Year: 1888

page_text: A communication from abroad by EDWARD L. SMITH, of Ansonia, in the State of
Connecticut, United States of America.
€ -
I, PHILIP MIDDLETON JUSTICE of 55 and 56 Chancery Lane in the County of
Middlesex Fellow of the Institute of Patent Agents do hereby declare the nature
of this invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :-
This invention relates to an improvement in the method of depositing copper for
the purpose of refining it, separating and saving the precious metals that it contains.
The depositing vat or cell is made of wood, and may be of any convenient size 'and
shape to meet the requirements of the case. It must be lined with some insulating
material and not with metal. An article sold as roofing cement, made from coal-tar,
is suitable for the purpose. Other materials however may be used. Such a vat is
represented in Fig. 1 of the drawings hereunto annexed. The solution used is
the ordinary acid solutions of sulphate of copper used in ordinary electro-typing
operations.
The copper to be deposited is first cast in plates of the proper size and form. The
plates so cast are not suspended in the solution as is usually done, but are placed
horizontally. As it would not be practicable in many cases to cast the plates large
enough to give a sufficient amount of surface several plates are laid side by side so as
to form one large plate. The layers are placed one above the other at a suitable.
distance apart. In the vats in actual use this space between the layers is one and
a half inches. The first or bottom layer rests on two strips of wood running
lengthwise of the vat. The plates are made of a length a little less than the width
of the vat. After the plates are placed in position on the strips other strips are placed
on the ends of these plates and these strips support another layer of plates..
In order to separate and save the insoluble foreign substance including silver or
gold, from the copper, cotton cloth is stretched from one strip to the other between
the layers of copper.

page_text: Fig. 2 represents, removed from the vat, a section of a series of layers of copper
plates extending across the vat. a, a, represent two plates of the top layer. The
lower layers are represented by the dark lines below. b, b, represent the strips of
wood which separate and support the plates. The horizontal broken lines below the
dark lines represent the cloth screens between the layers of copper. A section of one'
of these screens with the supporting strips is represented by Fig. 4.
Fig. 3 represents the layers for three vats, and the manner of connecting them to
form a connected series of cells. A vertical space c at the left of each series of layers
represents a narrow chamber formed by a partition across the end of each vat.
After the copper plates have been placed in position the vat is filled through the
chamber with the solution of sulphate of copper; an opening through the bottom of
the partition allowing the solution to enter the vat at the bottom and to rise through
the plates until the top one is covered.
Now taking the top plate as an anode, a conductor is brought from a dynamo
machine or battery and connected with this plate. The other pole of the dynamo is
connected with the bottom plate. The spaces between the plates containing solution
form separate cells in series, the plates forming conductors to connect the cells.
The copper is taken from the under surface of the top layer of plates and deposited
on the upper surface of the next layer below, and so on through the whole series; the
under surfaces of the plates being anodes and the upper one cathodes. The insoluble
foreign matters in the copper, including gold or silver, are liberated as the copper is
dissolved and fall upon the filters or screen, thus allowing pure copper only to be
deposited on the upper surfaces of the plates.
'
When the original copper of each plate has been transferred to the plate below or.
when the accumulation of foreign matters upon the filters is sufficient to interfere
with the progress of the deposit, the solution is to be drawn off, either through the
chamber by a pump or syphon or through a cock at the bottom of the vat. The
plates and. the filters with their contents can then be removed. If the copper has
not been wholly deposited the deposited copper can be separated from the undeposited
copper and the latter be again placed in the vat to be again acted upon.
Fig. 3 shows the manner in which the plates in several vats are connected into a
series of cells; the lower plate of one vat being connected with the upper plate of
another vat.
The number of cells in a circuit will be determined by the electromotive force of
the current and the resistance of the circuit.
The method above described for arranging depositing cells horizontally has several
important advantages over the common vertical arrangement. The silver, or other
foreign insoluble matter, is easily collected and removed. The space required for a
given amount of depositing is relatively small. So also is the amount of solution
required. The connection between the cells in one tank is made by the copper plates
themselves. The copper is easily handled and prepared for the vats.
It is well known that it is important that the density of the solution between two
plates which form an anode and opposite cathode should be the same between all
parts of the plates, in order to insure upon the whole surface of the cathode a
uniform deposit of copper in thickness and quality, and in order also to insure a
uniform consumption of copper from the whole surface of the anode. It is important
also in order to insure a uniform specific resistance in the solution between all parts of
the plates. But inasmuch as a solution of sulphate of copper is of greater specific
gravity than the free acid which is liberated by the depositing of the copper upon
the surface of the cathode such acid rises to the surface of the liquid while the solution
of sulphate of copper settles toward the bottom. Where, therefore, the arrangement
of plates is such that they stand on end, there is an ascending current before the
surface of the cathode and a descending current before the surface of the anode.
The chemical conditions at the top and bottom of the plates therefore soon become
very different, and so also does the electrical resistance of the liquid. When the
plates are small and the distance between them is large and the deposition is to be
carried on for a short time only, this is not a serious matter, but when the plates are

page_text: large, and thick deposits, requiring several days, are to be formed, these nonuniform
conditions become very important. The free acid attacks the upper portion of the
plates more rapidly than the lower portion and the deposition goes on most rapidly
at the lower portion of the cathode. To obviate these difficulties it is usual to provide
some means to keep the solution in motion, applied sometimes to each cell - and
sometimes to the whole series of cells, the liquid being made to flow continuously
through the whole series of cells. The former mode is objectionable because it
requires a complicated apparatus to act separately on each cell of the series, perhaps
of several hundred. The latter mode is objectionable because it requires a free liquid
connection between the series of cells.
In the arrangement herein described it is unnecessary to provide any means of
keeping up a circulation of the liquid, for the free acid liberated over the whole
horizontal surface of the cathode in each cell rises directly through the solution and
the screen to the surface of the anode above, and acts uniformly over the whole
surface. The deposition also takes place uniformly over the whole surface of the
cathode and thus uniform chemical and electrical conditions are secured over the
whole surface of each plate, and uniform liquid resistance between all parts of
the plates, and the action of the cells is entirely automatic.
There is another result of considerable importance due to the fact that a considerable
number of cells are placed in a vertical series. It is well known that electro
deposition proceeds more rapidly at a moderately high temperature than at a low
temperature, and means are sometimes adopted' to apply extraneous heat, but in the
arrangement herein described the heat generated by the current maintains the
temperature sufficiently high to insure rapid deposition, the loss of heat through
the walls of the tank and at the upper surface being very small, and much less than
where an artificial circulation of the liquid is maintained. A single horizontal cell
would present conditions most liable to loss of heat and any mechanical arrangement
for maintaining a circulation of the liquid would entail a loss of considerable
importance.
Another advantage of the described arrangement is that no change in the condition.
of the solution from evaporation takes place in the cells, the evaporation of the
liquid above the top plate not affecting the liquid in the cells themselves. As the
process of deposition goes on for many days the loss by evaporation must be
considerable and must constantly change the density of the solution where the cells.
are vertical. In the arrangement herein described no change occurs in the cells from
evaporation of the solution.
Having now particularly described and ascertained the nature of my said invention,
and in what manner the same is to be performed, as communicated to me by my
foreign correspondent, I declare that what I claim is :-
A vertical series of horizontal electro-depositing cells formed by horizontal plates
of the metal to be deposited, separated and supported by insulated supports, and
immersed in an electrolytic solution, with -screens interposed between the successive
plates, substantially as described, whereby insoluble matters are arrested as they are
liberated from the lower surface of the upper plate in each cell by the combined
action of said solution and electric current.
Dated this 28th day of November 1888.