IMPROVEMENTS IN EXTRACTING SILVER FROM LEAD
Year: 1866

page_text: LETTERS PATENT to Clemens Flemming Flach, of Call (Eifel), in the
Kingdom of Prussia, for the Invention of "IMPROVEMENTS IN EXTRACTING
SILVER FROM LEAD."
Sealed the 24th April 1867, and dated the 31st December 1866.
PROVISIONAL SPECIFICATION left by the said Clemens Flemming Flach
at the Office of the Commissioners of Patents, with his Petition, on the
31st December 1866.
I, CLEMENS FLEMMING FLACH, of Call (Eifel), in the Kingdom of Prussia,
do hereby declare the nature of the said Invention for "IMPROVEMENTS IN
EXTRACTING SILVER FROM LEAD," to be as follows:-
This system of desilvering lead may be divided into the three following
sections:-I. The desilvering lead by zinc; II. The purifying the desilvered
lead; III. The separating the silver out of the lead, zinc, and silver alloy.
No other apparatus is required for these operations except a small blast
furnace such as now used in lead works.
I. For desilvering, the lead and necessary quantity of zinc are melted
and thoroughly amalgamated together by stirring. After remaining at rest
for some time the alloy of lead, zinc, and silver floating on the top is taken
off. It requires for a lead containing 1000 grs. silver to a ton of lead 1p.c.
of zinc. For a lead containing 3000 grs. silver to a ton of lead 14 p.c. of
zinc is required; the remaining lead only contains 5 grs. of silver to the

page_text: ton. The silver alloy taken off as above mentioned is heated in a pot and
similarly treated until so much lead has cooled out of it that it contains 3 to
6 p.c. of silver.
II. The desilvered zinc holding lead is run down in a blast furnace with a
neutral or slightly basic siliceous slag, whereby the zinc will readily be
converted into dross. The run down lead is melted in a pot, and green wood
thrust into it until no trace of zinc and iron is contained in it. The lead
obtained will then be entirely free from other metals, it contains neither iron,
zinc, copper, antimony, or bismuth, lastly comes the desilvering of the silver
alloy.
The process of melting the zinc holding lead in a calcining furnace, and
then removing the remaining zinc in the lead by green wood is of comparatively
slight importance.
III. The alloy of lead, zinc, and silver is likewise run down in a small
blast furnace with the same neutral or weakly basic siliceous slag. The rich
holding lead obtained is then as usual refined in the cupel. The separation
of the metals in the lead zinc silver alloy may also be effected by means
of muriatic or sulphuric acid, the furnace process is however preferred. The
foregoing desilvering process gives a perfectly pure lead and in addition gives
a gain of from 3 to 4 per cent. of silver beyond what can be obtained by other
known methods.
SPECIFICATION in pursuance of the conditions of. the Letters Patent, filed
by the said Clemens Flemming Flach in the Great Seal Patent Office on
.the 29th June 1867.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, CLEMENS
FLEMMING FLACH, of Call (Eifel), in the Kingdom of Prussia, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Thirty-first day of December in the year of our
Lord One thousand eight hundred and sixty-six, in the thirtieth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me, the
said Clemens Flemming Flach, Her special licence that I, the said Clemens
Flemming Flach, my executors, administrators, and assigns, or such others
as I, the said Clemens Flemming Flach, 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

page_text: Britain and Ireland, the Channel Islands, and Isle of Man, an Invention
for "IMPROVEMENTS IN EXTRACTING SILVER FROM LEAD," upon the condition
(amongst others) that I, the said Clemens Flemming Flach, my exccutors
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 Scal Patent Office within six calendar
months next and immediately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Clemens Flemming Flach, 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 system of desilvering lead may be divided into the three following
sections:-I. The desilvering the lead by zinc; II. The purifying the desilvered
lead; III. The separating the silver from the alloy of lead, zinc, and silver.
With the exception of a small blast furnace no other apparatus or utensils are
required for these operations beyond such as are now for the most part used in
all lead works.
I. The essential conditions under which lead can be completely desilvered
with the smallest quantity of zinc consists in this, that the lead must have a
temperature of from 600° to 700° centigrade, or a complete alloy of silver
with zinc will not take place, and that except when large quantities of zinc
are employed the desilvering never follows in one operation, but the necessary
quantity of zinc must be distributed over two or three operations. For
desilvering also the lead must be placed in a pot furnished at the bottom
with a draw off tube and cock, and be heated to, from 600° to 700° centigrade,
then from to 1 per cent. of zinc, according to the amount of silver in the
lead, is put in and both mixed together by stirring, after three hours rest
and cooling the alloy of lead, zinc, and silver floating on the top is taken
off, and the operation is repeated two or three times with the addition of a
small amount of zinc. It requires zinc for lead for the three operations. For
a lead containing―

page_text: silver; the taken off silver alloy is highly heated in a pot by which so much lead
is cooled out that it then holds only from 3 to 8 p.c. silver. The cooled
out zinc holding lead containing about 200 grammes silver will in one
operation by placing in ½ p.c. zinc be brought down to 5 grammes silver in a
ton of lead.
•
II. The desilvered lead which contains zinc is then run down in a blast
furnace; this is effected most advantageously with a siliceous slag containing
about 33 per cent. siliceous earth. Several materials may be used, as slags
for example, iron slag, artificial or natural marl, lime, or argillaceous ironstone
and others; these, however, arc all when necessary brought by means of sand
or lime to contain the above per-centage of siliceous earth, whereby the zinc
oxide produced will be casily converted into dross. In order to have the
least loss of lead it is essential that the pressure of the air should be only
equal to 6-4 inches water pressure. The run down lead is melted in a pot,
and green wood placed in it, whereby the slight trace of zinc and iron remaining
therein is removed; the lead obtained is then free from other metals; it
contains neither iron, zinc, copper, antimony, or bismuth. It is only when
the antimony in the lead exceeds 10 per cent. that any trace of antimony is
left in the desilvered lead; in this case for removing the antimony the run
down lead must be placed in a calcining furnace and brought to a red heat,
or still better, some common salt is placed in the run down lead. In place
of melting down in a blast furnace one can also melt in a calcining furnace
the desilvered lead, which will be alloyed with zinc and then remove the
zinc still remaining in the lead by green wood; also without a blast furnace
or calcining furnace merely by keeping the lead heated for some hours
with wood, the whole of the zinc will be removed; the blast furnace process
is however to be preferred. Up to this time it was unknown that zinc could
be completely removed from lead by the use of green wood; steam can also
be employed.
III. The alloy of lead, zinc, and silver is likewise run down in a small
blast furnace with siliceous slag, only in this case the slag must contain
about 36 per cent. of siliceous earth. In the melting down no loss of silver
will be found to have taken place, and the pressure of air used therewith
should amount to 18 centimètres of water pressure; the rich lead obtained
is then as usual refined in the cupel. The zinc oxide can be taken off by a
comb or water apparatus; it also succeeds well to bring about the separation
of the metals in the alloy of lead, zinc, and silver by the wet way by means
of sulphuric or muriatic acid; the blast furnace process is however preferable
By the process of distilling off the zinc from the silver alloy too much loss of

page_text: silver arises. The desilvering of lead by zinc was first attempted by Parkes,
no gain was however found in the process because the method from want of
knowledge of the essential conditions was not economical and the lead always
remained alloyed with zinc.
According to my system not only is the desilvering entirely accomplished,
but (principally by the employment of the blast furnace process) this desilvering
process has become of great practical value.
By my system, which has many advantages, an entirely pure lead is
obtained, and there is in addition a gain of from 3 to 4 per cent. of silver as
compared with the old mode of treatment by Pattinson's process.
In witness whereof, I, the said Clemens Flemming Flach, have hereunto
hand and seal, this Twenty-fifth day of June, in the year of our
Lord One thousand eight hundred and sixty-seven.
set my
CLEMENS FLEMMING FLACH. (L.S.)