To enumerate the different means employed to make every sort of mould
exceeds the limits prescribed to this work. I shall merely indicate for
each species of moulding, what is common to all the operations; and I
shall then describe the fabrication of a few such moulds as appear most
proper to give general views of this peculiar art.
_Moulding in green sand._--The name green is given to a mixture of the
sand as it comes from its native bed, with about one twelfth its bulk of
coal reduced to powder, and damped in such a manner as to form a porous
compound, capable of preserving the forms of the objects impressed upon
it. This sand ought to be slightly argillaceous, with particles not
exceeding a pin’s head in size. When this mixture has once served for a
mould, and been filled with metal, it cannot be employed again except
for the coarsest castings, and is generally used for filling up the
bottoms of fresh moulds.
For moulding any piece in green sand, an exact pattern of the object
must be prepared in wood or metal; the latter being preferable, as not
liable to warping, swelling, or shrinkage.
A couple of iron frames form a case or box, which serves as an envelope
to the mould. Such boxes constitute an essential and very expensive part
of the furniture of a foundry. It is a rectangular frame, without bottom
or lid, whose two largest sides are united by a series of cross bars,
parallel to each other, and placed from 6 to 8 inches apart.
The two halves of the box carry ears corresponding exactly with one
another; of which one set is pierced with holes, but the other has
points which enter truly into these holes, and may be made fast in them
by cross pins or wedges, so that the pair becomes one solid body. Within
this frame there is abundance of room for containing the pattern of the
piece to be moulded with its encasing sand, which being rammed into the
frame, is retained by friction against the lateral faces and cross bars
of the mould.
When a mould is to be formed, a box of suitable dimensions is taken
asunder, and each half, No. 1. and No. 2., is laid upon the floor of the
foundry. Green sand is thrown with a shovel into No. 1. so as to fill
it; when it is gently pressed in with a rammer. The object of this
operation is to form a plane surface upon which to lay in the pattern
with a slight degree of pressure, varying with its shape. No. 1. being
covered with sand, the frame No. 2. is laid upon it, so as to form the
box. No. 2. being now filled carefully with the green sand, the box is
inverted, so as to place No. 1. uppermost, which is then detached and
lifted off in a truly vertical position; carrying with it the body of
sand formed at the commencement of the operation. The pattern remains
imbedded in the sand of No. 2., which has been exactly moulded upon a
great portion of its surface. The moulder condenses the sand in the
parts nearest to the pattern, by sprinkling a little water upon it, and
trimming the ill-shaped parts with small iron trowels of different
kinds. He then dusts a little well-dried finely-sifted sand over all the
visible surface of the pattern, and of the sand surrounding it; this is
done to prevent adhesion when he replaces the frame No. 1.
He next destroys the preparatory smooth bed or area formed in this
frame, covers the pattern with green sand, replaces the frame 1. upon 2.
to reproduce the box, and proceeds to fill and ram No. 1., as he had
previously done No. 2. The object of this operation is to obtain very
exactly a concavity in the frame No. 1., having the shape of the part of
the model impressed coarsely upon the surface formed at the beginning,
and which was meant merely to support the pattern and the sand sprinkled
over it, till it got imbedded in No. 2.
The two frames in their last position, along with their sand, may be
compared to a box of which No. 1. is the lid, and whose interior is
adjusted exactly upon the enclosed pattern.
If we open this box, and after taking out the pattern, close its two
halves again, then pour in melted metal till it fill every void space,
and become solid, we shall obviously attain the wished-for end, and
produce a piece of cast iron similar to the pattern. But many
precautions must still be taken before we can hit this point. We must
first lead through the mass of sand in the frame No. 1., one or more
channels for the introduction of the melted metal; and though one may
suffice for this purpose, another must be made for letting the air
escape. The metal is run in by several orifices at once, when the piece
has considerable surface, but little thickness, so that it may reach the
remotest points sufficiently hot and liquid.
The parts of the mould near the pattern must likewise be pierced with
small holes, by means of wires traversing the whole body of the sand, in
order to render the mould more porous, and to facilitate the escape of
the air and the gases. Then, before lifting off the frame No. 1., we
must tap the pattern slightly, otherwise the sand enclosing it would
stick to it in several points, and the operation would not succeed.
These gentle jolts are given by means of one or more pieces of iron wire
which have been screwed vertically into the pattern before finally
ramming the sand into the frame No. 1., or which enter merely into holes
in the pattern. These pieces are sufficiently long to pass out through
the sand when the box is filled; and it is upon their upper ends that
the horizontal blows of the hammer are given; their force being
regulated by the weight and magnitude of the pattern. These rods are
then removed by drawing them straight out; after which the frame No. 1.
may be lifted off smoothly from the pattern.
The pattern itself is taken out, by lifting it in all its parts at once,
by means of screw pins adjusted at the moment. This manœuvre is
executed, for large pieces, almost always by several men, who while they
lift the pattern with one hand, strike it with the other with small
repeated blows to detach the sand entirely, in which it is generally
more engaged than it was in that of the frame No. 1. But in spite of all
these precautions, there are always some degradations in one or other of
the two parts of the mould; which are immediately repaired by the
workman with damp sand, which he applies and presses gently with his
trowel, so as to restore the injured forms.
Hitherto I have supposed all the sand rammed into the box to be of one
kind; but from economy, the green sand is used only to form the portion
of the mould next the pattern, in a stratum of about an inch thick; the
rest of the surrounding space is filled with the sand of the floor which
has been used in former castings. The interior layer round the pattern
is called in this case, _new sand_.
It may happen that the pattern is too complex to be taken out without
damaging the mould, by two frames alone; then 3 or more are mutually
adjusted to form the box.
When the mould, taken asunder into two or more parts, has been properly
repaired, its interior surface must be dusted over with wood charcoal
reduced to a very fine powder, and tied up in a small linen bag, which
is shaken by hand. The charcoal is thus sifted at the moment of
application, and sticks to the whole surface which has been previously
damped a little. It is afterwards polished with a fine trowel.
Sometimes, in order to avoid using too much charcoal, the surfaces are
finally dusted over with sand, very finely pulverized, from a bag like
the charcoal. The two frames are now replaced with great exactness, made
fast together by the ears, with wedged bolts laid truly level, or at the
requisite slope, and loaded with considerable weights. When the casting
is large, the charcoal dusting as well as that of fine sand, is
suppressed. Every thing is now ready for the introduction of the fused
metal.
_Moulding in baked or used sand._--The mechanical part of this process
is the same as of the preceding. But when the castings are large, and
especially if they are tall, the hydrostatic pressure of the melted
metal upon the sides of the mould cannot be counteracted by the force of
cohesion which the sand acquires by ramming. We must in that case adapt
to each of these frames a solid side, pierced with numerous small holes
to give issue to the gases. This does not form one body with the rest of
the frame, but is attached extemporaneously to it by bars and wedged
bolts. In general no ground coal is mixed with this sand. Whenever the
mould is finished, it is transferred to the drying stove, where it may
remain from 12 to 24 hours at most, till it be deprived of all its
humidity. The sand is then said to be baked, or annealed. The
experienced moulder knows how to mix the different sands placed at his
disposal, so that the mass of the mould as it comes out of the stove,
may preserve its form, and be sufficiently porous. Such moulds allow the
gases to pass through them much more readily than those made of _green_
sand; and in general the castings they turn out are less vesicular, and
smoother upon the surface. Sometimes in a large piece, the three kinds
of moulding, that in green sand, in baked sand, and in loam, are
combined to produce the best result.
_Moulding in loam._--This kind of work is executed from drawings of the
pieces to be moulded, without being at the expense of making patterns.
The mould is formed of a pasty mixture of clay, water, sand, and cow’s
hair, or other cheap filamentous matter, kneaded together in what is
called the loam mill. The proportions of the ingredients are varied to
suit the nature of the casting. When the paste requires to be made very
light, horse dung or chopped straw is added to it.
[Illustration: 468 469 470]
I shall illustrate the mode of fabricating loam moulds, by a simple
case, such as that of a sugar pan. _Fig._ 468. is the pan. There is laid
upon the floor of the foundry, an annular platform of cast-iron _a b_,
_fig._ 469.; and upon its centre _c_, rests the lower extremity of a
vertical shaft, adjusted so as to turn freely upon itself, while it
makes a wooden pattern _e f_, _fig._ 470., describe a surface of
revolution identical with the internal surface reversed of the boiler
intended to be made. The outline _e g_, of the pattern is fashioned so
as to describe the surface of the edge of the vessel. Upon the part _a d
b d_, _fig._ 469., of the flat cast-iron ring, there must next be
constructed, with bricks laid either flat or on their edge, and clay, a
kind of dome, _h i k_, _fig._ 470., from two to four inches thick,
according to the size and weight of the piece to be moulded. The
external surface of the brick dome ought to be everywhere two inches
distant at least, from the surface described by the arc _e_, _f_. Before
building up the dome to the point _i_, coals are to be placed in its
inside upon the floor, which may be afterwards kindled for drying the
mould. The top is then formed, leaving at _i_, round the upright shaft
of revolution, only a very small outlet. This aperture, as also some
others left under the edges of the iron ring, enable the moulder to
light the fire when it becomes necessary, and to graduate it so as to
make it last long enough without needing more fuel, till the mould be
quite finished and dry. The combustion should be always extremely slow.
Over the brick dome a pasty layer of loam is applied, and rounded with
the mould _g e f_; this surface is then coated with a much smoother
loam, by means of the concave edge of the same mould. Upon the latter
surface, the inside of the sugar pan is cast; the line _e g_ having
traced, in its revolution, a ledge _m_. The fire is now kindled, and as
the surface of the mould becomes dry, it is painted over by a brush,
with a mixture of water, charcoal powder, and a little clay, in order to
prevent adhesion between the surface already dried and the coats of clay
about to be applied to it. The board _g e f_ is now removed, and
replaced by another, _g´ e´ f´_, _fig._ 471., whose edge _e´ f´_
describes the outer surface of the pan. Over the surface _e_, _f_, a
layer of loam is applied, which is turned and polished so as to produce
the surface of revolution _e´ f´_, as was done for the surface _e f_;
only in the latter case, the line _e´ g´_ of the board does not form a
new shoulder, but rubs lightly against _m_.
The layer of loam included between the two surfaces _e f_, _e´ f´_, is
an exact representation of the sugar pan. When this layer is well dried
by the heat of the interior fire, it must be painted like the former.
The upright shaft is now removed, leaving the small vent hole through
which it passed to promote the complete combustion of the coal. There
must be now laid horizontally upon the ears of the platform _d d_,
_fig._ 469., another annular platform _p q_, like the former, but a
little larger, and without any cross-bar.
[Illustration: 471 472 473]
The relative position of these two platforms is shown in _fig._ 473.
Upon the surface _e´ f´_, _fig._ 472., a new layer of loam is laid, two
inches thick, of which the surface is smoothed by hand. Then upon the
platform _p q_, _fig._ 473., a brick vault is constructed, whose inner
surface is applied to the layer of loam. This contracts a strong
adherence with the bricks which absorb a part of its moisture, while the
coat of paint spread over the surface _e´ f´_, prevents it from sticking
to the preceding layers of loam. The brick dome ought to be built
solidly.
The whole mass is now to be thoroughly dried by the continuance of the
fire, the draught of which is supported by a small vent left in the
upper part of the new dome; and when all is properly dry, the two iron
platforms are adjusted to each other by pin points, and _p q_ is lifted
off, taking care to keep it in a horizontal position. Upon this platform
are removed the last brick dome, and the layer of loam which had been
applied next to it; the latter of which represents exactly by its inside
the mould of the surface _e´ f´_, that is of the outside of the pan. The
crust contained between _e f_ and _e´ f´_ is broken away, an operation
easily done without injury to the surface _e f_, which represents
exactly the inner surface of the pan; or only to the shoulder _m_,
corresponding to the edge of the vessel. The top aperture through which
the upright shaft passed must be now closed; only the one is kept open
in the portion of the mould lifted off upon _p q_; because through this
opening the melted metal is to be poured in the process of casting. The
two platforms being replaced above each other very exactly, by means of
the adjusting pin-points, the mould is completely formed, and ready for
the reception of the metal.
[Illustration: 474 475]
When the object to be moulded presents more complicated forms than the
one now chosen for the sake of illustration, it is always by analogous
processes that the workman constructs his loam moulds, but his sagacity
must hit upon modes of executing many things which at first sight appear
to be scarcely possible. Thus, when the forms of the interior and
exterior do not permit the mould to be separated in two pieces, it is
divided into several, which are nicely fitted with adjusting pins. More
than two cast-iron rings or platforms are sometimes necessary. When
ovals or angular surfaces must be traced instead of those of revolution,
no upright shaft is used, but wooden or cast-iron guides made on
purpose, along which the pattern cut-out board is slid according to the
drawing of the piece. Iron wires and claws are often interspersed
through the brick work to give it cohesion. The core, kernel, or inner
mould of a hollow casting is frequently fitted in when the outer shell
is moulded. I shall illustrate this matter in the case of a gas-light
retort, _fig._ 474. The core of the retort ought to have the form _e e e
e_, and be very solid, since it cannot be fixed in the outer mould, for
the casting, except in the part standing out of the retort towards _m
m_. It must be modelled in loam, upon a piece of cast-iron called a
_lantern_, made expressly for this purpose. The lantern is a cylinder or
a truncated hollow cone of cast iron, about half an inch thick; and
differently shaped for every different core. The surface is perforated
with holes of about half an inch in diameter. It is mounted by means of
iron cross bars, upon an iron axis, which traverses it in the direction
of its length. _Fig._ 475. represents a horizontal section through the
axis of the core; _g h_ is the axis of the lantern, figured itself at _i
k k i_; _o i i o_ is a kind of disc or dish, perpendicular to the axis,
open at _i i_, forming one piece with the lantern, whose circumference
_o o_ presents a curve similar to the section of the core, made at right
angles to its axis. We shall see presently the two uses for which this
dish is intended. The axis _g h_ is laid upon two gudgeons, and handles
are placed at each of its extremities, to facilitate the operation in
making the core. Upon the whole surface of the lantern, from the point
_h_ to the collet formed by the dish, a hay cord as thick as the finger
is wound. Even two or more coils may be applied, as occasion requires,
over which loam is spread to the exact form of the core, by applying
with the hand a board, against the dish _o o_, with its edge cut out to
the desired shape; as also against another dish, adjusted at the time
towards _h_; while by means of the handles a rotatory movement is given
to the whole apparatus.
The hay interposed between the lantern and the loam, which represents
the crust of the core, aids the adhesion of the clay with the cast iron
of the lantern, and gives passage to the holes in its surface, for the
air to escape through in the casting.
When the core is finished, and has been put into the drying stove, the
axis _g h_ is taken out, then the small opening which it leaves at the
point _h_, is plugged with clay. This is done by supporting the core by
the edges of the dish, in a vertical position. It is now ready to be
introduced into the hollow mould of the piece.
[Illustration: 476]
This mould executed in baked sand consists of three pieces, two of which
absolutely similar, are represented, _fig._ 476., at _p q_, the third is
shown at _r s_. The two similar parts _p q_, present each the
longitudinal half of the nearly cylindrical portion of the outer surface
of the gas retort; so that when they are brought together, the cylinder
is formed; _r s_ contains in its cavity the kind of hemisphere which
forms the bottom of the retort. Hence, by adding this part of the mould
to the end of the two others, the resulting apparatus presents in its
interior, the exact mould of the outside of the retort; an empty
cylindrical portion _t t_, whose axis is the same as that of the
cylinder _u u_, and whose surface, if prolonged, would be every where
distant from the surface _u u_, by a quantity equal to the desired
thickness of the retort. The diameter of the cylinder _t t_ is precisely
equal to that of the core, which is slightly conical, in order that it
may enter easily into this aperture _t t_, and close it very exactly
when it is introduced to the collet or neck.
[Illustration: 477]
The three parts of the mould and the core being prepared, the two pieces
_p q_, must first be united, and supported in an upright position; then
the core must be let down into the opening _t t_, _fig._ 477. When the
plate or disc _o o_ of the core is supported upon the mould, we must see
that the end of the core is every where equally distant from the edge of
the external surface _u u_, and that it does not go too far beyond the
line _q q_. Should there be an inaccuracy, we must correct it by slender
iron slips placed under the edge of the disc _o o_; then by means of a
cast iron cross, and screw bolts _v v_, we fix the core immovably. The
whole apparatus is now set down upon _r s_, and we fix with screw bolts
the plane surface _q q_ upon _r r_; then introduce the melted metal by
an aperture _z_, which has been left at the upper part of the mould.
When, instead of the example now selected, the core of the piece to be
cast must go beyond the mould of the external surface, as is the case
with a pipe open at each end, the thing is more simple, because we may
easily adjust and fix the core by its two ends.
In casting a retort, the metal is poured into the mould set upright. It
is important to maintain this position in the two last examples of
casting; for all the foreign matters which may soil the metal during its
flow, as the sand, the charcoal, gases, scoriæ, being less dense than
it, rise constantly to the surface. The hydrostatic pressure produced by
a high gate, or filling-in aperture, contributes much to secure the
soundness and solidity of the casting. This gate piece being
superfluous, is knocked off almost immediately after, or even before
the casting cools. Very long, and somewhat slender pieces, are usually
cast in moulds set up obliquely to the horizon. As the metal shrinks in
cooling, the mould should always be somewhat larger than the object
intended to be cast. The iron founder reckons in general upon a linear
shrinkage of a ninety-sixth part; that is one-eighth of an inch per
foot.
[Illustration: 478]
_Melting of the cast-iron._--The metal is usually melted in a cupola
furnace, of which the dimensions are very various. _Fig._ 478.
represents in plan, section, and elevation, one of these furnaces of the
largest size; being capable of founding 5 tons of cast-iron at a time.
It is kindled by laying a few chips of wood upon its bottom, leaving the
orifice _c_ open, and it is then filled up to the throat with coke. The
fire is lit at _c_, and in a quarter or half an hour, when the body of
fuel is sufficiently kindled, the tuyère blast is set in action. The
flame issues then by the mouth as well as the orifice _c_, which has
been left open on purpose to consolidate it by the heat. Without this
precaution, the sides which are made up in argillaceous sand after each
day’s work, would not present the necessary resistance. A quarter of an
hour afterwards, the orifice _c_ is closed with a lump of moist clay,
and sometimes, when the furnace is to contain a great body of melted
metal, the clay is supported by means of a small plate of cast-iron
fixed against the furnace. Before the blowing machine is set a going,
the openings _g g g_ had been kept shut. Those of them wanted for the
tuyères are opened in succession, beginning at the lowest, the tuyères
being raised according as the level of the fused iron stands higher in
the furnace. The same cupola may receive at a time from one to six
tuyères, through which the wind is propelled by the centrifugal action
of an excentric fan or ventilator. It does not appear to be ascertained
whether there be any advantage in placing more than two tuyères facing
each other upon opposite sides of the furnace. Their diameter at the
nozzle varies from 3 to 5 inches. They are either cylindrical or
slightly conical. A few minutes after the tuyères have begun to blow,
when the coke sinks in the furnace, alternate charges of coke and pig
iron must be thrown in. The metal begins to melt in about 20 minutes
after its introduction; and successive charges are then made every 10
minutes nearly; each charge containing from 2 cwt. to 5 cwt. of iron,
and a quantity proportional to the estimate given below. The amount of
the charges varies of course with the size of the furnace, and the speed
required for the operation. The pigs must be previously broken into
pieces weighing at most 14 or 16 pounds. The vanes of the blowing fan
make from 625 to 650 turns per minute. The two cupolas represented
_fig._ 478., and another alongside in the plan, may easily melt 6-1/2
tons of metal in 2-3/4 hours; that is 2-1/3 tons per hour. This result
is three or four times greater than what was formerly obtained in
similar cupolas, when the blast was thrown in from small nozzles with
cylinder bellows, moved by a steam engine of 10 horses power.
In the course of a year, a considerable foundry like that represented in
the plan, _fig._ 467., will consume about 300 tons of coke in melting
1240 tons of cast iron; consisting of 940 tons of pigs of different
qualities, and 300 tons of broken castings, gate-pieces, &c. Thus, it
appears that 48 pounds of coke are consumed for melting every 2 cwt. of
metal.
Somewhat less coke is consumed when the fusion is pushed more rapidly to
collect a great body of melted metal, for casting heavy articles; and
more is consumed when, as in making many small castings, the progress of
the founding has to be slackened from time to time; otherwise, the metal
would remain too long in a state of fusion, and probably become too cold
to afford sharp impressions of the moulds.
It sometimes happens that in the same day, with the same furnace, pieces
are to be cast containing several proportions of different kinds of
iron; in which case, to prevent an intermixture with the preceding or
following charges, a considerable bed of coke is interposed. Though
there be thus a little waste of fuel, it is compensated by the improved
adaptation of the castings to their specific objects. The founding
generally begins at about 3 o’clock, P. M., and goes on till 6 or 8
o’clock. One founder, aided by four labourers for charging, &c., can
manage two furnaces.
The following is the work of a well-managed foundry in Derby.
200 lbs. of coke are requisite to melt, or bring down (in the language
of the founders), 1 ton of cast-iron, after the cupola has been brought
to its proper heat, by the combustion in it of 9 baskets of coak,
weighing by my trials, 40 pounds each, = 360 lbs.
The chief talent of the founder consists in discovering the most
economical mixtures, and so compounding them as to produce the desired
properties in the castings. One piece, for example, may be required to
have great strength and tenacity to bear heavy weights or strains;
another must yield readily to the chisel or the file; a third must
resist sudden alternations of temperature; and a fourth must be pretty
hard.
The filling in of the melted metal is managed in two ways. For strong
pieces, whose moulds can be buried in the ground at 7 or 8 yards
distance from the furnace, the metal may be run in gutters, formed in
the sand of the floor, sustained by plates or stones. The clay plug is
pierced with an iron rod, when all is ready.
When from the smaller size, or greater distance of the moulds, the
melted metal cannot be run along the floor from the furnace, it is
received in cast-iron pots or ladles, lined with a coat of loam. These
are either carried by the hands of two or more men, or transported by
the crane. Between the successive castings, the discharge hole of the
furnace is closed with a lump of clay, applied by means of a stick,
having a small disc of iron fixed at its end.
After the metal is somewhat cooled, the moulds are taken asunder, and
the excrescences upon the edges of the castings are broken off with a
hammer. They are afterwards more carefully trimmed or chipped by a
chisel when quite cold. The loss of weight in founding is about 6-1/2
per cent. upon the pig iron employed. Each casting always requires the
melting of considerably more than its own weight of iron. This excess
forms the gates, false seams, &c.; the whole of which being deducted,
shows that 1 cwt. of coke is consumed for every 3 cwt. of iron put into
the furnace; for every 138 cwt. of crude metal, there will be 100 cwt.
of castings, 32 of refuse pieces, and 6 of waste.
Explanation of the plates.
_Manner of constructing the Mould of a Sugar-pan._
_Fig._ 468. View of the pan.
-- 469. Flat ring of cast-iron for supporting the inner mould.
-- 470. Construction of the inner mould.
-- 471. Formation of the outer surface of the pan.
-- 472. Finished mould.
-- 473. Position of the two flat cast-iron rings, destined to
sustain the moulds of the inner and the outer surface.
_Gas-retort Moulding._
-- 474. Vertical projection, perpendicular to the axis of the
retort; and two sections, the one upright, the other
horizontal.
-- 475. Construction of the core of the retort.
-- 476. Disposition of the outer mould.
-- 477. Adjustment of the core in the mould.
-- 478. _Cupola furnace._ It is 3 feet wide within, and 13-1/2
high.
_m m_, solid body of masonry, as a basis to the furnace.
_b b_, octagonal platform of cast iron, with a ledge in which the plates
_a a a a_ are engaged.
_a a_, eight plates of cast iron, 1 inch thick, absolutely similar; only
one of them is notched at its lower part in _c_, to allow the melted
metal to run out, and two of the others have six apertures _g g g_, &c.
to admit the tuyères.
_c_, orifice for letting the metal flow out. A kind of cast iron gutter,
_e_, lined with loam is fitted to the orifice.
_d_, hoops of hammered iron, 4-1/4 inches broad; one half of an inch
thick for the bottom ones; and a quarter of an inch for the upper ones.
The intermediate hoops decrease in thickness from below upwards between
these limits.
_e_, cast iron gutter or spout, lined with loam, for running off the
metal.
_f f_, cylindrical piece of cast iron, for increasing the height and
draught of the furnace.
_g_, side openings for receiving the tuyères, of which there are six
upon each side of the furnace. Each of them may be shut at pleasure, by
means of a small cast iron plate _h_, made to slide horizontally in
grooves sunk in the main plate, pierced with the holes _g g_.
_k k_, interior lining of the surface, made of sand, somewhat
argillaceous, in the following way. After having laid at the bottom of
the furnace a bed of sand a few inches thick, slightly sloped towards
the orifice of discharge, there is set upright, in the axis of the
cupola, a wooden cylinder of its whole height, and of a diameter a
little less than that of the vacant space belonging to the top of the
furnace. Sand is to be then rammed in so as to fill the whole of the
furnace; after which the wooden cylinder is withdrawn, and the lining of
sand is cut or shaved away, till it has received the proper form.
This lining lasts generally 5 or 6 weeks, when there are 6 meltings
weekly.
_i i_, cast iron circular plate, through which the mouth of the furnace
passes, for protecting the lining in _k_ during the introduction of the
charges.
N N, level of the floor of the foundry. The portion of it below the
running out orifice consists of sand, so that it may be readily sunk
when it is wished to receive the melted metal in ladles or pots of large
dimensions.
[Illustration: 479]
The fan distributes the blast from the main pipe to three principal
points, by three branch tubes of distribution. A register, consisting of
a cast-iron plate sliding with friction in a frame, serves to intercept
the blast at any moment, when it is not desirable to stop the moving
power. A large main pipe of zinc or sheet iron is fitted to the orifice
of the slide valve. It is square at the beginning, or only rounded at
the angles; but at a little distance it becomes cylindrical, and
conducts the blast to the divaricating points. There, each of the
branches turns up vertically, and terminates at _b b_, _fig._ 479.,
where it presents a circular orifice of 7-1/2 inches. Upon each of the
upright pipes _b_, the one end of an elbow-tube of zinc _c c c c_,
_fig._ 479., is adjusted rather loosely, and the other end receives a
tuyère of wrought iron _d d_, through the intervention of a shifting
hose or collar of leather _c c d_, hooped with iron wire to both the
tube and the tuyère. The portion _c c c c_ may be raised or lowered, by
sliding upon the pipe _b_, in order to bring the nozzle of the tuyère _d
d_, to the requisite point of the furnace. The portion _c c c c_ may be
made also of wrought iron. A power of 4 horses is adequate to drive this
fan, for supplying blast to 3 furnaces.
The founders have observed the efflux of air was not the same when blown
into the atmosphere, as it was when blown into the furnaces; the
velocity of the fan, with the same impulsive power, being considerably
increased in the latter case. They imagine that this circumstance arises
from the blast being sucked in, so to speak, by the draught of the
furnace, and that the fan then supplied a greater quantity of air.
The following experimental researches show the fallacy of this opinion.
Two water syphons, _e e e_, _f f f_, made of glass tubes, one-fifth of
an inch in the bore, were inserted into the tuyère, containing water in
the portions _g g g_, _h h h_. The one of these _manometers_ for
measuring the pressure of the air was inserted at _k_, the other in the
centre of the nozzle. The size of this glass tube was too small to
obstruct in any sensible degree the outlet of the air. It was found that
when the tuyères of the fan discharged into the open air, the
expenditure by a nozzle of a constant diameter was proportional to the
number of the revolutions of the vanes. It was further found, that when
the speed of the vanes was constant, the expenditure by one or by two
nozzles was proportional to the total area of these nozzles. The
following formulæ give the volume of air furnished by the fan, when the
number of turns and the area of the nozzles are known.
25·32 S n
Volume = --------- (1)
1,000,000
0·86´6´7 S n
Volume = ------------ (2)
1,000,000
The volume is measured at 32° Fahr., under a pressure of 29·6 inches
barom.
S = is the total area of the orifices of the tuyères in square inches.
_n_ = the number of turns of the vanes in a minute.
After measuring the speed of the vanes blowing into the atmosphere, if
we introduce the nozzle of discharge into the orifice of the furnace, we
shall find that their speed immediately augments in a notable degree. We
might, therefore, naturally suppose that the fan furnishes more air in
the second case than in the first; but a little reflection will show
that it is not so. In fact, the air which issues in a cold state from
the tuyère encounters instantly in the furnace a very high temperature,
which expands it, and contributes, along with the solid matters with
which the furnace is filled, to diminish the facility of the discharge,
and consequently to retard the efflux by the nozzles. The oxygen gas
consumed is replaced by a like volume of carbonic acid gas, equally
expansible by heat. Reason leads us to conclude that less air flows from
the nozzles into the furnace than into the open atmosphere.
The increase in the velocity of the vanes takes place precisely in the
same manner, when after having made the nozzles blow into the
atmosphere, we substitute for these nozzles others of a smaller
diameter, instead of directing the larger ones into the furnace. Hence
we may conceive that the proximity of the charged furnace acts upon the
blast like the contraction of the nozzles. When the moving power is
uniform, and the velocity of the vanes remains the same, the quantity of
air discharged must also be the same in the two cases.
Two tuyères, one 5 inches in diameter, the other 4-1/2, and which,
consequently, presented a total area of 35-1/2 square inches, discharged
air into one of the furnaces, from a fan whose vanes performed 654 turns
in the minute. These two nozzles being briskly withdrawn from the
furnace, and turned round to the free air, while a truncated pasteboard
cone of 3-1/2 inches diameter was substituted for the nozzle of 4-1/2
inches, whereby the area of efflux was reduced to 29·3 square inches,
the velocity of the vanes continued exactly the same. The inverse
operation having been performed, that is to say, the two original
nozzles having been smartly replaced in the furnace, to discover whether
or not the moving power had changed in the interval of the experiment,
they betrayed no perceptible alteration of speed. From the measures
taken to count the speed, the error could not exceed 3 revolutions per
minute, which is altogether unimportant upon the number 654.
It follows, therefore, that when the vanes of the fan have the velocity
of 654 turns per minute, the expenditure by two nozzles, whose joint
area is 35-1/2 square inches, both blowing into a furnace, is to the
expenditure which takes place, when the same nozzles blow into the air,
as 35·5 is to 29·3; that is, a little more than 4-fifths.
If this be, as is probable, a general rule for areas and speeds
considerably different from the above, to find the quantity of air blown
into one or more furnaces by the fan, we should calculate the volume by
one of the above formulæ (1) or (2), and take 4-fifths of the result, as
the true quantity.
The fan A C here represented is of the best excentric form, as
constructed by Messrs. Braithwaite and Ericsson. D is the circular
orifice round the axis by which the air is admitted; and C C B is the
excentric channel through which the air is wafted towards the main
discharge pipe E.
FOUNTAIN; a stream of water rising up through the superficial strata of
the earth. See ARTESIAN WELLS.
FOXING, is a term employed by brewers to characterize the souring of
beer, in the process of its fermentation or ripening.
FRANKFORT BLACK; is made by calcining vine branches, and the other
refuse lees of the vinegar vats in Germany. They must be previously
washed.
FREEZING. (_Congelation_, Fr.; _Gefrierung_, Germ.) The three general
forms, solid, liquid, and gaseous, under one or other of which all kinds
of matter exist, seem to be immediately referrible to the influence of
heat; modifying, balancing, or subduing the attraction of cohesion.
Every solid may be liquefied, and every liquid may be vaporized, by a
certain infusion of caloric, whether this be regarded as a moving power,
or an elastic essence. The converse of this proposition is equally true;
for many gases, till lately styled permanent, may be liquefied, nay,
even solidified, by diminution of their temperature, either alone, or
aided by a condensing force, to bring their particles within the sphere
of aggregative attraction. When a solid is transformed into a liquid,
and a liquid into a gas or vapour, a quantity more or less considerable
of heat is absorbed, or becomes latent, to use the term of Dr. Black,
the celebrated discoverer of this great law of nature. When the opposite
transformation takes place, the heat absorbed is again emitted, or what
was latent becomes sensible caloric. Upon the first principle, or the
absorption of heat, are founded the various artificial methods of
producing cold and congelation.
Tables, exhibiting a collective view of all the Frigorific Mixtures
contained in Mr. Walker’s publication, 1808.
I.--Table consisting of Frigorific Mixtures, composed of ice, with
chemical salts and acids.
Frigorific Mixtures with Ice.
+-------------------------------+-----------------+------------+
| MIXTURES. | Thermometer |Deg. of cold|
| | sinks. | produced. |
+-------------------------------+-----------------+------------+
|Snow, or pounded ice 2 parts| } to -5° | * |
|Muriate of soda 1 | } | |
+-------------------------------+ }---------+------------+
|Snow, or pounded ice 5 parts| } | |
|Muriate of soda 2 |From } to -12°| * |
|Muriate of ammonia 1 | } | |
+-------------------------------+any } --------+------------+
|Snow, or pounded ice 24 parts| } | |
|Muriate of soda 10 |tempe- } to -18°| * |
|Muriate of ammonia 5 | } | |
|Nitrate of potash 5 |rature } | |
+-------------------------------+ }---------+------------+
|Snow, or pounded ice 12 parts| } | |
|Muriate of soda 5 | } to -25°| * |
|Nitrate of ammonia 5 | } | |
+-------------------------------+-----------------+------------+
|Snow 3 parts|From +32° to -23°| 55 |
|Diluted sulphuric acid 2 | | |
+-------------------------------+-----------------+------------+
|Snow 8 parts|From +32° to -27°| 59 |
|Muriatic acid 5 | | |
+-------------------------------+-----------------+------------+
|Snow 7 parts|From +32° to -30°| 62 |
|Diluted nitric acid 4 | | |
+-------------------------------+-----------------+------------+
|Snow 4 parts|From +32° to -40°| 72 |
|Muriate of lime 5 | | |
+-------------------------------+-----------------++-----------+
|Snow 2 parts|From +32° to -50°| 82 |
|Cryst. muriate of lime 3 | | |
+-------------------------------+-----------------+------------+
|Snow 3 parts|From +32° to -51°| 83 |
|Potash 4 | | |
+-------------------------------+-----------------+------------+
N. B.--The reason for the omissions in the last column of the preceding
table is, the thermometer sinking in these mixtures to the degree
mentioned in the preceding column, and never lower, whatever may be the
temperature of the materials at mixing.
II.--Table, consisting of Frigorific Mixtures, having the power of
generating or creating cold, without the aid of ice, sufficient for all
useful and philosophical purposes, in any part of the world at any
season.
Frigorific Mixtures without Ice.
+-------------------------------+-----------------+------------+
| MIXTURES. | Thermometer |Deg. of cold|
| | sinks. | produced. |
+-------------------------------+-----------------+------------+
|Muriate of ammonia 5 parts| | |
|Nitrate of potash 5 |From +50° to +10°| 40° |
|Water 16 | | |
+-------------------------------+-----------------+------------+
|Muriate of ammonia 5 parts| | |
|Nitrate of potash 5 |From +50° to +4° | 46 |
|Sulphate of soda 8 | | |
|Water 16 | | |
+-------------------------------+-----------------+------------+
|Nitrate of ammonia 1 part |From +50° to +4° | 46 |
|Water 1 | | |
+-------------------------------+-----------------+------------+
|Nitrate of ammonia 1 part | | |
|Carbonate of soda 1 |From +50° to -7° | 57 |
|Water 1 | | |
+-------------------------------+-----------------+------------+
|Sulphate of soda 3 parts|From +50° to -3° | 53 |
|Diluted nitric acid 2 | | |
+-------------------------------+-----------------+------------+
|Sulphate of soda 6 parts| | |
|Muriate of ammonia 4 |From +50° to -10°| 60 |
|Nitrate of potash 2 | | |
|Diluted nitric acid 4 | | |
+-------------------------------+-----------------+------------+
|Sulphate of soda 6 parts| | |
|Nitrate of ammonia 5 |From +50° to -14°| 64 |
|Diluted nitric acid 4 | | |
+-------------------------------+-----------------+------------+
|Phosphate of soda 9 parts|From +50° to -12°| 62 |
|Diluted nitric acid 4 | | |
+-------------------------------+-----------------+------------+
|Phosphate of soda 9 parts| | |
|Nitrate of ammonia 6 |From +50° to -21°| 71 |
|Diluted nitric acid 4 | | |
+-------------------------------+-----------------+------------+
|Sulphate of soda 8 parts|From +50° to 0° | 50 |
|Muriatic acid 5 | | |
+-------------------------------+-----------------+------------+
|Sulphate of soda 5 parts|From +50° to +3° | 47 |
|Diluted sulphuric acid 4 | | |
+-------------------------------+-----------------+------------+
N. B.--If the materials are mixed at a warmer temperature than that
expressed in the table, the effect will be proportionably greater; thus,
if the most powerful of these mixtures be made when the air is +85°, it
will sink the thermometer to +2°.
III.--Table consisting of Frigorific Mixtures selected from the
foregoing Tables, and combined so as to increase or extend cold to the
extremest degrees.
Combinations of Frigorific Mixtures.
+-------------------------------+-----------------+------------+
| MIXTURES. | Thermometer |Deg. of cold|
| | sinks. | produced. |
+-------------------------------+-----------------+------------+
|Phosphate of soda 5 parts| | |
|Nitrate of ammonia 3 |From 0° to -34° | 34 |
|Diluted nitric acid 4 | | |
+-------------------------------+-----------------+------------+
|Phosphate of soda 3 parts| | |
|Nitrate of ammonia 2 |From -34° to -50°| 16 |
|Diluted mixed acids 4 | | |
+-------------------------------+-----------------+------------+
|Snow 3 parts|From 0° to -46° | 46 |
|Diluted nitric acid 2 | | |
+-------------------------------+-----------------+------------+
|Snow 8 parts| | |
|Diluted sulphuric acid 3 |From -10° to -56°| 46 |
|Diluted nitric acid 3 | | |
+-------------------------------+-----------------+------------+
|Snow 1 part |From -20° to -60°| 40 |
|Diluted sulphuric acid 1 | | |
+-------------------------------+-----------------+------------+
|Snow 3 parts|From +20° to -48°| 68 |
|Muriate of lime 4 | | |
+-------------------------------+-----------------+------------+
|Snow 3 parts|From +10° to -54°| 64 |
|Muriate of lime 4 | | |
+-------------------------------+-----------------+------------+
|Snow 2 parts|From -15° to -68°| 53 |
|Muriate of lime 3 | | |
+-------------------------------+-----------------+------------+
|Snow 1 part |From 0° to -66° | 66 |
|Cryst. muriate of lime 2 | | |
+-------------------------------+-----------------+------------+
|Snow 1 part |From -40° to -73°| 33 |
|Cryst. muriate of lime 3 | | |
+-------------------------------+-----------------+------------+
|Snow 8 parts|From -68° to -91°| 23 |
|Diluted sulphuric acid 10 | | |
+-------------------------------+-----------------+------------+
N. B.--The materials in the first column are to be cooled, previously to
mixing, to the temperature required, by mixtures taken from either of
the preceding tables.
Water absorbs 1000 degrees of heat in becoming vapour; whence, if placed
in a saucer within an exhausted receiver, over a basin containing strong
sulphuric acid, it will freeze by the rapid absorption of its heat into
the vapour so copiously formed under these circumstances.
But the most powerful means of artificial refrigeration is afforded by
the evaporation of liquefied carbonic acid gas; for the frozen carbonic
acid thus obtained, has probably a temperature 100° under zero; so that
when a piece of it is laid upon quicksilver, it instantly congeals this
metal. The more copious discussion of this subject belongs to chemical
science.
FRENCH BERRIES; Berries of Avignon.
FRICTION, counteraction of; see LUBRICATION.
FRIT; see ENAMEL and GLASS.
FUEL; (_Combustible_, Fr; _Brennstoff_, Germ.).
Such combustibles as are used for fires or furnaces are called fuel, as
wood, turf, pitcoal. These differ in their nature, and in their power of
giving heat.
I. Wood, which is divided into hard and soft. To the former belong the
oak, the beech, the alder, the birch, and the elm; to the latter, the
fir, the pine of different sorts, the larch, the linden, the willow, and
the poplar.
Under like dryness and weight, different woods are found to afford equal
degrees of heat in combustion. Moisture diminishes the heating power in
three ways; by diminishing the relative weight of the ligneous matter,
by wasting heat in its evaporation, and by causing slow and imperfect
combustion. If a piece of wood contain, for example, 25 per cent. of
water, then it contains only 75 per cent. of fuel, and the evaporation
of that water will require 1/28 part of the weight of the wood. Hence
the damp wood is of less value in combustion by 8/28 or 2/7 than the
dry. The quantity of moisture in newly felled wood amounts to from 20 to
50 per cent.; birch contains 30, oak 35, beech and pine 39, alder 41,
fir 45. According to their different natures, woods which have been
felled and cleft for 12 months contain still from 20 to 25 per cent. of
water. There is never less than 10 per cent. present, even when it has
been kept long in a dry place, and though it be dried in a strong heat,
it will afterwards absorb 10 or 12 per cent. of water. If it be too
strongly kiln dried, its heating powers are impaired by the commencement
of carbonization, as if some of its hydrogen were destroyed. It may be
assumed as a mean of many experimental results, that 1 pound of
artificially dried wood will heat 35 pounds of water from the freezing
to the boiling point; and that a pound of such wood as contains from 20
to 25 per cent. of water will heat 26 pounds of ice-cold water to the
same degree. It is better to buy wood by measure than by weight, as the
bulk is very little increased by moisture. The value of different woods
for fuel is inversely as their moisture, and this may easily be
ascertained by taking their shavings, drying them in a heat of 140° F.,
and seeing how much weight they lose.
From every combustible the heat is diffused either by radiation or by
direct communication to bodies in contact with the flame. In a wood fire
the quantity of radiating heat is to that diffused by the air, as 1 to
3; or it is one fourth of the whole heating power.
II. _Charcoal._ The different charcoals afford, under equal weights,
equal quantities of heat. We may reckon, upon an average, that a pound
of dry charcoal is capable of heating 73 pounds of water from the
freezing to the boiling point; but when it has been for some time
exposed to the air, it contains at least 10 per cent. of water, which is
partially decomposed in the combustion into carburetted hydrogen, which
causes flame, whereas pure dry charcoal emits none.
A cubic foot of charcoal from soft wood weighs upon an average from 8 to
9 pounds, and from hard wood 12 to 13 pounds; and hence the latter are
best adapted to maintain a high heat in a small compass. The radiating
heat from charcoal fires constitutes one third of the whole emitted.
III. _Pitcoal._ The varieties of this coal are almost indefinite, and
give out very various quantities of heat in their combustion. The carbon
is the heat-giving constituent, and it amounts, in different coals, to
from 75 to 95 per cent. One pound of good pitcoal will, upon an average,
heat 60 pounds of water from the freezing to the boiling point. Small
coal gives out three-fourths of the heat of the larger lumps. The
radiating heat emitted by burning pitcoal is greater than that by
charcoal.
IV. _The coke of pitcoal._--The heating power of good coke is to that of
pitcoal as 75 to 69. One pound of the former will heat 65 pounds of
water from 32° to 212°; so that its power is equal to nine-tenths of
that of wood charcoal.
V. _Turf or peat._--One pound of this fuel will heat from 25 to 30
pounds of water from freezing to boiling. Its value depends upon its
compactness and freedom from earthy particles; and its radiating power
is to the whole heat it emits in burning, as 1 to 3.
VI. _Carburetted hydrogen or coal gas._--One pound of this gas, equal to
about 24 cubic feet, disengages in burning, as much heat as will raise
76 pounds of water from the freezing to the boiling temperature.
In the following table the fourth column contains the weight of
atmospherical air, whose oxygen is required for the complete combustion
of a pound of each particular substance.
+--------------------------+-----------+-----------+-----------+
| Species of combustible. | Pounds of | Pounds of | Weight of |
| |water which| boiling |atmospheric|
| |a pound can| water |air at 32°,|
| | heat from |evaporated | to burn 1 |
| |0° to 212°.|by 1 pound.| pound. |
+--------------------------+-----------+-----------+-----------+
|Perfectly dry wood | 35·00 | 6·36 | 5·96 |
|Wood in its ordinary state| 26·00 | 4·72 | 4·47 |
|Wood charcoal | 73·00 | 13·27 | 11·46 |
|Pitcoal | 60·00 | 10·90 | 9·26 |
|Coke | 65·00 | 11·81 | 11·46 |
|Turf | 30·00 | 5·45 | 4·60 |
|Turf charcoal | 64·00 | 11·63 | 9·86 |
|Carburetted hydrogen gas | 76·00 | 13·81 | 14·58 |
|Oil } | | | |
|Wax } | 78·00 | 14·18 | 15·00 |
|Tallow } | | | |
|Alcohol of the shops | 52·60 | 9·56 | 11·60 |
+--------------------------+-----------+-----------+-----------+
The quantity of air stated in the fourth column, is the smallest
possible required to burn the combustible, and is greatly less than
would be necessary in practice, where much of the air never comes into
contact with the burning body, and where it consequently never has its
whole oxygen consumed. The heating power stated in the second column is
also the maximum effect, and can seldom be realized with ordinary
boilers. The draught of air usually carries off at least 1/7 of the
heat, and more if its temperature be very high when it leaves the
vessel. In this case it may amount to one half of the whole heat or
more; without reckoning the loss by radiation and conduction, which
however may be rendered very small by enclosing the fire and flues
within proper non-conducting and non-radiating materials.
It appears that in practice, the quantity of heat which may be obtained
from any combustible in a properly mounted apparatus, must vary with the
nature of the object to be heated. In heating chambers by stoves, and
water boilers by furnaces, the effluent heat in the chimney which
constitutes the principal waste, may be reduced to a very moderate
quantity, in comparison of that which escapes from the best constructed
reverberatory hearth. In heating the boilers of steam engines, one pound
of coal is reckoned adequate to convert 7-1/2 pounds of boiling water
into vapour; or to heat 41-1/4 pounds of water from the freezing to the
boiling point. One pound of fir of the usual dryness will evaporate 4
pounds of water, or heat 22 pounds to the boiling temperature; which is
about two-thirds of the maximum effect of this combustible. According to
Watt’s experiments upon the great scale, one pound of coal can boil off
with the best built boiler, 9 pounds of water; the deficiency from the
maximum effect being here 10/57, or nearly one-sixth.
In many cases the hot air which passes into the flues or chimneys may be
beneficially applied to the heating, drying, or roasting of objects;
but care ought to be taken that the draught of the fire be not thereby
impaired, and an imperfect combustion of the fuel produced. For at a low
smothering temperature both carbonic oxide and carburetted hydrogen may
be generated from coal, without the production of much heat in the
fire-place.
To determine exactly the quantity of heat disengaged by any combustible
in the act of burning, three different systems of apparatus have been
employed; 1. the calorimeter of Lavoisier and Laplace, in which the
substance is burned in the centre of a vessel, whose walls are lined
with ice; and the amount of ice melted, measures the heat evolved; 2.
the calorimeter of Watt and Rumford, in which the degree of heat
communicated to a given body of water affords the measure of
temperature; and 3. by the quantity of water evaporated by different
kinds of fuel in similar circumstances.
[Illustration: 480]
If our object be to ascertain the relative heating powers of different
kinds of fuel, we need not care so much about the total waste of heat in
the experiments, provided it be the same in all; and therefore they
should be burned in the same furnace, and in the same way. But the more
economically the heat is applied, the greater certainty will there be in
the results. The apparatus, _fig._ 480., is simple and well adapted to
make such comparative trials of fuel. The little furnace is covered at
top, and transmits its burned air by _c_, through a spiral tube immersed
in a cistern of water, having a thermometer inserted near its top, and
another near its bottom, into little side orifices _a a_, while the
effluent air escapes from the upright end of the tube _b_. Here also a
thermometer bulb may be placed. The average indication of the two
thermometers gives the mean temperature of the water. As the water
evaporates from the cistern, it is supplied from a vessel placed
alongside of it. The experiment should be begun when the furnace has
acquired an equability of temperature. A throttle valve at _c_ serves to
regulate the draught, and to equalize it in the different experiments by
means of the temperature of the effluent air. When the water has been
heated the given number of degrees, which should be the same in the
different experiments, the fire may be extinguished, the remaining fuel
weighed, and compared with the original quantity. Care should be taken
to make the combustion as vivid and free from smoke as possible.
FULGURATION; designates the sudden brightening of the melted gold and
silver in the cupel of the assayer, when the last film of vitreous lead
and copper leaves their surface.
FULLER’S EARTH, (_Terre à foulon_, _Argile Smectique_, Fr.;
_Walkererde_, Germ.) is a soft, friable, coarse or fine grained mass of
lithomarge clay. Its colour is greenish, or yellowish gray; it is dull,
but assumes a fatty lustre upon pressure with the fingers, feels
unctuous, does not adhere to the tongue, and has a specific gravity
varying from 1·82 to 2·19. It falls down readily in water, into a fine
powder, with extrication of air bubbles, and forms a non-plastic paste.
It melts at a high heat into a brown slag. Its constituents are 53·0
silica; 10·0 alumina; 9·75 red oxide of iron; 1·25 magnesia; 0·5 lime;
24 water, with a trace of potash. Its cleansing action upon woollen
stuffs depends upon its power of absorbing greasy matters. It should be
neither tenacious nor sandy; for in the first case, it would not diffuse
itself well through water, and in the second it would abrade the cloth
too much. The finely divided silica is one of its useful ingredients.
Fuller’s earth is found in several counties of England; but in greatest
abundance in Bedfordshire, Berkshire, Hampshire, and Surry.
In the county of Surry there are great quantities of fuller’s earth
found about Nutfield, Ryegate, and Blechingley, to the south of the
Downs, and some, but of inferior quality, near Sutton and Croydon, to
the north of them. The most considerable pits are near Nutfield, between
which place and Ryegate, particularly on Redhill, about a mile to the
east of Ryegate, it lies so near the surface as frequently to be turned
up by the wheels of the waggons. The fuller’s earth to the north of the
road between Redhill and Nutfield, and about a quarter of a mile from
the latter place, is very thin; the seam in general is thickest on the
swell of the hill to the south of the road. It is not known how long
this earth has been dug in Surry; the oldest pit now wrought is said to
have lasted between 50 and 60 years, but it is fast wearing out. The
seam of fuller’s earth dips in different directions. In one, if not in
more cases, it inclines to the west with a considerable angle. There are
two kinds of it, the blue and the yellow: the former, on the eastern
side of the pit, is frequently within a yard of the surface, being
covered merely with the soil--a tough, wet, clayey loam. A few yards to
the west, the blue kind appears with an irony sand-stone, of nearly two
yards in thickness, between it and the soil. The blue earth in this pit
is nearly 16 feet deep. In some places the yellow kind is found lying
upon the blue; there seems, indeed, to be no regularity either in the
position or inclination of the strata where the fuller’s earth is found,
nor any mark by which its presence could be detected. It seems rather
thrown in patches than laid in any continued or regular vein. In the
midst of the fuller’s earth are often found large pieces of stone of a
yellow colour, translucent and remarkably heavy, which have been found
to be sulphate of barytes, encrusted with quartzose crystals. These are
carefully removed from the fuller’s earth, as the workmen say they often
spoil many tons of it which lie about them. There is also found with the
yellow fuller’s earth a dark brown crust, which the workmen consider as
injurious also. In Surry the price of fuller’s earth seems to have
varied very little, at least for these last 80 years. In 1730, the price
at the pit was 6_d._ a sack, and 6_s._ per load or ton. In 1744, it was
nearly the same. It is carried in waggons, each drawing from three to
four tons, to the beginning of the iron railway near Westham, along
which it is taken to the banks of the Thames, where it is sold at the
different wharfs for about 25_s._ or 26_s._ per ton. It is then shipped
off either to the north or west of England.
The next characteristic stratum, owing to its forming a ridge of
conspicuous hills through the country, is the Woburn land, a thick
ferruginous stratum, which below its middle contains a stratum of
fuller’s earth. This is thicker and more pure in Aspley and Hogstye-end,
two miles north-west of Woburn, than in any known place.
Fuller’s earth is found at Tillington, and consumed in the neighbouring
fulling mills.