AN IMPROVED METHOD OF TOUGHENING BRITTLE GOLD BULLION, OF REFINING ALLOYED GOLD
Year: 1867

page_text: LETTERS PATENT to Francis Bowyer Miller, of the City of Sydney, in the
Colony of New South Wales, Assayer, for the Invention of "AN IMPROVED
METHOD OF TOUGHENING BRITTLE GOLD BULLION, OF REFINING ALLOYED GOLD,
Sealed the 10th December 1867, and dated the 17th June 1867.
PROVISIONAL SPECIFICATION left by the said Francis Bowyer Miller
at the Office of the Commissioners of Patents, with his Petition, on the
17th June 1867.
I, FRANCIS BOWYER MILLER, of the City of Sydney, in the Colony of New
South Wales, Assayer, do hereby declare the nature of the said Invention
for "AN IMPROVED METHOD OF TOUGHENING BRITTLE GOLD BULLION, OF REFINING
ALLOYED GOLD, AND OF SEPARATING THEREPROM ANY SILVER THEY MAY CONTAIN,"
to be as follows:-
This Invention has for its object the toughening of brittle gold bullion, and
the refining of alloyed gold (whether naturally or artificially alloyed) while in
the melted state, together with the separation therefrom of any silver they may
contain. This I effect by means of chlorine gas or hydrochloric acid gas applied.
so that it may rise up amongst and through the alloyed gold in a molten state,
by which means chlorides of silver and of any other baser metals present are
formed and rise to the surface of the melted mass, while the gold remains
beneath in a purified and tough condition.

page_text: The operations requisite may be performed on the sole of a reverberatory or
other furnace, or in retorts made of some refractory material, but in carrying
out my Invention I prefer to employ good clay crucibles. White French
fluxing pots answer well for the purpose. The crucibles are prepared by
dipping them in a strong solution of borax in hot water, and subsequently
drying them; in these the gold to be operated on is melted in the ordinary
manner with the addition of one half per cent. of fused borax, a well-fitting
cover having first been luted over the mouth of each crucible employed. In
this cover are one or more holes to allow of the introduction of a tube or tubes
constructed of some suitable refractory material such as fire-clay descending
to the bottom of the crucible and down through which chlorine gas or hydro-
chloric acid gas is forced while the gold is still in a melted state. After the
chlorine gas or hydrochloric acid gas has been thus passed through the melted
gold for a sufficient time, which necessarily varies according to the quantity
and quality of the gold operated, on the silver and baser metals are converted
into chlorides, and rise to the surface of the refined gold. The more volatile
chlorides partially escape, and the remainder may be removed in any con-
venient manner by pouring the entire contents of the crucible into moulds,
and removing the cake of chloride when cold, or by allowing the gold to cool
sufficiently to set or become solid, but not to become so cold as to prevent the
more fusible chlorides from being poured off and subsequently reduced to the
metallic state by any of the well known methods.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Francis Bowyer Miller in the Great Seal Patent Office on
the 16th December 1867.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, FRANCIS
BOWYER MILLER, of the City of Sydney, in the Colony of New South Wales,
Assayer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Seventeenth day of June, in the year of our Lord
One thousand eight hundred and sixty-seven, in the thirtieth year of Her
reigu, did. for Herself, Her heirs and successors, give and grant unto
me, the said Francis Bowyer Miller, Her special license that I, the said
Francis Bowyer Miller, my executors, administrators, and assigns, or such
others as I, the said Francis Bowyer Miller, my executors, administrators,
and assigus, should at any time agree with, and no others, from time to time

page_text: 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 "AN IMPROVED METHOD OF TOUGHENING BRITTLE GOLD BULLION, OF REFINING
ALLOYED GOLD, AND OF SEPARATING THEREPROM ANY SILVER THEY MAY CONTAIN,"
upon the condition (amongst others) that I, the said Francis Bowyer
Miller, my executors or administrators, by an instrument in writing under
my, or their, or one of their bands 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 Francis Bowyer Miller, 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 the toughening of brittle gold bullion, and
the refining of alloyed gold (whether naturally or artificially alloyed) whilst in
a melted state, together with the separation therefrom of silver they may
contain. This I effect by means of chlorine gas (or hydrochloric acid gas, which
latter should be mixed with atmospheric air or oxygen) brought in contact
with the alloyed gold when the metal is in a molten state; in this manner the
silver present and any baser metals which render the gold brittle are converted
into chlorides whilst the gold remaius in a purified and tough condition.
Having thus stated the nature of my Invention, I will proceed to describe
the manner in which I prefer to operate.
I melt the gold to be operated on in a good clay crucible (plumbago
crucibles are not recommended); the pots known as "creusets de Paris," and
manufactured by Payen, Rue Pierre Levée, Paris, are very suitable, and the
sizes Nos. 12, 14, and 16, are most generally useful; they are suitable for
refining charges of 100, 250, and 500 ounces respectively. I prepare the
crucibles for use by dipping them into a strong and hot solution of borax, and
afterwards drying them ; the object of this preparation is to render them less
liable to absorb the melted chloride of silver; the crucible is heated in a
furnace, and the gold is melted in the usual way with a small quantity of borax,
say three-quarters per cent.; the crucible has a closely fitting cover with a
small hole bored through it, and when the metal is melted a fire-clay tube of,
say three-sixteenths of an inch, internal diameter, is inserted through this hole,
so as to dip into the molten gold down to the bottom of the pot; the upper end

page_text: of this tube is connected by a vulcanized india-rubber pipe with a glass or
stoneware vessel, in which chlorine is generated; the joints are tied round
with wire, and the india-rubber pipe is protected from the direct radiation of
the fire. The chlorine generator is fitted with a safety tube, say six feet long,
dipping at its lower end into the liquid in the generator, and the liquid stands
in this tube to such a height as is equivalent to the pressure necessary to force
the gas through the melted gold which is above the end of the fire-clay tube;
the current of gas through the metal is maintained for about three hours, and
the metal may advantageously be agitated from time to time by stopping the
flow of the gas for a moment by pinching the india-rubber pipe until the
pressure increases, and then allowing the accumulated gas to pass suddenly;
at the end of this operation the gold will be nearly pure, and the chloride of
silver formed will be found floating on its surface, together with such other
chlorides as may be formed and are not readily volatilized. The contents of
the crucible may be poured out altogether into moulds, so as to form ingots,
and the chlorides are in this case detached from the surfaces of the ingots
when they are cold; or by preference, the metal is allowed to cool in the
crucible until it sets, and the still liquid chlorides are then poured from its
surface into a mould, so as to form a slab; the borax is in this operation
retained in the crucible, and in this no difficulty will be found, as it is much
less fluid than the chlorides. The crucible still containing the gold is at once
replaced in the furnace until the purified gold is again melted, and it is then
cast into ingots; the crucible if it is to be used again should not be allowed to
cool, but be replaced in the furnace as soon as the charge is poured. The
chloride of silver and other chlorides mixed therewith are reduced to the
metallic state by one or other of the processes commonly employed for this
purpose, but very conveniently the slab of chlorides may be placed between
two flat pieces of wrought iron and immersed in water acidulated with
sulphuric acid and there left for a day or so until the reduction is complete;
the metal thus obtained is treated with nitric acid. The silver and other
baser metals are dissolved, whilst some gold is left undissolved and is collected
and remelted with other charges, or otherwise. The silver is precipitated
from the solution with common salt, as chloride of silver, by again reducing
which a pure silver may be obtained.
In the process above set forth hydrochloric acid gas mixed with atmospheric
air or oxygen may be passed into the molten gold in place of chlorine; the
operation is in all respects similar, except that a generator of hydrochloric acid
gas is substituted for the chlorine generator, connected by means of a
vulcanized india-rubber pipe with a gasholder, from which air or, by pre-

page_text: ference, oxygen can be supplied under pressure regulated by a stop-cock. A
mixture of hydrochloric acid gas with air or oxygen is thus obtained, which is
passed through the molten gold in the manner above described for the similar
operation with chlorine; this mixture of hydrochloric acid gas with air or
oxygen is however less efficient and convenient than chlorine, more especially
when the object is the separation of the silver rather than the toughening of the
gold by the removal of the baser metals it may contain. A very small quantity
of the silver contained in the alloyed gold will be volatilized during the process,
it may be recovered from time to time by treating the sweepings from the
flues. A much larger but still a small quantity of the chloride of silver is
taken up by the borax or is absorbed in the substance of the crucible; this I
recover by crushing the flux and the crucible when it is past further use, and
treating them with weak ammonia which dissolves out the chloride of silver,
and this is afterwards precipitated by the addition of an acid, and the silver is
reduced from it; or I place the powdered flux and crucible in a revolving
barrel with scrap wrought iron and mercury with sufficient water to form a
thin paste; by this means the silver is recovered as an amalgam, together
with a little gold.
I would remark that the details of the operation may be considerably varied
without departing from the Invention, which consists in bringing the alloyed
gold when in a molten state into contact with chlorine or hydrochloric acid
gas (the latter should be mixed with or be in the presence of atmospheric air
or oxygen) in such manner that the silver or the baser metals it may contain
may be separated from it as chlorides, as herein explained.
In witness whereof, I, the said Francis Bowyer Miller, have hereunto
set my hand and seal, this Seventeenth day of September, in the year
of our Lord One thousand eight hundred and sixty-seven.
Witness,
W. V. TRICKETT,
Solr., Sydney, N. S. W.
FRS. BOWYER MILLER. (L.S.)