No. 161.] 
47 
rately determined, as well as that of the flux to be used, of the 
slag or scoria formed during the process, and finally of the iron 
which is the result. Investigations of this kind have been prose- 
cuted for some years in Sweden, France, Germany and England, 
and the result has been the introduction of improvements by means 
of which the ores have been made to yield a larger quantity and a 
better quality of iron than was formerly obtained from them. 
It cannot be doubted, that if similar researches were made in 
our own State, they would have a most important influence upon 
the iron manufacture. 
It has already been stated, that when the ore is of great purity 
the process of reduction is exceedingly simple. But as the ores 
most generally used contain earthy bodies, as silica, alumina, &c. 
in considerable proportions, the business of the iron smelter con- 
sists in fusing the earths, and in oxidizing the ore by the agency 
of carbonaceous matter. But silica, when subjected to high heat 
in contact with oxide of iron, unites with it, and forms a silicate 
which cannot be reduced by carbon. It is therefore of great im- 
portance to prevent the formation of this compound. One of the 
means by which this end may be attained, is the roasting of the 
ore, an operation which is too often neglected by our manufactu- 
rers. By being previously roasted, the ore loses its water, if it 
contains any; the carbonic acid and volatile matters are also 
driven off, and it is brought to that porous state which permits the 
flame to come into contact with each of its panicles, and thus the 
metal is reduced before the silicates can be formed. Another ad- 
vantage gained by the roasting of the ore is, that we avoid in a 
great measure the evolution of the gases in the furnace, which not 
only obstruct the free passage of flame, but have a tendency to 
cool it. It is therefore of the greatest importance that particu- 
lar attention should be paid in all cases to the process of roasting; 
but especially so, when the more compact kinds of magnetic and 
specular ores are employed. As the operation is analogous to the 
burning of limestone, it may be performed either in the open air, 
or in furnaces constructed for the purpose, as may be found most 
convenient and economical.* 
In most cases, however, the roasting is not sufficient to effect the 
complete separation of the matters which prevent or retard the re- 
* For descriptions of processes and apparatus, see Dumas Traitdde Chimie appliqu^e 
aux arts, IV. 619. 
