IKuN S.MELTIM,, ETC.J 



CHEMISTRY. 



377 



which reaches from the German Ocean to the west coast ; 

 and the whole of the country from Ayr to Edinburgh is 

 dotted with iron furnaces, producing thousands of tons of 

 the metal annually. 



In England, Staffordshire and the neighbouring 

 countk : produce immense quantities of the ore ; and in 

 most c,.ics abundance of coal is obtained from mines or 

 seams, above and below those of the mineral. 



The ore, on being brought to the surface, is mixed with 

 small coal and roasted for many hours ; the mass is then 

 broken up and taken to the smelting furnace, whicli is 

 generally about thirty feet high ; mixtures of the ore, 

 coal, and limestone, which acts as a flux, are thrown into 

 the top of the furnace, and an intense heat is maintained 

 by means of powerful air-engines propelled by steam 

 power. Every twelve hours the bottom of the furnace 

 is tapped, and the melted metal is run into long furrows 

 called " sows," adjacent to which are smaller ones called 

 " pigs ;" when cool these are sent to market as pig-iron. 

 The following engraving represents the ordinary kind of 

 smelting fumace. 



Fig. ee. 



But the metal in this form is very brittle, and would 

 be almost useless unless further processes were brought 

 to bear on it. Being broken up into small pieces, the 

 pig-iron is then cast into a puddling furnace, in which it 

 is continually stirred about by means of a rake. After 

 a time it acquires a peculiar appearance, becomes soft 

 and agglutinated, and is then removed to a block, on 

 which it is hammered by steam hammers until all the 

 impurities are driven- out. It has now become fit for 

 rolling, and is thus fashioned at a white heat into sheet, 

 bar, or rod-iron. 



Iron may be protected from rust by either tinning its 

 surface or by covering it with a thin coating of zinc a 

 process which baa been termed "galvanising." It may 

 be drawn into very fine wire, being very tenacious. It 

 has the singular property of welding ; that is, two pieces 

 at a red heat may be united together if well hammered. 

 This property is only possessed by iron and platina. 



Iron may be cast into moulds of any form, and thus 

 castings of any size may be obtained. Cast-iron is of 

 inferior strength to bar or rod-iron, owing to its con- 



TOL. i. 



taining several impurities. Mr. Bessemer has introduced 

 an ingenious process for the purpose of making 

 " wrought" iron from the ore. This he effects by driving 

 air into the furnace whilst the iron is in a melted state. 

 By these means its impurities are burnt away. 



The most important combination of iron is that with 

 carbon ; and, as a late writer has remarked, most probably 

 nitrogen is also present in minute quantities, inasmuch 

 as a direct combination of carbon alone with iron does 

 not afford a substance corresponding in all its properties 

 with that known as steel. In many of their qualities 

 cast-iron and steel are similar; but the latter has an 

 elasticity, ductility, <fec., which, as physical charac- 

 teristics, constitute an enormous difference. Iron and 

 steel may be easily distinguished by dropping on each a 

 little nitric acid, when the pure iron will present only a 

 white appearance, whilst the steel will afford a black 

 mark, indicating the presence of carbon. 



The qualities and value of wrought-iron and steel 

 vary exceedingly, owing to the admixture of various 

 substances, such as phosphorus, silica, <fec. In England, 

 the best is that produced in Staffordshire ; but 

 this is exceeded by that obtained from Sweden. 

 Iron produced by the cold and hot blast also 

 varies in its characteristics. By the latter mode, 

 the iron has induced in it greater tenacity, 

 the air being heated to a temperature of GOO 

 to 700 degrees before it is admitted into the 

 smelting furnace. Iron produced by charcoal 

 is far better, in all respects, than that produced 

 by coke or coal. 



Of late years, the uses of iron and steel 

 have been enormously extended. With respect 

 to steel, we may remark, that steam-ships are 

 now entirely constructed of it; oven boilers and 

 the masts of vessels have been made from 

 it : some pieces of ordnance have been also 

 manufactured from steel ; and their extra- 

 ordinal y tenacity, we need not state, oreseuts a 



a aihantage. 



Iron combines with oxygen in four propor- 

 tions, Ihe symbols and properties of which are 

 as follows : The protoxide (Fe O) is produced 

 by adding a solution of potash to one of the 

 protoxide of iron, when a green precipitate is 

 produced. When this is boiled, a black powder 

 is the result. The peroxide (Fe,, Oj) is readily 

 obtained by adding an alkaline solution to the 

 nitrate of iron, and is a red-coloured substance. 

 The presence of this in nature gives the rich 

 red tint to the rocks of the old red sandstone, 

 and is the cause of the colour of blood, <fec. 

 The black oxide (Fe 3 , O,) lias, like the metal, 

 decided magnetic properties : it is familiarly 

 known in the scales so often seen when wrouglit- 

 iron has been heated to redness, and is a 

 common product of the blacksmith's shop. 

 Ferric acid (Fe O,) is the state in which iron 

 is f. HUM! combined with the largest proportion of oxygen. 

 Chlorine unites with iron in two proportions, forming 

 a proto-chloride (Fe Cl) when iron is dissolved in hydro- 

 chloric acid; and a sesqui-chloride (Fe 8 , C1 3 ) when 

 chlorine is passed over iron filings at a red heat. There 

 exist two sulphides of iron. That which is best known 

 constitutes the iron pyrites (Fe S ), so common as an 

 ore of the metal. The proto-sulphide is readily produced 

 by bringing a roll of sulphur in contact with a bar of 

 iron heated to redness. The metal will immediately be 

 seen to melt away ; and the dross which fulls down, and 

 which should be received in dry sand, forms the sub- 

 stance required. 



Iron and sulphuric acid readily combine to form the 

 sulphates, of which there are two ; one being produced 

 as a proto, and the other as a per-salt. The proto-sul- 

 pliate is obtained by dissolving iron in dilute sulphuric 

 acid : during the process, water is decomposed, and 

 abundance of hydrogen is evolved. The proto is easily 

 converted into the per-sulphate by exposure to the air, 

 or by the addition of nitrous or nitric acid, wken the 



