1 4 Metallurgy of Iron. 



silica, alumina, &c. The water and carbonic acid, being readily 

 volatile, are often expelled by a previous process of roasting. 

 When these oxyds of iron are beated to redness in contact with 

 charcoal, this material combines with the oxygen of the ore, and 

 the iron is set free or reduced to the metallic state, after which by 

 the further action of the combustible it is fused, and collects in a 

 liquid mass in the crucible below. The earthy ingredients of the 

 ore, with the ashes of the fuel, are also melted by the intense heat, 

 and form a kind of glass or slag, which floats upon the surface 

 of the molten metal, and from time to time both of these are 

 drawn off from the crucible. It is very important to give to these 

 earthy matters that degree of fluidity which shall permit their 

 ready separation from the reduced and melted iron, and to attain 

 this end, the different ores are generally mixed with certain ingre- 

 dients termed fluxes, which serve to augment the fusibility of the 

 slags. Limestone, sand, and clay may each of them be used for 

 this object with different ores. It will be kept in mind that the 

 fuel employed in the process of smelting, serves for two distinct 

 objects : first, as a combustible to heat the materials, and secondly, 

 as a reducing agent to remove the oxygen from the ore. 



The contents of a blast furnace in action consist then of a great 

 column of mingled ore and fuel, continually moving downward 

 towards the crucible, and constantly replenished from the top> 

 while a current of air and gases is continually traversing the mass 

 in a contrary direction. The investigations by Leplay and Ebel- 

 man on the theory of this operation have prepared the way for the 

 processes of Chenot, and we shall therefore state in a few words, 

 the results of their researches. They have shown in the first place, 

 that the direct agent in the reduction of the ore is a portion of the 

 carbon of the fuel in a gaseous state, and secondly, that this re- 

 duction is effected at a temperature far below that required tor the 

 fusion of the metal. The oxygen of the air entering by the blast, 

 is at first converted by combination with the ignited coal, into 

 carbonic acid, in which an atom of carbon is combined with two 

 atoms of oxygen, but as this gas, rising in the furnace, encounters 

 other portions of ignited coal, it takes up another equivalent of 

 carbon and forms carbonic oxyd gas, in which the two atoms of 

 oxygen are combined with two of carbon. This gas is the reduc- 

 ing agent, for when in its upward progress it meets with the ig- 

 nited oxyd of iron, the second atom of carbon in the gas takes from 

 the iron two atoms of oxygen to form a new portion of carbonic 

 acid, which passes on, while metallic iron remains. 



