IMPROVEMENTS IN SEPARATING SILVER FROM OTHER METALS
Year: 1851

page_text: 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 Twenty-fourth day of
June (One thousand eight hundred and fifty-one), in the fifteenth year of
Her reign, did, for Herself, Her heirs and successors, give and grant unto
me, the said Alexander Parkes, my exors, adñors, and assigns, Her especial
licence, full power, sole privilege and authority, that I, the said Alexander
Parkes, my exors, adñiors, 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 England, Wales, and the Town of Berwick-upon-Tweed, my Invention
of "IMPROVEMENTS IN SEPARATING SILVER FROM OTHER METALS;" in which said
Letters Patent is contained a proviso, that I, the said Alexander Parkes, shall
cause a particular description 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 there-.
unto 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 improve-
ments 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 nic on the Eleventh
day of June, One thousand eight hundred and fifty, among other matters I
describe 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
compared with what was formerly described, that different proportions of zinc
than those formerly mentioned are required, and the same should be varied
according 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 zinc, 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 proportion 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:-
ounces.
lbs.
To one ton of lead containing 14 of silver per ton, I add 224 of zinc.
"
"
"
"
"
21
28
"
33 6
"
"
44 8
"
وو
and so on. I do not however confine myself to this precise proportion of zinc,
as I have found the requisite quantity depends greatly on the purity of the

page_text: 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 oxidized. 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 close 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 a high 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 converted into oxides,

page_text: 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 allow 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 tube, protected outside by
fa 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
fordinary 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 subjected to
the ordinary process of cupellation. I have found it desirable to mix a small
quantity of finely pounded charcoal or coke dust with the alloys placed in
the distilling retorts for the purpose of reducing any.
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 Thirteenth day of December, One thousand eight
hundred and fifty-one.