Improvements in the Process of and Apparatus for the Electrolytic Decomposition of Solutions, and for the Immediate Separation therefrom of the Liquid or Dissolved Electrolytic Products:
Year: 1894

page_text: Date of Application (in United Kingdom), 14th June, 1894
Complete Specification Left, 13th Mar., 1895-Accepted, 13th - Apr., 1995.
Improvements in the Process of and Apparatus for the Electrolytic
Decomposition of Solutions, and for the Immediate Separation
therefrom of the Liquid or Dissolved Electrolytic Products:
I LÉON PAUL HULIN, of Modane (Savoie) France, Civil Engineer do hereby
declare the nature of this invention to be as follows:-
The electrolysis of saline solutions gives rise to the formation at the electrodes
of elementary products termed "ions" which appear either in the solid, liquid, or
gaseous state, according to the kind of salt which is decomposed.
The ions may be divided into two categories, riz. :—
1st. The insoluble ions;
2nd: The soluble ions.
When these products are insoluble in the electrolyte they separate of themselves
and their extraction may be effected by simple mechanical means; their insolubility
places them outside of the electrolytic circuit and beyond the reach of secondary
reactions. Under these conditions the electrolytic decomposition and the separation
of the products are complete.
When the electrolytic products (ions) are soluble in the electrolyte the progress
of the electrolytic operation and the results which ensue therefrom are materially
modified. The production of alkalies by the electrolysis of their salts in solution
may for instance serve as a typical example to facilitate the comprehension of the
developments hereafter set forth.
These ions, as soon as produced, become diffused throughout the salt solution
and form with the undecomposed salt mixed solutions which become gradually
richer in electrolytic products and proportionally poorer in the material operated
on until a point is reached at which the real output of the operation is almost nil.
The dispersion of the "ions" throughout the mother liquor is the primary cause of
the failures experienced in this kind of electrolytic operation.
It has not heretofore been possible to lay hold of the "ions" without having
allowed them to accumulate in the neighbourhood of the electrodes; but the total
decomposition of the primary electrolyte not being practicable in the midst of the
ions in excess, a considerable proportion of undecomposed salt is carried off
with them..
The accumulation of the ions in the electrolyte tends to cause them to
recombine, a tension of reconstitution is generated which increases with the
proportion of ions present so that the useful work is only the difference between
the electrolytic output and the consumption due to the reunion of the ionis.
The electrolytic action rapidly ceases to be totally efficient, for the dissolved
ions themselves form one or several electrolytes, either separately or by quiting

page_text: with the solvent or with any other element present. The result is the production
of what may be termed "lateral electrolysis" of which the importance increases as
the strength in ions. Consequently a state of equilibrium between these inverse
actions is inevitably reached, so that the electrolysis becomes factitious in that
there is no ascertainable output notwithstanding that there still remains in the
solution a considerable proportion of the salt to be decomposed. The useful effect
obtained by increasing the electromotive force at the electrodes in order to obtain
a more complete exhaustion is far from being proportional to this further
expenditure of electrical energy, for besides the causes of loss above set forth the
decomposition of the water of solution arises or increases. This parasitical
electrolysis is a considerable obstacle to the economical electrolysis of salts in
solution since it absorbs in pure waste an important part of the electric current
and its avoidance is therefore necessary in order to obtain a sufficient output in
industrial operations.
In order to overcome the anomalies above referred to, and particularly to avoid
the destruction of the products formed, recourse has been had heretofore to porous
diaphragms, septa, or partitions of various kinds, dialyzers, bells, and other
contrivances, dividing the electrolyte into fractions or compartments respectively
containing the anode and cathode. It has also been proposed to cause the ions to
enter into a combination which is more stable than the electrolyte, that is to say
into a molecular group whose thermo-chemical value is higher than that of the
compound submitted to electrolysis.
By these means the limit of useful decomposition is extended and the electrolysis
of the ions attenuated as well as their recombination, but the electrical resistance
is increased, the operation is complicated, and absolute constancy of the electrolytic
bath is not obtained. This is due to the fact that none of these expedients solves
the essential question, the fundamental condition upon which depends the avoidance
of the difficulties above indicated.
This radical solution of the question consists in effecting the immediate separation
of the soluble ions at the precise point and instant where and when they are
generated. It is this immediate separation which constitutes the very essence of
my invention and I will proceed to describe, with reference to the accompanying
drawings, forming part of this Specification various examples of the means whereby
it may be carried into practical effect.
The point of departure of my new method is based on the fact that the products
of electrolysis (ions) are formed only on the electrodes.
In examining this phenomenon in the case of the soluble ions I have ascertained
that the extreme surface of the electrolyte by which the current enters the solution,
that is to say the liquid layer without thickness which is the boundary of the bath
in contact with the electrode, was exclusively composed of the product of
electrolysis (ions).
In order to seize hold of and separate this layer at the very moment when it is
engendered by the electrolytic action, I devised the idea of causing it to pass
through the electrode itself, to the rear of the electrolyzed bath, by constructing the
electrode in the form of a filter. By this means two simultaneous and continuous
actions are established, viz. :-the electrolysis which produces the ions and the
filtration which separates them from the electrolyte, and this by means of a single
dévice, the filter electrode.
1 designate this characteristic combination electroly-filtration.
These conjoint actions have their values put in reciprocal harmony by means
which will be hereafter described with the apparatus.
The filter electrode may be constituted in various ways, provided that it achieves
the twofold object assigned to it. I employ by preference porous carbon in slabs,
whatever may be its origin and details of manufacture, provided that it is prepared
conformably with its destined use. This material is now manufactured by well
known methods it is a good conductor of electricity; it is sufficiently unattackable
under the conditions of its use; for my purpose, it is readily made in the form of

page_text: a homogeneous filtering medium, and it is cheap and commonly made of sizes
required in practice. With these filtering electrodes I construct a special
apparatus which I denominate an electroly-filter, which consists essentially of a
central compartment termed the electrolytic compartment which is limited on two
sides by each of the active faces of the two filter electrodes (anode and cathode)
and of two lateral compartments terined the evacuation compartments which are
contiguous to the inactive faces of the filter electrodes.
The liquid to be electrolyzed is continuously supplied to the electrolytic com-
partment, and penetrates whilst undergoing decomposition, the pores of the active
faces of the filter electrodes, the ions filtering continually through and passing out
at the inactive faces into the adjacent evacuation compartments where they are
collected.
This continual outflow of the ions through the electrodes is determined and
regulated by a difference of pressure between the electrolytic compartment and
the evacuation compartments.
Figures 1 and 2 represent in vertical section and plan an example of the complete
apparatus arranged in accordance with these essential principles, it being under-
stood that it may be modified and supplemented in details.
In a rectangular tank a of insulating material are placed parallel to one another
and at a certain distance from the ends two plates b, c, of conductive and porous
carbon, the dimensions of these plates being such as to make a tight joint d with
the sides and bottom of the tank. The two filter electrodes thus arranged divide
the tank into the three main compartments whereof the two outer ones are
provided with outflow apertures e at bottom respectively discharging into-
receptacles g, h. The middle electrolytic compartment is kept filled to a constant
level by any suitable feed apparatus which I have represented by the typical
supply vesself.
In order to enable the operation of my process and apparatus to be readily
understood I will take as an example the electro-chemical decomposition of a
solution of neutral sulphate of potash, it being understood that the process and
apparatus are equally applicable to the electrolysis of all salts in solution which
yield one or several soluble elements.
The decomposition of sulphate of potash as about to be described. has for its
principal object to produce a solution of caustic potash but I also obtain as a bye
product a solution of sulphuric acid.
In order to put the apparatus into active operation the electrolytic compartment X
is filled with a clarified solution of sulphate of potash and an electric current of
suitable strength is passed through the electrodes b, c, whereupon there is generated
conformably with the laws of electrolysis upon every point of the active surface of
the cathode a molecule of potash in a state of solution. Under the effect of
hydrostatic pressure this stratum of potassic molecules penetrates the substance
of the cathode and brings into contact therewith the adjacent stratum of liquid
containing undecomposed salt which is thereupon subjected to the electrolytic action
and which in turn passes off into the filtering orifices of the cathode.
There is thus brought about a continual renewal of the parallel vertical strata
of the liquid which become electrolyzed on coming into contact with the cathode
and which are absorbed by the latter and discharged at its opposite face into the
evacuation compartment Y. At the anode a similar phenomenon occurs it being in
this case a continuous succession of liquid strata in which is generated a solution of
sulphuric acid which under the pressure of the electrolyte passes as soon as formed
into the filtering substance of the anode and runs off at the inactive face thereot
into the other evacuation compartment Z. From the compartments Y, Z, the
solutions of potash and sulphuric acid run off by the outlets & and are received in
the respective vessels
h.
Instead of the filter electrodes being arranged in a vertical position they may be
placed horizontally the one above the other, as represented in Figure 3 in which
a is a frame of insulating material by which the electrodes are separated and against

page_text: which they are clamped by the vessels m aud secured together or to the inter-
mediate frame a by any suitable appliances, means being provided for making tight
joints at d. The solution to be decomposed is supplied continuously and at the
required pressure from a reservoir f placed at a higher level through a pipe i to
the space between the electrodes and passes off through the filter electrodes
after having undergone electrolytic action between which and the rate of evacuation
of the ions a proper relation is maintained. With this arrangement the liquid
pressure and consequently the filtration are uniform over all points of the surface
of the same electrode. The hydrostatic pressure which governs the output of the
electrolyzed liquid is so regulated as to correspond to the electrolytic decomposition,
or in other words the production and the evacuation of the ions is equalized either
by regulating the pressure which governs the filtration or the intensity of the
current which determines the rate of production.
The respective outputs of the anode and cathode are regulated conformably with
the relative values of the anion and cathion, either by selecting the electrodes
experimentally or by differentiating their surfaces and especially their thicknesses,
or by compensating the difference by the accumulation on one of them of the
filtered liquid as at Z in Figure 3. Here if as in the former case the solution
supplied to X is sulphate of potash, potash is collected at Y and sulphuric acid
at Z, these two solutions running off at the outlets e.
Besides the practical arrangements of the apparatus employed, my process
comprises, for the operation of said apparatus, the application of a special electrical
potential.
The production of alkalies by the electrolysis of their salts is the most important
of the various industries to which my electroly-filter may be applied.
Now the attempts which have been heretofore made in this direction have been
based on the total decomposition of a salt into its most simple elements. Thus for
example in treating a chloride of sodium solution for the extraction of soda at the
cathode and gaseous chlorine at the anode, a theoretical electromotive force of
about 2 to 3 volts is required; in practice from 4 to 6 volts and often more are
used for this kind of operation on account of the electrical resistance due to the
distance separating the electrodes in the electrolytic bath and the presence of
diaphragms.
The special features of my system are :-
1. A very low internal resistance by d.spensing with any diaphragm or partition
between the anode and cathode and by the fact that the electrodes may be placed
at a very small distance apart.
2. Absolute constancy of composition of the electrolyte.
3. The immediate and perfect separation of the dissolved ions and the absence
of polarization.
By these means I am enabled to isolate the alkalies from their salts by a simple
splitting up into their two binary elements, that is to say by liberating the base
(at the cathode) and the acid (at the anode) without further decomposition.
Ì thus avoid all parasitical consumption of the electrical energy brought into
action and all evolution of gases at the active surfaces of the electrodes and,
moreover, I am able to dispense with the use of expensive anodes of platinum.
In the case of a chloride of sodium solution for example soda is obtained at
the cathode and hydrochloric acid at the anode with a theoretical difference
of potential of
0-6 volt, whereas the decomposition of water requires
1.49 volts. The mean of these two limits, say 1 volt, is that which I prefer
to adopt in my process for the production of alkalies by means of my filter
electrodes.
13.7
23
=
The decomposition of chloride of sodium by my process is a curious example of
double exchange between the elements of the salt and those of the water in which
it is dissolved; the electric current only intervenes to furnish the balance of

page_text: energy necessary for the double decomposition that takes place and which may be
thus expressed symbolically :-
:-
NaCl +mHO + 06 volt = (NaO.HO+HO) + (HCl + n'HO)
Considering only the final result of my process it may be said that a solution of
sodium chloride filtered through two conductors between which there is maintained
a difference of potential of about 1 volt, yields on passing out a solution of soda
on the one hand and a solution of hydrochloric acid on the other hand, this output
being homogeneous and continuous.
My process is at once the most simple and most economical solution of the
industrial problem of transforming the chlorides and other salts of the alkalies
into caustic alkalies which may afterwards be converted into carbonates.
In the practical application of the process a sufficient number of electroly-filters
would be grouped together and connected up by suitable conductors or contacts
either in series or multiple are to a suitable source of electricity and so as to
conform to the conditions above specified. By suitable arrangements, which will
be readily imagined, a group of filter electrodes may be grouped together in a
single main tank. The electrodes, instead of being plane, may be of various forms
and they may be tubular, the external face being the active one and the interior
the evacuation compartment.
In the arrangement represented in Figures 1 and 2 the filtration is not uniform
over the whole height of the filter electrodes but in Figure 4 I have illustrated
special arrangement of the electrodes and compartments whereby the filtering
action is equalized over the whole height of a vertically placed electrode.
To accomplish this I cover over its whole width the upper part of the active
face of the electrode with a sheet of indiarubber j closely applied which descends
a sufficient distance below the upper edge of the tank, say to the level of k for
instance. The discharge outlets e instead of being at the bottom are situated in
the sides of the compartments a little above the level k so that at the back of the
electrodes there is a constant head of liquid of less height than that in the
electrolytic compartment X and which has the effect of equalizing the outflow
pressure of the electrolyte at all points of its height, the effective pressure upon
any given point of the electrode corresponding in fact to the difference of level
between the liquid in the middle compartment X and that in the outflow
compartment, that is to say to the height H.
In Figure 4 is the supply reservoir as before, whereby a constant level is
maintained, and Y, Z, are the compartments where the ious are collected and whence
they overflow through e into receptacles g and h.
Figure 5 illustrates a modification of the electroly-filter whose main features
are that the electrodes are vertical and have a uniform filtering action, the filtering
pressures are variable at will, the elements are readily dismountable, and are
applicable to the decomposition of all chemical compounds producing soluble
ions; this arrangement being particularly suitable for experimental work and
research in laboratories and works. In this figure the same letters of reference
have the same signification as in Figure 3, a being the intermediate frame between
the opposite sides of which and the outer chambers m and n are clamped the filter
electrodes b and c, tight joints being made at d, the whole being held together by
means of any suitable appliance, and e being the outlets by which the ions are
discharged into the receptacles y and h. f is the supply reservoir placed in
communication with the middle compartment X by the tube i; Y, Z, being the
compartments in which the ions are collected.
The filter electrode may also be employed in any other form of apparatus, with
or without partitions, and in combination with an ordinary electrode of any kind
in the case when for example the compound to be electrolyzed yields an
insoluble
ion and a soluble ion.
It may also be used with a higher difference of potential than that previously
indicated, but when gases are disengaged the regularity of the operation is

page_text: prejudiced as regards the electrolysis and filtration and the economical result is
inferior.
For the construction of the filter electrodes other suitable materials than carbon
may be employed; for instance metals in the spongy condition when there is no
liability of their being attacked, or agglomerated mixtures of conductive, insoluble,
and filtering materials either mounted on a support or forming a single piece.
The electrodes may also be formed by the superposition in the flat of thin
narrow strips of conductive material accurately superposed and pressed together
to a suitable degree so as to allow the liquid to filter between them. These strips
may be bound together by a frame, rods, or other means of support. They may
also be formed of cells or conductive frames filled with suitably compressed
powders or with porous or spongy substances.
I may also form the filter electrodes by juxtaposing either a metallic gauze or
a perforated conductive plate and a filtering medium such as fabric, asbestos, or the
like, or in other words by combining together a conductor and a suitable filtering
surface so as to cause them to act conjointly as electrode and filter.
In short I may use for the purposes of electroly-filtration, electrodes of conductive
material pierced with a great number of small holes very close together and
giving passage to the ions through the electrode, or metallic ganze of fine mesh
for the same purpose.
But these are mere modifications of, and are inferior to, the
true filter electrode, which is formed of a single material and acts both as conductor
.and filtering medium.
In carrying my process of electroly-filtration into effect 1 may according to
circumstances and according to the nature of the salts treated, either heat or cool
the solution under treatment or incidentally bring it under any required physical
or mechanical condition.
•
Dated this 14th dex of Luna 1904
L. P. HULIN,
By A. M. & Wm. Clark,
53, Chancery Lane, London, Chartered Patent Agents.
COMPLETE SPECIFICATION.
Improvements in the Process of and Apparatus for the Electrolytic
Decomposition of Solutions, and for the Immediate Separation
therefrom of the Liquid or Dissolved Electrolytic Products.
.
1, LEON PAUL HULIN, of Modane, (Savoie), France, Civil 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:
The electrolysis of saline solutions gives rise to the formation, at the electrodes,
of elementary products termed "ions," which appear either in the solid, liquid, or
gaseous state, according to the kind of salt which is decomposed.
The ions may be divided into two categories, viz. :-
1st. The insoluble ions;
2nd. The soluble ions.
When these products are insoluble in the electrolyte, they separate of themselves
and their extraction may be effected by simple mechanical means; their insolubility
places them outside of the electrolytic circuit and beyond the reach of secondary
reactions. Under these conditions the electrolytic decomposition and the separation
of the products are complete.
When the electrolytic products (ions) are soluble in the electrolyte, the progress
of the electrolytic operation, and the results which ensue therefrom, are materially

page_text: modified. The production of alkalies by the electrolysis of their salts in solution
may, for instance, serve as a typical example to facilitate the comprehension of the
developments hereafter set forth.
These ions, as soon as produced, become diffused throughout the salt solution
and form with the undecomposed salt mixed solutions which become gradually
richer in electrolytic products and proportionally poorer in the material operated
on, until a point is reached at which the real output of the operation is almost nil.
The dispersion of the "ions" throughout the mother liquor is the" primary cause
of the failures experienced in this kind of electrolytic operation.
"
It has not heretofore been possible to lay hold of the "ions without having
allowed them to accumulate in the neighbourhood of the electrodes; but the total
decomposition of the primary electrolyte not being practicable in the midst of the
ions in excess, a considerable proportion of undecomposed salt is carried off with
them.
The accumulation of the ions in the electrolyte tends to cause them to recombine,
a tension of reconstitution is generated which increases with the proportion of ions
present, so that the useful work is only the difference between the electrolytic
output and the consumption due to the reunion of the ions.
The electrolytic action rapidly ceases to be totally efficient, for the dissolved
ions themselves form one or several electrolytes, either separately or by uniting
with the solvent or with any other element present. The result is the production
of what may be termed "lateral electrolysis," of which the importance increases
as the strength in ions. Consequently a state of equilibrium between these inverse
actions is inevitably reached, so that the electrolysis becomes factitious in that
there is no ascertainable output, notwithstanding that there still remains in the
solution a considerable proportion of the salt to be decomposed. The useful effect
obtained by increasing the electro-motive force at the electrodes, in order to obtain
à more complete exhaustion, is far from being proportional to this further
expenditure of electrical energy, for besides the causes of loss above set forth the
decomposition of the water of solution arises or increases. This parasitical
electrolysis is a considerable obstacle to the economical electrolysis of salts in
solution, since it absorbs in pure waste an important part of the electric current and
its avoidance is therefore necessary in order to obtain a sufficient output in
industrial operations.
In order to overcome the anomalies above referred to, and particularly to avoid
the destruction of the products formed, recourse has been had, heretofore, to porous
diaphragms, septa, or partitions of various kinds, dialyzers, bells, and other con-
trivances, dividing the electrolyte into fractions or compartments respectively
containing the anode and cathode. It has, also, been proposed to cause the ions to
enter into a combination which is more stable than the electrolyte, that is to say
into a molecular group whose thermo-chemical value is higher than that of the
compound submitted to electrolysis.
By these means the limit of useful decomposition is extended and the electrolysis
of the ions attenuated as well as their recombination, but the electrical resistance
is increased, the operation is complicated, and absolute constancy of the electrolytic
bath is not obtained. This is due to the fact that none of these expedients solves
the essential question, the fundamental condition upon which depends the avoidance
of the difficulties above indicated.
This radical solution of the question consists in effecting the immediate separation
of the soluble ions at the precise point and instant where and when they are
generated. It is this immediate separation which constitutes the very essence of
my invention, and I will proceed to describe, with reference to the drawings
accompanying my Provisional Specification, various examples of the means whereby
it may be carried into practical effect.
The point of departure of my new method is based on the fact that the products.
of electrolysis (ions) are formed only on the electrodes.
In examining this phenomenon in the case of the soluble ions, I have ascertained

page_text: that the extreme surface of the electrolyte by which the current enters the solution,.
that is to say the liquid layer without thickness which is the boundary of the
bath in contact with the electrode, was exclusively composed of the product of
electrolysis (ions)..
In order to seize hold of, and separate, this layer at the very moment when it is
engendered by the electrolytic action, I devised the idea of causing it to pass
through the electrode itself, to the rear of the electrolyzed bath, by constracting
the electrode in the form of a filter. By this. means, two simultaneous and con-
tinuous actions are established, viz. :-the electrolysis which produces the ions and the
filtration which separates them from the electrolyte, and this by means of a single
device, the filter-electrode..
I designate this characteristic combination electroly-filtration.
These conjoint actions have their values put in reciprocal harmony by means
which will be hereafter described with the apparatus.
The filter-electrode may be constituted in various ways, provided that it achieves
the twofold object assigned to it. I employ by preference porous carbon in slabs,
whatever may be its origin and details of manufacture, provided that it is prepared
conformably with its destined use. This material is now manufactured by well
known methods; it is a good conductor of electricity; it is sufficiently unattackable
under the conditions of its use; for my purpose, it is readily made in the form of a
homogeneous filtering medium; and it is cheap, and commonly made of sizes
required in practice. With these filtering electrodes I construct a special apparatus
which I denominate an electroly-filter, which consists essentially of a central
compartment, termed the electrolytic compartment, which is limited on two sides
by each of the active faces of the two filter electrodes (anode and cathode) and of
two lateral compartments, termed the evacuation compartments, which are contiguous
to the inactive faces of the filter electrode.
The liquid to be electrolyzed is continuously supplied to the electrolytic com-
partment, and penetrates, whilst undergoing decomposition, the pores of the active
faces of the filter electrodes, the ions filtering continually through and passing out
at the inactive faces into the adjacent evacuation compartments, where they are
collected.
This continual outflow of the ions through the electrodes is determined and
regulated by a difference of pressure between the electrolytic compartment and the
evacuation compartments.
Figures 1 and 2 represent, in vertical section and plan, an example of the
complete apparatus arranged in accordance with these essential principles, it being
understood that it may be modified and supplemented in details.
In a rectangular tank a of insulating material are placed parallel to one another,
and at a certain distance from the ends two plates b, c, of conductive and porous
carbon, the dimensions of these plates being such as to make a tight joint d with
the sides and bottom of the tank. The two filter-electrodes thus arranged divide
the tank into the three main compartments whereof the two outer ones are provided
with outflow apertures e at bottom, respectively discharging into receptacles g,
The middle electrolytic compartment is kept filled to a constant level by any
suitable feed apparatus, which I have represented by the typical supply vessel f.
h.
In order to enable the operation of my process and apparatus to be readily
understood, I will take as an example the electro-chemical decomposition of a
solution of neutral sulphate of potash, it being understood that the process and
apparatus are equally applicable to the electrolysis of all salts in solution which
yield one or several soluble elements.
The decomposition of sulphate of potash as about to be described, has for its
principal object to produce a solution of caustic potash, but I also obtain, as a
bye-product, a solution of sulphuric acid.
In order to put the apparatus into active operation, the electrolytic com-
partment X is filled with a clarified solution of sulphate of potash and an electric
current of suitable strength is passed through the electrodes b, c, whereupon there

page_text: is generated conformably with the laws of electrolysis upon every point of the
active surface of the cathode a molecule of potash in a state of solution. Under
the effect of hydrostatic pressure this stratum of potassic molecules penetrates the
substance of the cathode and brings into contact therewith the adjacent stratum
of liquid containing undecomposed salt which is thereupon subjected to the
electrolytic action and which in turn passes off into the filtering orifices of the
cathode.
There is thus brought about a continual renewal of the parallel vertical strata of
the liquid which become electrolyzed on coming into contact with the cathode and
which are absorbed by the latter and discharged at its opposite face into the.
evacuation compartment y. At the anode a similar phenomenon occurs, it being, in
this case, a continuous succession of liquid strata in which is generated-a solution of
sulphuric acid which under the pressure of the electrolyte passes as soon as formed.
into the filtering substance of the anode and runs off at the inactive face thereof
into the other evacuation compartment 2. From the compartments y, the
solutions of potash and sulphuric acid run off by the outlets e and are received in
the respective vessels
h.
.
be
Instead of the filter-electrodes being arranged in a vertical position, they may
placed horizontally the one above the other, as represented in Figure 3, in which
a is a frame of insulating material by which the electrodes are separated and
against which they are clamped by the vessels m and n secured together or to the
intermediate frame a by any suitable appliances, means being provided for making
tight joints at d. The solution to be decomposed is supplied continuously and at
the required pressure from a reservoir placed at a higher level through a pipe i
to the space X between the electrodes, and passes off through the filter electrodes.
after having undergone electrolytic action between which and the rate of evacuation
of the ions a proper relation is maintained. With this arrangement the liquid
pressure, and consequently the filtration, are uniform over all points of the surface
of the same electrode. The hydrostatic pressure which governs the output of the
electrolyzed liquid is so regulated as to correspond to the electrolytic decomposition,
or in other words the production and the evacuation of the ions is equalized, either
by regulating the pressure which governs the filtration or the intensity of the
current which determines the rate of production.
The respective outputs of the anode and cathode are regulated conformably with
the relative values of the anion and cathion, either by selecting the electrodes:
experimentally or by differentiating their surfaces and especially their thicknesses,
or by compensating the difference by the accumulation, on one of them, of the
filtered liquid, as at in Figure 3. Here if, as in the former case, the solution
supplied to X is sulphate of potash, potash is collected at y and sulphuric acid at =,
these two solutions running off at the outlets e.
Besides the practical arrangements of the apparatus employed, my process
comprises, for the operation of said apparatus, the application of a special electrical
potential.
The production of alkalies by the electrolysis of their salts is the most important
of the various industries to which my electroly-filter may be applied.
Now the attempts which have been heretofore made in this direction have been
based on the total decomposition of a salt into its most simple elements. Thus, for
example, in treating a chloride of sodium solution for the extraction of soda at the
cathode and gaseous chlorine at the anode, a theoretical electromotive force of
about 2 to 3 volts is required; in practice from 4 to 6 volts, and often more, are
used for this kind of operation, on account of the electrical resistance due to the
distance separating the electrodes in the electrolytic bath and the presence of
diaphragms.
The special features of my system are:-
1. A very low internal resistance by dispensing with any diaphragm or partition
between the anode and cathode and by the fact that the electrodes may be placed
11 15
"

page_text: 2. Absolute constancy of composition of the electrolyte.
3. The immediate and perfect separation of the dissolved ions and the absence of
clarization.
By these means I am enabled to isolate the alkalies from their salts by a simple
splitting up into their two binary elements, that is to say by liberating the base (at
the cathode) and the acid (at the anode) without further decomposition. I thus
avoid all parasitical consumption of the electrical energy brought into action and
all evolution of gases at the active surfaces of the electrodes, and, moreover, I am
able to dispense with the use of expensive anodes of platinum.
13.7
23
=
In the case of a chloride of sodium solution, for example, soda is obtained at the
cathode and hydrochloric acid at the anode, with a theoretical difference of
potential of
0.6 volt, whereas the decomposition of water requires
1.49 volts. The mean of these two limits, say, 1 volt, is that which I prefer to
adopt in my process for the production of alkalies by means of my filter-
electrodes.
The decomposition of chloride of sodium by my process is a curious example of
double exchange between the elements of the salt and those of the water in which
it is dissolved; the electric current only intervenes to furnish the balance of
energy necessary for the double decomposition that takes place and which may be
thus expressed symbolically :-
:-
NaCl +mHO + 0.6 volt = (NaO.HOnHO) + (HCl + n'HO)
Considering only the final result of my process, it may be said that a solution of
sodium chloride filtered through two conductors between which there is maintained
a difference of potential of about 1 volt, yields on passing out a solution of soda on
the one hand and a solution of hydrochloric acid on the other hand, this output
being homogeneous and continuous..
My process is at once the most simple and most economical solution of the
industrial problem of transforming the chlorides and other salts of the alkalies into
caustic alkalies which may afterwards be converted into carbonates.
In the practical application of the process a sufficient number of electroly-filters
would be grouped together and connected up by suitable conductors or contacts,
either in series or multiple arc, to a suitable source of electricity and so as to
conform to the conditions above specified. By suitable arrangements, which will
be readily imagined, a group of filter-electrodes may be grouped together in a
single main tank. The electrodes, instead of being plane, may be of various forms
and they may be tubular, the external face being the active one and the interior
the evacuation compartment.
In the arrangement represented in Figures 1 and 2, the filtration is not uniform
over the whole height of the filter-electrodes, but in Figure 4 I have illustrated a
special arrangement of the electrodes and compartments whereby the filtering
action is equalized over the whole height of a vertically placed electrode.
To accomplish this, I cover over its whole width the upper part of the active
face of the electrode with a sheet of indiarubber j closely applied, which descends
a sufficient distance below the upper edge of the tank, say, to the level of k, for
instance. The discharge outlets e, instead of being at the bottom, are situated in
the sides of the compartments a little above the level k, so that at the back of the
electrodes there is a constant head of liquid of less height than that in the electro-
lytic compartment X and which has the effect of equalizing the outflow pressure of
the electrolyte at all points of its height, the effective pressure upon any given
point of the electrode corresponding in fact to the difference of level between the
liquid in the middle compartment X and that in the outflow compartment, that is
to say to the height H.
In Figure 4, f is the supply reservoir, as before, whereby a constant level is
maintained, and y, z, are the compartments where the ions are collected and whence
they overflow through e into receptacles g and h.

page_text: Figure 5 illustrates a modification of the electroly-filter whose main features are
that the electrodes are vertical and have a uniform filtering action, the filtering
pressures are variable at will, the elements are readily dismountable, and are
applicable to the decomposition of all chemical compounds producing soluble ions;
this arrangement being particularly suitable for experimental work and research in
laboratories and works. In this figure the same letters of reference have the same
signification as in Figure 3, a being the intermediate frame between the opposite
sides of which and the outer chambers m and n are clamped the filter electrodes b
and c, tight joints being made at d, the whole being held together by means of any
suitable appliance, and e being the outlets by which the ions are discharged into
the receptacles g and h. is the supply reservoir placed in communication with
the middle compartment X by the tube i; y, z, being the compartments in
which the ions are collected.
The filter-electrode may, also, be employed in any other form of apparatus;
with or without partitions; and in combination with an ordinary electrode of any
kind in the case when, for example, the compound to be electrolyzed yields an
insoluble ion and a soluble ion.
It may also be used with a higher difference of potential than that previously
indicated, but when gases are disengaged the regularity of the operation is
prejudiced as regards the electrolysis and filtration and the economical result is
inferior.
For the construction of the filter-electrodes other suitable materials than carbon
may be employed, for instance metals in the spongy condition when there is no
liability of their being attacked, or agglomerated mixtures of conductive, insoluble,
and filtering materials either mounted on a support or forming a single piece.
The electrodes may also be formed by the superposition in the flat of thin narrow
strips of conductive material accurately superposed and pressed together to a
suitable degree so as to allow the liquid to filter between them. These strips may
be bound together by a frame, rods, or other means of support. They may also be
formed of cells or conductive frames filled with suitably compressed powders or
with porous or spongy substances.
I may also form the filter electrodes by juxtaposing either a metallic gauze or a
perforated conductive plate and a filtering medium, such as fabric, asbestos, or the
like, or in other words by combining together a conductor and a suitable filtering
surface so as to cause them to act conjointly as electrode and filter.
In short, I may use for the purpose of electroly-filtration, electrodes of
conductive material pierced with a great number of small holes very close together
and giving passage to the ions through the electrode, or metallic gauze of fine
mesh for the same purpose.
But these are mere modifications of, and are inferior
to, the true filter-electrode, which is formed of a single material and acts both as
conductor and filtering medium.
In carrying my process of electroly-filtration into effect, I may, according to
circumstances and according to the nature of the salts treated, either heat or cool
the solution under treatment, or incidentally bring it under any required physical
or mechanical condition.
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. The herein described process denominated electroly-filtration, and in particular
the general method of operating, which consists in carrying off the dissolved or
liquid ions at the precise point and moment where and when they are generated on
the electrodes.
2. In the herein described process of electroly-filtration, the application of porous
electrodes or filter-electrodes having only one electrically active surface exposed to
the pressure of the electrolyte whilst the other electrically inactive surface is
subjected to a lesser pressure and gives passage to the ions.

page_text: 3. The several arrangements of electroly-filter apparatus having vertical or
horizontal electrodes herein described and illustrated in the annexed drawings.
4. The application of my process and apparatus to the manufacture of all liquid
products capable of being produced by electrolysis and preferably by the employ-
ment of such a difference of potential at the electrodes that ouly soluble ions are
formed in the operation upon the filter electrodes.
5. The manufacture of caustic soda and hydrochloric acid by the electroly-
filtration of a solution of sodium chloride at a difference of potential of about
1 volt, and also the manufacture of potash or other base from other salts than
chlorides, as specified.
Dated this 13th day of March 1895
A. M. & WM. CLARK,
53, Chancery Lane, London, Chartered Patent Agents.