IMPROVEMENTS IN SEPARATING OR EXTRACTING SILVER FROM LEAD
Year: 1861

page_text: PROVISIONAL SPECIFICATION left by George Henry Birkbeck at the
Office of the Commissioners of Patents, with bis Petition, on the 24th
April 1861. A communication from abroad by Jules Fredorick de la
Batie, Advocate, and Cle:nent Roswag, both of Paris, in the Empire of
France.
I, GEORGE HENRY BIRKBECK, of the Firm of Tongue and Birkbeck, of 34,
Southampton Buildings, Chancery Lane, in the County of Middlesex, Patent
Agents and Engineers, do hereby declare the nature of the Invention for
"IMPROVEMENTS IN SEPARATING OR EXTRACTING SILVER FROM LEAD," to be as
follows:-
This Invention has for its object improvements in the processes or means
employed for separating or extracting silver from lead by incorporating zinc
therewith, which process in itself is not new, this Invention depending on a
series of improved processes for this purpose. In carrying out this Invention
the first operation consists in fusing the lead containing silver and incorporating
the zinc therewith. For this purpose a suitable furnace is provided with a
melting pot or vessel in which the lead and zinc are melted, the zinc being
placed in suitable tubes or holders, and deposited after the lead is melted at
the bottom of the vessel, so that as it melts it rises up through the molten
lead by reason of its less, specific gravity, and by means of agitators it is uni-
formly distributed in its passage through the fluid lead. When the whole
of the zinc is melted and has risen to the surface of the molten lead the
zinc holders and the agitators are removed from the vessel and the alloy of

page_text: zinc and silver is skimmed off the surface to be operated upon as hereafter
described.
The molten lead which now contains a small per-centage of zinc is next run
off into the hollow of a reverberatory furnace such as is generally used for
annealing and refining lead and the zincy lead is purified by keeping it in a
state of fusion at a dull red heat, and subjecting it to the action of the
vapours or gases arising from the burning or decomposition of pieces of
wood enclosed in suitable tubes or holders below the surface of the molten
lead. The dross of the zinc (called seconds) is skimmed off during the pro-
cess and is added in another process to the alloy of zinc and silver previously
obtained. The lead thus refined is run into ingots for sale or use.
green
The next operation in separating the lead mechanically mixed with the
alloy of zinc and silver. For this purpose the alloy is placed upon gratings or
perforated plates in a closed vessel or chamber under and partly around which
the waste flame and heat from the boiler or the reverberatory furnace is con-
ducted by suitable flues so as to subject the alloy to a heat not exceeding 350°
Réaumur. The lead with the zinc deposited on the inclined bottom of the
closed vessel is added to the next annealing process. The "second dross," of
the annealing operations and the eliquated alloy proceeding from the last
operation are treated successively in a furnace similar to the ordinary "cupel "
furnace, the bed of the furnace is not prepared as is usual in such furnaces
with calcined bones, but with a mixture of clay and quick lime in about equal
parts well sifted and beaten down. A bath of lead is introduced into the bed
of the "cupel" furnace and litharge is produced in the ordinary manner, rich
dross is also produced. by treating it with coal dust and air from a fan or
bellows. By the combustion of the zinc it is converted into an oxide of
zine the silver being liberated is concentrated in the bath of lead contained
in the "cupel" furnace. The black litharge is abstracted after being acted
upon by the fire by a suitable orifice.
The lead is run off when sufficiently rich in silver (2 or 3 per cent.) by
allowing it to escape through a central orifice in the bed of the furnace which
is then restored ready for a fresh charge.
The management of the fire, and regulation of the heat of the furnace, is of
great importance, and requires considerable practice to avoid the loss of great
quantities of silver. The principle upon which this manipulation depends is
essentially as follows:-The simultaneous oxidation of the lead and of the
zinc of the alloy, the liberation of the metallic silver and its introduction into
the lead of the bath, the formation of a dross with the ashes or dust of coal,
the excess of the litharge and the oxide of zinc, this dross being treated by the

page_text: following process which consists in working the black litharge or transforma-
tion of the residues with zinc or black litharge in silver-bearing lead.
As in the residues of zinc or black litharge (the term used to designate the
dross obtained from the previous operation) there is a certain amount of lead
and silver, the proportion of the silver being in accordance with the amount
of concentration in the bath of lead and which it is necessary to extract by a
special process (which is that about to be described), the litharge is placed
in crucibles with about half its weight of "basic" and of black soap, the
crucibles (of cast iron) are introduced into an air furnace heated with coke,
the construction of which will be fully described and shown in the Complete
Specification of this Invention. The products of this melting process are
first lead containing silver directly capable of "cupellation" in small quan-
tities, and, secondly, of dross very rich in lead and in zinc which are reduced
in a cupola furnace..
The latter must always be melted separately for the lead obtained therefrom
is very hard and requires to be annealed separately.