The Sun.
London, England, 1856-09-06 00:00:00

THE IRON MANUFACTURE AND MB.
BESSEMER'S INVENTION.

(From the Birmingham Journal.)

In order that those whose studies or svocations have
left them unacquainted with the general nature of the
iron manufacture may the better comprehend the exact
bearings of a process, which is exciting an attention un-
psralleled in modern times, we will give such a brief
sketch of the process of manufacturing iron as will en-
able them, generally at all events, to estimate the im-
portance of Mr. Bessemer's invention.
The extraction of iron from the ore is effected by a
process, the general principles of which are very simple.
First, the ore is roasted ; that is to say, it is made into
heaps with coal, and ignited ; the carbonic acid and water
cf the mineral are driven off, and the ore is left in a porous
state, favourable to the subsequent processes. We
may regard the roasted ore as an impure oxide of iron,
containing, of course, all the earthy matter, and what-
ever was not volatile in the native mineral. If we re-
flect for a moment on what we have to accomplish in
order to obtain the iron from this compound, we shall
soon be able to devise the means of doing it. We have
iron combined with oxygen, and we wish to separate the
latter from the former, so as to leave the metal free.
How shall we accomplish this ? Clearly only by pre-
senting something to the compound which has a higher
affinity for oxygen than iron has. What is this ? It is
charcoal or carbon. This element, so inert at ordinary
temperatures as to be the most imperishable of things,
assumes, when heated strongly, an affinity for oxygen
more powerful than that of any other known substance ;
and there are few metallic oxides which do not yield oxy
gen to carbon at an elevated temperature, and thus libe-
rate the metal in a reguline or metallic state. This pro•
cess of depriving metallic oxides of their oxygen is called
reduction, and the reduction of the ores of iron, copper,
lead, zinc, &c., consists mainly in heating them, after
suitable preparation with carbon, and thereby deoxidis-
ing them. To reduce the iron, then, we have only to
heat it with charcoal. But since the ore contains a
large quantity of earthy matter, the particles of iron
when reduced would be held in this porous earthy mass
like water in a sponge, and although reduced, the metal
would remain in an unavailable form. How can we
separate the metal from the earthy matter I Not by
mechanical but by chemical means. If we mix with the
ore something which will form a readily fusible cora-
-1 pound with the earthy matter, that earthy matter will
liquefy, and the particles of melted iron will fall through
the liquid, and collect together into a mass. Lime is
used for this purpose. It is as though a sponge filled
with water dissolved on the application of a gentle heat,
the water in the sponge forming the lower stratum, and
the matter of the sponge itself a light oily liquid, floating
on the water. Our readers will now have a general
notion of the process which they see carried on so ex-
tensively in the neighbouring iron districts. Into huge
towers, which stud the country, day and night, and
from year's end to year's end, toiling engines pour
thousands of tons of the materials we have enumerated
—iron ore, coke, and lime. Blast engines force streams
of compressed air into the ignited materials, and the
mass slowly sinking in the tower, melts into two strata,
the one the slag, the other the iron. The former flows
off from an upper opening, and the latter is drawn off at
intervals from holes made in the lower part of the fur-
nace. The molten metal is conducted along channels
made in sand, and slowly filling rough moulds connected
with these channels gradually solidifies and constitutes
the pig iron of commerce. The coke, we have seen,
constitutes both the fuel from which the necessary heat
is produced, and the reducing agent, by which the oxide
of iron is deoxidised ; the lime makes the earthy matter
fusible, and enables the iron to separate itself there-
from.

The method of manufacture we have roughly described
produces iron, but not pure iron ; that has never been
produced but by the chemist, and but few eyes have
ever seen it. The iron produced is cast iron, which
consists mainly of iron, but is contaminated with a great
variety of impurities, from which it is difficult to free it.
In the reduction of iron from its ore, although we obtain
a product containing perhaps 05 per cent, of iron, the
remaining 5 per cent. consists of a long array of foreign
ingredients, all existing in one form of combination in
the materials employed ; these have been so affected
during the reduction of the iron as to have assumed a
state in which they could combine with iron, and hence
we discover that the iron drawn from the furnace is in-
variably contaminated with them. Although small in
quantity, the effect which these impurities have upon
the physical properties of the iron is truly wonderful.
One per cent. of phosphorus, or a scarcely less propor-
tion of sulphur, has a most prejudicial effect upon the
iron containing it. The principal element which, in the
blast furnace, enters into combination with iron, is car-
bon or charcoal. The metal is capable of combining
with 5 per cent. of its weight of carbon, and many kinds
of oast iron contain nearly this quantity. Steel is a
compound of iron and carbon, containing less carbon
than cast•iron ; and the production of steel from cast-
iron is simply the removal of a portion of the carbon.
If cast•iron from the blast furnace consisted of iron
and carbon only, the production of steel and wrought
iron therefrom would be easily effected ; but cast iron
contains, besides iron and carbon, the following impuri-
ties, some or all of them ; silicon, sulphur, phosphorus ;
and in minute quantity, aluminum, calcium, and potas-
sium. The conversion of cast iron into wrought iron
consists in the removal of these impurities. This purifi-
cation consists in the ordinary manufacture, in submit-
ting the iron to the action of air, and also to a mechani-
cal kneading and squeesing process ; these are effected
in the refinery and in puddling ; and it is these processes
which Mr. Bessemer proposes to supersede by his in-
vention.

The impurities in cast iron consists of substances, all
of which combine with oxygen at a high temperature ;
carbon forming carbonic acid ; sulphur, sulphurous
acid ; phosphorus, phosphoric acid ; silicon, silicic acid
(silica, or the matter of sand); aid so of the rest. Now
the exposure of cast iron to heat and air (containing
oxygen) is sufficient to cause the substances to form
oxygen compounds, either volatile or easily fusible, and
incapable of entering into combination with metallic iron.
But since these impurities are diffused in small quantity
through the mass of the iron, it is with great difficulty
that air can be brought to act upon them. This, how-
ever, is done efficiently, but at great trouble, fiat in the
refinery, and afterwards more completely in the puddling
process. The melted cast iron is'exposed in the refinery
to a strong heat, in contact with air, and a large propor-
tion of the carbon contained in the iron is burned off, as
carbonic oxide ; the silicon becomes oxidised as silicic
acid (silica), and the iron also oxidising, supplies a base
(oxide of iron), with which the silicic acid combines.
This compound constitutes the slag, which is formed in
the process. The action of the slag itself upon the im-
purities yet contained in the iron is a most interesting
chemical phenomenon, and will be noticed hereafter.
Where a very superior iron is required, charcoal is used
in this process instead of coke ; and the iron so made is
called "charcoal iron." The impurities contained in
ordinary coke are in part communicated to the iron, and
injure its quality. The minute details of the refinery
we need.not describe.

The iron thus partially purified is next puldled. It is
fused on the bed of a reverberatory furnace and vigor-
ously stirred about, so as to expose it to the action of the
air ; oxygen is rapidly absorbed, and the gaseous car•
bonic oxide formed escapes in bubbles, giving the ap-
pearance of boiling, and burning at the surface with a
blue flame. As the carbon is burned off, the fusibility
of the mass diminishes, and although the heat is in-
el-cased as the process proceeds, the molten metal passes
from a fluid to a spongy semi-fluid mass. The fearful
labour of the puddler now commences. He approaches
the furnace almost in a state of nudity, and on the end
of an iron bar collects from the bed of the furnace as
much iron a 3 he can lift. This ball, or bloom, he
swings through the air under a forge hammer, or other
compressing nrichine. The blows at first crush the soft
mass like dough, sending out showers of sparks, and
squeezing liquid drops from the interior of the metal.
The ball cools, the blows of the hammer now ring, the
fire shower grows faint, and the liquid drops are re-
placed by scaly masses, which fall from the now almost
solid metal. The kneading process is continued by
passing the metal between rolls, in the grooves of which
it is drawn out and compressed ; it is doubled up and
rolled, and heated and doubled up, and rolled again.
Have you ever seen, as you have travelled by railway
or otherwise at night, the mouth of a black furnace
opened on a sudden sending a ray, as of sunlight,
athwart the sky, and disclosing something within, so
blinding white, so blasting bright," that the eye closed
involuntarily I If you returned leisurely to the sight,
you observed half naked men darting across the light
beams, their motions seemingly more capricious and
more sudden than the dancing images in a phantasma-
goria. In a stray beam of the quivering light, you see
now and then the heavy rocking head of the steam en-
gine, and the greasy teeth of the cogwheels shoot by,
brighter than rows of pearls or falling water drops; the
blows of the forge hammer shake the earth, and the
whirring of the wheels make you giddy. What is all
this I It is puddling ; the conversion of cast-iron into
wrought-iron.
The metal so obtained is not pure, but it is sufficiently
so for commercial purposes. It contains carbon, silicon,
and other impurities ; but in quantities so minute as not
to affect its physical properties materially. It is a
curious fact, worth here noting, that some of those im-
purities which
it in
a most pernicious effect upon iron,
do not injure in direct proportion to their quantity,
but preserve their injurious action down to a certain
point only, and below that proportion appear to be
wholly inoperative.

The elimination of carbon, and the ether impurities
contained in cast-iron, and its consequent conversion
into wrought-iron, takes place by virtue of that beau-
tiful chemical process called cementation ' • a process in
which a chemical change is propagated through a solid
or nearly solid body from the exterior inwards, or the
reverse. This process is beautifully illustrated by the
annealing of cast-iron, or the production of malleable
iron articles, so largely practised in Birmingham and its
neighbourhood. Small articles made of cast iron are
imbedded in powdered peroxide of iron, and heated for
many hour?, or days. The oxygen in the oxide of iron
combines with the carbon of the cast iron, and withdraws

it; in short, burns the carbon. This removal of the
carbon, commencing at the surface, gradually proceeds
inwards, until the whole substance of the article has
been decarbonised, and the cast-iron converted into soft
wrought-iron, without the article having changed its
form. The converse takes place in the manufacture of
steel. In this case, the wrought-iron is heated with
carbon, and the combination of the latter with the
former, commencing at the surface, slowly penetrates the

aims.
In precisely the same way are the carbon and other
impurities removed from cast-iron, iu its conversion into
wrought•iron ; the slag containing oxide of iron playing
a most important part. The air can only act super-
ficially on a large mass of fused iron, even when it is
kept in motion ; but the oxide formed superficially is
mixed with the metal, and yields oxygen to the owben