AN IMPROVED PROCESS FOR PREPARING SULPHATES AND OBTAINING FINE SILVER THEREFROM
Year: 1869

page_text: LETTERS PATENT to William Robert Lake, of the "International
Patent Office," No. 8, Southampton Buildings, London, Consulting
Engineer, for the Invention of "AN IMPROVED PROCESS FOR PREPARING
SULPHATES AND OBTAINING FINE SILVER THEREFROM."-A communication
from abroad by Frederick Gutzkow, of San Francisco, California,
United States of America.
Sealed the 6th August 1869, and dated the 17th June 1869.
COMPLETE SPECIFICATION filed by the said William Robert Lake at
the Office of the Commissioners of -Patents, with his Petition and
Declaration, on the 17th June 1869, pursuant to the 9th Section
of the Patent Law Amendment Act, 1852.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
ROBERT LAKE, of the "International Patent Office," No. 8, Southampton
Buildings, London, Consulting Engineer, send greeting.
WHEREAS I am in possession of an Invention for "AN IMPROVED
PROCESS FOR PREPARING SULPHATES AND OBTAINING FINE SILVER THEREFROM," and
have petitioned Her Majesty to grant unto me, my executors, adminis-

page_text: trators, and assigns, Her Royal Letters Patent for the same, and have
made solemn Declaration that it has been communicated to me from
abroad by Frederick Gutzkow, of San Francisco, California, United
States of America.
NOW KNOW YE, that I, the said William Robert Lake, do hereby
declare that the following Complete Specification, under my hand and
seal, fully describes and ascertains the nature of the said Invention,
and in what manner the same is to be performed, in and by the
following statement :-
The said Invention consists in obtaining what in refining gold and
silver is called "fine silver," which I accomplish by preparing crystals
of sulphates of silver in the manner herein-after described, and by
reducing them with a solution of the compound which is known to
the trade as "green vitrol," that is sulphate of protoxide of iron.
The process at present employed in the refineries of gold and silver
which use sulphuric acid for dissolving the silver is the following:
The bullion is boiled in strong sulphuric acid till all the silver is
dissolved, and the solution thus formed is poured into water or a watery
solution of sulphate of copper, when most of the sulphate of silver will
fall down as a crystalline powder. It has then to be dissolved in the
said watery solution to free it from gold and from sulphate of lead, and
to obtain a clear solution, out of which the silver is precipitated by
copper. This is a very slow process because the sulphate of silver is
very little soluble in water, and it is very uncomfortable to the persons
employed in gold and silver refineries, on account of the vehement
generation of strongly arid water vapors in mixing the hot sulphuric
acid with water.
In my improved process the bullion is boiled in strong sulphuric
acid as usual, till all the silver is dissolved, but instead of pouring
the hot and saturated solution thus obtained into water I pour it
into sulphuric acid, which I will call the mother acid, and which is
contained in a cast-iron pan, or any other suitable apparatus. Such
acid has to be of a specific gravity of between 50° and 66° Beaumé,
and is to be heated to between 200° and 400° Fahrenheit, and I take
from five to twenty cubic feet of such acid for each one thousand
ounces (troy) of silver which I will refine at a time. That acid which
I consider the best adapted to the purpose of my Invention has a specific
gravity of 58° Beaumé, and a temperature of 250° Fahrenheit, and I

page_text: use ten cubic feet for one thousand ounces (troy) in bullion. If the
bullion which I have to refine contains more than five per cent. of lead
I prefer to take a larger volume of weaker acid, in order to facilitate
the settling of the sulphate of lead. If the volume, the specific gravity
and the temperature of the mother acid are within the limits stated
above, the saturated solution of sulphate of silver and the mother acid
will mix without the generation of any fumes, and without the separa-
ration of any sulphate of silver. The solution obtained is allowed to
settle till the gold and the sulphate of lead have settled down. Then
it is run off into another cast iron or leaden pan, which I will call the
precipitating pan, where it is left to cool to as low a temperature as
can conveniently be obtained, when a large proportion of crystals of
sulphate of silver will separate, mixed with some of the sulphates of
copper and iron. After about twelve hours cooling, which time may
be shortened by artificial means, the mother acid is pumped back whence
it came, is again heated and made ready to receive another charge of the
saturated solution of sulphate of silver, as described above. If preferred,
heat may be applied after the two solutions are mixed instead of before.
As the mother acid will increase in volume and specific gravity by
the free acid contained in the saturated solution of sulphate of silver
which it receives, the surplus is from time to time removed after the
crystals are separated and used for dissolving the silver bullion, and
the remaining mother acid is in the precipitating pan mixed with a
small quantity of water, so as to bring it again to 58° Beaumé, or to
that specific gravity which I choose to employ. By this small addition
of water nearly all the sulphate of silver which the mother acid still
contained is thrown down as a crystalline powder. The crystals or
crystalline powder so obtained, consisting principally of sulphate of
silver, I now subject to the reducing action of sulphate of protoxide of
iron, either in the same vessel where. they were formed, or in any other
suitable apparatus. The green vitrol is best adapted for use when
dissolved in water, and of a strength from fifteen (15°) to thirty (30°)
degrees Beaumé; in this solution the crystals are placed, and the whole
agitated by stirring, or the crystals may be thrown upon a filtering
apparatus, and the solution is poured or pumped upon them and allowed
to filter through the mass until all or nearly all of the sulphate is
reduced to metallic silver, forming a very dense mass which is in a
state exceedingly well adapted for the further and customary manipu-
lations well known to refiners of gold and silver, to wit, that of

page_text: sweetening, drying, and melting. The solution of green vitrol may
be used cold or hot; a high temperature not being requisite, and from
five (5) to twenty (20) cubic feet of a solution of twenty-five (25)
degrees Beaumé may be reckoned for the reduction of one thousand
(1,000) ounces (troy) of silver; the requisite quantity however will
depend in some degree upon the construction or choice of the apparatus
employed as well as other minor matters, the details of which being
well known to refiners need not be herein described: The oxidized
solution of sulphate of iron so obtained may be reduced again by
dissolving in it metallic iron or by other methods, I prefer the metallic
iron as it acts more easily and quickly than other methods or agents
and may be used over many times for the same purpose, as above
described.
Having thus particularly described the nature of the Invention, as
communicated to me by my foreign correspondent, and the manner of
performing the same, I wish it to be understood that I do not limit
myself to the exact details herein set forth, as they may be considerably
varied or modified according to the fineness of the bullion to be manipu-
lated and the quantity, strength, and volume of its agents used, but I
claim,―
First. The preparation of crystals of sulphate of silver, from their
solution in a sulphuric acid, the quantity, specific gravity, and volume
of such acid to be within the limits herein specified.
Second. The production of fine silver from such crystals by reducing
them to the metallic state by means of a solution of the compound
known in commerce as 66
green vitrol," and technically called sulphate
of iron, substantially as set forth.
: In witness whereof, I, the said William Robert Lake, have hereunto
set my hand and seal, this Seventeenth day of June, in the year
of our Lord One thousand eight hundred and sixty-nine.