178 -REPORT—1845, 
This mixture of gases contains,— 
1. The products of distillation of the coal. 
2. The products of its combustion. 
3. The carbonic acid generated during the reduction of the ore, and ex- 
pelled from the limestone. 
The proportion of nitrogen to oxygen, as deduced from these analyses, 
is 79'2 : 27:33, and 79:2 : 26°67, or an average of 79°2:27. The products 
of combustion of the coal give the proportion existing in atmospheric air 
79°2:20°8. Now as the amount of oxygen in the products of distillation of 
the coal is quite insignificant, and may be safely neglected in the calculation, 
the increase of oxygen from 20°8 to 27 must depend upon the carbonic acid 
of the limestone, and the oxygen of the ore given to carbon during the re- 
duction. But the gas collected at twenty-three and twenty-four feet deep, 
contains 27°6 and 26°5 oxygen to 79:2 nitrogen. Hence at this depth the 
gas must have already accumulated all the oxygen of the iron, and the car- 
bonie acid of the limestone. These facts warrant us in drawing the follow- 
ing conclusion,—That in hot-blast furnaces fed with coal, the reduction of 
the iron and expulsion of carbonic acid from the limestone takes place in 
the boshes of the furnace. 
We cannot define by direct observation the exact region of the furnace 
in which the melting of the iron and formation of the slag are effected, but as 
the large masses of ironstone cannot enter the hearth in any form except as 
a liquid, we may safely assume that the point of fusion is at the top of the 
hearth in hot-blast furnaces. 
With the object of rendering these processes more intelligible, we have 
shaded a section of the furnace so as to represent the different parts em- 
ployed in their special functions, the drawing being made to an exact scale. 
A B is the space in which the distillation proceeds, B C and C D show the 
region in which the reduction of the ore and evolution of the carbonic acid 
are effected, and in which the materials attain the temperature necessary for 
fusion. 
The marked difference between the results obtained in the continental fur- 
naces and those in this country will cease to excite surprise, when we bear in 
mind the different nature of the fuel employed. The principal reason of the 
great depression of the region of reduction in the furnaces of this country, is 
that almost all the body of the furnace is taken up in the process of coking ; 
and hence the point of reduction must be still further lowered if the pieces 
of coal be of'a large size. These pieces, often in bulk equal to a cubic foot, 
must remain a long time before the heat penetrates thoroughly through them, 
and the column of air ascending through this material must yield its heat in 
order to render gaseous above 30 per cent. of the fuel. Hence the depres- 
sion of the temperature of the upper half of the furnace becomes so great 
that it does not suffice for the reduction of the ore, nor is it sufficient for 
the expulsion of carbonic acid from the limestone. Another important 
cause lowering the region of reduction, is the high pressure at which the 
blast is thrown into the furnace, the pressure being six or seven times the 
amount of that used in Germany. The materials, on this account, traverse 
through the furnace much more speedily, and therefore require to pass 
through a larger space to become heated. All these circumstances have 
much less influence in the German and Swedish furnaces. The charcoal 
with which the latter are fed is a fuel almost completely coked, and the ma- 
terials, being in small fragments and thoroughly mixed, offer a heating sur- 
face at least a hundred times greater than that exposed in English furnaces. 
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