IM- PROVEMENTS IN PROCESSES OR MEANS. EMPLOYED FOR SEPARATING OR EXTRACTING SILVER FROM LEAD
Year: 1861

page_text: LETTERS PATENT to George Henry Birkbeck, of the Firm of Tongue &
Birkbeck, of 34, Southampton Buildings, Chancery Lane, in the County
of Middlesex, Patent Agents & Engineers, for the Invention of "IM-
PROVEMENTS IN PROCESSES OR MEANS. EMPLOYED FOR SEPARATING OR EXTRACTING
SILVER FROM LEAD."-A communication from abroad by Jules Frederic
de la Batie, Advocate, of Paris, in the Empire of France.
Sealed the 1st April 1862, and dated the 23rd October 1861.
PROVISIONAL SPECIFICATION left by the said George Henry Birkbeck
at the Office of the Commissioners of Patents, with his Petition, on the
23rd October 1861.
I, GEORGE HENRY BIRKBECK, of the Firm of Tongue & Birkbeck, of 34,
Southampton Buildings, Chancery Lane, in the County of Middlesex, Patent
Agents & Engineers, do hereby declare the nature of the Invention for "IM-
PROVEMENTS IN PROCESSES OR MEANS EMPLOYED FOR SEPARATING OR EXTRACTING
SILVER FROM LEAD," to be as follows:-
This Invention has for its object improvements in the processes or means
employed for separating or extracting silver from lead by incorporating zinc
therewith, which process in itself is not new, this Invention depending on a
series of improved processes for this purpose.

page_text: In carrying out this Invention the first operation consists in fusing the lead
containing silver and incorporating the zinc therewith. For this purpose a
suitable furnace is provided with a melting pot or vessel, in which the lead and
zinc are melted, the zinc being placed in suitable tubes or holders, and
deposited, after the lead is melted, at the bottom of the vessel, so that as it melts
it rises up through the molten lead by reason of its less specific gravity, and. by
means of agitators it is uniformly distributed in its passage through the fluid
lead. When the whole of the zinc is melted and has risen to the surface of
the molten lead, the zinc holders and the agitators are removed from the vessel,
and the alloy of zinc and silver is skimmed off the surface, to be operated upon
as hereafter described. The molten lead, which now contains a small per-
centage of zinc, is next run off into the hollow of a reverberatory furnace, such
as is generally used for annealing and refining lead, and the zincy lead is
purified by keeping it in a state of fusion at a dull red heat and subjecting it
to the action of the vapours or gases arising from the burning or decomposition
of pieces of green' wood enclosed in suitable tubes or holders below the surface"
of the molten lead; the dross of the zinc (called seconds) is skimmed off
during the process, and is added in another process to the alloy of zinc and
silver previously obtained. The lead thus refined is run into ingots for sale
or use. *
The next operation consists in separating the lead mechanically mixed with
the alloy of zinc and silver; for this purpose the alloy is placed upon gratings
or perforated plates in a closed vessel or chamber, under and partly around
which the waste flame and heat from the boiler or the reverberatory furnace
is conducted by suitable flues, so as to subject the alloy to a heat not exceed-
ing 350° Réaumur. The lead with the zinc deposited on the inclined bottom
of the closed vessel is added to the next annealing process. The "second
dross" of the annealing operations and the eliquated alloy proceeding from the
last operation are treated successively in a furnace, similar to the ordinary
'cupel" furnace; the bed of the furnace is not prepared as is usual in such
furnaces with calcined bones, but with a mixture of clay and quicklime in
about equal parts, well sifted and beaten down. A bath of lead is introduced
into the bed of the "cupel" furnace, and litharge is produced in the ordinary
manner; rich dross is also produced by treating it with coal dust and air from
a fan or bellows. By the combustion of the zinc it is converted into an oxide
of zinc, the silver being liberated is concentrated in the bath of lead contained
in the "cupel" furnace. The black litharge is abstracted after being acted
upon by the fire by a suitable orifice. The lead is run off when sufficiently

page_text: rich in silver (2 or 3 per cent.), by allowing it to escape through a central
orifice in the bed of the furnace, which is then restored ready for a fresh
charge.
The management of the fire and regulation of the heat of the furnace is of
great importance, and requires considerable practice to avoid the loss of great
quantities of silver. The principle upon which this manipulation depends is
essentially as follows:-The simultaneous oxidation of the lead and of the zinc
of the alloy, the liberation of the metallic silver, and its introduction into the
lead of the bath, the formation of a dross with the ashes or dust of coal, the
excess of the litharge, and the oxide of zinc; this dross being treated by
the following process, which consists in working the black litharge or trans-
formation of the residues with zinc or black litharge in silver bearing lead. As
in the residues of zinc or black litharge (the term used to designate the dross
obtained from the previous operation), there is a certain amount of lead and
silver, the proportion of the silver being in accordance with the amount of
concentration in the bath of lead, and which it is necessary to extract by a
special process (which is that about to be described). The litharge is placed
in crucibles with about half its weight of "basic" and of black soap, the cru-
cibles (of cast iron) are introduced into an air furnace heated with coke, the
construction of which will be fully described and shewn in the Complete Speci-
fication of this Invention.
The products of this melting process are, first, lead containing silver, directly.
capable of "cupellation" in small quantities; and, secondly, of dross, very rich
in lead and in zinc, which are reduced in a cupola furnace. The latter must
always be melted separately, for the lead obtained therefrom is very hard, and
requires to be annealed separately.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said George Henry Birkbeck in the Great Seal Patent Office, on
the 23rd April 1862.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, GEORGE
HENRY BIRKBECK, of the Firm of Tongue & Birkbeck, of 34, Southampton.
Buildings, Chancery Lane, in the County of Middlesex, Patent Agents and
Engineers, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-third day of October, in the year of our Lord

page_text: One thousand eight hundred and sixty-one, in the twenty-fifth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me, the
said George Henry Birkbeck, Her special licence, that I, the said. George
Henry Birkbeck, my executors, administrators, and assigns, or such others as
I, the said George Henry Birkbeck, my executors, administrators, and assigns,
should at any time agree with, and no others, from time to time and at all
times thereafter during the term therein expressed, should and lawfully might
make, use, exercise, and vend, within the United Kingdom of Great Britain
and Ireland, the Channel Islands, and Isle of Man, an Invention for "IM-
PROVEMENTS IN PROCESSES OR MEANS EMPLOYED FOR SEPARATING OR EXTRACTING
SILVER PROM LEAD," a communication to me from abroad by Jules Frederic de
la Batie, Advocate, of Paris, in the Empire of France, upon the condition
(amongst others) that I, the said George Henry Birkbeck, my executors
or administrators, by an instrument in writing under my, or their, or one of
their hands and seals, should particularly describe and ascertain the nature of
the said Invention, and in what manner the same was to be performed, and
cause the same to be filed in the Great Seal Patent Office within six calendar
months next and immediately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said George Henry Birkbeck, do hereby
declare the nature of the said Invention, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement thereof, that is to say :-.
This Invention has for its object improvements in the processes or means
employed for separating or extracting silver from lead by incorporating zinc
therewith, which process in itself is not new; this Invention depending on a
series of improved processes for this purpose..
In carrying out this Invention, the first operation consists in fusing the lead
containing silver, and incorporating the zinc therewith. For this purpose a
suitable furnace is provided with a melting pot or vessel, in which the lead
and zinc are melted, the zinc being placed in suitable tubes or holders, and
deposited after the lead is melted at the bottom of the vessel, so that as it
melts it rises up through the molten lead by reason of its less specific gravity,
and by means of agitators it is uniformly distributed in its passage through the
fluid lead. When the whole of the zinc is melted and has risen to the surface
of the molten lead the zinc holders and the agitators are removed from the
vessel and the alloy of zinc and silver is skimmed off the surface to be operated
upon, as hereafter described. The molten lead, which now contains a small
per-centage of zinc, is next run off into the hollow of a reverberatory furnace,

page_text: such as is generally used for annealing and refining lead, and the zincy lead is
purified by keeping it in a state of fusion at a dull red heat, and subjecting it
to the action of the vapours or gases arising from the burning or decomposition
of pieces of green wood enclosed in suitable tubes or holders below the surface
of the molten lead. The dross of the zinc (called seconds) is skimmed off
during the process, and is added in another process to the alloy of zinc and
silver previously obtained. The lead thus refined is run into ingots for sale
or use.
The next operation consists in separating the lead mechanically mixed with
the alloy of zinc and silver. For this purpose the alloy is placed upon gratings
or perforated plates in a closed vessel or chamber under and partly around
which the waste flame and heat from the boiler or the reverberatory furnace is
conducted by suitable flues, so as to subject the alloy to a heat not exceeding
350° Reaumur. The lead, with the zinc deposited on the inclined bottom, of
the closed vessel, is added to the next annealing process. The "second dross"
of the annealing operations, and the eliquated alloy proceeding from the last
operation are treated successively in a furnace similar to the ordinary "cupel"
furnace; the bed of the furnace is not prepared, as is usual in such furnaces,
with calcined bones, but with a mixture of clay and quicklime in about equal
parts, well sifted and beaten down. A bath of lead is introduced into the bed
of the "cupel" furnace and litharge is produced in the ordinary manner; rich
dross is also produced by treating it with coal dust and air from a fan or
bellows. By the combustion of the zinc it is converted into an oxide of zinc,
the silver being liberated is concentrated in the bath of lead contained in the
"cupel" furnace. The black litharge is abstracted after being acted upon by
the fire by a suitable orifice. The lead is run off when sufficiently rich in
silver (2 or 3 per cent.) by allowing it to escape through a central orifice in'
the bed of the furnace, which is then restored ready for a fresh charge.
The management of the fire and regulation of the heat of the furnace is of
great importance, and requires considerable practice to avoid the loss of great
quantities of silver. The principle upon which this manipulation depends is
essentially as follows:-The simultaneous oxidation of the lead and of the zinc
of the alloy, the liberation of the metallic silver, and its introduction into the
lead of the bath, the formation of a dross with the ashes or dust of coal, the
excess of the litharge, and the oxide of zinc, this dross being treated by the
following process, which consists in working the black litharge or transforma-
tion of the residues with zinc or black litharge in silver bearing lead.
As in the residues of zinc or black litharge (the term used to designate the

page_text: dross obtained from the previous operation), there is a certain amount of lead
and silver, the proportion of the silver being in accordance with the amount of
concentration in the bath of lead, and which it is necessary to extract by a
special process (which is that about to be described). The litharge is placed in
crucibles, with about half its weight of "basic" and of black soap, the crucibles
(of cast iron) are introduced into an air furnace heated with coke, the con-
struction of which is herein fully described and shown in the Drawing here-
unto annexed. The products of this melting process are, first, lead containing
silver directly capable of "cupellation" in small quantities, and, secondly, of
dross very rich in lead and in zinc, which are reduced in a cupola furnace.
The latter must always be melted separately for the lead obtained therefrom
is very hard, and requires to be annealed separately.
And in order that the Invention may be most fully understood and readily
carried into practice, I will proceed to describe the Drawing hereunto
annexed.
DESCRIPTION OF THE DRAWING.
In carrying out this Invention, five distinct operations or processes are
employed, which consist, first, in fusing or melting the lead containing silver,
and incorporating the same with zinc; second, softening or annealing the
desilvered lead; third, the eliquation of the alloy of zinc and silver; fourth,
the transformation of the alloy of zinc and silver obtained from silver bearing
lead capable of cupellation; fifth, the transformation of the residues of zinc in
lead capable of cupellation.
The order of the zinc process is as follows:-First, to concentrate the
silver (by dissolving it) into a small portion of metal (from about to 3 per
cent. of the weight of silver bearing lead according to the quantity contained);
second, to restore it by oxidation with a very small quantity of lead, which
then becomes capable of cupellation.
The following is the synoptical table of the operations :-
[See opposite.]
First operation. Fusion of the lead and incorporation of the zinc in the
melting pot or vessel shown in Figures 1 to 4 of the Drawing.
Figure 1 shows a transverse section of the desilvering melting pot or vessel;
Figure 2 is a plan; Figure 3 is a transverse section through the line 1, 2, of
Figure 2; and Figure 4 shows an external view of the same. The melting
tank or vessel X, formed with the flange N, rests on the cast-iron table or
plate M placed in the upper part of the furnace R; the boiler is likewise

page_text: curved by the blocks t placed in the body of the furnace. The plate O forms
a division for the flues surrounding the melting vessel X, which arrangement
effects great economy in the combustion, of the fuel. The flame from the
lower flues passes into the upper flue through the opening G, which is regu-
lated by a damper; S shows the outlet passage for the products of com-
bustion, the opening u serving to pick or clear the fire-bar V, underneath which
is the ash-pit Z. n is a small orifice for the purpose of conveying away the
smoke when it is necessary to light up to heat, or for the purpose of heating
the key or plug for discharging when it is desired to discharge the lead; f is
a discharge pipe which carries the plug or key for discharging or casting, con-
sisting of a lever jointed upon the part a at the point e, and terminating by a
handle d. This lever is pressed against the barrel or pipe W placed at the
centre of the discharge pipe f of the vessel X by a set screw tapped into the
arched piece b; this apparatus is bolted upon the flange 9 of the discharge
pipe f. The letters h show the notches or nicks which secure the axes of the
beaters or agitators B (Figure 3); these agitators are jointed at p upon a
connecting rod by means of the rod or bar k. The rings L are adjusted in
the notches g by a flat bar H bolted at its ends, as seen at y, Figure 5.
Manipulation. The lead being melted, the zinc is incorporated with it in
the melting vessel in the following manner :-The zinc moulded or cast in
cylinders is placed in the tubes or holders T (shown separately at Figures 6,
7, and 8), which are introduced into the melting vessel X in the position
shown at Figure 3, where they are fixed by wedges in the rings L fixed in
the notches g. The heat is then raised to about 370° Reaumur in order to
melt the zinc in the tubes or holders. The agitators B supported in the
melting vessel ✗ are then put in motion, and the zinc, owing to its less
specific gravity, rises to the surface, passing upwards through the holes or
orifices d in the upper surface of the cylinders or tubes T. When all the zinc
has risen to the surface of the lead, the tubes T are withdrawn, together with
the agitators B, and the alloy is skimmed off the surface. The next process
after this operation consists in running off the desilvered lead into the bed or
hollow of a reverberatory furnace when the second operation commences, which
consists in annealing the desilvered lead containing zinc. In place of causing
the beaters or agitators to move in the lead to equalize the action of the zinc,
the operating tube T may be alone employed, and furnished with a rather
long rod or handle, in order that it may be taken by the workman, and be let
down easily to the bottom of the vessel X. The holes or perforations are dis-
tributed according to the character of the cylinder, and upon half of the external

page_text: surface thereof. When the tube T has received a proper supply of zinc into
its interior and the lid has been refixed, the workman then lowers it down to
the bottom of the lead to be desilvered, and moves it backwards and forwards
under the bath from end to end of the vessel X. This operation prevents the
formation of oxydized dross, and saves a great expense in zinc; this last evil
is likewise diminished by the use of a deep melting vessel X by the previous
refining of the lead containing foreign matters. As the scum does not rise for a
period of 2 or 3 hours during that interval of time the same operation may be
carried on in another melting vessel ✗ placed side by side; by this arrange-
ment double the quantity of material may be treated in the same time. The
desilvered lead, containing from to per cent of zinc renders it unfit for
many purposes, and in order to purify it from or remove the zinc, it is intro-
duced, as before stated, into a reverberatory furnace of similar construction to
those which are commonly employed in lead works for annealing and refining
brittle or rough lead. The purification of the zincky lead is accomplished by
keeping it in a state of fusion at a dull red heat, and by mixing it with pieces
of green wood enclosed in tubes T similar to those previously described.
The dross of the zinc (called seconds) is skimmed off, and is added to the
alloy of zinc and silver obtained direct from the first melting, being previously
submitted to the process herein-after described (called eliquation). The
refined lead is run into ingots such as are usually sold. It may be remarked
here, that the scum ought to be formed at a low temperature as long as there
is plenty of zinc in the lead; but when the surface of the bath forms crusts
with difficulty, and requires a long time to do so, it is necessary to raise
the temperature to the height required for melting silver ore (litharge) by
increased heat, in order to cleanse the lead properly, and to render it saleable.
The greatest care must be used in the process for making the metal into pigs,
in order to prevent the presence of zinc. The refined lead thus formed into
ingots is suitable for sale or manufacturing purposes.
Description of third process called eliquation.-This process has for its
object the separation from the alloy of zinc and silver of the lead mechanically
mixed therewith; this is effected by submitting the alloy in a close vessel to a
heat below 360° Reaumur. The apparatus suitable for this purpose may be
arranged as shown at Figure 9. The division or chamber a is furnished with
two gratings 9 placed a short distance one above the other (or perforated
plates may be employed). The alloy of zinc and silver o placed in the
chamber a is heated by the waste heat from the melting vessel or from the
reverberatory furnace, the flues or passages Q, T, from which partly surround

page_text: the bottom, sides, and back of the chamber a, which may be made of cast-
iron, furnished with a door p and fastenings q, as shewn. The apparatus may
be simplified, and be reduced to a vessel made of strong sheet metal inclined
about 20 degrees, and terminated by a crucible situated at the bottom of the
door, and heated by a special fire arranged in the body of the brickwork of
the melting vessel for desilvering. There is in the same setting two cast-iron
melting vessels for the zincing and two in sheet metal for the melting pro-
cesses. When the lead is very rich (from 250 to 500 grammes for 100
kilogrammes) the eliquation may be suppressed, as it is generally necessary
to add some lead to the succeeding operation, an addition that may thus be
avoided.
65
Description of fourth process, for treating the dross containing silver and
zinc, or for the transformation of the alloy of zinc and silver, obtained as before
described, and capable of culpellation. The "second dross" of the annealing
operation, and the eliquated alloy obtained from the last (third) described pro-
cess, are treated successively in a furnace similar to what is known as the
cupel furnace." The bed or body of the furnace is not prepared as is usual
in such furnaces, with calcined bones, but with a mixture of clay and quick-
lime, in about equal parts well sifted and beaten down. A bath of lead is
introduced into the bed of the furnace as shown at Figures 10 and 11, and
litharge is produced in the ordinary manner. Rich dross is also produced by
treating it with coal dust, and introducing a blast of air from a fan or bellows.
By the combustion of the zinc, it is converted into an oxide of zinc at the same
time, the silver being liberated is concentrated in the bath of lead contained in
the cupel furnace. The black litharge is abstracted after being acted upon by
the fire, by means of the semi-annular orifice V. When the lead is sufficiently
rich in silver, (2 or 3 per cent), it is allowed to run off through the central
orifice s. The bed a, b, of the furnace is then restored, the hole s being.
stopped, and a fresh charge introduced.
.
The management of the fire, and the regulation of the heat, is of great.
importance, and requires practice and judgment in order to avoid the loss;
of valuable quantities of silver, and the principle upon which the manipulation
depends is essentially as follows:-First, the simultaneous oxydation of the
lead, and of the zinc of the alloy. Second, the liberation of the metallic
silver. Third, its introduction into the lead of the bath. Fourth, the,
formation of a dross with the ashes of the coal, the excess of the litharge;.
and the oxide of zinc, this dross being treated by the fifth operation or process.
The construction of the ordinary cupel furnace, being well understood in

page_text: metallurgy, it will not be necessary to illustrate the same by a Drawing.
This operation, instead of being performed in an ordinary refining vessel, may
be carried out in a simple reverberating furnace with cast-iron bottom without
inclination. The manipulation would remain the same as that above described,
except the application of the blast, which gives occasion to some loss of silver.
The essential point is to obtain a strong, slow oxidation of the zinc, and the
introduction of the metallic silver in an abundant bath of lead underneath.
As to the complete oxidation of the zinc, it is necessary to avoid too high a
temperature as it is formed by the oxide of lead retained by the dross; suffi-
cient fire is applied to make this lead rich, by casting into the mass 1 to 2
per cent. of fine pit coal, which should be incorporated with care.
The fifth operation consists in treating or working the black litharge, or
the transformation of the residues in silver bearing lead capable of cupel-
lation. As in the residues of zinc or black litharge (the term used to de-
signate the dross obtained from the previous process), there is a certain amount
of lead and silver, the proportion of the latter being in accordance with the
amount of concentration in the bath of lead, which it is necessary to extract
by a special process now about to be described. The litharge is placed in
crucibles with about half its weight of "scoria of basic," and of black soap.
The cast iron crucibles B are introduced into an air furnace (shown at Figure
12) heated with coke; P is a platform or surface, upon which the crucibles
Bare placed near the edge of the furnace bars 9, as shown; X is the ash-pit;
S are suitable openings in the sides of the furnace to introduce and withdraw
the crucibles; B and k are doors or openings which, together with the iron
bars or plates A, A, support the arch V which covers in the furnace. The
products of combustion are conducted away by the flues o, o, into the chimney
C. The products obtained from this melting process are, first, lead containing
silver capable of cupellation in small quantities, and, secondly, of dross very rich
in lead, and in zinc, which may be reduced in a cupola furnace. The latter
products must always be melted separately, for the lead obtained therefrom
is very hard, and requires to be annealed separately.
The working of the black litharge may be effected with greater certainty, in
the reverberatory reducing furnace by the addition of 10 per cent. of small
pit coal. The furnace must have a high temperature, and the bottom a
considerable inclination. It is the ordinary revivification, only the scoria or
dross remains in a refractory state, and only shows here and there some small
globules of lead undetached. This lead thus obtained of good quality.
Having thus fully described the nature of the Invention, and the best means

page_text: for carrying the same into practice, it should be clearly understood that the
arrangement of the several parts of the apparatus, together with the mode
of working the several processes may be greatly varied without departing
from the peculiar character of the Invention herein fully described and set
forth.
In witness whereof, I, the said George Henry Birkbeck, have hereunto set
my hand and seal, this Twenty-third day of April, in the year of our
Lord One thousand eight hundred and sixty-two.
0 Witness,
GEORGE HENRY BIRKBECK. (L.S.)
J. G. TONGUE, Agent Patent,
34, Southampton Buildings.