FOOT at ae 
On the Blast Furnace in the Manufacture of Iron. 175 
The specular, magnetic, and siliceous ores are reduced with 
much more difficulty ; most of the ore in these cases reaching 
the boshes but slightly altered, they being principally dependent 
upon the direct action of coal for their reduction ; this circum- 
stance largely increases. the consumption of coal when any of 
these ores are employed; and the amount of caloric made latent, 
im consequence of the reduction requiring the direct action of the 
coal, is very great, whereas in the reduction of the ore by car- 
bonic oxide no heat becomes latent: for the heat rendered latent 
by the oxygen of the ore becoming gaseous, is compensated by 
the sensible heat produced by the .combination of the carbonic 
oxide with the oxygen. Where the reduction is produced by the 
carbon, with the formation of carbonic oxide, 1598 unities of 
heat are made sensible, while 6216 are rendered latent, giving a 
difference of absolute loss of 4618. 
It should be the object of the metallurgist to reduce as much 
of the iron as possible by the oxide of carbon. Magnetic, sili- 
ceous and other hard ores should be reduced to smaller fragments 
than those softer and more easily managed. Were it possible to 
reduce them to powder without the danger of choking the fur- 
nace, it would be all the better, as the great object is to have a 
large extent of surface exposed to the carbonic oxide. The dif- 
ferent capacity of different ores for reduction, shows the necessity 
of having furnaces of different dimensions for them respectively. 
The matter which covers the melted metal in the crucible, and 
that which adheres to the interior of the hearth, contain silicate 
of iron and charcoal in a pasty state, and there is consequently a 
constant reduction of the oxide of iron, which gives rise to carbonic 
oxide ; this gas. bubbles through the slag, which if drawn off at 
this time, will, when cold, present a porous structure, a sure in- 
dication that the furnace is not working. well and that the slag it- 
self contams much of the ore.in the form of a silicate. 
4. Composition of the gas in various parts of the furnace du- 
ring its operation.—The analyses lately made by Ebelman are 
the most accurate and best detailed that we are in possession of. 
- What follows has reference to a furnace worked with charcoal. 
