other manufacture, could be carried on. 

 The next great improvement was the introduction 

 of the hot-blast by Neilson of Glasgow in 1830, 

 which, roundly speaking, saved about one-half of 

 the fuel previously required to produce a given 

 amount of iron. Since then, several plans have 

 been tried for still further saving fuel, chiefly by 

 collecting and burning the gases generated in the 

 furnace to produce heat ; it being well known that, 

 in the case of open-mouthed furnaces, at least 

 two-thirds of the heating power of the coal is 

 wasted through the escape of combustible <;ases 

 into the air. It is not a little remarkable that a 

 plan for the utilisation of these gases was p;. tented 



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