The hearths of cast iron rest upon cast-_A Dictionary of Arts, Manufactures and Mines containing a clear exposition of their principles and practice

four or five; which are supported on pedestals of cast iron placed on

large blocks of stone. Such an arrangement is shown in the figure, where

also the square hole _a_, _fig._ 592., for heating the rake irons, may

be observed. The length of the hearth is usually six feet; and its

breadth varies from one part to another. Its greatest breadth, which is

opposite the door, is four feet. In the furnace, whose horizontal plan

is given above, and which produces good results, the sole exhibits, in

this part, a species of ear, which enters into the mouth of the door. At

its origin towards the fireplace, it is 2 feet 10 inches wide; from the

fire it is separated, moreover, by a low wall of bricks (the

fire-bridge) 10 inches thick, and from 3 inches to 5 high. At the other

extremity its breadth is 2 feet. The curvature presented by the sides of

the sole or hearth is not symmetrical; for sometimes it makes an

advancement, as is observable in the plan. At the extremity of the sole

furthest from the fire, there is a low rising in the bricks of 2-1/2

inches, called the altar, for preventing the metal from running out at

the _floss-hole_ when it begins to fuse. Beyond this shelf the sole

terminates in an inclined plane, which leads to the _floss_, or outlet

of the slag from the furnace. This _floss_ is a little below the level

of the sole, and is hollowed out of the basement of the chimney. The

slag is prevented from concreting here, by the flame being made to pass

over it, in its way to the sunk entry of the chimney; and there is also

a plate of cast iron near this opening, on which a moderate fire is kept

up to preserve the fluidity of the scoriæ, and to burn the gases that

escape from the furnace, as also to quicken the draught, and to keep the

remote end of the furnace warm. On the top of this iron plate, and at

the bottom of the inclined plane, the cinder accumulates in a small

cavity, whence it afterwards flows away; whenever it tends to congeal,

the workman must clear it out with his rake.

The door is a cast-iron frame filled up inside with fire-bricks; through

a small hole in its bottom the workmen can observe the state of the

furnace. This hole is at other times shut with a stopper. The chimney

has an area of from 14 to 16 inches.

The hearth stands 3 feet above the ground. Its arched roof, only one

brick thick, is raised 2 feet above the fire-bridge, and above the level

of the sole, taken at the middle of the furnace. At its extreme point

near the chimney, its elevation is only 8 inches; and the same height is

given to the opening of the chimney.

In most iron-works the sole is covered with a layer of refractory sand,

from 2-1/2 to 3 inches thick, which is lightly beat down with a shovel.

At each operation a portion of the sand is carried away; and is replaced

before another. Within these few years, there has been substituted for

the sand a body of pounded slags; a substitution which has occasioned,

it is said, a great economy of iron and fuel.

The fine metal obtained by the coke is _puddled_ by a continuous

operation, which calls for much care and skill on the part of the

workmen. To charge the puddling furnace, pieces of _fine metal_ are

successively introduced with a shovel, and laid one over another on the

sides of the hearth, in the form of piles rising to the roof; the middle

being left open for puddling the metal, as it is successively fused.

Indeed, the whole are kept as far separate as possible, to give free

circulation to the air round the piles. The working door of the furnace

is now closed, fuel is laid on the grate, and the mouth of the

fire-place as well as the side opening of the grate, are both filled up

with coal, at the same time that the damper is entirely opened.

The fine metal in about twenty minutes comes to a white-red heat, and

its thin-edged fragments begin to melt and fall in drops on the sole of

the furnace. At this period the workman opens the small hole of the

furnace door, detaches with a rake the pieces of fine metal that begin

to melt, tries to expose new surfaces to the action of the heat, and in

order to prevent the metal from running together as it softens, he

removes it from the vicinity of the fire-bridge. When the whole of the

fine metal has thus got reduced to a pasty condition, he must lower the

temperature of the furnace, to prevent it from becoming more fluid. He

closes the damper, takes out a portion of the fire, and the ribs of the

grate, and also throws a little water sometimes on the semi-fused mass.

He then works about with his paddle the clotty metal, which swells up,

with the discharge of gaseous oxide of carbon, burning with a blue

flame, as if the bath were on fire. The metal becomes finer by degrees,

and less fusible; or in the language of the workmen, it begins to get

_dry_. The disengagement of the oxide of carbon diminishes, and soon

stops. The workmen continue meanwhile to puddle the metal till the whole

charge be reduced to the state of incoherent sand; and at that time, the

ribs of the grate are replaced, the fire is restored, and the register

is progressively opened up. With the return of the heat, the particles

of metal begin to agglutinate, the charge becomes more difficult to

raise, or in the labourers’ language, it _works heavy_. The refining is

now finished, and nothing remains but to gather the iron into balls. The

founder with his paddle takes now a little lump of metal, as a nucleus,

and makes it roll about on the surface of the furnace, so as to collect

more metal, and form a ball of about 60 or 70 pounds weight. With a kind

of rake, called in England a _dolly_, and which he heats beforehand, the

workman sets this ball on that side of the furnace most exposed to the

action of the heat, in order to unite its different particles; which he

then squeezes together to force out the scoriæ. When all the balls are

fashioned, (they take about 20 minutes work,) the small opening of the

working door is closed with a brick, to cause the heat to rise, and to

facilitate the welding. Each ball is then lifted out, either with tongs,

if roughing rollers are to be used as in Wales, or with an iron rod

welded to the lump as a handle, if the hammer is to be employed, as in

Staffordshire. Thus we see that the operation lasts in whole from 2

hours to 2-1/2; in a quarter of an hour, the fine metal melts at its

edges, when the puddling begins, in order to effect its division; at the

end of an hour or an hour and a half, the metal is entirely reduced to a

sand; a state that is kept up for half an hour by continual stirring;

and finally, the balling operation takes nearly the same time.

The charge for each operation is from 3-1/2 to 4 hundred weight; and

sometimes the cuttings of bar-ends are introduced, which are puddled

apart. The loss of iron is here very variable, according to the degree

of skill in the workman, who by negligence may suffer a considerable

body of iron to scorify or to flow into the hearth and raise the bottom.

In good working, the loss is from 8 to 10 per cent. In Wales, the

consumption of coal is estimated at one ton for every ton of fine metal.

About five puddling furnaces are required for the service of one

smelting furnace and one finery. The hearth of the puddling furnace

should be exposed to heat for 12 hours before the work begins on the

Mondays; and on the Saturdays, the old sole must be cleared out, by

melting it off; and running it out by the floss-hole.

Mr. Schafthault obtained, in May, 1835, a patent for the conversion of

cast into wrought iron, by adding a mixture of black oxide of manganese,

common salt and potter’s clay, in certain small portions, successively

to the melting iron in the puddling furnace.

_The reheating furnaces_, _balling furnaces_, or mill furnaces, are

analogous to the puddling furnaces, but only of larger dimensions.

The wood charcoal forge hearth is employed for working up scrap iron

into boiler plate, &c. Here 22 bushels of charcoal are consumed in

making one ton of iron of that description, from boiler plate parings.

_Machines for forging and condensing the iron._--In England there are

employed for the forging and drawing out of the iron, cast-iron hammers

of great weight, and cylinders of different dimensions, for beating out

the balls, or extending the iron into bars, as also powerful shears.

These several mechanisms are moved either by a steam engine, as in

Staffordshire, and in almost all the other counties of England, or by

water-wheels when the localities are favourable, as in many

establishments in South Wales. We shall here offer some details

concerning these machines.

The main driving shaft usually carries at either end a large toothed

wheel, which communicates motion to the different machines through

smaller toothed wheels. Of these, there are commonly six, four of which

drive four different systems of cylinders, and the two others work the

hammer and the shears. The different cylinders of an iron work should

never be placed on the same arbor, because they are not to move

together, and they must have different velocities, according to their

diameter. In order to economise time and facilitate labour, care is

taken to associate on one side of the motive machine the hammer, the

shears, and the reducing cylinders; and on the other side, to place the

several systems of cylinders for drawing out the iron into bars. For the

same reason the puddling furnaces ought to be grouped on the side of the

hammer; and the reheating furnaces on the other side of the works.

[Illustration: 596]

The hammers, _fig._ 596., are made entirely of cast iron; they are

nearly 10 feet long, and consist usually of two parts, the helve _c_,

and the head or pane _d_. The latter enters with friction into the

former, and is retained in its place by wedges of iron or wood. The head

consists of several faces or planes receding from each other; for the

purpose of giving different forms to the ball lumps. A ring of cast-iron

_a_, called the _cam-ring bag_, bearing movable cams _b b_, drives the

hammer _d_, by lifting it up round its fulcrum _f_, and then letting it

fall alternately. In one iron work, this ring was found to be 3 feet in

diameter, 18 inches thick, and to weigh 4 tons. The weight of the helve

(handle) of the corresponding hammer was 3 tons and a half, and that of

the head of the hammer, 8 hundred weight.

The anvil _e_ consists also of two parts; the one called the pane of the

anvil, is the counterpart of the pane of the hammer; it likewise weighs

8 hundred weight. The second _g_, named the stock of the anvil, weighs 4

tons. Its form is a parallelopiped, with the edges rounded. The _bloom_,

or rough ball, from the puddle furnace, is laid and turned about upon

it, by means of a rod of iron welded to each of them, called a _porter_.

Since the weight of these pieces is very great, and the shocks very

considerable, the utmost precautions should be taken in setting the

hammer and its anvil upon a substantial mass of masonry, as shown in the

figure, over which is laid a double, or even quadruple flooring of wood,

formed of beams placed in transverse layers close to each other. Such

beams possess an elastic force, and thereby partially destroy the

injurious reaction of the shock. In some works, a six-feet cube of cast

iron is placed as a pedestal to the anvil.

Forge hammers are very frequently mounted as levers of the first kind,

with the centre of motion about one-third or one-fourth of the length of

the helve from the cam wheel. The principle of this construction will be

understood by inspection of _fig._ 605. The short end of the lever which

is struck down by the tappet _c_, is driven against the end of an

elastic beam _a_, and immediately rebounds, causing the long end to

strike a harder blow upon the anvil _s_.

The shears are composed of two branches, the one fixed and the other

movable, each formed of two pieces. The fixed branch is a cast-iron

plate, which forms one mass with a horizontal base fixed to a piece of

wood or cast iron buried in the ground. A sharpened chisel is fastened

to its upper part by screws and nuts. The movable branch is likewise of

cast iron; it bears an axis round which it turns, and this axis passes

through the fixed part. It is also furnished with a cutting chisel,

fixed on by nuts and screws. An excentric or an ellipse, moved directly

by a toothed wheel, lifts the movable branch of the shears, and forces

it to cut the iron bars presented to it. The pressure exerted by these

scissors is such, that they can cut without difficulty, iron bars,

one-half or two-thirds of an inch thick.

_Cylinders._--The compression between cylinders now effects, in a few

seconds, that condensation and distribution of the fibres, which 40

years ago, could not be accomplished till after many heats in the

furnace, and many blows of the hammer. The cylinders may be

distinguished into two kinds; 1. those which serve to draw out the ball,

called _puddling rolls_, or roughing rolls, and which are, in fact,

reducing cylinders; 2. the cylinders of extension, called _rollers_, for

drawing into bars the massive iron after it has received a welding, to

make it more malleable. This second kind of cylinders is subdivided

into several varieties, according to the patterns of bar iron that are

required. These may vary from 2 inches square to less than one-sixth of

an inch.

Beneath the cylinders there is usually formed an oblong fosse, into

which the scoriæ and the scales fall when the iron is compressed. The

sides of this fosse, constructed of stone, are founded on a body of

solid masonry, capable of supporting the enormous load of the cylinders.

Beams of wood form in some measure the sides of this pit, to which

cylinders may be made fast, by securing them with screws and bolts.

Massive bars of cast iron are found, however, to answer still better,

not only because the uprights and bearers may be more solidly fixed to

them, but because the basement of heavy metal is more difficult to

shatter or displace, an accident which happens frequently to the wooden

beams. A rill of water is supplied by a pipe to each pair of cylinders,

to hinder them from getting hot; as also to prevent the hot iron from

adhering to the cylinder, by cooling its surface, and perhaps producing

on it a slight degree of oxidizement.

The shafts are one foot in diameter for the hammer and the roughing

rolls; and six inches where they communicate motion to the cylinders

destined to draw the iron into bars.

The _roughing rolls_ are employed either to work out the lump or ball

immediately after it leaves the puddling furnace, as in the Welsh

forges, or only to draw out the piece, after it has been shaped under

the hammer, as is practised in most of the Staffordshire establishments.

These roughing cylinders are generally 7 feet long, including the

trunnions, or 5 feet between the bearers, and 18 inches diameter; and

weigh in the whole from 4 to 4-1/2 tons. They contain from 5 to 7

grooves, commonly of an elliptical form, one smaller than another in

regular progression, as is seen in _fig._ 597. The small axis of each

ellipse, as formed by the union of the upper and under grooves, is

always placed in the vertical direction, and is equal to the great axis,

or horizontal axis of the succeeding groove; so that in transferring the

bar from one groove to another, it must receive a quarter of a

revolution, whereby the iron gets elongated in every direction.

Sometimes the roughing rolls serve as preparatory cylinders, in which

case they bear towards one extremity rectangular grooves, as the figure

exhibits. Several of these large grooves are bestudded with small

asperities analogous to the teeth of files, for biting the lump of iron,

and preventing its sliding. On a level with the under side of the

grooves of the lower cylinder, there is a plate of cast iron with

notches in its edge adapted to the grooves. This piece called the apron,

rests on iron rods, and serves to support the balls and bars exposed to

the action of the rollers, and to receive the fragments of ill-welded

metal, which fall off during the drawing. The _housing frames_ in which

the rollers are supported and revolve, are made of great strength. Their

height is 5 feet; their thickness is 1 foot in the side perpendicular to

the axis of the cylinders, and 10 inches in the other. Each pair of

bearers is connected at their upper ends by two iron rods, on which the

workmen rest their tongs or pinchers for passing the lump or bar from

one side of the cylinders to the other.

The cods or bushes are each composed of two pieces; the one of hard

brass, which presents a cylindrical notch, is framed into the other

which is made of cast iron, as is clearly seen in _fig._ 597.

The iron bar delivered from the square grooves, is cut by the shears

into short lengths, which are collected in a bundle in order to be

welded together. When this bundle of bars has become hot enough in the

furnace, it is conveyed to the rollers; which differ in their

arrangement according as they are meant to draw iron from a large or

small piece. The first, _fig._ 597., possess both elliptical and

rectangular grooves; are 1 foot in diameter and 3 feet long between the

bearers. The bar is not finished under these cylinders, but is

transferred to another pair, whose grooves have the dimensions proper

for the bar, with a round, triangular, rectangular, or fillet form. The

triangular grooves made use of for square iron, have for their profile,

an isosceles triangle slightly obtuse, so that the space left by the two

grooves together may be a rhombus, differing little from a square, and

whose smaller diagonal is vertical. When the bar is to be passed

successively through several grooves of this kind, the larger or

horizontal diagonal of each following groove is made equal to the

smaller or upright of the preceding one, whereby the iron must be turned

one fourth round at each successive draught, and thus receive pressure

in opposite directions. Indeed the bar is often turned in succession

through the triangular and rectangular grooves, that its fibres may be

more accurately worked together. The decrement in the capacity of the

grooves follows the proportion of 15 to 11.

When it is intended to reduce the iron to a small rod, the cylinders

have such a diameter, that three may be set in the same housing frame.

The lower and middle cylinders are employed as roughing rollers, while

the upper and middle ones are made to draw out the rod. When a rod or

bar is to be drawn with a channel or gutter in its face, the grooves of

the rollers are suitably formed.

[Illustration: 598]

To draw out square rods of a very small size, as nail-rods, a system of

small rollers is employed, called _slitters_. Their ridges are

sharp-edged, and enter into the opposite grooves 2-1/2 inches deep; so

that the flat bar in passing between such rollers is instantaneously

divided into several slips. For this purpose the rollers represented in

_fig._ 598. may be put on and removed from the shaft at pleasure.

The velocity of the cylinders varies with their dimensions. In one work,

cylinders for drawing out iron of from one-third to two-thirds of an

inch thick, make 140 revolutions per minute; while those for iron of

from two-thirds of an inch to 3 inches, make only 65. In another work,

the cylinders for two inch iron, make 95 revolutions per minute; those

for iron from two-thirds of an inch to an inch and a third, make 128;

and those for bars from one-third to two-thirds of an inch, 150. The

_roughing rollers_ move with only one-third the velocity of the drawing

cylinders.

The shingling and plate-rolling mill is represented in _fig._ 597. The

shingling mill, for converting the blooms from the balling furnace into

bars, consists of two sets of grooved cylinders, the first being called

_puddling rolls_ or _roughing rolls_; the second are for reducing or

drawing the iron into mill-bars, and are called simply _rolls_.

[Illustration: 597]

_a_, _a_, _a_, _a_, are the powerful uprights or standards called

_housing frames_, of cast iron, in which the gudgeons of the rolls are

set to revolve; _b_, _b_, _b_, _b_, are bolt rods for binding these

frames together at top and bottom; _c_, are the roughing rolls, having

each a series of triangular grooves, such that between those of the

upper and under cylinder, rectangular concavities are formed in the

circumference with slightly sloping sides. The end groove to the right

of _c_, should be channelled like a rough file, in order to take the

better hold of the blooms, or to bite the metal as the workmen say; and

give it the preparatory elongation for entering into and passing through

the remaining grooves till it comes to the square ones, where it becomes

a mill-bar. _d_, _d_, are the smooth cylinders, hardened upon the

surface, or _chilled_ as it is called, by being cast in iron moulds, for

rolling iron into plates or hoops. _e_, _e_, _e_, _e_, are strong screws

with rectangular threads, which work by means of a wrench or key, into

the nuts _e´ e´ e´ e´_, fixed in the standards; they serve to regulate

the height of the plummer blocks or bearers of the gudgeons, and thereby

the distance between the upper and under cylinders. _f_ is a junction

shaft; _g_, _g_, _g_, are solid coupling boxes, which embrace the two

separate ends of the shafts, and make them turn together. _h_, _h_, are

junction pinions, whereby motion is communicated from the driving shaft

_f_, through the under pinion to the upper one, and thus to both upper

and under rolls at once. _i_, _i_, are the pinion standards in which

their shafts run; they are smaller than the uprights of the rolls. _k_,

_k_, are screws for fastening the head pieces _l_ to the top of the

pinion standards. All the standards are provided with sole plates _m_,

whereby they are screwed to the foundation beams, _n_, of wood or

preferably iron, as shown by dotted lines; _o o_ are the binding screw

bolts. Each pair of rolls at work is kept cool by a small stream of

water let down upon it from a pipe and stop-cock.

In the cylinder drawing, the workman who holds the ball in tongs, passes

it into the first of the elliptical grooves; and a second workman on the

other side of the cylinders, receives this lump, and hands it over to

the first, who re-passes it between the rollers, after bringing them

somewhat closer to each other, by giving a turn to the adjusting

pressure screws. After the lump has passed five or six times through the

same groove, it has got an elliptical form, and is called in England a

_bloom_. It is next passed through a second groove of less size, which

stretches the iron bar. In this state it is subjected to a second pair

of cylinders, by which the iron is drawn into flat bars, 4 inches broad

and half an inch thick. Fragments of the ball or bloom fall round about

the cylinders; which are afterwards added to the puddling charge. In a

minute and a half, the rude lump is transformed into bars, with a

neatness and rapidity which the inexperienced eye can hardly follow. A

steam engine of thirty-horse power can _rough down_ in a week, 200 tons

of coarse iron.

This iron called mill-bar iron, is however of too inferior a quality to

be employed in any machinery; and it is subjected to another operation,

which consists in welding several pieces together, and working them into

a mass of the desired quality. The iron bars while still hot, are cut by

the shears into a length proportional to the size of iron bar that is

wanted; and four rows of these are usually laid over each other into a

heap or pile, which is placed in the _re-heating_ furnace above

described, and exposed to a free circulation of heat; one pile being set

crosswise over another. In a half or three quarters of an hour, the iron

is hot enough, and the pieces now sticking together, are carried in

successive piles to the bar-drawing cylinders, to be converted into

strong bars, which are reckoned of middle quality. When a very tough

iron is wanted, as for anchors, another welding and rolling must be

given. In the re-heating ovens, the loss is from 8 to 10 per cent. on

the large bar iron, and from 10 to 12 in smaller work. A ton of iron

consumes in this process, about 150 lbs. of coals.

It is thought by many that a purer iron is obtained by subjecting the

balls as they come out of the puddling furnace, to the action of the

hammer at first, than to the roughing rollers; and that by the latter

process vitrified specks remain in the metal, which the hammer expels.

Hence, in some works, the balls are first worked under the forge-hammer;

and these _stampings_ being afterwards heated in the form of pies or

cakes piled over each other, are passed through the roughing rollers.

Having given ample details concerning the manufacturing processes used

in England for making cast iron, it may be proper to subjoin a few

observations upon its chemical constitution. It has been generally

believed and taught that the dark gray cast iron, No. 1. or No. 2.,

contains more carbon than the white cast iron; and that the superior

quality of the former in tenacity and softness, is to be ascribed to

that excess. But the distinguished German metallurgist, M. Karsten, in

his instructive volume, “Handbuch der Eisenhüttenkunde,” or manual of

the art of smelting iron ores, has proved, on the contrary, that the

white cast iron contains most charcoal; that this substance exists in it

in a state of combination with the whole body of the iron; that the

foliated or lamellar white cast iron contains as much carbon as iron can

absorb in the liquid state; and that this constitutes a compound of 4

atoms of iron combined with 1 of charcoal, or 112 + 6; or 5-1/3 per

cent.; whereas the dark gray cast iron contains generally from 3 to 4

per cent., in the state of plumbago merely dispersed through the metal.

He has further confirmed his opinion, by causing the white variety to

pass into the gray, and reciprocally. Thus, dark gray cast metal melted

and suddenly cooled, gives a silvery white metal, hard and brittle. On

the other hand, when the white cast iron is cooled very slowly after

fusion, the condition of the carbon in it changes, and a dark gray cast

iron is obtained. These phenomena shew that the graphite or plumbago,

which requires a high temperature for its formation, cannot be produced

but by a slow cooling, which allows the carbon to agglomerate itself in

the iron in the state of graphite; while under a rapid congelation, the

carbon remains dissolved in the mass, and produces a white metal. Hence

we may understand how each successive fusion of dark gray iron hardens

and whitens it, though in contact with coke, by completing that chemical

dissolution of the carbon on which the white state depends.

In the manufacture of the blackest No. 1. cast iron, it sometimes

happens that a considerable quantity of a glistening carburet of iron

appears, floating on the top of the metal as it is run out into the

sand-moulds. This substance is called _kish_ by the English workmen; and

it affords a sure test of the good state of the furnace and quality of

the iron.

The most remarkable fact relative to the smelting of cast iron, is the

difference of product between the workings of the summer and the winter

season, though all the materials and machinery be the same. In fact, no

cold-blast furnace will carry so great a burden in summer as in winter,

that is, afford so great a product of metal, or bear so great a charge

of ore with the same quantity of coke. This difference is undoubtedly

due to the dilated and humid state of the atmosphere in the warm season.

A very competent judge of this matter, states the diminution in summer

at from one-fifth to one-seventh, independently of deterioration of

quality.

Some of the foreign irons, particularly certain Swedish and Russian

bars, are imported into Great Britain in large quantities, and at prices

much greater than those of the English bars, and therefore the modes of

manufacturing such excellent metal deserve examination. All the best

English cast steel, indeed, is made from the hoop L, iron from

Dannemora, in Sweden.

The processes pursued in the smelting works of the Continent have

frequently in view to obtain from the ore malleable iron directly, in a

pure or nearly pure state. The furnaces used for this purpose are of two

kinds, called in French, 1. _Feux de Loupes_, or _Forges Catalanes_; and

2. _Fourneaux à pièce_, or _Forges Allemandes_.

[Illustration: 599]

[Illustration: 600]

In the Catalan, or French method, the ore previously roasted in a kiln

is afterwards strongly torrefied in the forge before the smelting

begins; operations which follow in immediate succession. Ores treated in

this way should be very fusible and very rich; such as black oxide of

iron, hematites, and certain spathose iron ores. From 100 parts of ore,

50 of metallic iron have been procured, but the average product is 35.

The furnaces employed are rectangular hearths, _figs._ 599. and 600.,

the water-blowing machine being employed to give the blast. See

METALLURGY. There are three varieties of this forge; the Catalan, the

Navarrese, and the Biscayan. The dimensions of the first, the one most

generally employed, are as follows: 21 inches long, in the direction _p

f_, _fig._ 600.; 18-1/2 broad, at the bottom of the hearth or _creuset_,

in the line A B; and 17 inches deep, _fig._ 599. The tuyère, _q p_, is

placed 9-1/2 inches above the bottom, so that its axis is directed

towards the opposite side, about 2 inches above the bottom. But it must

be movable, as its inclination needs to be changed, according to the

stage of the operation, or the quantity of the ores. It is often raised

or lowered with pellets of clay; and even with a graduated circle, for

the workmen make a great mystery of this matter. The hearth is lined

with a layer of _brasque_ (loam and charcoal dust worked together), and

the ore after being roasted is sifted; the small powder being set aside

to be used in the course of the operation. The ore is piled up on the

side opposite to the blast in a sharp saddle ridge, and it occupies

one-third of the furnace. In the remaining space of two-thirds, the

charcoal is put. To solidify the small ore on the hearth, it is covered

with moist cinders mixed with clay.

The fire is urged with moderation during the first two hours, the

workman being continually employed in pressing down more charcoal as the

former supply burns away, so as to keep the space full, and prevent the

ore from crumbling down. By a blast so tempered at the beginning, the

ore gets well calcined, and partially reduced in the way of cementation.

But after two hours, the full force of the air is given; at which period

the fusion ought to commence. It is easy to see whether the torrefaction

be sufficiently advanced, by the aspect of the flame, as well as of the

ore, which becomes spongy or cavernous; and the workman now completes

the fusion, by detaching the pieces of ore from the bottom, and placing

them in front of the tuyère. When the fine siftings are afterwards

thrown upon the top, they must be watered, to prevent their being blown

away, and to keep them evenly spread over the whole surface of the light

fuel. They increase the quantity of the products, and give a proper

fusibility to the scoriæ. When the scoriæ are viscid, the quantity of

siftings must be diminished; but if thin, they must be increased. The

excess of slag is allowed to run off by the _chio_ or floss hole. The

process lasts from five to six hours, after which the pasty mass is

taken out, and placed under a hammer to be cut into lumps, which are

afterwards forged into bars.

Each mass presents a mixed variety of iron and steel; in proportions

which may be modified at pleasure; for by using much of the siftings,

and making the tuyère dip towards the sole of the hearth, iron is the

chief product; but if the operation be conducted slowly, with a small

quantity of siftings, and an upraised tuyère, the quantity of steel is

more considerable. This primitive process is favourably spoken of by M.

Brongniart. The weight of the lump of metal varies from 200 to 400

pounds. As the consumption of charcoal is very great, amounting in the

Palatinate or Rheinkreis to seven times the weight of iron obtained,

though in the Pyrenees it is only thrice, the Catalan forge can be

profitably employed only where wood is exceedingly cheap and abundant.

The _Fourneaux à pièce_ of the French, or _Stuck-ofen_ of the Germans,

resembles _fig._ 313., (COPPER); the tuyère (not shown there) having a

dip towards the bottom of the hearth, where the smelted matter collects.

When the operation is finished, that is at least once in every 24 hours,

one of the sides of the hearth must be demolished, to take out the pasty

mass of iron, more or less pure. This furnace holds a middle place in

the treatment of iron, between the Catalan forge and the cast-iron

_floss-ofen_, or high-blast furnaces. The _stuck-ofen_ are from 10 to 15

feet high, and about 3 feet in diameter at the hearth. Most usually

there is only one aperture for the tuyère and for working; with a small

one for the escape of the slag; on which account, the bellows are

removed to make way for the lifting out of the lump of metal, which is

done through an opening left on a level with the sole, temporarily

closed with bricks and potters’ clay, while the furnace is in action.

This outlet being closed, and the furnace filled with charcoal, fire is

kindled at the bottom. Whenever the whole is in combustion, the roasted

ore is introduced at the top in alternate charges with charcoal, till

the proper quantity has been introduced. The ore falls down; and

whenever it comes opposite to the tuyère the slag begins to flow, and

the iron drops down and collects at the bottom of the hearth into the

mass or _stuck_; and in proportion as this mass increases, the

_floss-hole_ for the slag and the tuyère is raised higher. When the

quantity of iron accumulated in the hearth is judged to be sufficient,

the bellows are stopped, the scoriæ are raked off, the little brick wall

is taken down, and the mass of iron is removed by rakes and tongs. This

mass is then flattened under the hammer, into a cake from 3 to 4 inches

thick, and is cut into two lumps, which are submitted to a new

operation; where it is treated in a peculiar refinery, lined with

charcoal _brasque_, and exposed to a nearly horizontal blast. The above

mass seized in the jaws of powerful tongs, is heated before the tuyère;

a portion of the metal flows down to the bottom of the hearth, loses its

carbon in a bath of rich slags or fused oxides, and forms thereby a mass

of iron thoroughly refined. The portion that remains in the tongs

furnishes steel, which is drawn out into bars.

This process is employed in Carniola for smelting a granular oxide of

iron. The mass or _stuck_ amounts to from 15 to 20 hundred weight, after

each operation of 24 hours. Eight strong men are required to lift it

out, and to carry it under a large hammer, where it is cut into pieces

of about 1 cwt. each. These are afterwards refined, and drawn into bars

as above described. These furnaces are now almost generally abandoned on

the Continent, in favour of _charcoal high or blast furnaces_.

_Fig._ 313. represents a _schachtofen_, (but without the tuyère, which

may be supposed to be in the usual place), and is, like all the

continental _Hauts Fourneaux_, remarkable for the excessive thickness of

its masonry. The charge is put in at the throat, near the summit of the

octagonal or square concavity, for they are made of both forms. At the

bottom of the hearth there is a dam-stone with its plate, for permitting

the overflow of the slag, while it confines the subjacent fluid metal;

as well as a tymp-stone with its plate, which forms the key to the front

of the hearth; the boshes are a wide funnel, almost flat, to obstruct

the easy descent of the charges, whereby the smelting with charcoal

would proceed too rapidly. The bottom of the hearth is constructed of

two large stones, and the hinder part of one great stone, called in

German _rückstein_ (back stone), which the French have corrupted into

_rustine_. In other countries of the Continent, the boshes are

frequently a good deal more tapered downwards, and the hearth is larger

than here represented. The refractory nature of the Hartz iron ores is

the reason assigned for this peculiarity.

In Sweden there are blast-furnaces, _schachtofen_, 35 feet in height,

measured from the boshes above the line of the hearth, or _creuset_.

Their cavity has the form of an elongated ellipse, whose small diameter

is 8 feet across, at a height of 14 feet above the bottom of the hearth;

hence, at this part, the interior space constitutes a belly

corresponding with the upper part of the boshes. In other respects the

details of the construction of the Swedish furnaces resemble the one

figured above. Marcher relates that a furnace of that kind whose height

was only 30 feet, in which brown hydrate of iron (_hematite_) was

smelted, yielded 47 _per cent._ in cast iron, at the rate of 5 hundred

weight a day, or 36 hundred weight one week after another; and that in

the production of 100 pounds of cast iron, 130 pounds of charcoal were

consumed. That furnace was worked with forge bellows, mounted with

leather.

The decarburation of cast iron is merely a restoration of the carbon to

the surface, in tracing inversely the same progressive steps as had

carried it into the interior during the smelting of the ore. The oxygen

of the air, acting first at the surface of the cast metal, upon the

carbon which it finds there, burns it: fresh charcoal, oozing from the

interior, comes then to occupy the place of what had been dissipated;

till, finally, the whole carbon is transferred from the centre to the

surface, and is there converted into either carbonic acid gas or oxide

of carbon; for no direct experiment has hitherto proved which of these

is the precise product of this combustion.

This diffusibility of carbon through the whole mass of iron constitutes

a movement by means of which cast iron may be refined even without

undergoing fusion, as is proved by a multitude of phenomena. Every

workman has observed that steel loses a portion of its steely properties

every time it is heated in contact with air.

On the above principle, cast iron may be refined at one operation. Three

kinds of iron are susceptible of this continuous process:--1. The

speckled cast-iron, which contains such a proportion of oxygen and

carbon as with the oxygen of the air and the carbon of the fuel may

produce sufficient and complete saturation, but nothing in excess. 2.

The dark gray cast-iron. 3. The white cast-iron. The nature of the crude

metal requires variations both in the form of the furnaces, and in the

manipulations.

Indeed malleable iron may be obtained directly from the ores by one

fusion. This mode of working is practised in the Pyrenees to a

considerable extent. All the ores of iron are not adapted for this

operation. Those in which the metallic oxide is mixed with much earthy

matter, do not answer well; but those composed of the pure black oxide,

red oxide, and carbonate, succeed much better. To extract the metal from

such ores, it is sufficient to expose them to a high temperature, in

contact either with charcoal, or with carbonaceous gases; the metallic

oxide is speedily reduced. But when several earths are present, these

tend continually, during the vitrification which they suffer, to retain

in their vitreous mass the unreduced oxide of iron. Were such earthy

ores, as our ironstones, to be put into the low furnaces called

_Catalan_, through which the charges pass with great rapidity, and in

which the contact with the fuel is merely momentary, there would be

found in the crucible or hearth merely a rich metallic glass, instead of

a lump of metal.

In smelting and refining by a continuous operation, three different

stages may be distinguished:--1. The roasting of the ore to expel the

sulphur, which would be less easily separated afterwards. The roasting

dissipates likewise the water, the carbonic acid, and any other volatile

substances which the minerals may contain. 2. The deoxidizement and

reduction to metal by exposure to charcoal or carburetted vapours. 3.

The melting, agglutination, and refining of the metal to fit it for the

heavy hammers where it gets nerve. There are several forges in which

these three operations seem to be confounded into a single one, because,

although still successive, they are practised at one single heating

without interruption. In other forges, the processes are performed

separately, or an interval elapses between each stage of the work. Three

systems of this kind are known to exist:--1. The Corsican method; 2. The

Catalan with wood charcoal; and 3. The Catalan with coke.

The furnaces of Corsica are a kind of semicircular basins, 18 inches in

diameter, and 6 inches deep. These are excavated in an area, or a small

elevation of masonry, 8 or 10 feet long by 5 or 6 broad, and covered in

with a chimney. This area is quite similar to that of the ordinary

hearths of our blast-furnaces.

The tuyère stands 5 or 6 inches above the basin, and has a slight

inclination downwards. In Corsica, and the whole portion of Italy

adjoining the Mediterranean shores, the iron ore is an oxide similar to

the specular ore of the Isle of Elba. This ore contains a little water,

some carbonic acid, occasionally pyrites, but in small quantity. Before

deoxidizing the ore, it is requisite to expel the water and carbonic

acid combined with the oxide, as well as the sulphur of the pyrites.

The operations of roasting, reduction, fusion, and agglutination are

executed in the same furnace. These are indeed divided into two stages,

but the one is a continuation of the other. In the first, the two

primary operations are performed at once;--the reduction of a portion of

the roasted ore is begun at the same time that a portion of the raw ore

is roasted: these two substances are afterwards separated. In the second

stage, the deoxidizement of the metal is continued, which had begun in

the preceding stage; it is then melted and agglutinated, so as to form a

ball to be submitted to the forge-hammer.

The roasted pieces are broken down to the size of nuts, to make the

reduction of the metal easier. In executing the first step, the basin

and area of the furnace must be lined with a _brasque_ of charcoal dust,

3, 4, or even 5 inches thick: over this _brasque_ a mound is raised with

lumps of charcoal, very hard, and 4 or 5 inches high. A semi-circle is

formed round the tuyère, the inner radius of which is 5 or 6 inches.

This mass of charcoal is next surrounded with another pile of the

roasted and broken ores, which must be covered with charcoal dust. The

whole is sustained with large blocks of the raw ore, which form

externally a third wall.

These three piles of charcoal, with roasted and unroasted ore, are

raised in three successive beds, each 7 inches thick: they are separated

from each other by a layer of charcoal dust of about an inch, which

makes the whole 24 inches high. This is afterwards covered over with a

thick coat of pounded charcoal.

The blocks of raw ore which compose the outward wall form a slope; the

larger and stronger pieces are at the bottom, and the smaller in the

upper part. The large blocks are sunk very firmly into the charcoal

dust, to enable them better to resist the pressure from within.

On the bottom of the semicircular well formed within the charcoal lumps,

kindled pieces are thrown, and over these, pieces of black charcoal;

after which the blast of a water-blowing machine (_trompe_) is given.

The fire is kept up by constantly throwing charcoal into the central

well. At the beginning of the operation it is thrust down with wooden

rods, lest it should affect the building; but when the heat becomes too

intense for the workmen to come so near the hearth, a long iron rake is

employed for the purpose. At the end of about 3 hours, the two processes

of roasting and reduction are commonly finished: then the raw ore no

longer exhales any fumes, and the roasted ore, being softened, unites

into lumps more or less coherent.

The workman now removes the blocks of roasted ore which form the outer

casing, rolls them to the spot where they are to be broken into small

pieces, and pulls down the _brasque_ (small charcoal) which surrounds

the mass of reduced ore.

The second operation is executed by cleaning the basin, removing the

slags, covering the basin anew with 2 or 3 brasques, (coats of pounded

charcoal), and piling up to the right and the left, two heaps of

charcoal dust. Into the interval between these conical piles two or

three baskets of charcoal are cast, and on its top some cakes of the

reduced crude metal being laid, the blast is resumed. The cakes, as they

heat, undergo a sort of liquation, or sweating, by the action of the

earthy glasses on the unreduced black oxide present. Very fusible slags

flow down through the mass; and the iron, reduced and melted, passes

finally through the coals, and falls into the slag basin below. To the

first parcel of cakes, others are added in succession. In proportion as

the slags proceeding from these run down, and the melted iron falls to

the bottom, the thin slag is run off by an upper overflow or _chio_

hole, and the reduced iron kept by the heat in the pasty condition,

remains in the basin: all its parts get agglutinated, forming a soft

mass, which is removed by means of a hooked pole in order to be forged.

Each lump or _bloom_ of malleable iron requires 3 hours and a half for

its production.

The iron obtained by this process is in general soft, very malleable,

and but little steely. In Corsica four workmen are employed at one

forge. The produce of their labour is only about 4 cwt. of iron from 10

cwt. of ore and 20 of charcoal, mingled with wood of beech and chestnut.

Though their ore contains on an average 65 per cent. of iron, only about

40 parts are extracted; evincing a prodigious waste, which remains in

the slags.

The difference between the Corsican and the Catalonian methods consists

in the latter roasting the ore at a distinct operation, and employing a

second one in the reduction, agglutination, and refining of the metal.

In the Catalonian forges, 100 pounds of iron are obtained from 300

pounds of ore and 310 pounds of charcoal; being a produce of only 33 per

cent. It may be concluded that there is a notable loss, since the sparry

iron ores, which are those principally smelted, contain on an average

from 54 to 56 per cent. of iron. The same ores smelted in the ordinary

blast furnace produce about 45 per cent. of cast iron.

On the Continent, iron is frequently refined from the cast metal of the

blast furnaces by three operations, in three different ways. In one, the

pig being melted, with aspersion of water, a cake is obtained, which is

again melted in order to form a second cake. This being treated in the

refinery fire, is then worked into a _bloom_. In another system, the pig

iron is melted and cast into plates: these are melted anew in order to

obtain crude balls, which are finally worked into blooms. In a third

mode of manufacture, the pig-iron is melted and cast into plates, which

are roasted, and then strongly heated, to form a bloom.

The French fusible ores, such as the silicates of iron, are very apt to

smelt into white cast iron. An excess of fluxes, light charcoals, too

strong a blast, produce the same results. A surcharge of ores which

deranges the furnace and affords impure slags mixed with much iron, too

rapid a slope in the boshes, too low a degree of heat, and too great

condensation of the materials in the upper part of the furnace; all tend

also to produce a white cast iron. In its state of perfection, white

cast iron has a silver colour, and a bright metallic lustre. It is

employed frequently in Germany for the manufacture of steel, and is then

called _steel floss_, or _lamellar floss_, a title which it still

retains, though it be hardly silver white, and have ceased to be

foliated. When its colour takes a bluish-gray tinge, and its fracture

appears striated or splintery, or when it exhibits gray spots, it is

then styled _flower floss_. In a third species of white cast iron we

observe still much lustre, but its colour verges upon gray, and its

texture is variable. Its fracture has been sometimes compared to that of

a broken cheese. This variety occurs very frequently. It is a white cast

iron, made by a surcharge of ore in the furnace. If the white colour

becomes less clear and turns bluish, if its fracture be contorted, and

contains a great many empty spaces or air-cells, the metal takes the

name of _cavernous-floss_, or _tender-floss_. The whitest metal cannot

be employed for casting. When the white is mixed with the gray cast

iron, it becomes _riband_ or _trout_ cast iron.

[Illustration: 601]

[Illustration: 602]

_The German refining forge._--_Figs._ 601, 602. represent one of the

numerous refinery furnaces so common in the Hartz. The example is taken

from the _Mandelholz_ works, in the neighbourhood of Elbingerode. _Fig._

602. is an elevation of this forge. D is the refinery hearth, provided

with two pairs of bellows. _Fig._ 601. is a vertical section, showing

particularly the construction of the crucible or hearth in the refinery

forge D. C is an overshot water-wheel, which gives an alternate

impulsion to the two bellows _a b_ by means of the revolving shaft _c_,

and the cams or tappets _d f e g_.

D, the hearth, is lined with cast-iron plates. Through the pipe _l_,

cold water may be introduced, under the bottom plate _m_, in order to

keep down, when necessary, the temperature of the crucible, and

facilitate the solidification of the _loupe_ or bloom. An orifice _n_,

_figs._ 601, 602., called the _chio_ (floss hole), allows the melted

slag or cinder to flow off from the surface of the melted metal. The

copper pipe or nose piece _p_, _fig._ 600., conducts the blast of both

bellows into the hearth, as shown at _b x_, _fig._ 602., and D _g p_

_fig._ 600.

The substance subjected to this mode of refinery, is a gray carbonaceous

cast iron, from the works of Rothehütte. The hearth D, being filled and

heaped over with live charcoal, upon the side opposite to the tuyère

_x_, _figs._ 601, 602, long pigs of cast iron are laid with their ends

sloping downwards, and are drawn forwards successively into the hearth

by a hooked poker, so that the extremity of each may be plunged into the

middle of the fire, at a distance of 6 or 8 inches from the mouth of the

tuyère. The workman proceeds in this way, till he has melted enough of

metal to form a _loupe_. The cast iron, on melting, falls down in drops

to the bottom of the hearth; being covered by the fused slags, or

vitreous matters more or less loaded with oxide of iron. After running

them off by the orifice _n_, he then works the cast iron by powerful

stirring with an iron rake (_ringard_), till it is converted into a mass

of a pasty consistence.

During this operation, a portion of the carbon contained in the cast

iron combines with the atmospherical oxygen supplied by the bellows, and

passes off in the form of carbonic oxide and carbonic acid. When the

lump is coagulated sufficiently, the workman turns it over in the

hearth, then increases the heat so as to melt it afresh, meanwhile

exposing it all round to the blast, in order to consume the remainder of

the carbon, that is, till the iron has become ductile, or refined. If

one fusion should prove inadequate to this effect, two are given. Before

the conclusion, the workman runs off a second stratum of vitreous slag,

but at a higher level, so that some of it may remain upon the metal.

The weight of such a _loupe_ or _bloom_ is about 2 cwts., being the

product of 2 cwts. and 7/10 of pig iron; the loss of weight is therefore

about 26 per cent. 149 pounds of charcoal are consumed for every 100

pounds of bar iron obtained. The whole operation lasts about 5 hours.

The bellows are stopped as soon as the bloom is ready; this is

immediately transferred to a forge hammer, such as is represented _fig._

605.; the cast-iron head of which weighs 8 or 9 cwts. The bloom is

greatly condensed thereby, and discharges a considerable quantity of

semi-fluid cinder. The lump is then divided by the hammer and a chisel

into 4 or 6 pieces, which are re-heated, one after another, in the same

refinery fire, in order to be forged into bars, whilst another pig of

cast iron is laid in its place, to prepare for the formation of a new

bloom. The above process is called by the Germans _klump-frischen_, or

lump-refining. It differs from the _durch-brech-frischen_, because in

the latter, the lump is not turned over in mass, but is broken, and

exposed in separate pieces successively to the refining power of the

blast near the tuyère. The French call this _affinage par portions_; it

is much lighter work than the other.

The quality of the iron is tried in various ways; as first, by raising a

bar by one end, with the two hands over one’s head, and bringing it

forcibly down to strike across a narrow anvil at its centre of

percussion, or one-third from the other extremity of the bar; after

which it may be bent backwards and forwards at the place of percussion

several times; 2. a heavy bar may be laid obliquely over props near its

end, and struck strongly with a hammer with a narrow pane, so as to

curve it in opposite directions; or while heated to redness, they may be

kneed backwards and forwards at the same spot, on the edge of the anvil.

This is a severe trial, which the hoop L, Swedish iron, bears

surprisingly, emitting as it is hammered, a phosphoric odour, peculiar

to it and to the bar iron of Ulverstone, which also resembles it, in

furnishing a good steel. The forging of a horseshoe is reckoned a good

criterion of the quality of iron. Its freedom from flaws is detected by

the above modes; and its linear strength may be determined by suspending

a scale to the lower end of a hard-drawn wire, of a given size, and

adding weights till the wire breaks. The treatises of Barlow and

Tredgold may be consulted with advantage on the methods of proving the

strength of different kinds of iron, in a great variety of

circumstances.

Steel of cementation, or blistered steel and cast steel, are treated

under the article STEEL. But since in the conversion of cast iron into

wrought iron, by a very slight difference in the manipulations, a

species of steel may be produced called _natural steel_, I shall

describe this process here.

[Illustration: 603]

_Fig._ 603. is a view of the celebrated steel iron works, called

Königshütte (_king’s-forge_), in Upper Silesia, being one of the best

arranged in Germany, for smelting iron ore by means of coke. The front

shown here is about 400 English feet long. _a a_ are two blast furnaces.

A third blast furnace, all like the English, is situated to the left of

one of the towers _b_. _b b_ are the charging towers, into which the ore

is raised by machinery from the level of the store-houses _l l_, up to

the mouth of the furnaces _a a_; _c c_ point to the positions of the

boilers of the two steam engines, which drive two cylinder bellows at

_f_. _n n n n_ are arched cellars placed below the store-houses _l l_,

for containing materials and tools necessary for the establishment.

[Illustration: 604]

_Figs._ 599., 604., are vertical sections of the forge of Königshütte,

for making natural steel; _fig._ 599. being drawn in the line A B of the

plan, _fig._ 600. _a_ is the bottom of the hearth, consisting of a

fire-proof gritstone; _b_ is a space filled with small charcoal, damped

with water, under which, at _n_, in _fig._ 604., is a bed of well rammed

clay; _d_ is a plate of cast iron, which lines the side of the hearth

called rückstein (backstone) in German, and corrupted by the French into

_rustine_; _f_ is the plate of the counter-blast; _g_ the plate of the

side of the tuyère: behind, upon the face _d_, the fire-place or hearth

is only 5-1/2 inches deep; in front as well as upon the lateral faces,

it is 18 inches deep. By means of a mound made of dry charcoal, the

posterior face _d_, is raised to the height of the face _f_. _i_, _fig._

600., is the floss-hole, by which the slags are run off from the hearth

during the working, and through which, by removing some bricks, the lump

of steel is taken out when finished.

_k l m_ are pieces of cast iron, for confining the fire in front, that

is towards the side where the workman stands; _o_ is the level of the

floor of the works; _p_ a copper tuyère; it is situated 4-1/2 inches

above the bottom _a_, slopes 5 degrees towards it, and advances 4 inches

into the hearth or fire-place, where it presents an orifice, one half

inch in horizontal length, and one inch up and down; _q_ the nose pipes

of two bellows, like those represented in _fig._ 602., and under

SILVER; the round orifice of each of them within the tuyère being one

inch in diameter. _r_ is the lintel or top arch of the tuyère, beneath

which is seen the cross section of the pig of cast iron under operation.

For the production of natural steel, a white cast iron is preferred,

which contains little carbon, which does not flow thin, and which being

cemented _over or above the wind_, falls down at once through the blast

to the bottom of the hearth in the state of steel. With this view, a

very flat fire is used; and should the metal run too fluid, some

malleable lumps are introduced to give the mass a thicker pasty

consistence.

If the natural steel be supposed to contain too little carbon, which is

a very rare case, the metal bath covered with its cinder slag, is

diligently stirred with a wooden pole, or it may receive a little of the

more highly carburetted iron. If it contains the right dose of carbon,

the earthy and other foreign matters are made progressively to sweat

out, into the supernatant slag. When the mass is found by the trial of a

sample to be completely converted, and has acquired the requisite

stiffness, it is lifted out of the furnace, by the opening in front,

subjected to the forge hammer, and drawn into bars. In Sweden, the

cast-iron pigs are heated to a cherry-red, and in this state broken to

pieces under the hammer, before they are exposed in the steel furnace.

These natural steels are much employed on the Continent in making

agricultural implements, on account of their cheapness. The natural

steel of Styria is regarded as a very good article.

Wootz is a natural steel prepared from a black ore of iron in Hindostan,

by a process analogous to that of the Catalan hearth, but still simpler.

It seems to contain a minute portion of the combustible bases of alumina

and silica, to which its peculiar hardness when tempered, may possibly

be ascribed. It is remarkable for the property of assuming a damask

surface, by the action of dilute sulphuric acid, after it has been

forged and polished. See DAMASCUS and STEEL.

[Illustration: 605]

_Fig._ 605. is the German forge-hammer; to the left of 1, is the axis of

the rotatory cam, 2, 3, consisting of 8 sides, each formed of a strong

broad bar of cast iron, which are joined together to make the octagon

wheel. 4, 5, 6, are cast-iron binding rings or hoops; made fast by

wooden wedges. _b_, _b_, are standards of the frame work _e_, _l_, _m_,

in which the helve of the forge hammer has its fulcrum near _u_. _h_,

the sole part of the frame. Another cast-iron base or sole is seen at

_m_. _n_ is a strong stay, to strengthen the frame-work. At _r_ two

parallel hammers are placed, with cast-iron heads and wooden helves. _s_

is the anvil, a very massive piece of cast iron. _t_ is the end of a

vibrating beam, for throwing back the hammer from it forcibly by recoil.

_x y_ is the outline of the water-wheel which drives the whole. The cams

or tappets are shown mounted upon the wheel 6, _g_, 6.

_Analysis of Irons._--Oxidized substances cannot exist in metallic iron,

and the foreign substances it does contain are present in such small

quantities, that it is somewhat difficult to determine their amount. The

most intricate point is, the proportion of carbon. The free carbon,

which is present only in gray cast iron, may, indeed, be determined

nearly, for most of it remains after solution of the metal in acids. The

combined charcoal, however, changes by the action of muriatic acid into

gas and oil; sulphuric acid also occasions a great loss of carbon, and

nitric acid dissipates it almost entirely. Either nitre or chloride of

silver may be employed to ascertain the amount of carbon; but when the

iron contains chromium and much phosphorus, the determination of the

carbon is attended with many difficulties.

The quantity of sulphur is always so small, that it can scarcely be

ascertained by the weight of the precipitate of sulphate of barytes from

the solution of the iron in nitro-muriatic acid. The iron should be

dissolved in muriatic acid; and the hydrogen, as it escapes charged with

the sulphur, should be passed through an acidulous solution of acetate

of lead. The weight of the precipitated sulphuret shows the amount of

sulphur, allowing 13·45 of the latter for 100 of the former. In this

experiment the metal should be slowly acted upon by the acid. Cast iron

takes from 10 to 15 days to dissolve, steel from 8 to 10, and malleable

iron 4 days. The residuum of a black colour does not contain a trace of

sulphur.

Phosphorus and chromium are determined in the following way. The iron

must be dissolved in nitro-muriatic acid, to oxygenate those two bodies.

The solution must be evaporated cautiously to dryness in porcelain

capsules, and the saline residuum heated to redness. A little chloride

of iron is volatilized, and the remainder resembles the red-brown oxide.

This must be mixed with thrice its weight of carbonate of potash, and

fused in a platinum crucible; the quantity of iron being from 40 to 50

grains at most.

The mixture after being acted upon by boiling water, is to be left to

settle, to allow the oxide to be deposited, for it is so fine as to pass

through a filter. If the iron contained manganese, this would be found

_at first_ in the alkaline solution; but manganese spontaneously

separates by exposure to the air. The alkaline liquor must be

supersaturated with muriatic acid, and evaporated to dryness. The liquor

acidulated, and deprived of its silica by filtration, is to be

supersaturated with ammonia; when the alumina will precipitate in the

state of a subphosphate. When the liquor is now supersaturated with

acetic acid, and then treated with acetate of lead, a precipitate of

phosphate of lead almost always falls. There is hardly a bit of iron to

be found which does not contain phosphorus. The slightest trace of

chrome is detected by the yellow colour of the lead precipitate; if this

be white there is none of the colouring metal present.

100 parts of the precipitated phosphate of lead contain, after

calcination, 19·4 parts of phosphoric acid. The precipitate should be

previously washed with acetic acid, and then with water. These 19·4

parts contain 8·525 parts of phosphorus.

Cast iron sometimes contains calcium and barium, which may be detected

by their well-known reagents, oxalate of ammonia, and sulphuric acid. In

malleable iron they are seldom or never present.

The charcoal found in the residuum of the nitro-muriatic solution is to

be burned away under a muffle. The solution itself contains along with

the oxide of iron, protoxide of manganese, and other oxides, as well as

the earths, and the phosphoric and arsenic acids. Tartaric acid is to be

added to it, till no precipitate be formed by supersaturation with

caustic ammonia. The ammoniacal liquor must be treated with

hydrosulphuret of ammonia as long as it is clouded, then thrown upon a

filter. The precipitate is usually very voluminous, and must be well

washed. The liquor which passes through is to be saturated with muriatic

acid, to decompose all the sulphurets.

The solution still contains all the earths and the oxide of titanium,

besides the phosphoric acid. It is to be evaporated to dryness, whereby

the ammonia is expelled, and the carbonaceous residuum must be burned

under a muffle. If the iron contains much phosphorus, the ashes are

strongly agglutinated. They are to be fused as already described along

with carbonate of potash, and the mass is to be treated with boiling

water. The residuum may be examined for silica, lime, barytes, and oxide

of titanium. Muriatic acid being digested on it, then evaporated to

dryness, and the residuum treated with water; will leave the silica.

Caustic ammonia, poured into the solution, will separate the alumina, if

any be present, and the oxide of titanium; but the former almost never

occurs.

Manganese is best sought for by a distinct operation. The iron must be

dissolved at the heat of boiling water, in nitro-muriatic acid; and the

solution, when very cold, is to be treated with small successive doses

of solution of carbonate of ammonia. If the iron has been oxidized to a

maximum, and if the liquor has been sufficiently acid, and diluted with

water, it will retain the whole of the manganese. This process is as

good as that by succinate of ammonia, which requires many precautions.

The liquor is often tinged yellow by carbon, after it has ceased to

contain a single trace of iron oxide. As soon as litmus paper begins to

be blued by carbonate of ammonia, we should stop adding it; immediately

throw the whole upon a filter, and wash continuously with cold water.

What passes through is to be neutralized with muriatic acid, and

concentrated by evaporation. It may contain besides manganese, some

lime, or barytes. It should therefore be precipitated with

hydrosulphuret of ammonia, the hydrosulphuret of manganese should be

collected, dissolved in strong muriatic acid, filtered, and treated, at

a boiling heat, with carbonate of potash. The precipitate, well washed

and calcined, contains, in 100 parts, 72·75 parts of metallic manganese.

The copper, arsenic, lead, tin, bismuth, antimony, or silver, are best

separated by a stream of sulphuretted hydrogen gas passed through the

solution in nitro-muriatic acid, after it is largely diluted with water.

The precipitate must be cautiously roasted in a porcelain test, to burn

away the large quantity of sulphur which is deposited in consequence of

the conversion of the peroxide of iron into the protoxide. If nothing

remains upon the test, none of these metals is present. If a residuum be

obtained, it must be dissolved in nitro-muriatic acid, and subjected to

examination. But, in fact, carbon, sulphur, phosphorus, silicon, and

manganese, are the chief contaminators of iron.

Chloride of silver affords the means of determining the proportion of

carbon contained in iron, and of ascertaining the state in which that

substance exists in the metal. Fused chloride of a pale yellow colour

must be employed. The operation is to be performed in close vessels,

with the addition of a great deal of water, and a few drops of muriatic

acid. The carbonaceous residuum is occasionally slightly acted upon. We

may judge of this circumstance by the gases disengaged, as well as by

the appearance of the charcoal.

Ductile iron and soft steel, as well as white cast-iron which has been

rendered gray by roasting, when decomposed by chloride of silver, afford

a blackish-brown unmagnetic charcoal, and a plumbaginous substance

perfectly similar to what is extracted from the same kinds of iron, by

solution in acids. A portion of this plumbago is also converted into

charcoal of a blackish brown colour, by the action of the chloride.

Hence this agent does not afford the means of obtaining what has been

called the poly-carburet, till it has produced a previous decomposition.

But we obtain it, in this manner, purer and in greater quantity than we

could by dissolving the metal in the acids. The only subject of regret

is, that we possess no good criterion for judging of the progress of

this analytical operation.

Gray cast iron leaves, besides the polycarburet, a residuum of plumbago,

and carbon which was not chemically combined with the iron; while

tempered steel and white cast iron afford merely a blackish brown

charcoal; but the operation is extremely slow with the latter two

bodies, because a layer of charcoal forms upon the surface, which

obstructs their oxidizement. For this reason the white cast iron ought

to be previously changed into gray by fusion in a crucible lined with

charcoal, before being subjected to the chloride of silver; if this

process be employed for tempered steel, the combined carbon becomes

merely a polycarburet. It would not be possible to operate upon more

than 15 grains, which require from 60 to 80 times that quantity of the

chloride, and a period of 15 days for the experiment.

The residuum, which is separable from the silver only by mechanical

means, should be dried a long time at the heat of boiling water. It

contains almost always iron and silica. After its weight is ascertained,

it is to be burned in a crucible of platinum till the ashes no longer

change their colour, and are not attractable by the magnet. The

difference between the weights of the dried and calcined residuum is the

weight of the charcoal. The oxide of iron is afterwards separated from

the silica by muriatic acid.

In operating upon gray cast iron, we should ascertain separately the

proportion of graphite or plumbago, and that of the combined charcoal.

To determine the former, we dissolve a second quantity of the cast iron

in nitric acid, with a little muriatic; the residuum, which is graphite,

is separated from the silica and the combined carbon by the action of

caustic potash. After being washed and dried, it must be weighed. The

weight of the graphite obtained being deducted from the quantity of

carbon resulting from the decomposition effected by the chloride of

silver, the remainder is the amount of the chemically combined carbon.

By employing muriatic acid, we could dissipate at once the combined

carbon; but this method would be inexact, because the hydrogen

disengaged would carry off a portion of the graphite.

According to Karsten, Mushet’s table of the quantities of carbon

contained in different steels and cast irons is altogether erroneous. It

gives no explanation why, with equal proportions of charcoal, cast iron

constitutes at one time a gray, soft, granular metal, and at another, a

white, hard, brittle metal in lamellar facets. The incorrectness of

Mushet’s statement becomes most manifest when we see the white lamellar

cast iron melted in a crucible lined with charcoal, take no increase of

weight, while the gray cast iron treated in the same way becomes

considerably heavier.

Analysis has never detected a trace of carbon _unaltered_ or of graphite

in white cast iron, if it did not proceed from small quantities of the

gray mixed with it; while perfect gray cast iron affords always a much

smaller quantity of carbon altered by combination, and a much greater

quantity of graphite. Neither kind of cast iron, however, betrays the

presence of any oxygen. Steel affords merely altered carbon, without

graphite; the same thing holds true of malleable iron; while the iron

obtained by fusion with 25 per cent. of scales of iron contains no

carbon at all.

The graphite of cast iron is obtained in scales of a metallic aspect,

whereas the combined carbon is obtained in a fine powder. When the white

cast iron has been roasted, and become gray, and is as malleable as the

softest gray cast iron, it still affords no graphite as the latter does,

though in appearance both are alike. Yet in their properties they are

still essentially dissimilar.

With 4-1/4 per cent. of carbon, the white cast iron preserves its

lamellar texture; but with less carbon, it becomes granular and of a

gray colour, growing paler as the dose of carbon is diminished, while

the metal after passing through an indefinite number of gradations,

becomes steely cast iron, very hard steel, soft steel, and steely

wrought iron.

The steels of the forge and the cast steels examined by Karsten,

afforded him from 2·3 to 1-1/4 per cent. of carbon; in the steel of

cementation, (blistered steel) he never found above 1-3/4 of carbon.

Some wrought irons which ought to contain no charcoal, hold as much as

1/2 per cent. and they then approach to steel in nature. The softest and

purest irons contain still 0·2 per cent. of carbon.

The quantity of graphite which gray cast iron contains, varies,

according to Karsten’s experiments, from 2·57 to 3·75 per cent.; but it

contains besides, some carbon in a state of alteration. The total

contents in carbon varied from 3·15 to 4·65 per cent. When the

congelation of melted iron is very slow, the carbon separates, probably

in consequence of its crystallizing force, so as to form a gray cast

iron replete with plumbago. If the gray do not contain more charcoal

than the white from which it has been formed, and if it contain the

charcoal in the state of mechanical mixture, then it can have little or

none in a state of combination, even much less than what some steels

contain. Hence we can account for some of its peculiarities in reference

to white cast iron; such as its granular texture, its moderate hardness,

the length of time it requires to receive annealing colours, the

modifications it experiences by contact of air at elevated temperatures,

the high degree of heat requisite to fuse it, its liquidity, and finally

its tendency to rust by porosity, much faster than the white cast iron.

We thus see that carbon may combine with iron in several manners; that

the gray cast iron is a mixture of steely iron and plumbago; that the

white, rendered gray and soft by roasting, is a compound of steely iron

and a carburet of iron, in which the carbon predominates; and that

untempered steel is in the same predicament.

For the following analyses of cast irons, we are indebted to MM. Gay

Lussac and Wilson.

TABLE.--In 100 parts.

+----------------------+------+-----+-----+-----+-------+------------+

| | |bon. | ca. |pho- |ganese.| |

| | | | |rus. | | |

+----------------------+------+-----+-----+-----+-------+------------+

|White cast from Siegen|94·338|2·690|0·230|0·162|2·590 |By wood |

|Do. Coblentz |94·654|2·441|0·230|0·185|2·490 | do. |

|Do. a. d. Champ |96·133|2·324|0·840|0·703|a trace| do. |

|Do. Isère |94·687|2·636|0·260|0·280|2·137 | do. |

|Gray Nivernais |95·673|2·254|1·030|1·043|a trace| do. |

|Do. Berry |95·573|2·319|1·920|0·188| do |Mix. of coke|

| | | | | | | & do.|

|Do. a. d. Champ |95·971|2·100|1·060|0·869| do. |Charcoal |

|Do. Creusot |93·385|2·021|3·490|0·604| do. |Coke |

| Comté |95·689|2·800|1·160|0·351| do. | do. |

|Do. Wales |94·842|1·666|3·000|0·492| do. | do. |

|Do. Do. |95·310|2·550|1·200|0·440| do. | do. |

|Do. Do. |95·150|2·450|1·620|0·780| do. | do. |

+----------------------+------+-----+-----+-----+-------+------------+

Karsten has given the following results as to carbon, in 100 parts of

gray cast iron.

+--------------------------------+-----+----+----+----------------+

| |bined|car-|tal | |

| |car- |bon.|car-| |

| |bon. | |bon.| |

+--------------------------------+-----+----+----+----------------+

|Siegen, from brown iron-stone | 0·89|3·71|4·60|By wood charcoal|

|and sparry iron | 1·03|3·62|4·65| do. |

|Malapane, from spherosiderite | 0·75|3·15|3·90| do. |

|Königshütte, from brown ore | 0·58|2·57|3·15| coke |

|Do. at a lower smelting heat | 0·95|2·70|3·65| do. |

+--------------------------------+-----+----+----+----------------+

[Illustration: 606 607]

_Fig._ 607. represents in section, and _fig._ 606. in plan, the famous

cupola furnace for casting iron employed at the Royal Foundry in Berlin.

It rests upon a foundation _a_, from 18 to 24 inches high, which

supports the basement plate of cast iron, furnished with ledges, for

binding the lower ends of the upright side plates or cylinder, _e_. Near

the mouth there is a top-plate _d_, made in several pieces, which serves

to bind the sides at their upper end, as also to cover in the walls of

the shaft. These plates are most readily secured in their places by

screws and bolts. Within this iron case, at a little distance from it,

the proper furnace-shaft _e_, is built with fire-bricks, and the space

between this and the iron is filled up with ashes. The sole of the

hearth _f_, over the basement-plate, is composed of a mixture of

fire-clay and quartz-sand firmly beat down to the thickness of 6 or 8

inches, with a slight slope towards the discharge-hole for running off

the metal. _g_ is the _form_ or the tuyère (there are sometimes one on

each side); _h_ the nose pipe; the discharge aperture _i_ is 12 inches

wide and 15 inches high; across which the sole of the hearth is rammed

down. During the melting operation, this opening is filled up with

fire-clay; when it is completed, a small hole merely is pierced through

it at the lowest point, for running off the liquid metal. The hollow

shaft should be somewhat wider at bottom than at top. Its dimensions

vary with the magnitude of the foundry. When 5 feet high, its width at

the level of the tuyère or blast-hole may be from 20 to 22 inches. From

250 to 300 cubic feet of air per minute are required for the working of

such a cupola. For running down 100 pounds of iron, after the furnace

has been brought to its heat, 48 pounds of ordinary coke are used; but

with the hot blast much less will suffice. The furnace requires feeding

with alternate charges of coke and iron every 8 or 10 minutes. The waste

of iron, by oxidization and slag, amounts in most foundries to fully 5

per cent. For carrying off the burnt air, a chimney-hood is commonly

erected over the cupola. See FOUNDRY.

The double-arched air or wind-furnace used in the foundries of

Staffordshire for melting cast iron, has been found advantageous in

saving fuel, and preventing waste by slag. It requires fire-bricks of

great size and the best composition.

The main central key-stone is constructed of large fire-bricks made on

purpose; against that key-stone the two arches press, having their

abutments at the sides against the walls. The highest point of the roof

is only 8 inches above the melted metal. The sole of the hearth is

composed of a layer of sand 8 inches thick, resting upon a bed of iron

or of brickwork. The edge of the fire-bridge is only 3 inches above the

fluid iron.

In from 2 to 4 hours from 1 to 3 tons of metal may be founded in such a

furnace, according to its size; but it ought always to be heated to

whiteness before the iron is introduced. 100 pounds of cast iron require

from 1 to 1-1/2 cubic foot of coal to melt them. The waste varies from 5

to 9 per cent.

I shall conclude the subject of iron with a few miscellaneous

observations and statistical tables. Previously to the discovery by Mr.

Cort, in 1785, of the methods of puddling and rolling or shingling iron,

this country imported 70,000 tons of this metal from Russia and Sweden;

an enormous quantity for the time, if we consider that the cotton and

other automatic manufactures, which now consume so vast a quantity of

iron, were then in their infancy; and that two years ago, the whole of

our importation from these countries did not exceed 40,000 tons. From

the following table of the prices of bar iron in successive years, we

may infer the successive rates of improvement and economy, with slight

vicissitudes.

+------+-----------------+

|Years.| Per Ton. |

+------+-----------------+

| |_£ s._ _£ s._|

| 1824 | 9 0 to 10 0 |

| 1825 |10 0 -- 14 0 |

| 1826 | 8 10 -- 10 0 |

| 1827 | 8 0 -- 9 0 |

| 1828 | 7 10 -- 8 0 |

| 1829 | 5 10 -- 7 0 |

| 1830 | 5 5 -- 6 0 |

| 1831 | 5 5 -- 5 10 |

| 1832 | 5 0 -- 5 10 |

| 1833 | 5 10 -- 6 0 |

| 1834 | 6 0 -- 6 10 |

| 1835 | 5 10 -- 7 0 |

+------+-----------------+

I have been informed upon good authority that the total production of

iron in Great Britain, in the year 1836, was almost exactly ONE MILLION

OF TONS!

The export of iron that year, in bars, rods, pigs, castings, wire,

anchors, hoops, nails, and old iron, amounted to 189,390 tons; in

unwrought steel to 3,014, and in cutlery, to 21,072; in whole to

213,478: leaving apparently for internal consumption 776,522 tons, from

which however one tenth probably should be deducted for waste, in the

conversion of the bar iron. Hence 700,000 tons may be taken as the

approximate quantity of iron made use of in the United Kingdom, in the

year 1836.

The years 1835 and 1836 being those of the railway mania over the world,

produced a considerable temporary rise in the price of bar iron; but as

this increased demand caused the construction of a great many more

smelting and refining furnaces, it has tended eventually to lower the

prices; an effect also to be ascribed to the more general use of the hot

blast.

The relative cost of making cast iron at Merthyr Tydvil in South Wales,

and at Glasgow, was as follows, eight or nine years ago.

_At Merthyr._

_s._ _Tons. Cwts. Qrs._ _£ s. d._

Raw mine at 10 per ton, 3 7 0 1 13 6

Coal at 6 2 16 0 0 16 6

Limestone 1 5 2 0 1 4

Other charges 0 9 1

--------

Total Cost 3 0 5

_At Glasgow._

_s. d._ _Tons. Cwts._ _£ s. d._

Raw mine at 4 6 3 10 0 16 3

Splint Coal at 2 5 5 15 0 14 0

Limestone at 0 3 0 14 0 3 6

Coals for the engine 1 10 0 3 0

Other charges 1 1 0

--------

Total cost 2 17 9

The cost is still nearly the same at Merthyr, but it has been greatly

decreased at Glasgow.

The saving of fuel by the hot-blast is said to be in fact so great, that

blowing cylinders, which were adequate merely to work three furnaces at

the first period, were competent to work four furnaces at the last

period. The saving of materials has moreover been accompanied by an

increase of one-fourth in the quantity of iron, in the same time; as a

furnace which turned out only 60 tons a week with the cold blast, now

turns out no less than 80 tons. That the iron so made is no worse, but

probably better, when judiciously smelted, would appear from the

following statement. A considerable order was not long since given to

four iron-work companies in England, to supply pipes to one of the

London water companies. Three of these supplied pipes made from the

cold-blast iron; the fourth, it is said, supplied pipes made with the

hot-blast iron. On subjecting these several sets of pipes to the

requisite trials by hydraulic pressure, the last lot was found to stand

the proof far better than any of the former three.--That iron was made

with raw coal.

I have been since told by eminent iron-masters of Merthyr, that this

statement stands in need of confirmation, or is probably altogether

apocryphal, and that as they find the hot blast weakens the iron, they

will not adopt it.

Between the cast irons made in different parts of Great Britain, there

are characteristic differences. The Staffordshire metal runs remarkably

fluid, and makes fine sharp castings. The Welsh is strong, less fluent,

but produces bar iron of superior quality. The Derbyshire iron also

forms excellent castings, and may be worked with care into very good bar

iron. The Scotch iron is very valuable for casting into hollow wares, as

it affords a beautiful smooth skin from the moulds, so remarkable in the

castings of the Carron company, in Stirlingshire, and of the Phœnix

foundry, at Glasgow. The Shropshire iron resembles the Staffordshire in

its good qualities.

The average quantity of fine metal obtainable from the forge-pigs at

Merthyr Tydvil, from the finery furnace, is one ton for 22-1/2 cwt. of

cast iron, with a consumption of about 9-1/2 cwt. of coal per ton.

_Estimate of the average cost of erecting three blast furnaces._

A Dictionary of Arts, Manufactures and Mines containing a clear exposition of their principles and practice · 第 220 / 421 题

The hearths of cast iron rest upon cast-iron pillars, to the number of