Improvements in Apparatus and Means for the Electrolysis of Alkaline Chlorides.
Year: 1892

page_text: Date of Application, 24th May, 1892
Complete Specification Left, 24th Feb., 1803-Accepted, 6th May, 1893
PROVISIONAL SPECIFICATION.
Improvements in Apparatus and Means for the Electrolysis of
Alkaline Chlorides.
I, DESMOND GERALD FITZ-GERALD of 46 Loughborough Road, Brixton, in
the County of London, Electrician do hereby declare the nature of this invention
to be as follows :-
:-
The use as an anode of peroxide of lead, in the compact, coherent and conductive
form in which it is known as lithanode has hitherto been confined to the electrolysis
of earthy chlorides. This substance is in fact rapidly attacked by alkalies; so
that, if it be used in the electrolysis of alkaline chlorides, it must be effectually
protected, by means of a diaphragm or otherwise, from contact with the alkali
liberated at the cathode.
In practice, however, it is very desirable to reduce as far as possible the resistance
opposed to the passage of the current, and, consequently, to dispense, wholly or in
part, with the diaphragm. It is obviously desirable, also, to reduce the expenditure
of electrical energy in effecting the electrolytic decomposition of the salt. It is
well known that gases, in becoming liberated, absorb or render potential a large
amount of energy, which may subsequently become evident as heat when the gas
is condensed by solution or otherwise. Thus it can be shown that 2-3 volts are
theoretically requisite (in addition to the electromotive force to overcome the resistance
of the circuit and the " spurious back-electromotive force") to effect the decom-
position of a solution of common salt when the gases chlorine and hydrogen are
But when the liberation of
evolved respectively at the anode and the cathode.
these gases is obviated, by causing them to enter into combination within the
electrolytic cell, the decomposition can be effected under a balancing force
of 109 volt. In order to bring about the combination of chlorine to form a
hypochlorite, and at the same time to obtain the alkali of the salt as a hydrate, it
is sometimes desirable or necessary to use two solutions; that which is to be in
contact with the anode differing in composition from that to be in contact with the
cathode.
Now my invention consists, firstly, of an electrolytic tank in which the use of a
porous diaphragm separating the anode and the cathode may be either wholly
dispensed with or may be limited to a portion, usually the upper portion, of the
electrolytic cell. In the lower portion of the cell, at least, mixture or diffusion of
the two portions of electrolyte, or of two different electrolytes, to be respectively
acted upon by the anode and the cathode, is obviated by the vis viva due to the
motion of the two portions of fluid, which are caused to flow over the surfaces of
the two electrodes.
My invention involves, secondly, means for obviating the evolution of gases
within the electrolytic tank, which latter usually consists of a number of electrolytic
cells or anode and cathode alternations. With this view, I mix with the portion of
fluid to be subjected to the action of one of the electrodes a substance, in a state
of solution or in suspension, which will absorb the gas which otherwise would be
liberated. Thus, for instance, in the electrolysis of an alkaline chloride (which
may be in conjunction or admixture with an earthy chloride) I mix lime with the
portion of fluid-such as a solution of sodic chloride, or a mixed solution of. sodic
and calcic chlorides-which is to be brought into contact with the anode, preferably
of lithanode. And that portion of fluid which is to be brought into contact with
the cathode may hold in suspension a substance, such as the hydrated oxide of
copper, which is capable of absorbing hydrogen. Or I bring directly or indirectly

page_text: into conductive contact with the electrode a substance, forming a coating upon it or
upon a conductor connected to it, which will absorb the gas which otherwise would
be set free. Thus, for instance, I construct a copper cathode of large surface and
preferably of cellular form, and I coat the exterior and interior surfaces with oxide
or oxychloride of copper, which will prevent the evolution of hydrogen from the
electrode. Or, with the same object in view, I attach to the cathode plates or
elements coated with the oxide or the oxychloride of copper or of lead.
Dated this 24th day of May 1892.
COMPLETE SPECIFICATION.
Improvements in Apparatus and Means for the Electrolysis of
Alkaline Chlorides.
I, DESMOND GERALD FITZ-GERALD of 94 Loughborough Road, Brixton, in
the County of London, Electrician, 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 :-
My invention relates to the electrolysis of sodic or potassic chlorides with a view
to the production on the one hand of the corresponding hydroxide and on the
other hand to cause the chlorine either to enter into combination by means of a
basic oxide which is insoluble or nearly insoluble in water or to be evolved in the
gaseous condition.
My invention therefore has, first, for its object to avoid the consumption of
energy necessary for the evolution of the chlorine in the gaseous condition by pro-
viding means whereby it may be caused to enter into combination when in the
nascent condition and, secondly, it has for its object to enable an anode of peroxide
of lead (in the compact coherent and conductive form in which it is known as
lithanode) to be employed and for this purpose I provide means whereby the
anode is protected from being attacked by any alkali which may find its way
from the cathode compartment, the chlorine being absorbed by the same means if
desired.
It has been found that lithanode although liable to be very rapidly attacked by
caustic alkali is not similarly acted on by insoluble or nearly insoluble basic oxides
and I avail myself of this fact by the employment in the anode compartment of
such a basic oxide both to fix the chlorine and to protect the anode from the action
of the alkali generated in the cathode compartment should it become diffused in the
anode compartment. The insoluble basic oxide I prefer to employ is lime, magnesia,
or zinc oxide and in the case of using lithanode as the anode this material is
effectually protected from the action of any alkali that may find its way into the
anode compartment by the fact that the insoluble oxide forms under the action of
the chlorine generated in the anode compartment a soluble compound which
compound is decomposable by alkali with the formation of the corresponding
compound of the alkali metal and precipitation of the original insoluble oxide.
Of the three basic oxides mentioned lime is generally to be preferred by reason of
its cheapness, which will admit of the production of a chlorine compound which,
after being used for bleaching or other purpose, may be run to waste.
In practice I prefer to take an electrolytic tank (or number of tanks coupled in
series or in parallel) divided into compartments by porous diaphragms. In the
cathode compartment I place a nearly, but not quite, saturated aqueous solution of
the sodic or potassic chloride and take care to keep the solution as nearly as
possible at the same degree of saturation by the addition of chloride (dry or in
solution as may be required) as the electrolytic operation proceeds. If the cathode
employed be such that hydrogen is evolved (for instance iron) it will be necessary
to add water or chloride in solution in order to keep the volume and degree of
saturation of the electrolyte constant, but if a cathode (such as copper for instance

page_text: coated with its oxide) capable of oxidising the hydrogen be employed then no loss
of water due to the evolution of hydrogen will occur.
The object of keeping the electrolyte verging on the point of saturation is to
render it as conductive and obtain as strong a solution of alkali as possible.
As regards the anode compartment the mode of operating will depend upon
whether it be required to fix or to evolve the chlorine. In the first case I may
either place in this compartment a solution of chloride of sodium together with a
quantity of one of the insoluble basic oxides (lime for instance) sufficient to absorb
all the chlorine generated. Or instead of starting with chloride of sodium and
insoluble basic oxide, I may start with a mixture of insoluble basic oxide such as
specified and the corresponding metallic chloride, the oxide always being in
sufficient quantity to absorb all the chlorine generated and the chloride solution of
sufficient strength to be highly conductive. If it be desired to evolve chlorine gas
the solutions may be the same but it is not necessary to use the insoluble basic
oxide except in conjunction with alkaline chloride for the purpose of forming a
soluble compound such as will be decomposed by the alkali, in order to protect the
lithanode from the action of any of the latter which might diffuse from the cathode
to the anode compartment.
If a platinum or carbon anode be used, no precautions are necessary for its
protection from the alkali and the invention then resides in the production of
alkali simultaneously with the production of a bleaching compound, by the absorption
of the nascent chlorine by means of an insoluble basic oxide, thereby economizing
the power which would be required for the evolution of gaseous chlorine.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is
1. In the process of electrolytically decomposing a solution of sodic or potassic
chloride, the use in the anode compartment of an insoluble or nearly insoluble basic
oxide for the purpose of fixing the nascent chlorine and thereby economising power,
substantially as specified.
2. In the process of electrolytically decomposing a solution of sodic or potassic
chloride, the use in conjunction with an anode of peroxide of lead of a chlorine
compound (of which the corresponding basic oxide is insoluble or nearly insoluble
in water) whereby to neutralize any alkali coming from the cathode compartment
and so protect the anode, as specified.
3. In the process of electrolytically decomposing a solution of sodic or potassic
chloride, the use in conjunction with an anode of peroxide of lead of an insoluble
or nearly insoluble basic oxide for the twofold purpose of fixing the nascent chlorine
and forming a soluble chlorine compound capable of neutralizing any alkali coming
from the cathode compartment and so protecting the anode, as specified.
Dated this 24th day of February 1893.
DESMOND G. FITZ-GERALD,
By A. M. & Wm. Clark,
53, Chancery Lane, London, Chartered Patent Agents.