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ON THE GASES EVOLVED FROM IRON FURNACES. 157 
6. Olefiant gas. 
7. Carburetted hydrogen, of unknown composition. 
8. Hydrogen. 
9. Sulphuretted hydrogen. 
10. Aqueous vapour. 
An iron furnace must be viewed as an apparatus destined to carry on 
chemical processes of the most various kind. These operations begin at the 
top of the furnace, and stretch downwards to its hearth in well-defined suc- 
cession. The final products of all these operations appear partly at the hearth 
and partly at the mouth; in the latter in the form of a column of combustible 
gas, in the former in the liquid form of slag and cast iron. The nature of 
the combustible gas stands in a relation so intimate to the changes suffered 
by the materials put into the furnace, that its different composition in the 
various regions of the furnace indicates the changes suffered by the materials 
introduced as they descend in their way to the entrance of the blast. Now as 
the examination of this column of air in its various heights in the furnace 
must be the key to the questions upon which the theory and practice of the 
manufacture of iron depend, it is of the first importance to subject it to a 
rigid examination. The successive changes suffered by the column of gas 
in its passage can only be elucidated by a direct examination of its com- 
position in the various regions of the furnace. We can however employ a 
method to ascertain the average composition of the gas escaping from the 
mouth of the furnace ; for although the method does not give the compo- 
sition itself, it enables us to fix the narrow limits between which it varies. 
In order, however, to understand the part played by the coal itself in the 
formation of gas from the furnace, it is necessary to examine closely the 
phenomena which would ensue were the furnace filled with nothing else ex- 
cept the fuel. On this account we must recapitulate the results obtained 
in an inquiry formerly instituted in Germany by one of us, as this may 
be considered established by the repetition of the experiments by others, and 
by the numerous appliances to practice which have already resulted from 
them. It was shown by these experiments, which receive renewed confir- 
mation and extension from our present inquiry,— 
1st. That the oxygen introduced by the blast is burned in the immediate 
vicinity of the tuyére; 
2nd. That the oxygen is converted into carbonic oxide also in the imme- 
diate vicinity of the tuyére; and finally, 
8rd. That the coal loses all its gaseous products of distillation much above 
the point at which its combustion commences. 
It is therefore clear that the gasification of the coal, if such a term be ad- 
missible, must take place in the regular course of the furnace, at two points 
quite separated from each other. At a certain depth from the mouth of 
the furnace the gases due to the distillation or coaking of the coal must 
escape. Further down in the furnace the gasification will be completed, be- 
cause the coal freed from its volatile products must here enter into combus- 
tion. These products of distillation and combustion, mixed with the nitrogen 
of the atmospheric air, forms the column of gas which appears as a combus- 
tible gas at the mouth of the furnace. Now when we consider that the 
quantity of coal which loses its gases in traversing the distillatory part of the 
furnace must correspond to that burnt before the tuyére by the air intro- 
duced in the blast, it follows that the composition of the gases evolved from 
the furnace will be given if we add the products of distillation of any given 
