IMPROVEMENTS IN THE TREATMENT OF AURIFEROUS, ARGENTIFEROUS, AND OTHER ORES
Year: 1868

page_text: LETTERS PATENT to William Spence, of 8, Quality Court, in the
County of Middlesex, Patent Agent,
for
the Invention of
"IMPROVEMENTS IN THE TREATMENT OF AURIFEROUS, ARGENTIFEROUS, AND
OTHER ORES." A communication from abroad by Louis Edouard
Rivot, of Paris, in the Empire of France, Professor in the
Imperial School of Mines and Engineer in Chief of Mines.
-
Sealed the 2nd February 1869, and dated the 4th August 1868.
PROVISIONAL SPECIFICATION left by the said William Spence at the
Office of the Commissioners of Patents, with his Petition, on the
4th August 1868.
I, WILLIAM SPENCE, of 8, Quality Court, in the County of Middlesex,
Patent Agent, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN THE TREATMENT OF AURIFEROUS, ARGENTIFEROUS, AND OTHER
ORES," (being a communication to me from abroad by Louis Edouard
Rivot, of Paris, in the Empire of France, Professor in the Imperial
School of Mines and Engineer in Chief of Mines,) to be as follows;―
This Invention has reference to ores containing gold and silver, to
those which like the red ores of America are easily treated by methods
Price S

page_text: already known, as well as to ores which yield only imperfect results
when so treated, as, for example, grey coppers, arsenic pyrites, mixtures
of different sulphurets of tellurium.
The Invention includes, two modes of treatment, one of which is
especially applicable to auriferous and argentiferous ores containing
copper, from which it is required to separate the gold, silver, and copper.
The other node of treatment is applicable to gold and silver ores in
which the copper is not required to be separated.
In the first mode of treatment the ores are first ground and intimately
mixed with a suitable proportion of iron pyrites. The ores thus ground
and mixed with iron pyrites are heated by superheated steam in suitable
heating apparatus, but by preference in a rotating cylinder through
which the superheated steam is passed. The heated or roasted ores
are then amalgamated by a simple process of trituration with a suitable
proportion of mercury, but without the addition of any reagents.
The apparatus preferred to be used for this purpose consists of a
circular trough, within which four grinding stones revolve round a
common centre, rakes and scrapes being also carried round with them
and arranged so as to act between them. The next part of the process
is the separation of the amalgams dissolved in mercury in excess from
the dross. This is followed by the compression of the mercury, which
operation is the same as usual, having for its object the separation of a
great part of the free mercury. The remaining operations, consisting
of the distillation of the mercury, the fusion of the precious metals,
and the treatment of the residuums for copper, are conducted as
usual.
The second mode of treatment under this Invention consists of the
following operations:-The ores are first ground and intimately mixed
with a suitable proportion of oxyde of manganese, oxyde of iron, or of
pyrites previously roasted with a blast. The next operation is roasting
or heating by superheated steam the direct amalgamation without the
addition of reagents, and afterwards a series of operations the same as
in the former mode of treatment.
The two modes of treatment differ only in one essential point. in
the first-named mode there is an addition of iron pyrites in order to
provide for the expulsion by the action of steam of nearly the whole
of the arsenic and the antimony, thereby facilitating the requisite treat-
ment of the residuums for copper. In the second mode of treatment

page_text: the ores are submitted to the action of steam, having been previously
mixed with oxyde of manganese, oxyde of iron, or pyrites roasted under
blast in order to obtain as rapidly as possible the result common to
both modes of treatment, that is to say, the extraction of the whole of
the gold and silver in the state of metal. The residuums contain a
considerable proportion of arsenic and antimony and cannot in general
be treated for copper.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said William Spence in the Great Seal. Patent Office
on the 4th February 1869.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
SPENCE, of 8, Quality Court, in the County of Middlesex, Patent Agent.
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Fourth day of August, in the year
of our Lord One thousand eight hundred and sixty-eight, in the thirty-
second year of Her reign, did, for Herself, Her heirs and successors, give
and grant unto me, the said William Spence, Her special licence that
I, the said William Spence, my executors, administrators, and assigns,
or such others as I, the said William Spence, my executors, adminis
trators, 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 "IMPROVEMENTS IN
THE TREATMENT OF AURIFEROUS, ARGENTIFEROUS, AND OTHER ORES" being
a communication to me from abroad by Louis Edouard Rivot, of Paris,
in the Empire of France, Professor in the Imperial School of Mines
and Engineer in Chief of Mines, upon the condition (amongst others)
that I, the said William Spence, 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

page_text: six calendar months next and immediately after the date of the said
Letters Patent.
NOW KNOW YE, that I, the said William Spence, 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; reference being had to the Drawings hereunto
annexed, and to the letters, and figures marked thereon (that is to
say):-
This Invention has reference to ores containing gold and silver, to
those which like the red ores of America are easily treated by methods
already known, as well as ores which yield only imperfect results when
so treated, as, for example, grey coppers, arsenic pyrites, mixtures of
different sulphurets of tellurium.
The Invention includes two modes of treatment, one of which is
especially applicable to auriferous and argentiferous ores containing
copper from which it is required to separate the gold, silver, and copper.
The other mode of treatment is applicable to gold and silver ores in
which the copper is not required to be separated.
In the first mode of treatment the ores are first ground and intimately
mixed with a suitable proportion of iron pyrites. The ores thus ground
and mixed with iron pyrites are heated by superheated steam in suitable
heating apparatus, but by preference in a rotary cylinder, through
which the superheated steam is passed. The heated or roasted ores are
then amalgamated by a simple process of trituration with a suitable
proportion of mercury, but without the addition of any reagents. The
apparatus preferred to be used for this purpose consists of a circular
trough within which four grinding stones revolve round a common
centre, rakes and scrapers being also carried round with them and
arranged so as to act between them. The next part of the process is the
separation of the amalgams dissolved in mercury in excess from the
dross. This is followed by the compression of the mercury, which opera-
tion is the same as usual, having for its object the separation of a great
part of the free mercury. The remaining operations, consisting of the
distillation of the mercury, the fusion of the precious metals, and the
treatment of the residuums for copper, are conducted as usual.
The second mode of treatment under this Invention consists of the
following operations:-The ores are first ground and intimately mixed

page_text: with a suitable proportion of oxyde of manganese, oxyde of iron, or of
pyrites previously roasted with a blast. The next operation is roasting
or heating by superheated steam, then direct amalgamation without the
addition of reagents, and afterwards a series of operations the same as
in the former mode of treatment.
The two modes of treatment differ only in one essential point. In the
first named mode there is an addition of iron pyrites, in order to provide
for the expulsion by the action of steam of nearly the whole of the
arsenic and the antimony, thereby facilitating the requisite treatment of
the residuums for copper.
In the second mode of treatment the ores are
submitted to the action of steam, having been previously mixed with
oxyde of manganese, oxyde of iron, or pyrites roasted under blast in
order to obtain as rapidly as possible the result common to both modes
of treatment, that is to say, the extraction of the whole of the gold and
silver in the state of metal. The residuums contain a considerable
proportion of arsenic and antimony and cannot in general be treated for
copper.
Having thus stated the nature of the said Invention, I will proceed to
describe more particularly in what manner the same is to be performed,
by reference to the accompanying Drawings and the following description
thereof.
DETAILS OF OPERATIONS
First. Grinding and Mixing. The proportion of pyrites in the first
mode of treatment, and that of the oxyde of manganese, of the oxyde
of iron, or pyrites roasted under blast in the second mode, depend on
the nature of the auriferous or argentiferous minerals. They are easily
determined by previous experiments. Some examples are cited which
may serve as instructions for carrying out the processes:-Grey copper
to matrix of ore about fifty per cent. of matrix. Equal parts must be
employed, say one hundred per cent. of iron pyrites nearly free from
matrix, and that in both modes of treatment. Arsenical auriferous
pyrites about fifty per cent. of matrix with quartz will require one
hundred per cent. of pyrites.
In the second mode of treatment the pyrites are roasted under
blast. Sulphur of antimony and mock ore almost without matrix
requires one hundred and fifty per cent. of pyrites. The pyrites are
roasted under blast before passing to the grinding. All the apparatus
employed for grinding and the porphyrisation of ores may be employed

page_text: The
for the purpose. In each case the most economical will be used.
only essential condition is to obtain a reduction to a very fine powder
and a thorough mixture of the gold and silver ores with either crude
or roasted pyrites.
Second operation. Roasting by Superheated Steam.-This operation
may be carried on in furnaces of different kinds, generally in all furnaces
in which it is possible to heat ores (mixed with pyrites crude or roasted)
to a dull red heat by submitting them to the action of superheated steam
protected from the contact of air. The essential condition in effect is
that the steam alone may be free to act on the ore, and that this may be
kept to the temperature of a little below a dull red heat, and in any case
not above such a heat.
Two arrangements of reverberating furnaces are herein-after shown,
and preference is given to a rotating furnace, the application of which
is entirely new in the metallurgy of gold and silver. The furnaces may
be heated, according to economical conditions of different localities, with
wood, oil, or other fuel. The arrangement of the fire-places may be
varied according to the nature of the fuel used, as is well known to
metallurgists.
Reverberating Furnace Heated with Oil.-In Sheet I. Fig. 1 is a
vertical section of this furnace. The oil is supplied on to the fire-place
by the lateral door. The flame passes along the crown of the furnace
and through the flues c into the chimney. The ore is supplied on to the
bottom by the two lateral doors, which serve also for rakings during the
operation. The steam supplied by a generator capable of evaporating
about one cubic metre per hour enters by the pipe a, passes by the four
branches a united by bends and placed against the partition wall of the
bridge and on the bridge itself and reaches the distributing pipe a"; this
pipe is perforated horizontally throughout its whole length with an open-
ing through which the steam expands into a film in the furnace a few
centimetres above the ore.
The operation is conducted in the following manner:-The furnace
being heated to a little above a dull red heat, the ore is charged and
laid regularly over the bottom of a thickness of seven to eight centi-
metres. As soon as the ore is charged the steam is turned on and the
fire stirred so as to bring the ore as soon as possible to a dull red heat
and maintain it thereat or a little above this degree of heat. At regular
intervals the mineral is stirred in order to renew the surfaces in contact

page_text: with the steam.
The operation is finished when there is no longer
any sulphuretted.hydrogen given off; the discharging is then proceeded
with. The supply of steam is stopped and the ore is raked forward
towards the working doors. Should it be preferred the ore may be
caused to fall directly into iron wheel barrows, so as to be carried into a
magazine, or it may be caused to fall into arched spaces formed in the
bottom through two rectangular openings m in front of the working
doors. The continuance of the operation depends on the nature of the
ores; it is very long when grey copper is under treatment if the copper
is required to be withdrawn and a mixture made with a very strong
proportion of crude pyrites. The success of the operation depends
much on the skill of the workman, who has to regulate the fire and
the supply of steam in such a manner that the films of steam may
separate the ores from the flames from the bridge to the flue. Therein
lies a difficulty which would be greater in furnaces heated with wood in
which the flames are very oxydising. In order to avoid this difficulty
a furnace is proposed like that shewn in Figures 2 and 3 of Sheet I.
It is a reverberating furnace in which the frames are separated from
the ore by metal plates arranged horizontally on a level with the
bridge. Fig. 2 is a vertical section of the furnace, and Fig. 3 is a
horizontal section. The flame on issuing from the fire first heats the
pipes a', by which the steam is caused to circulate before expanding
over the ore; it afterwards passes over the metal plates f and makes
them red hot, it finally reaches the chimney by the two flues c.
The
ore is charged on to the bottom by the three lateral doors; it is only
warmed by reverberation from the red-hot plates which causes a little
more rapid consumption of fuel, but it is compensated by the action
of the flames by the metal plates. The operation is carried on as in the
furnace above described.
Thirdly. Rotating Furnace. In this arrangement the ores are placed
in a horizontal metal cylinder of large dimensions. The superheated.
steam enters at one of the ends of the cylinder, the steam in excess
and the products of the action of the steam escape at the other end
of the cylinder and pass into a chimney a little elevated. The cylinder
turns slowly on its axis, this motion by renewing the surfaces in contact
with the steam dispenses with all raking by hand. The cylinder is
arranged in a furnace of particular form heated with wood or mineral
fuel, the flames first superheat the steam and serve also to bring the

page_text: cylinder up to a suitable temperature for the action of the steam, and
they finally pass into the same chimney, which receives the products
issuing from the cylinder.
Figures 4, 5, and 6, Sheet II., represent in longitudinal, horizontal,
and transverse sections this arrangement of rotating furnace. The fuel
is fed through the door p into the fire-place f. The flames are divided
by the wall e which extends up to the crown of the furnace, and they
descend under the cylinder C rising again on the other side in order to
reach the four flues b and become reunited in the horizontal flue a
which conducts them to the chimney B. The steam enters from the
generator by the pipe v' and escapes from the furnace by the third pipe
; this latter is bent into the interior of the furnace, and is connected
by the junction A with the pipe y fixed to the cylinder. Owing to its
passing through the three pipes all surrounded by the flames of the
fire-place the steam is raised to the required temperature. The brick-
work is removed in a line parallel with the cylinder, and on each side
above its axis it is shielded by plates of metal as shewn in the Drawing.
The two partition walls of the furnace corresponding with the two ends of
the cylinder are formed by plates of metal strengthened by four strong
braces. The furnace is covered over the cylinder by iron plates forming a
roof and strengthened by braces. The cylinder C is of iron or other metal
and has in its interior eight projecting ribs. These internal ribs extend
the whole length of the cylinder; the object of them is to force the ore
to change its position during the slow motion of the cylinder, and they
are intended in combination with the rotary motion to produce the effect
of the raking of the ores carried on in reverberatory furnaces. The
external grooves are only useful for holding the three rings m, m³, m¹¹.
These rings have flanges and bear on the three pairs of rollers g, g', g".
The two ends of the cylinder have covers, one of which E carries the
pipe by which the superheated steam enters; it is furnished with two
ports for charging and discharging. The other end E' carries the exit
pipe leading to the chimney; a port is made in this pipe in order to
admit of the attendant observing the nature of the gases which are
emitted by the action of the steam. The partition wall of the chimney
is pierced with a circular hole lined with metal, and of a diameter a
little larger than that of the pipe in order that the latter may turn freely
with the cylinder. Motion is given to the cylinder by means of two
toothed wheels R, R', fitted inside the furnace and fixed on the cylinder
in the same manner as the rings m, m³, m¹¹; these wheels are driven by

page_text: The
the two pinions r, r', fixed on an axle above the cylinder and outside
the furnace. The motion ought to be very slow and adapted to the
degree of tenuity of the ores. In ordinary cases the cylinder would
make only from twenty to thirty revolutions per hour. The admission
of the steam into the cylinder requires a special arrangement.
steam must pass without loss from the stationary pipe of the superheater
into the turning pipe at the end of the cylinder. It is also necessary to
keep out from this latter pipe the external air drawn in by the passage
of the steam. This end can be attained by different arrangements. One
mode is shewn in the section Fig. 2. is the stationary pipe which
receives the steam from the superheater; y is the pipe turning with the
cylinder. The pipe y is a little widened at its extremity and surrounds
with a jet of water the extremity of the pipe ; its ends being smooth
rub against the vertical surface of the small ear o cast with the pipe v¹¹.
The junction of the two pipes is surrounded by the metal box A
closed at one end by the annular ear o cast with the stationary
pipe v
At the other end of the box is carried an annular flange B',
the outer surface of which being slightly conical is carefully ground and
polished. The flange has an opening large enough for the passage of
the enlarged part of the pipe y. This latter is tightly surrounded by a
collar M, the flange of which is formed so as to correspond with the
flange B'. When the two pipes are in position the collar M is pressed
into contact with the flange B'. By this means there is no other outlet
left for the escape of superheated steam or the admission of external air
than very slight joints. For still greater security steam from the boiler
is admitted into the box A by the pipe t. The box A is supported by
a metal frame formed so as to leave a space through which the attendant
may work the requisite tools for charging and discharging the cylinder.
DESCRIPTION OF THE WORKING.
Each operation is divided into three periods, charging, action of the
steam, and discharging.
First Operation. Charging. The cylinder is fixed in the position
shewn in Fig. 4. The two doors P, P', are opened. The ore is charged
through a hopper not shewn in the Drawing; a moveable iron plate
conducts the ore from the hopper into the cylinder by the door P¹;
at the same time an attendant with a rake presses the ore to the bottom
of the cylinder and regulates its thickness. The two doors are then
closed.

page_text: Second Operation. Action of the Steam.-The cylinder is set in
motion, being caused to turn from left to right, that is to say, in the
direction of the movement of the flames passing under the cylinder.
The steam is admitted in such quantity as to have a slow movement
within the cylinder. The fire is stirred so as to bring the cylinder to a
dull red heat. The action of the steam soon commences and the orifice o
of the chimney may be opened.
The time required to complete the roasting varies according to the
nature of the ores under treatment. The following are the tests by
which the completion of the roasting may be ascertained:---First, when
on looking through the orifice o of the chimney no yellow vapor is seen
to escape from the cylinder, and a scarcely sensible vapor is perceived;
secondly, when on introducing through the door I of the outlet pipe a
paper impregnated with a salt of lead (for example, acetate of lead) the
paper is not sensibly injured.
Third Operation. Discharging.-The roasting being completed the
further admission of steam is prevented and the cylinder is stopped in.
the same position as for charging. The two doors P and P¹ are opened;
the attendant by means of a rake causes the ore to fall either on to the
bottom or into iron wheelbarrows, by which it may be carried to any
convenient place.
It may be here remarked with reference to the first mode of treatment
herein-before described that the object in view in the use of superheated
steam is to drive off the arsenic, antimony, and sulphur, to bring the
gold and silver into the state of metal by causing the other metals to
pass into the state of oxydes. The action of steam on sulphurs, arsenic,
and other like substances has been studied by various scientific persons
and engineers, and various speculations have been proposed and experi-
ments made, but not extending to the application to the metallurgy of
copper, gold, and silver. Reference is made to what has been done by
others in order to state that under this Patent it is not intended to claim
any principle but the arrangement of operations and apparatus. Rever-
berating furnaces with metal plates and rotating furnaces are new in the
treatment of gold and silver ores.
With reference to the second of the two modes of treatment herein-
before described an oxydising reagent is used at the same time as the
steam, such as the oxyde of manganese, the oxyde of iron, or of roasted
pyrites, and by that means the present process is distinguished from

page_text: other modes of operation hitherto proposed. The process of roasting
by superheated steam, as described, gold and silver ores mixed with a
due proportion of oxyde of manganese, oxyde of iron, or of iron pyrites
roasted under blast of air is new in the treatment of gold and silver
ores, as also the apparatus described as used for the purpose.
The mode in which the oxydising reagent acts is easily understood.
Taking for example arsenical pyrites mixed with its weight of oxyde
of iron resulting from the roasting of pyrites under blast of air, the
oxide of iron intimately mixed with arsenical pyrites yields the greater
part of its oxygen to the sulphur, the arsenic and the iron of the pyrites
producing sulphuric acid, arsenic acid, and protoxyde of iron. As these
reactions take place in an atmosphere of steam the protoxyde of iron
is constantly brought to the state of a magnetic oxyde, which continues
its oxydising action until all the sulphur, all the arsenic, and all the
iron of the arsenical pyrites become oxidysed. The steam itself acts
on the arsenical pyrites. From the two actions combined there results
great rapidity in the operation. This is a point of essential importance,
for slowness in the action of steam on the mixtures of ores and crude
pyrites has long been an obstacle to the adoption of steam in the treat-
ment of gold and silver ores. In the rotating furnace the roasting by
superheated steam is not continued for more than eight hours for the
most difficult ores mixed with a due proportion of pyrites previously
well roasted in air. In both modes of treatment as described it is
essential for the temperature not to exceed that of a dull red heat, the
reactions are even active at a lower temperature.
AMALGAMATION OF ROASTED ORES.
As roasted ores contain gold and silver in a state of metal dis-
seminated generally in very fine particles in the metallic oxydes and in
the earthy matrices amalgamation consists only in a prolonged tritura-
tion with a due proportion of mercury. It is useless to employ reagents,
such as salt, magistral, or others. The process of amalgamation may
be carried on in all well-known apparatus, revolving butts, American
pans, and generally in all apparatus in which the grannular particles
of roasted ores may be brought in close and prolonged contact with
mercury. For this purpose it is proposed to employ an apparatus which
has not hitherto been used herein, and which is represented in Figures 7
and 8, Sheet III. Fig. 7 is a vertical section in the line 1, 2, of Fig. 8,

page_text: and Fig. 8 is a horizontal section. The roasted ores and the mercury
are placed in the annular trough M, the bottom of which is horizontal;
the trituration is produced by vertical millstones R, R', R", R¹¹, which
are connected by arms to a vertical axle S. Motion is transmitted to
the axle S by the aid of bevil gear T placed below the bed.
To the
same axle are fixed four arnis a, b, c, d, the iron knives A, B, and
the rakes C, D. The use of the knives is to bring constantly under
the millstones the materials which are carried into the corners of the
trough M. The knives serve to divide and separate from the bottom
of the trough the materials broken by the millstones. The combination
of the arms of the four millstones in the box H differs a little from that
of the arms of the knives, as is shewn in Fig. 7. The millstones are
required to roll over materials of different thickness, and consequently
their axes are required to be capable of working at a suitable inclination.
These axes are connected together by braces a¹¹ to prevent them from
bending,, while admitting of the requisite inclination of the axes. The
arrangement of the rakes C, D, and their connection with the arms
are the same as those of the knives. The discharging door is a plate of
metal P moveable in two grooves and closing when it is in position the
continuation of the trough M; it is strengthened externally by braces,
which also support the channel or outlet for the materials Q.
materials pass out of the trough in a state of suspension in water; they
fall into the wooden receptacle R which is large enough to keep in the
mercury, and which is furnished with a wooden cock or tap at the
bottom. The bottom of the receptacle is inclined towards the cock or
tap. The water carrying with it the divided materials pass out of the
receptacle by the wooden spout U and into apparatus adapted to collect
the last portions of mercury. The receptacle R is covered with a lid
having a flanged opening u. The flanges prevent the falling out of the
material.
The
Fourthly. Separation of the Amalgam.-The operation differs in no
essential point from the common practice. The foreign material
separated from the liquid mercury is deposited in wooden vertical butts
in which is put a suitable quantity of fresh mercury. The said foreign
material is put in suspension for several hours by means of suitable
apparatus, as, for example, horizontal arms fixed to a vertical axis turn-
ing slowly. The particles of amalgam fall by degrees on to the surface
of the mercury and are dissolved with more or less rapidity; the upper

page_text: The
portion of the agitated liquid is drawn off at regular intervals.
mercury is withdrawn only at long intervals when it is charged with.
a certain quantity of amalgam. The foreign matter drawn off still
retains some particles of mercury and of amalgam; these are caused
to pass along wooden channels slightly inclined and so arranged as to
cause the said materials to drop from one to another. The argentiferous
and auriferous mercury is collected in channels. The foreign matters
are at last conveyed into depositing, vessels and are kept until they have
been assayed. It may be useful in certain cases to submit them to a
second amalgamation.
Fifthly. Compression of the Mercury.-The liquid mercury contain-
ing the dissolved amalgams is compressed in bags or otherwise. The
operation differs in nothing from that usually practised, its object being
to separate a large portion of the free mercury.
The remaining operations are, sixthly, distillation of the mercury.
Seventhly, fusion of the precious metals. And eighthly, treatment of
the residuums for copper. All these operations are performed in modes
well known to metallurgists.
Having thus described the nature of the said Invention communicated
to me from abroad as aforesaid, I hereby declare that what I claim as.
of the said Invention is,-
First. The several operations herein-before described taken together.
Secondly. The use of superheated steam for roasting auriferous and
argentiferous ores, the ores being intimately mixed with a suitable pro-
portion whether of crude pyrites, oxyde of manganese, oxyde of iron,
or of pyrites previously roasted under blast of air according to the nature
of the minerals, also according to whether or not it is required to extract
copper as well as gold and silver.
Thirdly. The amalgamation without the addition of reagents, thereby
rendering the use of superheated steam for roasting both possible and
economical.
Fourthly. The arrangement of reverberatory furnaces as described,
also rotary furnaces adapted for roasting by means of superheated steam.

page_text: And, lastly. The arrangement of millstones turning in an annular
trough serving for amalgamation, also the carrying on of the operation
in this apparatus as described.
In witness whereof, I, the said William Spence, have hereunto set
my hand and seal, the Fourth day of February, in the year of our
Lord One thousand eight hundred sixty-nine.
Witness,
W. A. JACKSON,
8, Quality Court,
Chancery Lane.
WILLIAM SPENCE. (L.S.)