1. Calcination of the ore. 2. Melting of the calcined ore. 3.
Calcination of the coarse metal. 4. Melting of the calcined coarse
metal. 5. Calcination of the fine metal (second matt). 6. Melting of the
calcined fine metal. 7. Roasting of the coarse copper. In some smelting
works, this roasting is repeated four times; in which case a calcination
and a melting are omitted. In the Havod works, however, the same saving
is made without increasing the number of roastings. 8. Refining or
toughening the copper.
Besides these operations, which constitute the treatment of copper
properly speaking, two others are sometimes performed, in which only the
scoriæ are melted. These may be designated by the letters _a_ and _b_.
_a_ is the re-melting of the portion of the scoriæ of the second
process, which contain some metallic granulations. _b_ is a particular
melting of the scoriæ of the fourth operation. This fusion is intended
to concentrate the particles of copper in the scoriæ, and is not
practised in all smelting works.
_First operation. Calcination of the ore._--The different ores, on
arriving from Cornwall and other districts where they are mined, are
discharged in continuous cargoes at the smelting works, in such a way,
that by taking out a portion from several heaps at a time, a tolerably
uniform mixture of ores is obtained; which is very essential in a
foundry, because, the ores being different in qualities and contents,
they act as fluxes upon each other. The ore thus mixed is transported
to the works in wooden measures that hold a hundred-weight. The workmen
entrusted with the calcination convey the ore into the hoppers of the
calcining furnace, whence it falls into the hearth; other workmen spread
it uniformly on the surface by iron rakes. The charge of a furnace is
from three tons to three tons and a half. Fire is applied and gradually
increased, till, towards the end of the operation, the temperature be as
high as the ore can support without melting or agglutinating. To prevent
this running together, and to aid the extrication of the sulphur, the
surfaces are renewed, by stirring up the ore at the end of every hour.
The calcination is usually completed at the end of 12 hours, when the
ore is tumbled into the arch under the sole of the furnace. Whenever the
ore is cold enough to be moved, it is taken out of the arch, and
conveyed to the calcined heap.
The ore in this process hardly changes weight, having gained in
oxidizement nearly as much as it has lost in sulphur and arsenic; and if
the roasting has been rightly managed, the ore is in a black powder,
owing to the oxide of iron present.
_Second operation. Fusion of the calcined ore._--The calcined ore is
likewise given to the melters in measures containing a hundred-weight.
They toss it into hoppers, and after it has fallen on the hearth, they
spread it uniformly. They then let down the door, and lute it tightly.
In this fusion there are added about 2 cwt. of scoriæ proceeding from
the melting of the calcined matt, to be afterwards described. The object
of this addition is not only to extract the copper that these scoriæ may
contain, but especially to increase the fusibility of the mixture.
Sometimes also, when the composition of the ore requires it, lime, sand,
or fluor spar is added; and particularly the last fluxing article.
The furnace being charged, fire is applied, and the sole care of the
founder is to keep up the heat so as to have a perfect fusion; the
workman then opens the door, and stirs about the liquid mass to complete
the separation of the metal (or rather of the matt) from the scoriæ, as
well as to hinder the melted matter from sticking to the sole. The
furnace being ready, that is, the fusion being perfect, the founder
takes out the scoriæ by the front door, by means of a rake. When the
matt is thus freed from the scoriæ, a second charge of calcined ore is
then introduced to increase the metallic bath; which second fusion is
executed like the first. In this way, new charges of roasted ore are put
in till the matt collected on the hearth rises to a level with the
door-way, which happens commonly after the third charge. The tap hole is
now opened; the matt flows out into the pit filled with water, where it
is granulated during its immersion; and it collects in the pan placed at
the bottom. The granulated matt is next conveyed into the matt
warehouse. The oxidation with which the grains get covered by the action
of the water, does not allow the proper colour of the matt or coarse
metal to be distinguished; but in the bits which stick in the gutter, it
is seen to be of a steel gray. Its fracture is compact, and its lustre
metallic. The scoriæ often contain metallic grains; they are broken and
picked with care. All the portions which include some metallic particles
are re-melted in an accessory process. The rejected scoriæ have been
found to be composed of siliceous matter 59, oxide of copper 1, oxide of
tin 0·7.
In this operation, the copper is concentrated by the separation of a
great part of the matters with which it was mixed or combined. The
granulated matt produced, contains in general 33 per cent. of copper; it
is therefore four times richer than the ore; and its mass is
consequently diminished in that proportion. The constituent parts are
principally copper, iron, and sulphur.
The most important point to hit in the fusion just described, is to make
a fusible mixture of the earths and the oxides, so that the matt of
copper may, in virtue of its greater specific gravity, fall to the
under-part, and separate exactly from the slag. This point is attained
by means of the metallic oxides contained in the scoriæ of the fourth
operation, of which 2 cwt. were added to the charge. These consist
almost entirely of black oxide of iron. When the ores are very difficult
to melt, a measure of about half a hundred-weight of fluor spar is
added; but this must be done with precaution, for fear of increasing the
scoriæ too much.
The business goes on day and night. Five charges are commonly put
through hands in the course of 24 hours; but when all circumstances are
favourable, that is to say, when the ore is fusible, when the fuel is of
the first quality, and when the furnace is in good condition, even six
charges a day have been despatched.
The charge is a ton and a half of calcined ore, so that a melting
furnace corresponds nearly to a calcining furnace; the latter turning
out nearly 7 tons of calcined ore in 24 hours.
The workmen are paid by the ton.
_Third operation. Calcination of the coarse metal, or the matt._--The
object of this operation is principally to oxidize the iron, an
oxidation easier to execute, than in the first calcining, because the
metal is now disengaged from the earthy substances, which screened it
from the action of the air.
This calcination is executed in the furnace already represented, _fig._
296, 297, 298. page 318. exactly in the same way as the ore was
calcined. The metal must be perpetually stirred about, to expose all its
surfaces to the action of the hot air, and to hinder the clotting
together. The operation lasts 24 hours; during the first six, the fire
should be very moderate, and thereafter gradually increased to the end
of the calcination. The charge is, like that of the first, 3 tons and a
half.
_Fourth operation. Melting of the calcined coarse metal, or calcined
matt._--In the fusion of this first calcined matt, some scoriæ of the
latter operations must be added, which are very rich in oxide of copper,
and some crusts from the hearth, which are likewise impregnated with it.
The proportion of these substances varies according to the quality of
the calcined matt.
In this second fusion, the oxide of copper contained in the scoriæ, is
reduced by the affinity of the sulphur, one portion of which passes to
the state of acid, while the other forms a subsulphuret with the copper
become free. The matt commonly contains a sufficient quantity of sulphur
to reduce the oxide of copper completely; but if not, which may happen
if the calcination of the matt has been pushed too far, a small quantity
of uncalcined matt must be introduced, which, by furnishing sulphur,
diminishes the richness of the scoriæ, and facilitates the fusion.
The scoriæ are taken out by the front door, by drawing them forward with
a rake. They have a great specific gravity; are brilliant with metallic
lustre, very crystalline, and present, in the cavities, crystals like
those of pyroxene; they break easily into very sharp-edged fragments.
They contain no granulated metal in the interior; but it sometimes
occurs, on account of the small thicknesses of the stratum of scoriæ,
that these carry off with them, when they are withdrawn, some metallic
particles.
These scoriæ, as we have already stated, under the fusion of the roasted
ore, are in general melted with it. In some cases, however, a special
melting is assigned to them.
The matt obtained in this second fusion is either run out into water
like the first, or moulded into pigs (ingots), according to the mode of
treatment which it is to undergo. This matt, called by the smelters
_fine metal_ when it is granulated, and _blue metal_ when it is in pigs,
is of a light grey colour, compact, and bluish at the surface. It is
collected in the first form when it is to be calcined anew; and in the
second, when it must immediately undergo the operation of _roasting_.
Its contents in copper are 60 _per cent._ This operation, which is but
sometimes had recourse to, lasts 5 or 6 hours. The charge is 1 ton.
(_b_) _Particular fusion of the scoriæ of the fourth operation._--In
re-melting these scoriæ, the object is to procure the copper which they
contain. To effect this fusion, the scoriæ are mixed with pulverized
coal, or other carbonaceous matters. The copper and several other metals
are deoxidized, and furnish a white and brittle alloy. The scoriæ
resulting from this melting are in part employed in the first melting,
and in part thrown away. They are crystalline, and present crystals
often in the cavities, which appear to belong to bisilicate of iron.
They have a metallic lustre, and break into very sharp-edged fragments.
The white metal is melted again, and then united to the product of the
second fusion.
_Fifth operation. Calcination of the second matt, or fine metal of the
smelter._--This is executed in precisely the same way as that of the
first matt. It lasts 24 hours; and the charge is usually 3 tons.
_Sixth operation. Melting of the calcined fine metal._--This fusion is
conducted like that of the first matt. The black copper, or coarse
copper, which it produces, contains from 70 to 80 per cent. of pure
metal; it is run into ingots, in order to undergo the operation of
roasting.
The scoriæ are rich in copper; they are added to the fusion of the
calcined coarse metal of the fourth operation.
In the smelting houses of Messrs. Vivian, at Hafod, near Swansea, the
fifth and sixth operations have been omitted of late years. The second
matt is run into pigs, under the name of _blue metal_, to be immediately
exposed to the roasting.
The disposition of the canal _a a´_, _fig._ 302., which introduces a
continuous current of air to the hearth of the furnace, accelerates and
facilitates the calcination of the matt; an advantage which has
simplified the treatment, by diminishing the number of calculations.
_Seventh operation. Roasting of the coarse copper, the product of the
sixth operation._ The chief object of this operation is oxidizement; it
is performed either in an ordinary roasting furnace, or in the one
belonging to _fig._ 302., which admits a constant current of air. The
pigs of metal derived from the preceding melting are exposed, on the
hearth of the furnace, to the action of the air, which oxidizes the iron
and other foreign metals with which the copper is still contaminated.
The duration of the roasting varies from 12 to 24 hours, according to
the degree of purity of the crude copper. The temperature should be
graduated, in order that the oxidizement may have time to complete, and
that the volatile substances which the copper still retains may escape
in the gaseous form. The fusion must take place only towards the end of
the operation.
The charge varies from a ton and a quarter to a ton and a half. The
metal obtained is run out into moulds of sand. It is covered with black
blisters, like steel of cementation; whence it has got the name of
blistered copper. In the interior of these pigs, the copper presents a
porous texture, occasioned by the ebullition produced by the escape of
the gases during the moulding. The copper being now almost entirely
purged from the sulphur, iron, and the other substances with which it
was combined, is in a fit state to be refined. This operation affords
some scoriæ; they are very heavy, and contain a great deal of oxide of
copper, sometimes even metallic copper.
These scoriæ, as well as those of the third melting and of the refining,
are added to the second fusion, as we have already stated, in describing
the fourth operation.
In some works, the roasting is repeated several times upon the _blue
metal_, in order to bring it to a state fit for refining. We shall
afterwards notice this modification of the treatment.
_Eighth operation. Refining or toughening._--The pigs of copper intended
for refining are put upon the sole of the refining furnace through the
door in the side. A slight heat is first given, to finish the roasting
or oxidation, in case this operation has not already been pushed far
enough. The fire is to be increased by slow degrees, so that, by the end
of 6 hours, the copper may begin to flow. When all the metal is melted,
and when the heat is considerable, the workman lifts up the door in the
front, and withdraws with a rake the few scoriæ which may cover the
copper bath. They are red, lamellated, very heavy, and closely resemble
protoxide of copper.
The refiner takes then an assay with a small ladle, and when it cools,
breaks it in a vice, to see the state of the copper. From the appearance
of the assay, the aspect of the bath, the state of the fire, &c., he
judges if he may proceed to the toughening, and what quantity of wooden
spars and wood charcoal he must add to render the metal malleable, or,
in the language of the smelters, bring it to the proper pitch. When the
operation of refining begins, the copper is brittle or dry, and of a
deep red colour approaching to purple. Its grain is coarse, open, and
somewhat crystalline.
To execute the refining, the surface of the metal is covered over with
wood charcoal, and stirred about with a spar or rod of birch wood. The
gases which escape from the wood, occasion a brisk effervescence. More
wood charcoal is added from time to time, so that the surface of the
metal may be always covered with it, and the stirring is continued with
the rods, till the operation of refining be finished; a circumstance
indicated by the assays taken in succession. The grain of the copper
becomes finer and finer, and its colour gradually brightens. When the
grain is extremely fine, or _closed_, when the trial pieces half cut
through and then broken, present a silky fracture, and when the copper
is of a fine light red, the refiner considers the operation to be
completed; but he verifies still further the purity of the copper, by
trying its malleability. For this purpose, he takes out a sample in his
small ladle, and pours it into a mould. When the copper is solidified,
but still red-hot, he forges it. If it is soft under the hammer, if it
does not crack on the edges, the refiner is satisfied with its
ductility, and he pronounces it to be in its _proper state_. He orders
the workmen to mould it; who then lift the copper out of the furnace in
large iron ladles lined with clay, and pour it into moulds of the size
suitable to the demands of commerce. The ordinary dimensions of the
ingots or pigs are 12 inches broad, 18 long, and from 2 to 2-1/2 thick.
The period of the refining process is 20 hours. In the first six, the
metal heats, and suffers a kind of roasting; at the end of this time it
melts. It takes four hours to reach the point at which the refining,
properly speaking, begins; and this last part of the process lasts about
4 hours. Finally, 6 hours are required to arrange the moulds, cast the
ingots, and let the furnace cool.
The charge of copper in the refining process depends upon the dimensions
of the furnace. In the Hafod works, one of the most important in
England, the charge varies from 3 to 5 tons; and the quantity of pure
copper manufactured in a week is from 40 to 50 tons.
The consumption of fuel is from 15 to 18 parts of coal, for one part of
refined copper in pigs.
When the copper offers difficulties in the refining, a few pounds of
lead are added to it. This metal, by the facility with which it
scorifies, acts as a purifier, aiding the oxidation of the iron and
other metals that may be present in the copper. The lead ought to be
added immediately after removing the door to skim the surface. The
copper should be constantly stirred up, to expose the greatest possible
surface to the action of the air, and to produce the complete oxidation
of the lead; for the smallest quantity of this metal alloyed in copper,
is difficult to clear up in the lamination; that is to say, the scale of
oxide does not come cleanly from the surface of the sheets.
The operation of refining copper is delicate, and requires, upon the
part of the workmen, great skill and attention to give the metal its due
ductility. Its surface ought to be entirely covered with wood charcoal;
without this precaution, the refining of the metal would _go back_, as
the workmen say, during the long interval which elapses in the moulding;
whenever this accident happens, the metal must be stirred up anew with
the wooden pole.
Too long employment of the wooden rod gives birth to another remarkable
accident, for the copper becomes more brittle than it was prior to the
commencement of the refining; that is, when it was _dry_. Its colour is
now of a very brilliant yellowish red, and its fracture is fibrous. When
this circumstance occurs, when the refining, as the workmen say, has
_gone too far_, the refiner removes the charcoal from the top of the
melted metal; he opens the side door, to expose the copper to the action
of the air, and it then resumes its malleable condition.
Mr. Vivian, to whom we owe the above very graphic account of the
processes, has explained, in a very happy manner, the theory of
refining. He conceives, we may conclude, that the copper in the _dry
state_, before the refining, is combined with a small portion of oxygen,
or, in other words, that a small portion of oxide of copper is diffused
through the mass, or combined with it; and that this proportion of
oxygen is expelled by the deoxidizing action of the wood and charcoal,
whereby the metal becomes malleable. 2. That when the refining process
is carried too far, the copper gets combined with a little charcoal.
Thus copper, like iron, is brittle when combined with oxygen and
charcoal; and becomes malleable only when freed entirely from these two
substances.
It is remarkable, that copper, in the _dry state_, has a very strong
action upon iron; and that the tools employed in stirring the liquid
metal become very glistening, like those used in a farrier’s forge. The
iron of the tools consumes more rapidly at that time, than when the
copper has acquired its malleable state. The metal requires, also, when
_dry_, more time to become solid, or to cool, than when it is refined; a
circumstance depending, probably, upon the difference in fusibility of
the copper in the two states, and which seems to indicate, as in the
case of iron, the presence of oxygen.
When the proper refining point has been passed, another very remarkable
circumstance has been observed; namely, that the surface of the copper
oxidizes more difficultly, and that it is uncommonly brilliant;
reflecting clearly the bricks of the furnace vault. This fact is
favourable to the idea suggested above, that the metal is in that case
combined with a small quantity of carbon; which absorbs the oxygen of
the air, and thus protects the metal from its action.
Copper is brought into the market in different forms, according to the
purposes which it is to serve. What is to be employed in the manufacture
of brass is granulated. In this condition it presents more surface to
the action of zinc or calamine, and combines with it more readily. To
produce this granulation, the metal is poured into a large ladle,
pierced with holes, and placed above a cistern filled with water, which
must be hot or cold, according to the form wished in the grains. When it
is hot, round grains are obtained analogous to lead shot; and the copper
in this state is called _bean shot_. When the melted copper falls into
cold water perpetually renewed, the granulations are irregular, thin,
and ramified; constituting _feathered shot_. The _bean shot_ is the form
employed in brass making.
Copper is also made into small ingots, about 6 ounces in weight. These
are intended for exportation to the East Indies, and are known in
commerce by the name of Japan copper. Whenever these little pieces are
solidified, they are thrown, while hot, into cold water. This immersion
slightly oxidizes the surface of the copper, and gives it a fine red
colour.
Lastly, the copper is often reduced into sheets, for the sheathing of
ships, and many other purposes. The Hafod works possess a powerful
rolling mill, composed of four pairs of cylinders. It is moved by a
steam engine, whose cylinder has 40 inches diameter. See the
representation of the rolling mill of the Royal Mint, under GOLD.
The cylinders for rolling copper into sheets are usually 3 feet long,
and 15 inches in diameter. They are uniform. The upper roller may be
approached to the under one, by a screw, so that the cylinders are
brought closer, as the sheet is to be made thinner.
The ingots of copper are laid upon the sole of a reverberatory furnace
to be heated; they are placed alongside each other, and they are formed
into piles in a cross-like arrangement, so that the hot air may pass
freely round them all. The door of the furnace is shut, and the workman
looks in through a peep-hole from time to time, to see if they have
taken the requisite temperature; namely, a dull red. The copper is now
passed between the cylinders; but although this metal be very malleable,
the ingots cannot be reduced to sheets without being several times
heated; because the copper cools, and acquires, by compression, a
texture which stops the progress of the lamination.
These successive heatings are given in the furnace indicated above;
though, when the sheets are to have a very great size, furnaces
somewhat different are had recourse to. They are from 12 to 15 feet
long, and 5 wide. See BRASS.
The copper, by successive heating and lamination, gets covered with a
coat of oxide, which is removed by steeping the sheets for a few days in
a pit filled with urine; they are then put upon the sole of the heating
furnace. Ammonia is formed, which acts on the copper oxide, and lays
bare the metallic surface. The sheets are next rubbed with a piece of
wood, then plunged, while still hot, into water, to make the oxide scale
off; and lastly, they are passed cold through the rolling press to
smooth them. They are now cut square, and packed up for home sale or
exportation.
The following estimate has been given by MM. Dufrénoy and Elie de
Beaumont of the expense of manufacturing a ton of copper in South Wales.
_£_ _s._ _d._
12-1/2 tons of ore, yielding 8-1/2 _per cent._ of copper 55 0 0
20 tons of coals 8 0 0
Workmen’s wages, rent, repairs, &c. 13 0 0
------------
76 0 0
------------
The exhalations from the copper smelting works are very detrimental to
both vegetable and animal life. They consist of sulphurous acid,
sulphuric acid, arsenic and arsenious acids, various gases and fluoric
vapours, with solid particles mechanically swept away into the air,
besides the coal smoke. Mr. Vivian has invented a very ingenious method
of passing the exhalations from the calcining ores and _matts_ along
horizontal flues or rather galleries of great dimensions, with many
crossings and windings of the current, and exposure during the greater
part of the circuit to copious showers of cold water. By this simple and
powerful system of condensation, the arsenic is deposited in the bottoms
of the flues, the sulphurous acid is in a great measure absorbed, and
the nuisance is remarkably abated.
The following figures represent certain modifications of the copper
calcining and smelting copper furnaces of Swansea.
[Illustration: 303 304]
_Fig._ 304. is the section of the roasting furnace lengthwise; _fig._
303. the ground plan; in which _a_ is the fire-door; _b_ the grate; _c_
the fore-bridge; _d_ the chimney; _e e_ working apertures on each of the
long sides of the furnace, through which the ore is introduced, spread,
and turned over; _f f_ cast-iron hoppers; _g g_ openings in the vaulted
roof; _h_ the hearth-sole; _i i_ holes in this; _k_ a vaulted space
under the hearth. The hearth has a suitable oval shape, and is covered
with a flat arch. Its length is 16 feet, breadth 13-1/2, mean height 2
feet.
[Illustration: 305 306]
_Fig._ 305. is a longitudinal section of the melting furnace; _fig._
306. the ground plan in which _a_ is the fire door; _b_ the grate; _c_
the fire bridge; _d_ the chimney; _e_ the side openings; _f_ the working
doors; _g_ the raking-out hole; _h_ iron spouts, which conduct the
melted metal into pits filled with water.
The melting furnace is altogether smaller; but its firing hearth is
considerably larger than in the roasting furnace. The long axis of the
oval hearth is 14 feet; its short axis 10 feet; its mean height 2 feet.
The principal ore smelted at Chessy is the azure copper, which was
discovered by accident in 1812. Red copper ore, also, has come into
operation there since 1825. The average metallic contents of the richest
azure ore are from 33 to 36 per cent.; of the poorer, from 20 to 24. The
red ore contains from 40 to 67 parts in 100. The ore is sorted, so that
the mean contents of metal may be 27 per cent., to which 20 per cent. of
limestone are added; whence the cinder will amount to 50 per cent. of
the ore. A few per cents. of red copper slag, with some quicklime and
_gahrslag_, are added to each charge, which consists of 200 pounds of
the above mixture, and 150 pounds of coke. When the furnace (_fourneau à
manche_, see the Scotch smelting hearth, under LEAD), is in good action,
from 10 to 14 such charges are worked in 12 hours. When the crucible is
full of metal at the end of this period, during which the cinder has
been frequently raked off, the blast is stopped, and the _matt_ floating
over the metal being sprinkled with water and taken off, leaves the
black copper to be treated in a similar way, and converted into
_rosettes_. The refining of this black copper is performed in a kind of
reverberatory furnace.
The cinders produced in this reduction process are either vitreous and
light blue, which are most abundant; cellular, black, imperfectly fused
from excess of lime; or, lastly, red, dense, blistery, from defect of
lime, from too much heat, and the passage of protoxide into the cinders.
They consist of silicate of alumina, of lime, protoxide of iron; the red
contain some silicate of copper.
[Illustration: 307 308]
The copper-refining furnace at Chessy, near Lyons, is of the kind called
_Spleiss-ofen_ (split hearths) by the Germans. _Fig._ 307. is a section
lengthwise in the dotted line A B of _fig._ 308., which is the ground
plan.
The foundation-walls are made of gneiss; the arch, the fire-bridge, and
the chimney, of fire-bricks. The hearth, _a_, is formed of a dense
mixture of coal-dust, upon a bottom of well-beat clay _b_, which reposes
upon a bed of brickwork _c_. Beneath this there is a slag bottom _d_;
_e_ is the upper, and _f_ the under discharge hole. The hearth is
egg-shaped; the longer axis being 8 feet, the shorter 6-1/2 feet: in the
middle it is 10 inches deep, and furnished with the outlets _g g_, which
lead to each of the _Spleiss-hearths_ _h h_, _fig._ 308. These outlets
are contracted with fire-bricks _i i_, till the proper period of the
discharge. The two hearths are placed in communication by a canal _h_;
they are 3-1/2 feet in diameter, 16 inches deep; are floored with
well-beat coal ashes, and receive about 27 cwt. for a charge.
_l_ is the grate; _m_, the fire-bridge; _n_, the boshes in which the
_tuyères_ lie; _o_, the chimney; _p_, the working door through which the
slags may be drawn off. Above this is a small chimney, to carry off the
flame and smoke whenever the door is opened.
The smelting _post_ or charge, to be purified at once, consists of 60
cwt. of black copper, to which a little granular copper and copper of
cementation is added; the consumption of pit-coal amounts to 36 cwt. As
soon as the copper is melted, the bellows are set a-going, and the
surface of the metal gets soon covered with a moderately thick layer of
cinder, which is drawn off. This is the first skimming or _decrassage_.
By and by, a second layer of cinder forms, which is in like manner
removed; and this skimming is repeated, to allow the blast to act upon
fresh metallic surfaces. After 4 or 5 hours, no more slag appears, and
then the fire is increased. The melted mass now begins to boil or work
(_travailler_), and continues so to do, for about 3/4 of an hour, or an
hour, after which the motion ceases, though the fire be kept up. The
_gahrproof_ is now taken; but the metal is seldom fine in less than 3/4
of an hour after the boil is over. Whenever the metal is run off by the
tap-hole into the two basins _i i_, called SPLIT-HEARTHS, a reddish
vapour or mist rises from its surface, composed of an infinite number of
minute globules, which revolve with astonishing velocity upon their
axes, constituting what the Germans called _spratzen_ (crackling) of the
copper. They are composed of a nucleus of metal, covered with a film of
protoxide, and are used as sand for strewing upon manuscript. The copper
is separated, as usual, by sprinkling water upon the surface of the
melted metal, in the state of _rosettes_, which are immediately immersed
in a stream of water. This refining process lasts about 16 or 17 hours;
the skimmings weigh about 50 cwt.; the refuse is from 15 to 17 per
cent.; the loss from 2 to 3 per cent. The _gahrslag_ amounts to 11 cwt.
[Illustration: 309 310 311]
The refining of the eliquated copper (called _darrlinge_) from which the
silver has been sweated out by the intervention of lead, can be
performed only in small hearths. The following is the representation of
such a furnace, called, in German, _Kupfergahrheerd_. _Fig._ 309. is the
section lengthwise; _fig._ 310. is the section across; and _fig._ 311.
is the ground plan, in which _a_ is the hearth-hollow; _b_, a massive
wall; _c_, the mass out of which the hearth is formed; _d_, cast-iron
plates covering the hearth; _e_, opening for running off the liquid
slag; _f_, a small wall; _g_, iron curb for keeping the coals together.
The hearth being heated with a bed of charcoal, 3/4 cwt. of _darrlinge_
are laid over it, and covered with more fuel: whenever this charge is
melted, another layer of the coal and _darrlinge_ is introduced, and
thus in succession till the hearth become full, or contain from 2-1/4 to
2-1/2 cwt. In Neustadt 7-1/2 cwt. of _darrlinge_ have been refined in
one furnace, from which 5 cwt. of _gahrcopper_ has been obtained. The
blast oxidizes the foreign metals, namely, the lead, nickel, cobalt, and
iron, with a little copper, forming the _gahrslag_; which is, at first,
rich in lead oxide, and poor in copper oxide; but, at the end, this
order is reversed. The slag, at first blackish, assumes progressively a
copper red tint. The slag flows off spontaneously along the channel _e_,
from the surface of the hearth. The _gahre_ is tested by means of a
proof rod of iron, called _gahr-eisen_, thrust through the _tuyère_ into
the melted copper, then drawn out and plunged in cold water. As soon as
the _gahrspan_ (scale of copper) appears brownish red on the outside,
and copper red within, so thin that it seems like a net-work, and so
deficient in tenacity that it cannot be bent without breaking, the
refining is finished. The blast is then stopped; the coals covering the
surface, as also the cinders must be raked off the copper, after being
left to cool a little; the surface is now cooled by sprinkling water
upon it, and the thick cake of congealed metal (_rondelle_) is lifted
off with tongs, a process called _schleissen_ (slicing), or
_sheibenreissen_ (shaving), which is continued till the last convex cake
at the bottom of the furnace, styled the _kingspiece_, is withdrawn.
These _rondelles_ are immediately immersed in cold water, to prevent the
oxidation of the copper; whereupon the metal becomes of a cochineal red
colour, and gets covered with a thin film of protoxide. Its under
surface is studded over with points and hooks, the result of tearing the
congealed disc from the liquid metal. Such cakes are called _rosette_
copper. When the metal is very pure and free from protoxide, these cakes
may be obtained very thin, one 24th of an inch for example.
The refining of two cwts. and a half of _darrlinge_ takes three quarters
of an hour, and yields one cwt. and a half of _gahr copper_ in 36
rosettes, as also some _gahrslag_. Gahr copper generally contains from
1-1/2 to 2-1/2 per cent. of lead, along with a little nickel, silver,
iron, and aluminum.
_Smelting of the Mansfeldt copper schist, or bituminous
Mergelschiefer._--The cupreous ore is first roasted in large heaps, of
2000 cwts., interstratified with brush-wood, and with some slates rich
in bituminous matter, mixed with the others. These heaps are 3 ells
high, and go on burning 15 weeks in fair and 20 in rainy weather. The
bitumen is decomposed; the sulphur is dissipated chiefly in the form of
sulphurous acid; the metal gets partially oxidized, particularly the
iron, which is a very desirable circumstance towards the production of a
good smelting slag. The calcined ore is diminished one-tenth in bulk,
and one-eighth in weight; becoming of a friable texture and a dirty
yellow gray colour. The smelting furnaces are cupolas (_schachtofen_),
14 to 18 feet high; the fuel is partly wood charcoal, partly coke from
the Berlin gas-works, and Silesia. The blast is given by cylinder
bellows, recently substituted for the old barbarous _Blasebälgen_, or
wooden bellows of the household form.
The cupreous slate is sorted, according to its composition, into slate
of lime, clay, iron, &c., by a mixture of which the smelting is
facilitated. For example, 1 post or charge may consist of 20 cwt. of the
ferruginous slate, 14 of the calcareous, 6 of the argillaceous, with 3
of fluor spar, 3 of rich copper slags, and other refuse matters. The
nozzle at the _tuyère_ is lengthened 6 or 8 inches, to place the melting
heat near the centre of the furnace. In 15 hours 1 fodder of 48 cwts. of
the above mixture may be smelted, whereby 4 to 5 cwts. of _matte_ (crude
copper, called _Kupferstein_ in Germany) and a large body of slags are
obtained. The _matte_ contains from 30 to 40 per cent. of copper, and
from 2 to 4 _loths_ (1 to 2 oz.) of silver. The slags contain at times
one-tenth their weight of copper.
The _matte_ is composed of the sulphurets of copper, iron, silver, zinc,
along with some arsenical cobalt and nickel. The slaty slag is raked off
the surface of the melted _matte_ from time to time. The former is
either after being roasted six successive times, smelted into black
copper; or it is subjected to the following concentration process. It is
broken to pieces, roasted by brushwood and coals three several times in
brick-walled kilns, containing 60 cwts., and turned over after every
calcination; a process of four weeks’ duration. The thrice roasted mass,
called _spurrost_, being melted in the cupola _fig._ 313. with
ore-cinder, yields the _spurstein_, or concentrated _matte_. From 30 to
40 cwts. of spurrost are smelted in 24 hours; and from 48 to 60 per
cent. of _spurstein_ are obtained, the slag from the slate smelting
being employed as a flux. The spurstein contains from 50 to 60 per cent.
of copper, combined with the sulphurets of copper, of iron, and silver.
The spurstein is now mixed with _dünnstein_ (a sulphuret of copper and
iron produced in the original smeltings) roasted six successive times,
in a quantity of 60 cwts., with brushwood and charcoal; a process which
requires from 7 to 8 weeks. The product of this six-fold calcination is
the _Gahrrost_ of the Germans (done and purified); it has a colour like
red copper ore, varying from blue gray into cochineal red; a granular
fracture; it contains a little of the metal, and may be immediately
reduced into metallic copper, called _kupfermachen_. But before smelting
the mass, it is lixiviated with water, to extract from it the soluble
sulphate, which is concentrated in lead pans, and crystallized.
The lixiviated _gahröste_ mixed with from 1/4 to 1/5 of the lixiviated
_dünnsteinrost_, and 1/6 to 1/10 of the copper slate slag, are smelted
with charcoal or coke fuel in the course of 24 hours, in a mass of 60 or
80 cwts. The product is black copper, to the amount of about 1/4 the
weight, and 1/6 of _dünnstein_, or _thin matte_. This black copper
contains in the cwt. from 12 to 20 loths (6 to 10 oz.) of silver. The
_dünnstein_ consists of from 60 to 70 per cent. of copper combined with
sulphur, sulphuret of iron and arsenic; and when thrice roasted, yields
a portion of metal. The black copper lies undermost in the crucible of
the furnace, above it is the _dünnstein_, covered with the stone slag,
or copper cinder, resulting from the slate-smelting. The slags being
raked off, and the crucible sufficiently full, the eye or nozzle hole is
shut, the _dünnstein_ removed by cooling the surface, and breaking the
crust, which is about 1/4 to 1/2 inch thick. The same method is adopted
for taking out the black copper in successive layers. For the
de-silvering of this, and similar black coppers, see SILVER.
[Illustration: 312 313 314 315]
_Fig._ 312. is a vertical section through the form or _tuyère_ in the
dotted line A B of _fig._ 314. _Fig._ 313. is a vertical section in the
dotted line C D of _fig._ 315. _a_ is the shaft of the furnace, _b_ the
rest, _c c_ the forms; _d_ the sole or hearth-stone, which has a slope
of 3 inches towards the front wall; _e e_, &c. casing walls of fire
bricks; _f f_, &c. filling up walls built of rubbish stones; _g g_ a
mass through which the heat is slowly conducted; _h h_ the two holes
through one or other of which alternately the product of the smelting
process is run off into the fore-hearth. Beneath the hearth-sole there
is a solid body of loam; and the fore-hearth is formed with a mixture of
coal-dust and clay; _k_ is the discharge outlet. _Fig._ 314. is a
horizontal section of the furnace through the hole or eye in the dotted
line E F of _fig._ 312.; _fig._ 315. a horizontal section of the shaft
of the furnace through the form in the dotted line G H of _figs._ 312
and 313. The height of the shaft, from the line E F to the top, is 14
feet; from E to G, 25 inches; from _c_ to the line below _b_, 2 feet;
from that line to the line opposite _g g_, 2 feet. The width at the line
_g g_ is 3 feet 3 inches, and at _c_ 26 inches. The basins _i i_, _fig._
314., are 3 feet diameter, and 20 inches deep.
The refining of copper is said to be well executed at Seville, in Spain;
and, therefore, some account of the mode of operating there may be
acceptable to the reader.
The first object is to evaporate in a reverberatory furnace all the
volatile substances, such as sulphur, arsenic, antimony, &c., which may
be associated with the sulphur; and the second, to oxidize and to
convert into scoriæ the fixed substances, such as iron, lead, &c., with
the least possible expense and waste. The minute quantities of gold and
silver which resist oxidation cannot be in any way injurious to the
copper. The hearth is usually made of a refractory sand and clay with
ground charcoal, each mixed in equal volumes, and worked up into a
doughy consistence with water. This composition is beat firmly into the
furnace bottom. But a quartzose hearth is found to answer better, and to
be far more durable; such as a bed of fire-sandstone.
Before kindling the furnace, its inner surface is smeared over with a
cream-consistenced mixture of fire-clay and water.
The cast pigs, or blocks of black or crude copper, are piled upon the
hearth, each successive layer crossing at right angles the layer beneath
it, in order that the flame may have access to play upon the surface of
the hearth, and to heat it to a proper pitch for making the metal flow.
The weight of the charge should be proportional to the capacity of the
furnace, and such that the level of the metallic bath may be about an
inch above the nozzle of the bellows; for, were it higher, it would
obstruct its operation, and were it too low, the stream of air would
strike but imperfectly the surface of the metal, and would fail to
effect, or would retard at least, the refining process, by leaving the
oxidation and volatilization of the foreign metals incomplete.
As the scoriæ form upon the surface, they are drawn off with an iron
rabble fixed to the end of a wooden rod.
Soon after the copper is melted, charcoal is to be kindled in three iron
basins lined with loam, placed alongside the furnace, to prepare them
for receiving their charge of copper, which is to be converted in them,
into _rosettes_.
The bellows are not long in action before the evaporation of the mineral
substances is so copious, as to give the bath a boiling appearance; some
drops rise up to the roof of the reverberatory, others escape by the
door, and fall in a shower of minute spherical globules. This phenomenon
proves that the process is going on well; and, when it ceases, the
operation is nearly completed. A small proof of copper, of the form of a
watch-case, and therefore called _montre_, is taken out from time to
time, upon the round end of a polished iron rod, previously heated. This
rod is dipped two or three inches into the bath, then withdrawn and
immersed in cold water. The copper cap is detached from the iron rod, by
a few blows of a hammer; and a judgment is formed from its thickness,
colour, and polish, as to the degree of purity which the copper has
acquired. But these _watches_ need not be drawn till the small rain,
above spoken of, has ceased to fall. At the end of about 11 hours of
firing, the numerous small holes observable in the first _watch_ samples
begin to disappear; the outer surface passes from a bright red to a
darker hue, the inner one becomes of a more uniform colour, and always
less and less marked with yellowish spots. It will have acquired the
greatest pitch of purity that the process can bestow, when the _watches_
become of a dark crimson colour.
Care must be taken to stop this refining process at the proper time;
for, by prolonging it unduly, a small quantity of cupreous oxide would
be formed, which, finding no oxygen to reduce it, would render the whole
body of copper hard, brittle, and incapable of lamination.
The basins must now be emptied of their burning charcoal, the opening of
the _tuyère_ must be closed, and the melted copper allowed to flow into
them through the tap-hole, which is then closed with loam. Whenever the
surface is covered with a solid crust, it is bedewed with water; and as
soon as the crust is about 1-1/2 inch thick it is raised upon hooks
above the basin, to drain off any drops, and then carried away from the
furnace. If these cakes, or rosettes, be suddenly cooled by plunging
them immediately in water, they will assume a fine red colour, from the
formation of a film of oxide.
Each refining operation produces, in about 12 hours, 1-7/10 tons of
copper, with the consumption of about 4/5 of a ton of dry wood.
Care should be taken that the copper cake or _rosette_ be all solidified
before plunging it into water, otherwise a very dangerous explosion
might ensue, in consequence of the sudden extrication of oxygen from the
liquid metal, in the act of condensation. On the other hand, the cake
should not be allowed to cool too long in the air, lest it get
peroxidized upon the surface, and lose those fine red, purple, and
yellow shades, due to a film of the protoxide, which many dealers
admire.
When a little oxide of antimony and oxide of copper are combined with
copper, they occasion the appearance of micaceous scales in the
fractured faces. Such metal is hard, brittle, yellowish within, and can
be neither laminated nor wire-drawn. These defects are not owing to
arsenic, as was formerly imagined; but, most probably, to antimony in
the lead, which is sometimes used in refining copper. They are more
easily prevented than remedied.
According to M. Frèrejean, proprietor of the great copper works of
Vienne, in Dauphiny, too low a temperature or too much charcoal, gives
to the metal a cubical structure, or that of divergent rays; in either
of which states it wants tenacity. Too high a temperature, or too rapid
a supply of oxygen, gives it a brick red colour, a radiated
crystallization without lustre, or a very fine grain of indeterminate
form; the last structure being unsuitable for copper that is to be
worked under the hammer or in the rolling-press. The form which
indicates most tenacity is radiated with minute fibres glistening in
mass. Melted copper will sometimes pass successively through these three
states in the space of ten minutes.
[Illustration: 316]
_Fig._ 316. represents a _roasting mound_ of copper pyrites in the Lower
Hartz, near Goslar, where a portion of the sulphur is collected. It is a
vertical section of a truncated quadrangular pyramid. A layer of wooden
billets is arranged at the base of the pyramid in the line _a a_.
C, a wooden chimney which stands in the centre of the mound with a small
pile of charcoal at its bottom, _c_; _d d_ are large lumps of ore
surrounded by smaller pieces; _f f_, are rubbish and earth to form a
covering. A current of air is admitted under the billets by an opening,
in the middle of each of the four sides of the base _a a_, so that two
principal currents of air cross under the vertical axis C of the
truncated pyramid, as indicated in the figure.
The fire is applied through the chimney C; the charcoal at its bottom
_c_, and the pile _a a_ are kindled. The sulphureous ores _d_, _f_, are
raised to such a high temperature as to expel the sulphur in the state
of vapour.
In the Lower Hartz a roasting mound continues burning during four
months. Some days after it is kindled the sulphur begins to exhale, and
is condensed by the air at the upper surface of the pyramid. When this
seems impregnated with it, small basins l l are excavated, in which some
liquid sulphur collects; it is removed from time to time with iron
ladles, and thrown into water, where it solidifies. It is then refined
and cast into roll brimstone.
A similar roasting mound contains, in the Lower Hartz, from 100 to 110
tons of ore and 730 cubic feet of wood. It yields in four months about
one ton and a half of sulphur from copper pyrites. Lead ore is treated
in the same way, but it furnishes less sulphur.
There are usually from 12 to 15 roasting heaps in action at once for
three smelting works of the Lower Hartz. After the first roasting two
heaps are united to form a third, which is calcined anew, but under a
shed; the ores are then stirred up and roasted for the third time,
whence a crude mixture is procured for the smelting-house.
The most favourable seasons for roasting in the open air are spring and
autumn; the best weather is a light wind accompanied with gentle rain.
When the wind or rain obstruct the operation, this inconvenience is
remedied by planks distributed round the upper surface of the truncated
pyramid over the sulphur basins.
_Manufacturing assays of copper._--The first thing is to make such a
sample as will represent the whole mass to be valued; with which view,
fragments must be taken from different spots, mixed, weighed, and ground
together. A portion of this mixture being tried by the blow-pipe, will
show, by the garlic or sulphurous smell of its fumes, whether arsenic,
sulphur, or both, be the mineralizers. In the latter case, which often
occurs, 100 gr. or 1000 gr. of the ore are to be mixed with one half its
weight of saw-dust, then imbued with oil, and heated moderately in a
crucible till all the arsenical fumes be dissipated. The residuum being
cooled and triturated, is to be exposed in a shallow earthen cup to a
slow roasting heat, till the sulphur and charcoal be burned away. What
remains being ground and mixed with half its weight of calcined borax,
one-twelfth its weight of lamp black, next made into a dough with a few
drops of oil, is to be pressed down into a crucible, which is to be
covered with a luted lid, and to be subjected, in a powerful air
furnace, first to a dull red heat, and then to vivid ignition for 20
minutes. On cooling and breaking the crucible, a button of metallic
copper will be obtained. Its colour and malleability indicate pretty
well the quality, as does its weight, the relative value of the ore. It
should be cupelled with lead, to ascertain if it contains silver or
gold. See ASSAY, and SILVER.
If the blow-pipe trial showed no arsenic, the first calcination may be
omitted; and if neither sulphur nor arsenic, a portion of the ground ore
should be dried, and treated directly with borax, lamp black and oil. It
is very common to make a dry assay of copper ores, by one roasting and
one fusion along with 3 parts of black flux; from the weight of the
metallic button the richness of the ore is inferred.
The humid assay is more exact, but it requires more skill and time.
The sulphur and the silica are easily got rid of, by the acids which do
not dissolve them, but only the metallic oxides and the other earths.
These oxides may then be thrown down by their appropriate reagents, the
copper being precipitated in the state of either the black oxide, or
pure metal. 105 parts of black oxide represent 100 of copper. Before
entering upon the complete analysis of an ore, preliminary trials should
be made, to ascertain what are its chief constituents. If it be
sulphuret of copper, or copper pyrites, without silver or lead, 100
grains exactly of its average powder may be weighed out, treated in a
matras with boiling muriatic acid for some time, gradually adding a few
drops of nitric acid, till all action ceases, or till the ore be all
dissolved. The insoluble matter found floating in the liquid contains
most of the sulphur; it may be separated upon a filter, washed, dried,
and weighed; then verified by burning away. The incombustible residuum,
treated by muriatic acid, may leave an insoluble deposit, which is to be
added to the former. To the whole of the filtered solutions carbonate of
potash is to be added; and the resulting precipitate, being washed, and
digested repeatedly in water of ammonia, all its cupric oxide will have
been dissolved, whenever the ammonia is no longer rendered blue.
Caustic potash, boiled with the ammoniacal solution, will separate the
copper in the state of black oxide; which is to be thrown upon a filter,
washed, dried, and weighed. The matter left undissolved by the ammonia,
consists of oxide of iron, with probably a little alumina. The latter
being separated by caustic potash, the iron oxide may be also washed,
dried, and weighed. The powder which originally resisted the muriatic
acid, is silica.
_Assay of copper ores, which contain iron, sulphur, silver, lead, and
antimony._
100 grains of these ores, previously sampled, and pulverized, are to be
boiled with nitric acid, adding fresh portions of it from time to time,
till no more of the matter be dissolved. The whole liquors which have
been successively digested and decanted off, are to be filtered and
treated with common salt, to precipitate the silver in the state of a
chloride.
The nitric acid, by its reaction upon the sulphur, having generated
sulphuric acid, this will combine with the lead oxidized at the same
time, constituting insoluble sulphate of lead, which will remain mixed
with the gangue. Should a little nitrate of lead remain in the liquid,
it may be thrown down by sulphate of soda, after the silver has been
separated. The dilute liquid being concentrated by evaporation, is to be
mixed with ammonia in such excess as to dissolve all the cupric oxide,
while it throws down all the oxide of iron and alumina; which two may be
separated, as usual, by a little caustic potash. The portion of ore
insoluble in the nitric acid, being digested in muriatic acid, every
thing will be dissolved except the sulphur and silica. These being
collected upon a filter, and dried, the sulphur may be burned away,
whereby the proportion of each is determined.
_Ores of the_ oxide _of copper_, are easily analyzed by solution in
nitric acid, the addition of ammonia, to separate the other metals, and
precipitation by potash. The _native carbonate_ is analyzed by calcining
100 grains; when the loss of weight will shew the amount of water and
carbonic acid; then that of the latter may be found, by expelling it
from another 100 grains, by digestion in a given weight of sulphuric
acid. The copper is, finally, obtained in a metallic state by plunging
bars of zinc into the solution of the sulphate.
The _native arseniates of copper_ are analyzed by drying them first at a
moderate heat; after which they are to be dissolved in nitric acid. To
this solution, one of nitrate of lead is to be added, as long as it
occasions a precipitate; the deposit is to be drained upon a filter, and
the clear liquid which passes through, being evaporated nearly to
dryness, is to be digested in hot alcohol, which will dissolve every
thing except a little arseniate of lead. This being added to the
arseniate first obtained, from the weight of the whole, the arsenic
acid, constituting 35 per cent., is directly inferred. The alcoholic
solution being now evaporated to dryness, the residue is to be digested
in water of ammonia, when the cupric oxide will be dissolved, and the
oxide of iron will remain. The copper is procured, in the state of black
oxide, by boiling the filtered ammoniacal solution with the proper
quantity of potash.
_The analysis of muriate of copper_--_atacamite_--is an easy process.
The ore being dissolved in nitric acid, a solution of nitrate silver is
added, and from the weight of the chloride precipitated, the equivalent
amount of muriate or chloride of copper is given; for 100 of chloride of
silver represent 93 of chloride of copper, and 43·8 of its metallic
basis. This calculation may be verified by precipitating the copper of
the muriate from its solution in dilute sulphuric acid, by plates of
zinc.
_The phosphate of copper_ may be analyzed either by solution in nitric
acid, and precipitation by potash; or by precipitating the phosphoric
acid present, by means of acetate of lead. The phosphate of lead thus
obtained, after being washed, is to be decomposed by dilute sulphuric
acid. The insoluble sulphate of lead being washed, dried, and weighed,
indicates by its equivalent the proportion of phosphate of lead, as also
of phosphate of copper; for 100 of sulphate of lead correspond to 92·25
phosphate of lead, and 89·5 phosphate of copper; and this again to 52·7
of the black oxide.
Copper forms the basis of a greater number of important ALLOYS than any
other metal. With zinc it forms Brass in all its varieties; which see.
BRONZE and BELL METAL are alloys of copper and tin. This compound is
prepared in crucibles when only small quantities are required; but in
reverberatory hearths, when statues, bells, or cannons are to be cast.
The metals must be protected as much as possible during their
combination from contact of air by a layer of pounded charcoal,
otherwise two evils would result, waste of the copper by combustion, and
a rapid oxidizement of the tin, so as to change the proportions and
alter the properties of the alloy. The fused materials ought to be well
mixed by stirring, to give uniformity to the compound. See BRONZE.
An alloy of 100 of copper and 4·17 of tin has been proposed by M.
Chaudet for the ready manufacture of _medals_. After melting this alloy
he casts it in moulds made of such bone-ash as is used for cupels. The
medals are afterwards subjected to the action of the coining press, not
for striking them, for the mould furnishes perfect impressions, but for
finishing and polishing them.
By a recent analysis of M. Berthier, the bells of the _pendules_, or
ornamental clocks, made in Paris, are found to be composed, of copper
72·00, tin 26·56, iron 1·44, in 100 parts.
An alloy of 100 of copper and 14 of tin is said by M. Dussaussy to
furnish tools, which hardened and sharpened in the manner of the
ancients, afford an edge nearly equal to that of steel.
Cymbals, gongs, and the _tamtam_ of the Chinese are made of an alloy of
100 of copper with about 25 of tin. To give this compound the sonorous
property in the highest degree it must be subjected to sudden
refrigeration. M. D’Arcet, to whom this discovery is due, recommends to
ignite the piece after it is cast, and to plunge it immediately into
cold water. The sudden cooling gives the particles of the alloy such a
disposition that, with a regulated pressure by skilful hammering, they
may be made to slide over each other, and remain permanently in their
new position. When by this means the instrument has received its
intended form, it is to be heated and allowed to cool slowly in the air.
The particles now take a different arrangement from what they would have
done by sudden refrigeration; for instead of being ductile they possess
such an elasticity, that on being displaced by a slight compression,
they return to their primary position after a series of extremely rapid
vibrations; whence a very powerful sound is emitted. Bronze, bell-metal,
and probably all the other alloys of tin with copper present the same
peculiarities.
The alloy of 100 of copper with from 60 to 33 of tin forms common
_bell-metal_. It is yellowish or whitish gray, brittle, and sonorous,
but not so much so as the preceding. The metal of house-clock bells
contain a little more tin than that of church-bells, and the bell of a
repeater contains a little zinc in addition to the other ingredients.
The bronze-founder should study to obtain a rapid fusion, in order to
avoid the causes of waste indicated above. Reverberatory furnaces have
been long adopted for this operation; and among these, the elliptical
are the best. The furnaces with spheroidal domes are used by the
bell-founders, because their alloy being more fusible, a more moderate
melting heat is required; however, as the rapidity of the process is
always a matter of consequence, they also would find advantage in
employing the elliptical hearths (_see the form of the melting furnace,
as figured under Smelting of copper ores_.) Coal is now universally
preferred for fuel.
The alloy of 100 of copper with 50 of tin, or more exactly of 32 of the
former with 14-1/2 of the latter, constitutes _speculum_ metal, for
making mirrors of reflecting telescopes. This compound is nearly white,
very brittle, and susceptible of a fine polish with a brilliant surface.
The following compound is much esteemed in France for making specula.
Melt 2 parts of pure copper and 1 of grain-tin in separate crucibles,
incorporate thoroughly with a wooden spatula, and then run the metal
into moulds. The lower surface is the one that should be worked into a
mirror.
Mr. Edwards, in the Nautical Almanack for 1787, gave the following
instructions for making speculum metal.
The quality of the copper is to be tried by making a series of alloys
with tin, in the proportion of 100 of the former to 47, to 48, to 49,
and to 50 of the latter metal; whence the proportions of the whitest
compound may be ascertained. Beyond the last proportion, the alloy
begins to lose in brilliancy of fracture, and to take a bluish tint.
Having determined this point, take 32 parts of the copper, melt, and add
one part of brass and as much silver, covering the surface of the
mixture with a little black flux; when the whole is melted, stir with a
wooden rod, and pour in from 15 to 16 parts of melted tin (as indicated
by the preparatory trials), stir the mixture again, and immediately pour
it out into cold water. Then melt again at the lowest heat, adding for
every 16 parts of the compound 1 part of white arsenic, wrapped in
paper, so that it may be thrust down to the bottom of the crucible. Stir
with a wooden rod as long as arsenical fumes rise, and then pour it into
a sand mould. While still red hot, lay the metal in a pot full of very
hot embers, that it may cool very slowly, whereby the danger of its
cracking or flying into splinters is prevented.
Having described the different alloys of copper and tin, I shall now
treat of the method of separating these metals from each other as they
exist in old cannons, damaged bells, &c. The process employed on a very
great scale in France during the Revolution, for obtaining copper from
bells, was contrived by Fourcroy; founded upon the chemical fact that
tin is more fusible and oxidizable than copper.
1. A certain quantity of bell metal was completely oxidized by
calcination in a reverberatory furnace; the oxide was raked out, and
reduced to a fine powder.
2. Into the same furnace a fresh quantity of the same metal was
introduced; it was melted, and there was added to it one half of its
weight of the oxide formed in the first operation. The temperature was
increased, and the mixture well incorporated; at the end of a few hours,
there was obtained on the one hand copper almost pure, which subsided in
a liquid state, and spread itself upon the sole of the hearth, while a
compound of oxide of tin, oxide of copper, with some of the earthy
matters of the furnace collected on the surface of the metallic bath in
a pasty form. These scoriæ were removed with a rake, and as soon as the
surface of the melted copper was laid bare, it was run out. The scoriæ
were levigated, and the particles of metallic copper were obtained after
elutriation. By this process, from 100 pounds of bell metal, about 50
pounds of copper were extracted, containing only one _per cent._ of
foreign matters.
3. The washed scoriæ were mixed with 1/8 their weight of pulverised
charcoal; the mixture was triturated to effect a more intimate
distribution of the charcoal; and it was then put into a reverberatory
hearth, in which, by aid of a high heat, a second reduction was
effected, yielding a fluid alloy consisting of about 60 parts of copper
and 20 of tin; while the surface of the bath got covered with new scoriæ
containing a larger proportion of tin than the first.
4. The alloy of 60 of copper with 40 of tin was next calcined in the
same reverberatory furnace, but with stirring of the mass. The air in
sweeping across the surface of the bath, oxidized the tin more rapidly
than the copper; whence proceeded crusts of oxide that were skimmed off
from time to time. This process was continued till the metallic alloy
was brought to the same standard as bell metal, when it was run out to
be subjected to the same operations as the metal of No. 1.
The layers of oxide successively removed in this way were mixed with
charcoal, and reduced in a _fourneau à manche_, or Scotch lead smelting
furnace.
I shall not prosecute any further the details of this complicated
process of Fourcroy; because it has been superseded by a much better one
contrived by M. Bréant. He employed a much larger quantity of charcoal
to reduce the scoriæ rich in tin; and increased the fusibility by adding
crushed oyster-shells, bottle glass, or even vitrified scoriæ, according
to the nature of the substance to be reduced; and he treated them
directly in a reverberatory furnace.
The metal, thus procured, was very rich in tin. He exposed it in masses
on a sloping hearth of a reverberatory furnace, where, by a heat
regulated according to the proportions of the two metals in the alloy,
he occasioned an eliquation or sweating out of the tin. Metallic drops
were seen to transpire round the alloyed blocks or pigs, and, falling
like rain, flowed down the sloping floor of the furnace; on whose
concave bottom the metal collected, and was ladled out into moulds. When
the alloy, thus treated, contained lead, this metal was found in the
first portions that sweated out. The purest tin next came forth, while
the last portions held more or less copper in solution. By fractioning
the products, therefore, there was procured:
1. Tin with lead.
2. Tin nearly pure.
3. Tin alloyed with a little copper.
A spongy mass remained, exhibiting sometimes beautiful crystallizations;
this mass, commonly too rich in copper to afford tin by liquation, was
treated by oxidizement. In this manner, M. Bréant diminished greatly the
reductions and oxidations; and therefore incurred in a far less degree
the enormous waste of tin, which flies off with the draught of air in
high and long continued heats. He also consumed less fuel as well as
labour, and obtained purer products of known composition, ready to be
applied directly in many arts.
He treated advantageously in this manner more than a million of
kilogrammes (1000 tons) of scoriæ, for every 2 cwts. of which he paid 40
_centimes_ (four-pence), while several million kilogrammes of much
richer scoriæ had been previously sold to other refiners at 5 _centimes_
or one _sous_.
I have said that the ancients made their tools and military weapons of
bronze. Several of these have been analyzed, and the results are
interesting.
An antique sword found in 1799, in the peat moss of the Somme, consisted
of copper 87·47; tin 12·53, in 100 parts.
The bronze springs for the balistæ, according to Philo of Byzantium,
were made of copper 97, tin 3.
Hard and brittle nails afforded by analysis, 92 of copper, and 8 of tin.
Of three antique swords found in the environs of Abbeville, one was
found to consist of 85 of copper to 15 of tin. The nails of the handle
of this sword were flexible; they were composed of copper 95, tin 5.
Another of the swords consisted of 90 of copper and 10 of tin; and the
third, of 96 copper, with 4 tin.
A fragment of an ancient scythe afforded to analysis 92·6 copper, and
7·4 tin.
The process of coating copper with tin, exemplifies the strong affinity
between the two metals. The copper surface to be tinned is first cleared
up with a smooth sandstone; then it is heated and rubbed over with a
little sal ammoniac, till it be perfectly clean and bright: the tin,
along with some pounded rosin, is now placed on the copper, which is
made so hot as to melt the tin, and allow of its being spread over the
surface with a dossil or pad of tow. The layer thus fixed on the copper
is exceedingly thin; Bayen found that a copper pan, 9 inches in diameter
and 3-1/4 inches deep, being weighed immediately before and after
tinning, became only 21 grains heavier. Now as the area tinned,
including the bottom, amounted to 155 square inches, 1 grain of tin had
been spread over nearly 7-1/2 square inches; or only 20 grains over
every square foot.
_Copper and Arsenic_ form a white-coloured alloy, sometimes used for the
scales of thermometers and barometers; for dials, candlesticks, &c. To
form this compound, successive layers of copper clippings and white
arsenic are put into an earthen crucible; which is then covered with sea
salt, closed with a lid, and gradually heated to redness. If 2 parts of
arsenic have been used with 5 of copper, the resulting compound commonly
contains one tenth of its weight of metallic arsenic. It is white,
slightly ductile, denser, and more fusible than copper, and without
action on oxygen at ordinary temperatures; but, at higher heats, it is
decomposed with the exhalation of arsenious acid. The white copper of
the Chinese consists of 40·4 copper; 31·6 nickel; 25·4 zinc; and 2·6
iron. This alloy is nearly silver white; it is very sonorous, well
polished, malleable at common temperatures, and even at a cherry red,
but very brittle at a red-white heat. When heated with contact of air,
it oxidizes, burning with a white flame. Its specific gravity was 8·432.
When worked with great care, it may be reduced to thin leaves, and to
wires as small as a needle. See GERMAN SILVER, _infra_.
Tutenag, formerly confounded with white copper, is a different
composition from the above. Keir says it is composed of copper, zinc,
and iron; and Dick describes it as a short metal, of a grayish colour,
and scarcely sonorous. The Chinese export it, in large quantities, to
India.
COPPER, WHITE, or _German silver_. M. Gersdorf, of Vienna, states, that
the proportions of the metals in this alloy should vary according to the
uses for which it is destined. When intended as a substitute for silver,
it should be composed of 25 parts of nickel, 25 of zinc, and 50 of
copper. An alloy better adapted for rolling, consists of 25 of nickel,
20 of zinc, and 60 of copper. Castings, such as candlesticks, bells,
&c., may be made of an alloy, consisting of 20 of nickel, 20 of zinc,
and 60 of copper; to which 3 of lead are added. The addition of 2 or
2-1/2 of iron (in the shape of tin plate?) renders the packfong much
whiter but, at the same time, harder and more brittle.
Keferstein has given the following analysis of the genuine German
silver, as made from the original ore found in Hildburghausen, near
Suhl, in Henneberg:--
Copper 40·4
Nickel 31·6
Zinc 25·4
Iron 2·6
-----
100·0
Chinese packfong, according to the same authority, consists of 5 parts
of copper, alloyed with 7 parts of nickel, and 7 parts of zinc.
The best alloy for making plummer blocks, bushes, and steps for the
steel or iron gudgeons, and pivots of machinery to run in, is said to
consist of 90 parts of copper, 5 of zinc, and 5 of antimony.
A factitious protoxide of copper, of a fine red colour, may be made by
melting together, with a gentle heat, 100 parts of sulphate of copper,
and 59 of carbonate of soda in crystals, and continuing the heat till
the mass become solid. This being pulverized, and mixed exactly with 15
parts of copper filings, the mixture is to be heated to whiteness, in a
crucible, during the space of 20 minutes. The mass, when cold, is to be
reduced to powder, and washed. A beautiful metallic pigment may be thus
prepared, at the cost of 2_s._ a pound.
All the oxides and salts of copper are poisonous; they are best
counteracted by administering a large quantity of sugar, and
sulphuretted hydrogen water.
The following scientific summary of copper ores in alphabetical order
may prove acceptable to many readers, amid the present perplexing
distribution of the native metallic compounds in mineralogical systems.