Improvements relating to the Electrolytic Decomposition of Alkaline Salts.
Year: 1898

page_text: Date of Application, 5th Sept., 1898
Complete Specification Left, 5th June, 1899-Accepted, 2nd Sept., 1899
PROVISIONAL SPECIFICATION.
Improvements relating to the Electrolytic Decomposition of Alkaline
Salts.
I, EDWIN EDSER, of 34, Mexfield Road, Putney, S.W., Gentleman, do hereby
declare the nature of this invention to be as follows:-
This invention relates to the electrolytic decomposition of alkaline salts and
more especially for the production of alkaline hydrates in which process an
amalgam of the alkaline metal is formed as an intermediate product.
The invention has for its object to provide an electrolytic cell that shall be
simple in construction efficient in operation and in which there shall be a
minimum of electric resistance and perfect purity of the resulting product.
The invention consists in the provision within an electrolytic cell of a partition
composed of a series of troughs so shaped and disposed as to contain a quantity
of mercury which seals the interstices between the troughs and so effectually pre-
vents the mixture of the respective liquids contained in the compartments
separated by such partition while permitting by means of the mercury through
electric communication between the compartments. In action an amalgam is
formed upon one side of the partition by the deposit of the alkaline metal upon
the mercury while upon the other caustic alkali is produced by the action of the
metal upon the water.
The invention further consists in detail features of construction and arrange-
ment which are hereinafter described.
In carrying the invention into effect a vessel is provided which is divided into
two compartments by means of a partition consisting of vertical series of longi-
tudinally extending troughs of V or similar section made of any convenient
electrically non-conducting substance or of any other suitable material which for
insulation may be coated with enamel or varnish. These troughs are so shaped
and disposed one above the other that when nearly filled with mercury the spaces
between the troughs shall be sealed and the partition will thereby effectually
separate the two compartments which it divides so that no mixture of the liquids
contained in the respective compartments can take place.
The one compartment is nearly filled with a solution of alkaline salt, say
chloride of sodium (Na CI), that is to be electrolized while the other is nearly
filled with water or weak solution of caustic alkali, (Na OH). Electrodes com-
posed of suitable substances are provided and these are connected to a dynamo or
other source of electric current.
On the passage of an electric current through the cell in such a direction that
it passes from the brine solution through the mercury to the alkaline solution
sodium amalgam will be formed upon the free surface of the mercury which is in
contact with the solution of chloride of sodium. Sodium will pass through the
mercury and form caustic soda upon contact with the water in the other compart-
ment, at which the other free surface of the mercury in the respective troughs
is exposed.

page_text: The chlorine liberated in the first or anode compartment and the hydrogen
liberated in the second or cathode compartment may be collected for use.
The process may be rendered continuous by supplying brine solution to the
lower part of the first compartment and drawing off the weakened solution near
the surface in the same compartment while water may be supplied to the second
compartment near the surface and the strong alkaline solution withdrawn from
a point near the bottom of the same compartment. A number of such cells may
be provided whose respective compartments shall be connected together so that
the brine solution shall flow from the anode compartment of one cell to the
anode compartment of another in succession whilst water may be introduced
and caused to flow through the respective cathode compartments in the series of
cells in an opposite direction to the flow of the brine solution becoming stronger
as it passes through each cell.
Instead of providing a longitudinal partition a circular partition may be pro-
vided consisting of a series of circular troughs such partition dividing the cell
into an inner central compartment and an outer annular compartment in which
respectively the brine solution may be supplied and the alkaline solution produced.
Mercury may be poured into the series of troughs by filling the uppermost and
permitting overflow into the trough immediately beneath and so on until the
whole series of troughs are filled with mercury.
For convenience in filling the troughs and to preclude spilling of the mercury
while also to ensure that each trough shall be filled, the troughs may be provided
with one of their walls upwardly extending beyond the other, the alternate edges
of the troughs upon each side being extended so that the downward flow of mercury
shall be over the lower edge of one trough and the overflow received by the
extended side of the trough next beneath, or, instead of providing a continuous
extension of the alternate sides of the troughs, a partial extension alone may be
alternately provided and arranging that the overflow shall be limited to a particular
part of the edge of each trough.
In order to procure the maximum amount of surface of mercury exposed upon
each side of the partition to the salt and alkaline solutions, the troughs are pre-
ferably provided of a shallow V section with downwardly extending ribs which
latter alone dip into the mercury provided in the adjacent trough. No limitation,
however, is placed to such a construction of the partition as instead the troughs
may be provided so as to fit one within the other thereby providing an inter-
stitial space between of the same depth; or any other suitable shape and dis-
position of the troughs may be made without departing from the essential feature
of the invention. Again no limitation is placed to the vertical disposition of the
troughs forming the partition when provided to extend horizontally in the cell
as the partition may obviously be disposed in an inclined position. In order to
ensure that the density of liquid in the one compartment shall not so exceed
that in the other as to break the mercury seals and so effect admixture of the
liquids an equalising or regulating arrangement may be provided. Such equalis-
ing or regulating arrangement may consist of a U tube provided beneath the cell
and connecting the two compartments, in the arms of which tube pistons may be
provided between which mercury is placed so that any difference of pressure in
the compartments will effect a downward movement of one piston and an upward
movement of the other and to such an extent that a port may be opened which
permits a quantity of the denser liquid to flow out thereby equalising the density
in the two compartments.
Further, in another manner of carrying the invention into effect a horizontal
partition may be provided composed of a number of elements of substantially
section such elements being arranged side by side and each providing a channel
for the reception of the mercury upon one side and a flange for dipping into the
channel of the next so that when sufficient mercury is poured into each of the
elements previously laid in horizontal series in connection one with the other,
the vessel is divided into two compartments effectually separated by the mercury

page_text: seals for when once the lower or cathode compartment has been completely filled
with weak alkaline solution the upper or annode compartment may be filled with
a brine solution without any fear of the two liquids mixing. Electrodes are
placed in the respective compartments. Strong brine solution is continuously
fed into the upper compartment near the partition and withdrawn from near the
top of that compartment while water is fed into the upper part and alkali solution
withdrawn from the lower part of the lower compartment.
A hood may be provided in the lower compartment by means of which the
hydrogen gas evolved may be withdrawn and similarly means may be provided
for the withdrawal of the chlorine gas evolved in the upper compartment.
It is obvious that no limitation is placed to the particular shape or disposition
of the troughs forming the partition nor to the shape and disposition of the
partition.
By the provision of such a cell the use of moving parts for the agitation or move-
ment of the mercury is obviated while a thoroughly efficient cell is simply and
economically provided according to this invention.
Dated this 5th dox of Santombor 1898
Improvements relating to the Electrolytic Decomposition of Alkaline
Salts.
I, EDWIN EDSER, of 34, Mexfield Road, Putney, London, S.W., Gentleman, 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 the electrolytic decomposition of alkaline salts and
more especially for the production of alkaline hydrates in which process an
amalgam of the alkaline metal is formed as an intermediate product.
The invention has for its object to provide an electrolytic cell that shall be
simple in construction efficient in operation and in which there shall be a
minimum of electric resistance, a minimum amount of mercury employed and
perfect purity of the resulting products.
The invention consists in the provision within an electrolytic cell of a partition
composed of a series of troughs so shaped and disposed as to contain a quantity
of mercury which seals the interstices between the troughs and so effectually pre-
vents the mixture of the respective liquids contained in the compartments
separated by such partition while permitting by means of the mercury through
electric communication between the compartments. In action an amalgam is
formed upon one side of the partition by the deposit of the alkaline metal upon
the mercury while upon the other caustic alkali is produced by the action of the
diffused sodium upon the water.
The invention further consists in detail features of construction and arrange-
ment which are hereinafter described.
-
The invention is illustrated in the accompanying drawings in which:
Figure 1 is a sectional elevation of an electrolytic cell made according to the
invention.
Figure 2 is a plan corresponding thereto but with the gas collecting hood
removed.
Figure 3 is a sectional end elevation corresponding to Figure 1, and

page_text: Figure 4 is a part sectional plan on the line 1, 2, Figure 1.
Figure 5 is a front detail elevation of a preferable form of cathode plate
employed in the combining compartment of the cell.
Figure 6 is a sectional elevation of an equalising or regulating arrangement
that may be employed.
Figures 7, 8, and 9 are respectively part sectional elevation, plan and sectional
elevation of a modification in construction.
Figure 10 is a detail plan of the lid or cover to the inner compartment of the
cell illustrated in Figures 7 8, and 9.
Figures 11, 12 and 13 are respectively sectional elevation, sectional plan, and
plan of a further constructional modification.
Figure 14 is a diagrammatic elevation of a modification in construction wherein
a series of separate compartments are employed divided by means of troughs con-
taining mercury.
Figure 15 is a constructional modification wherein a horizontal partition instead
of a vertical partition is employed consisting of a series of troughs containing
mercury having its surface exposed to the upper and lower compartment formed
by such partition.
Figures 16, 17, 18 and 18* illustrate diagrammatically means that may be
employed for filling a vertical series of troughs.
Figure 19 illustrates in diagrammatic section a method of continuous working
by the connection of a series of cells, and
Figure 20 illustrates in diagrammatic section the connection of a series of cells
with the intermediate salt boxes by means of which the salt solution is
strengthened and maintained at a constant density.
Figures 21 and 22 are sectional detail views of the troughs employed according
to the invention to form a separating partition.
In carrying the invention into effect as illustrated in Figures 1 to 5 of the
accompanying drawings, a vessel a is provided which is divided into two com-
partments by means of two partitions consisting of vertical series of longitudinally
extending troughs c of V or similar section made of any convenient electrically
non-conducting substance or of any other suitable material. These troughs c are
held within frames bb consisting of lateral vertical members d and lower longi-
tudinal members e and the extremities of the troughs are retained within the
frames. The frames are connected together by means of the lateral walls f
on each side, and a bottom plate g. by means of which the space between the
partitions is completely enclosed to form a central compartment. Plates / effect
the encloure of the central compartment at its upper part. The troughs c are so
shaped and disposed one above the other that when nearly filled with mercury the
spaces between the troughs shall be filled and sealed and partitions or frames bb
will thereby effectually separate the compartments which they divide, so that
no mixture of the liquids contained in the respective compartments can take place.
The frames bb are integrally formed with a cross frame i which is carried upon
base supports j. The cross frame i has a central aperture m through which the
carbon rods or plates are introduced into the central inner compartment k. The
carbon plates are suspended upon a rod whose extremities are downwardly
diverted into troughs n, formed in the cross frame i and filled with mercury.
The wire terminals are placed in the interior openings o of the troughs n and by
means of the mercury the current is led into the cell. A channel is formed in
the cross frame i round the aperture m into which mercury is poured to form a
gas-tight seal for a gas collecting hood. by means of which the gas forming in
the inner compartment is led away. The mercury surfaces are protected from
the action of the chlorine by a layer of vaseline or other oil.
The cathodes of the exterior compartment are preferably formed of metallic
frames s upon which iron wire is stretched or woven. The frames s are sus-
pended from the cross frame which is recessed at u and for the purpose; and
the extremities of the frames s are downwardly diverted into small troughs

page_text: provided in the cross frame. These troughs are filled with mercury and serve
to receive the wire terminals by means of which the current is led away. The
recesses u v permit of the free egress from the cell of the gas generated in the
exterior compartment y. A copper or other metallic strip is fitted within
recesses provided in the lateral members d of the frames b b and copper or other
metallic pins 3 are driven or inserted transversely, so as to connect such strip with
the frame and serve for supporting the troughs c and for the electric connection
of the strip with the mercury contained in the several troughs c of the series.
The strips are provided with an upper hooked extremity 4 passing within
troughs 5 formed in the cross frame i and filled with mercury. By such means
the current may be led out through the mercury, as hereafter described.
As illustrated in Figure 22 the trough C instead of being provided of insulating
material as in Figure 21 may be of metal preferably covered by means of mica 51
or other such insulating material, upon the surface in contact with the liquids
in the respective compartments, while the ribs or flanges 52 are preferably
amalgamated so that thereby a better contact will be effected with the mercury
in the troughs, and thereby leakage of liquid from one compartment to the other
may be prevented.
The inner compartment is nearly filled with a solution of alkaline salt,-say
chloride of sodium (Na Cl) that is to be electrolysed, while the outer compart-
ment y is nearly filled with water or a solution of caustic alkali (Na O H).
On the connection of the cell with a dynamo or other source of electric current
the sodium chloride solution is electrolysed in the inner compartment and
sodium as a cation is deposited upon the mercury in the several troughs c, and
chlorine as an anion is set free passing upward into the hood q and away to be
utilized in production of bleaching powder or for other purpose, while the sodium
amalgam thus formed with the mercury diffuses through to the free surfaces of
the mercury in the outer chamber and there the sodium becomes chemically
and electrolytically dissolved on contact with water so that sodium hydrate is
formed and hydrogen gas as a cation is evolved at the cathode r which may if
desired be collected for use.
In Figures 7, 8, 9, and 10 a constructional modification is illustrated wherein
an exterior containing vessel a which may be of porcelain or other suitable
non-conducting material is employed and a base part 13 which may likewise be of
porcelain serves to support the partitions b, band their containing frames. In
this case two end plates 14 are provided also preferably of porcelain and have both
two circular vertical recesses 15 on each side for retaining the extremities of the
troughs c. The troughs are firmly fitted to the end plates 14 by means of copper
or other metal rods 16 which are provided in the recesses 15 and are each fitted
with transverse supporting wires or strips of metal 3 upon which the edges of
the troughs c rest, and the whole are fitted together by letting in a luting 17 of
paraffin wax or other suitable cement. The respective lowermost troughs 18
have their extremities resting upon the respective bases 19 of the end plates 14
while their downwardly projecting edges or flanges 20 protrude into a channel 21
provided in the base part 13 which is filled with mercury so that an effective seal
may be formed thereby. The channel 21 extends around and near the edge of
the base 13 and the seal is completed at the respective ends by a flange 22 pro-
vided upon the base 19 of the respective end plates in continuation of the flanges 20
upon the lowermost trough of each series. Each of the end plates 14 is provided
centrally at its upper extremity with a small trough 23 for the reception of mer-
cury a contact screw 24 in each case projecting from the exterior into the trough
to which the terminals of a dynamo may be connected for leading the current in
to the cell.
A cover plate 25 is fitted upon and connects the tops of the end plates 14. The
upper parts of the partitions b, b, as in the former case are provided with plates h
whose upper edges engage with grooves 26 provided on the underside of the cover
plate 25 so as to form a gas tight joint. The cover plate 25 is secured in position

page_text: by means of screws passing into the copper rods 16, the screws at the same time
serving as terminals by means of which current may be led out of the mercury
partition; the current thereby being utilized in the decomposition of the salt
but not in the solution of the metal.
The cover plate 25 is provided with a channel 27 which is filled with mercury
and effects a seal on the insertion therein of the edges of the collecting hood g
by means of which the chlorine gas evolved in the inner compartment is led
away.
Iron cathodes r are suspended in the outer compartment upon each side, the
hooked extremities w of such cathodes entering within small troughs 28 provided
in terminal connections 29 secured by means of screws to the sides of the outer
vessel, screws 30 serving as a metallic connection with the mercury in the
respective troughs 28 and for connecting the return wires of the dynamo.
The electrolytic action in this cell is the same as that of the modification illus-
trated in Figures 1, 2, 3, 4, and 5; while in each case the process may be rendered
continuous by supplying brine solution at 9, to the lower part of the inner com-
ment and drawing off the weakened solution near the surface at 10, in the same
compartment while water may be supplied to the outer compartment at 11 near
the surface and the strong alkaline solution may be withdrawn at 12 near the
bottom of the same compartment.
As illustrated in Figure 19 a number of such cells k, y, k, y, may be provided
whose respective compartments k, k, and y, y, may be connected together so that
the brine solution shall flow from the brine compartment, k, of one cell to the
brine compartment of the other in succession whilst water may be introduced
and caused to flow through the respective alkali compartments y, y, in the series
of cells in an opposite direction to the flow of the brine solution becoming stronger
as it passes through cach cell.
As illustrated in the diagrammatic elevation at Figure 20 the brine solution
may be caused to circulate through a series of cells such as k, y, and k, y, and the
solution maintained at a constant density by passing through intermediate recep-
tacles 31 containing salt such receptacles 31 being preferably provided with
alternate partitions 32 by means of which the solution is caused to have a tortuous
passage, so as to come in contact with a great quantity of salt, and thereby become
saturated before passage through the next cell in the series.
The weakened brine solution from the topmost cell in the series may be con-
nected to the lowermost of the salt receptacles 31. Water may be led directly
to each of the compartments y in the series.
In the employment of the cells for the production of chlorine and caustic soda,
the current may be first run through from the carbon anode to the mercury
cathode thence out of the cell. By such means the mercury is charged with
sodium, and the current may be then run from the carbon anode out of the cell
by way of the iron cathode immersed in the alkali solution. Owing to a want
of perfect efficiency in the electrolytic action in the brine compartment insufficient
sodium amalgam is produced to render the formation of the alkali continuous
and care is necessary in regulation, for on the one hand a scarcity of sodium
in the mercury may lead to the oxidisation of the mercury surface in the alkali
compartment, while too great a quantity would lead to the recombination of the
sodium with the chlorine, and the formation of other products as well as the
hardening of the amalgam, by which the efficiency of the cell would be impaired.
The current could however, be conducted from the carbon anode to the mercury
cathode, and the mercury cathode could be connected with the iron cathode by a
conductor of negligible resistance. The current flowing through the alkaline
solution would then be due merely to the chemical combination of the sodium
and the water.
A high efficiency can be obtained by providing a greater current passing through
the brine solution than through the alkaline solution by providing a wire of

page_text: suitable resistance between the mercury cathode and iron cathode and connecting
the carbon anode and iron cathode with the dynamo or with the supply mains.
As illustrated in Figures 11, 12, and 13 a circular wall or partition 33 may be
provided instead of a longitudinal partition. Such circular wall or partition
dividing the cell into an inner central compartment k and an outer annular com-
partment y in which respectively the brine solution may be supplied, and the
alkaline solution produced.
These circular troughs 34 are spaced apart, and supported by means of distance
pieces 35 placed at intervals. Instead of employing a partition such as 33, to divide
the cell into an inner central chamber and an outer chamber the partition may
divide the cell into two lateral chambers; or the troughs instead of forming a
dividing partition may form the base of the chamber, and form the seals of an
alternate series of brine and alkali chambers 36, 37, as illustrated in Figure 14
in which all the parts are lettered similarly to the same parts in the other
figures. Suitable outlets 38 are provided for conducting the chlorine gas away
and similar outlets might be provided for the hydrogen gas if required.
Further in another manner of carrying the invention into effect as illustrated
in Figure 15 a horizontal partition 39 may be provided composed of a number of
elements 40 of substantially section such elements being arranged side by
side and each providing a channel for the reception of the mercury upon one
side and a flange for dipping into the channel of the next element so that when
sufficient mercury is poured into each of the elements previously laid in horizontal
series in connection one with the other, the vessel is divided into two compart-
ments 41, 42 effectually separated by the mercury seals for when once the lower
or cathode compartment 42 has been completely filled with weak alkaline solution
the upper or anode compartment 41 may be filled with a brine solution without
any fear of two liquids mixing. Electrodes and rare placed in the respective com-
partments. Strong brine solution is continuously fed into the upper compart-
ment near the partition and withdrawn from near the top of that compartment
while water is fed into the upper part and alkali solution withdrawn from the
lower part of the lower compartment.
A hood 43 is provided in the lower compartment by means of which the hydro-
gen gas evolved may be withdrawn and similarly a hood 44 may be provided for
the withdrawal of the chlorine gas evolved in the upper compartment.
In order to procure the maximum amount of surface of mercury exposed upon
each side of the partition to the salt and alkaline solutions, the troughs are
preferably provided of a shallow V section with downwardly extending ribs, as
illustrated in the figures which latter alone dip into the mercury provided in
the adjacent trough. No limitation however, is placed to such a construction of
the partition as instead, the troughs may be provided so as to fit one within the
other thereby providing an interstitial space between of constant depth; or any
other suitable shape and disposition of the troughs may be made without departing
from the essential feature of the invention. Again no limitation is placed to the
vertical disposition of the troughs forming the partition when provided to extend
horizontally in the cell as the partition may obviously be disposed in an inclined
position.
In order to ensure that the hydraulic head of liquid in the one compartment
shall not so exceed that in the other as to break the mercury seals and so effect
admixture of the liquids an equalising or regulating arrangement may be provided
as illustrated in Figure 6. Such equalising or regulating arrangement may con-
sist of a U tube provided beneath the cells and connecting the two compart-
ments and y in the arms of which tube pistons 6, 6, may be provided between
which mercury 7 is placed so that any difference of pressure in the compartments
will effect a downward movement of one piston and an upward movement of
the other and to such an extent that a port may be opened which permits a
quantity of the denser liquid to flow out thereby equalising the hydraulic head
in the two compartments.

page_text: Mercury may be poured into the series of troughs e by filling the uppermost
and permitting overflow into the trough immediately beneath and so on until
the whole series of troughs are filled with mercury.
For convenience in filling the troughs and to preclude spilling of the mercury
while also to ensure that each trough shall be filled, the troughs may be provided
as illustrated in Figure 16 with one of their walls 45 upwardly extending beyond
the other, the alternate edges of the troughs upon each side being extended so
that the downward flow of mercury shall be over the lower edge of one trough and
the overflow received by the extended side 45 of the trough next beneath. Or,
instead of providing a continuous extension of the alternate sides of the troughs,
a partial extension or lip 46 alone may be alternately provided as illustrated in
Figure 18 and arranging that the overflow shall be limited to a particular part 47
of the edge of each trough. Or as illustrated in Figure 17 the mercury may be
guided by capillary action by means of a hook and stem 48 made from amal-
gamated copper wire.
The filling of the troughs may however be effected by the means illustrated
in Figure 18, which are shown as applied in the cell illustrated in Figures 1 to 5.
This consists of a strip 8 which is connected in each case to the plate and
preferably connected also to the contiguous edges of the troughs. The troughs are
nicked at their edges, as indicated at 49 and 50. The alternate nicks not being
in the same vertical line so that the mercury flowing through a nick or recess
in the edge of the one trough shall be guided by the strip 8 to fall into the next
trough.
It is obvious that no limitation is placed to the particular shape or disposition
of the troughs forming the partition, nor to the shape and disposition of the
partition.
By the provision of such a cell the use of the moving parts for the agitation
or movement of the mercury is obviated, while a thoroughly efficient cell is simply
and economically provided according to this invention.
In the use of a cell such as hereinbefore described it has been found that sodium
completely and rapidly diffuses through the mercury cells, so as thereby not to
necessitate any agitation whatever, and this constitutes a distinguishing advantage
of the invention.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is:-
1. In an apparatus for the electrolytic decomposition of alkaline salts the
provision of a series of troughs or of a partition composed of a series of troughs
separating the decomposing and combining compartments and containing a
quantity of mercury which has free surfaces exposed in the decomposing and
combining compartments separated by such troughs for the purpose and sub-
stantially as described.
2. In an apparatus for the electrolytic decomposition of alkaline salts the
provision of a partition separating the decomposing and combining compart-
ments and composed of a series of troughs containing a quantity of mercury which
has free surfaces exposed in the decomposing and combining compartments
separated by such partition each of the troughs being formed with a downwardly
projecting rib or member which protrudes within the mercury contained in the
trough beneath or beside it for the purpose and substantially as described.
3. In an apparatus for the electrolytic decomposition of alkaline salts the pro-
vision of a horizontal partition composed of a series of troughs composed of
elements of substantially section each of which forms a channel into which the
edge of the adjacent element may enter and so effectively seal the upper and
lower compartments separated by such partition for the purpose and substantially
as described.

page_text: 4. In an apparatus for the electrolytic decomposition of alkaline salts the
provision of a series of alternate decomposing and combining compartments
separated by means of separate mercury seals substantially as described with
reference to Figure 14 of the accompanying drawings.
5. In the electrolytic decomposition of alkaline salts an apparatus constructed
as herein before described with reference to Figures 1 to 5 of the accompanying
drawings.
6. In the electrolytic decomposition of alkaline salts an apparatus con-
structed as hereinbefore described with reference to Figures 7 to 10 of the accom-
panying drawings.
7. In the electrolytic decomposition of alkaline salts an apparatus constructed
as herein before described with reference to Figures 11 to 13 of the accompanying
drawings.
Dated this 5th day of June 1899.
MARKS & CLERK,
18, Southampton Buildings, London, W.C.,
13, Temple Street, Birmingham, and 25, Cross Street, Manchester,
Agents.