Improvements in or relating to the Electro-chemical Decomposition of Solutions of Salts.
Year: 1894

page_text: Date of Application, 22nd Nov., 1894-Accepted, 19th Jan., 1895
COMPLETE SPECIFICATION.
Improvements in or relating to the Electro-chemical Decomposition
of Solutions of Salts.
I, JAMES CHARLES RICHARDSON, of 19 Claremont Square, in the County of
London, N., Electro-chemical Engineer, 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:-
These improvements relate to the electro-chemical decomposition of solutions of
salts.
In electrolytic processes, as hitherto carried out, wherein mercury is employed
for a cathode, in electrolytes, such as alkali salts in solution, as a carrier of the
cations (sodium, potassium, &c.) from the electrolyte to another chamber wherein
they are given up to a solvent, the mercury becomes "polarized" with hydrogen
after giving up these cations (or "kathions").
This fact appears to be overlooked or ignored; but by the present invention the
serious difficulties connected with it are successfully overcome.
The following simple formulæ may represent the displacement of hydrogen in the
case of dissolving out sodium from a mercury cathode with water per se:
understood.
The excess of hydrogen escapes as gas, but a portion, more or less constant, and
in a condensed and active form, remains in contact with the mercury, which is
objectionable, and not remediable by simple mechanical means, and detracts from
the commercial value of such electrolytic processes as referred to.
According to this invention, the mercury is joined up as an anode in the cation
solvent liquor, or electrolyte, with a cathode having in contact with it cupric
oxide (CuO), or like combination with negative base.
By thus joining up the mercury by a conductor with a negative cathode
having CuO in contact, the hydrogen is prevented to a large extent from being
liberated on the mercury, but appears at the CuO-cathode, where it is taken up
chemically and the copper reduced, thus:
.
2 (Na + H2O) = 2 Na HO + H₂.
H₂+ CuO = H₂O + Cu.
It will be observed that when both sodium and hydrogen are combined with
mercury, and though the hydrogen be in infinitesimal weight proportion, they both
act potentially positive to copper, that is to say, they easily displace copper in its
oxygen combination under the conditions prescribed; and accompanying such
ponderable displacement is useful electric displacement, showing itself in the
current set up along the conductor joining the mercury to the copper.
This invention may be carried out in an iron tank divided into cells or chambers
for containing separately the solution under treatment and the cation solvent.
The mercury cathode circulates throughout the cells, while the additional cathode
of cupric oxide occupies a position in the presence of the cation solvent.
The oxide of copper is placed in contact with the metallic iron of the tank in
proximity to the mercury, upon suitable large surfaced metallic shelves or supports.
If it be desired to avoid metallic connection to the tank, the cathode, or cathodes,

page_text: is, or are, suspended in the solvent solution, but connected to the mercury by a
suitable metallic conductor, as a copper or iron wire or rod, or amalgamated plate
or gauze, as before mentioned; and which, of course, applies to the case where
slate is employed for the receptacle.
The cathode (CuO) referred to is conveniently and efficiently constructed, for
example, of copper or iron gauze, and in close contact with this gauze is placed
cupric oxide (CuO), which may be oxidised copper scrap, as copper scale, in a
more or less finely divided condition, resting on the gauze (a layer not thicker than
an inch say) when it is placed horizontally, and, for vertical use, supported on,
against or around the gauze, or large surface plate or grid, or equivalent, by a
perforated or latticed support, or equivalent, allowing of the free passage of the
electrolyte to the cathode surface.
Connected to such cathode, which, of course, dips into, or is totally immersed in,
the cation solvent, is a metallic conductor, a wire, rod or rods, or equivalent, as
will be understood, for making good connection to the mercury or amalgamated
surfaces carrying the cations. As long as they are so connected, and the oxide of
copper not wholly exhausted, the hydrogen is taken up. It is advisable, however,
not to press the oxide of copper to its extreme limits, but to renew it before
complete exhaustion.
The cathode surface contact of oxide, as previously indicated, should be large
and regular for dense currents, which will be understood.
When the copper is
reduced it is, as well-known, readily re-oxidised by heating in air, and otherwise.
The oxide, nor the metallic copper, is not appreciably soluble in the aqueous cation
solvent. The fear of loss in that respect is therefore dispelled.
In addition to the CuO cathode being employed after the manner already
described, I sometimes place it in the electrolytic circuit proper (as a shunt or
direct), in a series in which there is an anode | electrolyte mercury ||
mercury+cation | electrolyte | OCu cathode. No hydrogen appears, for the
reasons already given.
In this series, the first electrolyte is the salt in solution to be decomposed, and
the second, water dissolving and holding the cation products.
In the accompanying drawing, I have shewn apparatus wherein my invention
may be carried out.
Fig. 1 shews, in sectional elevation, a horizontal arrangement, and
Fig. 2 is a similar view of a vertical arrangement.
Referring to Figure 1, A is a tank of slate or other suitable material containing
separate cells for the solution under treatment, and for the cation solvent.
a are the cells for containing a solution to be electrolysed, and 6 is a cell
containing water, or other cation solvent. The cell a (of which the drawing
indicates a pair) is closed, save for the solution supply pipe a*, and the gas exit
at a contains an anode e immersed in the solution, and a mercurial cathode d.
This cathode is composed of a stream of mercury flowing to and fro beneath the
partitions e, across the floor of the cells a and b, the movement of the mercury
being caused by tilting the tank, or in any other convenient manner.
The cell b, which may be open at the top, contains, besides the cation solvent, 4
a tray f, of cupric oxide, in electrical connection with the mercury d by means of
the rods f¹.
In Figure 2, A is a vertical tank of iron or other suitable material. The cell a,
containing the anode c, is lined with slate and is provided with a bottom basin of
insulating material. a* is the salt supply pipe, and a* the exit for the gas.
5
el is a porous partition dividing the cell a from the mercurial cathode d, which is
an endless band of tinned iron or other suitable metal dipping into the mercury
trough d, and travelling vertically over rollers d' d² mounted in the tank sides.
e is a solid partition placed within the band, and extending upwards from the
mercury, into which it dips, to above the level of the liquids in the tank. b is the 5
cell containing the cation solvent, divided from the electrolyte under treatment by
the said partition e. f is a metallic lattice supporting cupric oxide. For the

page_text: connection between the mercury cathode and the cupric oxide, the base of the
tank A may be utilized. Wash-out holes are preferably provided for the cells,
furnished with suitable stop cocks not shewn.
The leading wires for the current are indicated in the drawing, and marked
respectively and
11
From the foregoing, it will be seen that if CuO be placed in contact with
mercury-sodium, or mercury carrying sodium, in water, it will take up the hydrogen
as well as if attached to a separate cathode, and in like manner take up the
hydrogen liberated from weak acid compounds, dissolving the cations from the
mercury, but the reduced copper is amalgamated. With manganese dioxide, and
some other oxides, amalgamation would not follow, but there are other drawbacks
to its application; the reduced compound is not a conductor like copper etc.
The principle of this invention having thus been clearly laid down, and the
methods to be pursued to put it into successful application without experiment
being fully explained, I do not confine myself to any general or particular
mechanical method of applying it, because there are many, as is obvious.
It should be observed that by removing the hydrogen from the region of the
mercury in the manner herein explained, the chances of its entering the anode
compartment in certain forms of apparatus in which mercury is employed, are
greatly diminished, if not wholly prevented. It is known that serious explosions
have resulted, at times, and are likely to happen in the future, from apparatus
defective in the direction just indicated, as when electrolysing alkali chloride
solutions, to which purpose this invention would usefully apply.
It should also be observed that in the example given of an electrolytic series, in
which the ultimate element displaced is copper, electrical as well as chemical
advantages follow.
The objections set out are therefore completely obviated in a simple and efficient
manner by this invention, and electrolytic apparatus of the kind alluded to is
rendered more useful for industrial, manufacturing purposes than hitherto.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed; I would have it to be
clearly understood that I do not claim the general employment of mercury as a
cathode in electrolysing solutions, nor do I claim the general employment of cupric
oxide for electrolytic purposes, but what 1 do claim is :-
(1.) In electro-chemical processes, wherein miercury is employed after the manner
described, the method of taking up hydrogen, by an additional cathode, substantially
as set forth and shown.
(2.) In electro-chemical decomposition, the employment of cupric oxide, Cu O,
or its equivalent, in conjunction with a cation solvent and mercury cathode,
substantially as described.
(3.) The method of effecting electro-chemical decomposition of solutions (with a
mercury cathode, after the manner described) by which the ultimate element
displaced in a series is potentially lower than hydrogen, for example, copper,
substantially as set forth.
(4.) In electro-chemical decomposition, the method set forth by which ions are
removed from mercury electrodes by aqueous solutions without the liberation of
hydrogen gas, substantially as described.
(5.) The combination of electrodes and electrolytes, acting together, substantially
as described.
(6.) The removal of sodium and potassium and hydrogen ions from mercury
cathodes in the manner and substantially as described.
Dated his 2nd day of November 1894
JAMES C. RICHARDSON.