IMPROVEMENTS IN SEPA- RATING SILVER FROM OTHER METALS
Year: 1852

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ALEXANDER
PARKES, of Birmingham, send greeting.
WHEREAS Her present most Excellent Majesty Queen Victoria, by Her
Royal Letters Patent under the Great Seal of the United Kingdom of Great
Britain and Ireland, bearing date at Westminster, the Eighth day of March,
(One thousand eight hundred and fifty-two), in the fifthteenth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me, the
said Alexander Parkes, my exors, admors, and assigns, Her especial licence,
full power, sole privilege and authority, that I, the said Alexander Parkes, my
exors, admors, and assigns, or such others as I, the said Alexander Parkes,
my exors, admors, or assigns, should at any time agree with, and no others,
from time to time and at all times during the term of years therein expressed,
should and lawfully might make, use, exercise, and vend, within the Islands of
Jersey, Guernsey, Alderney, Sark, and Man, and in all Her Majesty's
Colonies and Plantations abroad, my Invention of "IMPROVEMENTS IN SEPA-
RATING SILVER FROM OTHER METALS;" in which said Letters Patent is contained
a proviso, that I, the said Alexander Parkes, shall cause a particular descrip-
tion of the nature of my said Invention, and in what manner the same is to be
performed, by an instrument in writing under my hand and seal, to be inrolled
in Her Majesty's High Court of Chancery within six calendar months next
and immediately after the date of the said in part recited Letters Patent, as in
and by the same, reference being thereunto had, will more fully and at large
appear.
NOW KNOW YE, that in compliance with the said proviso, I, the said
Alexander Parkes, do hereby declare that the nature of the said Invention,

page_text: and the manner in which the same is to be performed, are fully described and
ascertained in and by the following statement thereof, that is to say:-
They consist, first, of certain improvements in the methods of employing
zinc for the purpose of separating silver from lead.
And secondly, of improvements in afterwards separating the silver from the
alloy of zinc and other metals produced by the first-mentioned process.
In the Specification of a former Patent granted to me on the Eleventh day
of June, One thousand eight hundred and fifty, among other matters I
described the separating of silver from lead by the use of zinc, and I have
discovered that when lead contains a very small proportion of silver as com-
pared with what was formerly described, that different proportions of zinc than
those formerly mentioned are required, and the same should be varied accord-
ing to the actual quantity of silver, in order most conveniently to separate
such small quantities from the lead. And in order that my Invention may be
better understood, I will now describe the best method I am acquainted with
for carrying the same into effect.
I take the lead, from which I wish to extract the silver, in the ordinary state
in which it comes from the smelting furnace, and melt it in an iron pot of
any convenient capacity, introducing a piece of green timber for the purpose
of removing as much of the impurities as possible, as is well understood. I
add thereto a certain quantity of melted zinc, dependent on the quantity of
silver present in the lead, which quantity is previously ascertained by assay,
and I stir or agitate the whole well together for several minutes to secure an
intimate admixture.
The lead, previous to the addition of the zine, should be heated to the
temperature of melted zinc, and after the mixing has been properly effected
should cool down gradually, so as to allow the zinc and silver to rise to the
surface. As regards the quantity of zinc to be used, I have found the propor-
tion of one part of zinc to every hundred parts of the lead to be desilverized,
when such lead contains fourteen ounces of silver per ton, is sufficient, and in
the same ratio for a greater or less quantity of silver; for example:-
IL

page_text: the mixed metals have been cooled down and the lead is about to set,
the zinc and silver having risen to the surface, I remove the alloy of
these metals from the surface of the melted lead by means of a skinner
or flat perforated ladle. I have found that lead which has been treated
with zinc to remove silver therefrom retains a quantity of zinc which is
prejudicial to the lead, making it brittle; and I have also found that such
zinc may be removed from the lead in the following manner:-I run such
lead whilst still melted into a heated reverberatory furnace, I allow it to
remain in this furnace until it becomes of a dull red heat, at which point I
find that the zinc rises to the surface of the lead and there becomes oxidised,
I then tap the lead into an iron pot and pole it with green wood in the usual
manner to separate any oxide of lead that may be present, and then ladle it
into the ordinary moulds. The time required for this process depends on the
size of the furnace and the quantity of lead operated on. I have found that
from two to two and a half hours is generally sufficient for quantities of three
tons, extending, when melted, over a surface of twenty-five to thirty square
feet. The oxide of zinc remains in the furnace, and is afterwards removed
therefrom. The alloy of silver, zinc, lead, and other metals or impurities
obtained according to my Invention from the surface of the melted lead I.
first concentrate by separating as much of the lead as possible. I effect this
by placing it in a pot or other vessel of iron having a perforated bottom and.
a cover or lid fitting loose on the top. I heat this vessel till nearly red hot,
when a large proportion of lead will escape through the holes at the bottom,
and the weight of the alloy will be consequently reduced.
This lead, so
separated, if the process has been carefully conducted by avoiding to heat the
same to too high a degree, will be found to contain only a very minute
quantity of silver, and may be purified or refined in the manner previously
described; should it, however, contain sufficient silver to make it worth
repeating the process, it must be returned to the mixing pot for that purpose.
The concentrated alloy so obtained may be treated in two ways. Firstly, it
may be oxidised by subjection to a low heat, and then digested in sulphuric
or muriatic acids diluted with from four to six times their bulk of water;
secondly, it may be distilled in retorts properly constructed, thereby separating
the zinc in the metallic form, and leaving the lead and silver to be afterwards
treated in the manner usually adopted. In the first of these two operations
I place the alloy in close retorts or muffles and subject it to a low heat. By.
continually stirring with an iron rake the metals become partly oxidized and
disintegrated, and at length fall down to a fine powder; the heat must then
be raised until the metals (with the exception of the silver) are completely

page_text: converted into oxides; the powder so obtained is then placed in cisterns or
vats containing dilute sulphuric or muriatic acid, the oxide of zinc becomes
dissolved, and the silver falls to the bottom, and may be recovered by any of
the known methods. In the second operation I place the concentrated alloy
in retorts of a similar shape and size to those used for the distillation of zinc;
they should be made of the best Stourbridge clay or other suitable material, and
well tempered and dried. I have also found that a wrought-iron tubė, pro-
tected outside by a clay retort, and coated inside with a lining of pounded bones
and charcoal, to answer the purpose perfectly. The retorts are placed in a
furnace of the ordinary description, and the distillation of the zinc carried on in
the manner well understood and practised. After the separation of the zinc
the silver, lead, and other metals, if any, remaining on the bottom of the retort,
may be tapped out through a small hole in the back of the retort, and sub-
jected to the ordinary process of cupellation. I have found it desirable to
mix a small quantity of finely powdered charcoal or coke dust with the alloys
placed in the distilling retorts for the purpose of reducing any oxides that may
be present.
Having now described the nature of my Invention, and the manner in
which the same is to be carried out, I would observe that I do not confine
myself to the exact details of the several processes herein described, as the
same may be varied without departing from my Invention.
In witness whereof, I, the said Alexander Parkes, have hereunto set my
hand and seal, this Second day of September, One thousand eight
hundred and fifty-two.
the year of our Lord 1852, the aforesaid Alexander Parkes came before our
said Lady the Queen in Her Chancery, and acknowledged the Specification
aforesaid, and all and every thing therein contained and specified, in form
above written. And also the Specification aforesaid was stamped according to
the tenor of the Statute made for that purpose.
Enrolled the Fourth day of September, in the year of our Lord One
thousand eight hundred and fifty-two.