IRON AND STEEL. 
71 
In the economy of iron-smelting, the collection of the gases 
escaping from the top of the blast-furnace, and their utilization, 
must not be forgotten. The chemical changes which are going 
on within the conical tower — where incandescent coal or coke, 
oxide of non, and carbonate of lime are meeting with the oxy- 
gen and nitrogen of the air, at a very high temperature— are of 
a curious and complicated nature. They have been imperfectly 
studied. The experiments of Bunsen and Playfair at the Alfre- 
ton furnace, and those of Levi and Schmidt on charcoal-furnaces, 
gave some indications, which might, if followed out, have led to 
important results. The laborious nature of the investigation, 
and the difficulties attending it, appear to have checked all 
further inquiry. We know, consequently, but little of the 
rationale of the smelting process, which may be briefly stated 
to be as follows. 
The gases formed during the operations going forward in 
the white hot mass — carbonic oxide, and much volatile com- 
bustible matter, — very complicated in its constitution, ascend 
at a high temperature. As the ore is supplied to the furnace, 
it meets those powerful reducing agents, and a portion of the 
oxide of iron is reduced to the metallic state. Combination 
also takes place between the iron and the silica and alumina 
present in the ore. The chemical affinities of the lime-flux then 
come into play. Silicates of lime and alumina are formed, and 
the slag thus produced contains but little non; the metal being- 
liberated, probably in the condition of pure or malleable iron. 
This descends further in the furnace, and, at the high tempera- 
ture which there exists, it becomes liquid, combming with the 
carbon to form carburet of iron. Still descending through the 
material, there is no doubt but silicon and other alkaline metals 
combme with and materially influence the character of the iron. 
The cast iron obtained is very variable in its composition ; it 
must, however, be regarded as a compound of iron and carbon, 
about four equivalents of the former to one of the latter, or, iron 
94 - 9, carbon 5T. When all this has been effected, immense 
volumes of gases intensely heated escape. These were formerly 
absolute ivasie. They are now collected, and carried, by means 
of pipes, to other furnaces, where, under favourable conditions, 
they can be made to produce a temperature varying from 3,210° 
Fahr. to 3,632° Fahr. It is stated on good authority that the 
saving of fuel with two furnaces making 240 tons of iron per 
week, by applying the waste gases to the blast-engine and hot- 
air stoves, has been £1,200 a year ! 
Such are the advances which have been made in the manipu- 
latory details of iron manufacture, by which we are enabled to 
make cheaper iron than any other country in the world. With 
the chief varieties of cast non, viz., dark grey, bright grey, 
