iron. 299 



country is principally extracted from clay iron stone. The ore, 

 broken into small pieces, is first roasted, to drive off any extraneous 

 volatile matter, and then exposed to a strong heat in a blast fur- 

 nace, along with limestone and coke. The lime, which is used as 

 a flux, combines with the earthy ingredients, (alumina and slica,) 

 and promotes their vitrification, while the carbon of the coke 

 unites with the oxygen of the oxide, leaving the metallic iron in a 

 liquid state, which is then allowed to run into large ingots, called 

 pigs, in sand moulds, and forms what is called crude, or cast iron. 

 In this state, however, it is not perfectly pure, and requires to be 

 again fused with charcoal, urged by the blow of a large pair of 

 bellows, When it assumes the consistence of paste, it is pressed 

 between steel rollers, which force out the remaining impurities, 

 as they retain the liquid form longer than the pure iron. The same 

 effect is produced by striking it with a forge hammer : in this state 

 it is called malleable, forged, or bar iron. 



Purified or bar iron has a grey or blackish -white colour ; 

 it is very malleable and ductile, and is susceptible of a 

 very high polish. Its specific gravity is about 7 "8. It is one 

 of the most infusible of the metals, but at a temperature 

 considerably below its melting point it becomes soft, and 

 possesses the property of welding to great perfection. It is at- 

 tracted by the magnet, and capable of having the magnetic virtue 

 imparted to it. The affinity of iron for oxygen is very great : it 

 is soon tarnished and oxidized when exposed to the air, particu- 

 larly if it be moist. It burns with great splendour in oxygen gas, 

 and when heated to redness in the open air, it absorbs oxygen 

 rapidly, and is converted superficially into black scales ; these 

 scales are separated by percussion, and form what is commonly 

 called the black oxide of iron. 



Tron has been long used medicinally, and appears to be the only 

 metal having any sensible activity, which is not noxious to the 

 animal system. When administered internally, its effects are those 

 of a powerful tonic ; it increases the force of the circulation, gives 

 the blood, it has been affirmed, a more florid hue, promotes diges- 

 tion excites the healthy secretions, or restrains them when they 

 have been morbidly increased ; it imparts a degree of energy to 



