Improvements in the Electrolytic Production of Oxides and Salts which are Insoluble or Practically Insoluble in the Electrolyte.
Year: 1895

page_text: Date of Application, 6th Aug.. 1895-Accepted, 14th Sept., 1895
COMPLETE SPECIFICATION.
Improvements in the Electrolytic Production of Oxides and Salts
which are Insoluble or Practically Insoluble in the Electrolyte.
I, CARL LUCKOW of Cologne-Deutz, in the German Empire, Chemist, 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 production from very weak solutions by means of
electrolysis of metallic oxides and salts which are insoluble or difficultly soluble in
the electrolyte.
In carrying this invention into effect metallic plates are arranged as electrodes
in suitable boxes or the like, and are connected as alternately positive and negative
electrodes opposite to each other with distances between each plate and the next of
from 10 to 20 millimeters. Closer distances between the plates would favour the
formation of bridges between them during the electrolytic action and a greater
distance between them would increase the resistance too much. In a large battery
the plates will have a thickness of from 5 to 10 millimeters. In place of plane
plates the electrodes may be formed in any other suitable shape such as cylindrical,
or they may be perforated or formed from netting or the like. Their surfaces may
be either smooth or roughened or corrugated, but bright smooth and massive
electrodes are the most serviceable. When mercury is employed as an electrode it
is placed in suitable pots or dishes. The solid electrodes must be arranged at a
considerable distance above the floor of the cell or the like in which they are
arranged so as to be held out of contact with the precipitated metallic oxides aud
salts, especial care being taken to keep the negative electrode out of contact as
otherwise a reduction of the precipitate would take place.
The metal of which the anode is to be formed is determined by the solution to
be treated and the precipitate to be obtained. Thus for instance if super-oxide of
lead or carbonate or chromate of lead is to be obtained the anode is of soft lead,
for the oxide and salts of copper a copper anode is used, for the zinc oxides and
salts a zinc anode is employed, and similarly in all other cases the anode is of the
same metal as the oxide or salt to be produced.
The best results are obtained if the cathode is of the same shape size and
thickness and of the same metal as the anode, because, (1), the tension between the
pairs of electrodes is at minimum during the passage of a current and thus a certain
current will be able to exert a maximum effect; and, 2, so that the current may be
eversed when the anode becomes worn and the former cathode may become the
anode thus allowing the work to be carried on almost continuously and with great
economy. To obtaiu the same results however the anode may be originally of
great thickness and the cathodes be very thin or formed from sheets of 1 or
2 millimeters thickness.
The cells containing the electrodes are filled with the hereinafter mentioned
solutions of metallic salts as electrolytes and a moderate current proportionate to
the surfaces of the electrodes is passed through them, the cells and the plates being
arranged either in parallel or series or in a combination of parallel and series.
The passage of the current sets up a powerful oxidation at the anodes and the
products of this oxidation are the substances which it is the object of this invention
to obtain. The oxidising effect of the current upon the anodes depends, 1, upon
the salts and the mixings of the electrolytes and principally upon their acids or

page_text: halogens, 2, upon the reaction of the electrolyte whether alkaline neutral or acid,
and upon the quantities of free bases or acids, 3, upon the degree of dilution of the
electrolyte, and 4, upon the metal of which the anodes are composed.
The oxidation may appear in two ways. In the first, the positive electrode, that
is the one attached to the positive pole of the source of current, becomes coated
evenly with layers of oxides and super-oxides which are insoluble in the electrolyte-
and which during the passage of the current become constantly thicker and
penetrate more deeply into the substance of the electrode until in a length of time
governed by the thickness of the plate it is completely converted into a mass of
anhydrous oxide or super-oxide. These layers of oxides are in a state of excessively
fine division but adhere firmly to the anode and have great coherency in themselves.
Plates for secondary batteries may thus be economically formed if they are with-
drawn at the proper time from the effect of the current, that is as soon as a
sufficient layer of the superoxides has been formed upon them.
The oxidation of the anodes may however be manifested during the electrolysis
by the oxides and super-oxides immediately detaching themselves from the anodes
and falling in a state of the finest division upon the floor of the cell where they
quickly accumulate. The anodes become constantly thinner but always remain
bright. In this manner are produced oxides and superoxides which are finely
divided, chemically pure, and are anhydrous.
By carefully choosing the electrolytes and considering their reaction and the
strength of the current employed, complete control may be obtained over the
formation of the oxides and superoxides which either remain attached to the anodes
or fall to the bottom of the cell.
As an example of how this invention may be carried into effect I will now
describe the production of oxide of lead.
Anodes of soft lead are placed in a very
dilute neutral or weakly acid sulphate or phosphate or borate solution, or in a
weakly alkaline chloride solution, or in a very dilute electrolyte of certain mixtures
of chlorides with sulphates, phosphates, borates, carbonates or sub-chloric acid salts
(hypochlorous acid salts), or in very dilute neutral or weakly acid solutions of
sulphates phosphates borates and the like, with the addition of very small and
accurately determined quantities of nitrates acetates chlorates or perchlorates, or in
very dilute solutions of bi-sulphates with the addition of greater quantities of
phosphates borates and the like. The passage of the current causes the immediate
formation of pure finely divided anhydrous bluish black brown superoxide. A
large quantity is obtained in an extremely short time By this process the entire
cost of producing 100 kilograms of chemically pure superoxide of lead is, reckoning
the ampere hour at about one eighth of a penny, only 3 shillings, so that absolutely
pure superoxide of lead would at usual lead prices cost 20 to 23 shillings
per 100 kilograms.
The anodes dissolve quickly but evenly so that in the course of time they become
very thin. The metal of the anode however does not enter into solution into the
electrolyte but is immediately and completely precipitated as an insoluble salt.
The electrolytes consist of such mixtures that the acids which form insoluble salts
with the metal of the anodes are always present in sufficient quantity to fulfil their
function. It thus follows that none of the metal is to be found in the electrolyte
and that none of it is deposited upon the cathodes.
The electrolytes are therefore mixed and chosen to fulfil this purpose so that
the current with the help of the suitably strong acid, as for example hydrochloric
acid, or with the help of a halogen as for example chlorine will decompose the
anodes and form insoluble salts which are immediately precipitated. The acids or
halogens must of course be replaced as they are used up.
In the manufacture of white lead the electrolyte consists of a very dilute
solution of either nitrates, acetates or chlorates with the addition of soluble
carbonates or bi-carbonates in fixed proportions. The electrolyte must not be
allowed to become more than weakly alkaline and the used carbonic acid must be
replaced constantly by an equivalent quantity introduced under a slight pressure.

page_text: The dilute electrolytes must have only a weakly alkaline reaction, the carbonates
must therefore be present in sufficient quantity, forming about one fourth; whenever
possible, bicarbonates should be used.
If the carbonic acid be not introduced into the electrolyte at the proper time
and in sufficient quantities free salt bases (basic salts) will be formed on the cathode
in increasing quantities thus rendering the electrolyte increasingly alkaline as the
acids of the carbonates form salts with the metal of the anode which are insoluble
in the electrolyte while the bases remain in a free state. The production of the
white lead accordingly is rapidly decreased with the deficient supply of carbonic
acid and the consequent increased alkalinity of the liquid. The product, too,
suffere, becoming more and more crystalline and less finely divided. In case
little or no carbonic acid be contained within the electrolyte, which latter thus
becomes strongly alkaline and concentrated, the anode is still decreasingly dissolved
by the passage of the current but remains in solution as there is no acid to change
it into an insoluble salt, and as a natural consequence spongy lead will be formed
upon the cathode as soon as the electrolyte is saturated.
With the increasing alkalinity the anodes lose their brightness and become
covered with an increasing crust of crystalline carbonate of lead which oxidises
as hydrated oxide and afterwards as hydrated superoxide. The dissolution of the
anode will thus gradually cease. These appearances differ however according to
the constitution of the electrolyte and are dependent upon the continuity of strong
oxygenated acids which dissolve the metal of the anode under the influence of the
current and transform it into an insoluble salt.
In the case of electrolytes consisting of a mixture of nitrates with carbonates
or with bicarbonates the current always reduces very easily the nitric acid
appearing at the anode to nitrous acid at the cathode and sometimes to ammonia,
even if carbonic acid be introduced in excessive quantities. These electrolytes thus
become strongly alkaline and shew a distinctly alkaline reaction soon after the
termination of the current, and after the expiration of some time the ammonia may
be easily smelt.
In the nitrous or ammonia combination the anodes cease to be dissolved and the
cutient oxidises their surfaces to hydrated oxide or peroxide. The carbonic acid
which has been introduced would certainly favour the oxidation of the ammonia
into nitrous acid and the further oxidation of the latter into nitric acid. The
instability of nitric acid under the influence of an electric current however renders
it most unsuitable for the purposes of this invention.
Acetic acid is much more
stable and suitable for the purposes of this invention but the same objectionable
result may still be obtained if the acetic acid becomes reduced at the positive pole.
All oxygenated acids which produce insoluble combinations with lead oxidise the
lead anodes under a current to peroxide of lead.
Thoroughly stable under all conditions are hydrochloric acid and perchloric
acid. They are neither reduced nor decomposed by the passage of a current and
therefore electrolytes consisting of a mixture of chlorates or perchlorates with
bicarbonates are by far the most suitable for the production of white lead according
to this invention.
These two strongly oxygenated acids show themselves in certain conditions more
stable under a current than even sulphuric acid.
If desired the carbonate or bi-carbonate may be omitted from the electrolytes,
and carbonic acid may be simply added, but it is preferred to add the carbonates.
The carbonic acid required may be economically obtained from chimneys furnaces
or the like and utilised after the necessary cleansing or washing.
The formation of the basic lead carbonate in the dilute solutions is as follows:-
On the passage of a current either of the four strongly oxygenated acids which
produce soluble compounds of lead, viz., nitric, chloric, acetic, and perchloric acids
whichever is contained in the electrolyte, commences to energetically dissolve the
lead of the anodes but the carbonic acid which is present in abundant quantities
combines at once with all the dissolved lead forming at once a dazzlingly white

page_text: salt which is amorphous basic lead carbonate or white lead, and which is deposited
in a state of extremely fine division upon the floor of the cell.
A characteristic of this process is that the electrolytes of chlorates or
perchlorates with carbonates regenerate themselves if there is a sufficiency of
carbonic acid. They thus remain unchanged and no trace of lead enters into
solution. The white lead originates at the anodes and falls immediately to the
floor of the cell. The process resembles the chamber process but in this wet
process the product is much greater and is more finely divided. No metallic lead
can get into the white lead nor can any spongy lead form on the cathode as no lead
ever comes into solution in the electrolyte.
Experiments have shewn that the best and most suitable electrolytes contain
about 1-5 of anhydrous salts. The proportions of the salts employed are about
3 parts of the nitrates or the acetates or the chlorates to 1 part of the carbonate
or bi-carbonate. For example, 3 parts of sodium chloride and one part of
bi-carbonate of soda may be used. The most suitable strength of current is one
ampere to each square decimeter of one side of the anodes. With a distance
between plates of from 12 to 15 m/m the pressure in the cells amounts on the
passage of the current to 2 volts. Thus a dynamo having a pressure of 150 volts
would operate 75 couples in series. The preferred electrolyte consists of chlorates
and carbonates and the reduced white lead is abundant and exceeds all others in
its covering powers.
When sufficient white lead has accumulated in the cells it is
removed and filtered, dried and packed.
In the manufacture of chromate of lead a weakly acid or a neutral or a weakly
alkaline electrolyte is employed consisting of a dilute solution of nitrates or
acetates or chlorates with the addition of chromic acid or chromates. The acid
dissolves the lead anode and the chromic acid precipitates it at once as an
amorphous and finely divided chromate of lead. The action in the cell is similar
to that previously described with reference to white lead. The chromic acid must
be replaced as it is used up.
The colour of the chromate of lead depends upon the bath, a neutral electrolyte
producing a magnificent chrome yellow which becomes lighter it the solution
becomes more acid, and redder as it becomes more alkaline. Weak acid solutions
therefore produce fiery citron yellow products and weak alkaline solutions a
magnificent orange chrome. If the alkalinity is increased a chrome red is
produced.
In the preparation of the fiery yellow chromate the electrode must not be allowed
to become too acid or the production will cease and the anode will become coated
with a layer of oxide and peroxide. A dripping apparatus is preferably employed
to add the necessary quantities of chromic acid or of the chromates to the electro-
lyte. The solution employed has about the strength and the proportions of salts
as those particularly described for the production of white lead. An electrolyte
which will produce an orange chromate of lead consists of a mixture of perchlorate
of potassium with chromate of posassium. The production of ied chromates requires
the electrolyte to be made still more alkaline by the addition preferably of sodium
hydrate. The curient required is approximately 1 ampere to each square decimeter of
one side of the anodes. The pressure required to overcome the resistance between
plates is in weakly acid solutions 1-5 volts: in neutral solutions 1.7 to 1.8 volts: and
in weakly alkaline solutions from 1.9 to 2 volts. A dynamo having a pressure of
150 volts would thus operate from 83 to 100 couples in series for the production of
yellow chromate of lead, and from 75 to 78 couples for the production of orange
chromates. The cost of producing 100 kilograms of chemically pure yellow
chromate of lead amounts to from 70 to 80 shillings and for 100 Kilograms of
chemically pure orange chromate to about 50 shillings.
Chromate of copper is produced in a similar manner to the chromate of lead,
copper anodes being used. The electrolyte consists of a mixture of either a nitrate
a sulphate a chloride or a chlorate with chromic acid or a soluble chromate. The
copper dissolves upon the passage of a current and is precipitated as chromate of

page_text: copper by the chromic acid present. With a neutral or weakly acid electrolyte a
brown red chromate is produced, and with a weakly alkaline electrolyte a green
chromate is formed. The more acid the solution the brighter becomes the brown
red chromate. until in a strong acid solution the copper is no longer precipitated.
With an increased alkalinity the deeper but more dull becomes the green colour
of the deposit. An electrolyte consisting of a very dilute solution of 6 parts of
chlorate of sodium to 1 part of red chromate of sodium may be employed for the
production of the red chromate of copper, while for the green chromate a weak
solution of 4 parts of sodium chloride or chloride of potassium with one part of
yellow chromate of potassium may be employed. It is preferred to render the
1st solution slightly alkaline before electrolysis commences by the addition of
sodium hydrate or potassium hydrate. The used up chromic acid must of course
be replaced during the process.
In a similar manner and by the employment of suitable electrolytes and anodes,
may be produced black oxide of nickel, white oxide of zinc, the blue green basic
copper carbonate, the light blue acid copper phosphate, the white basic zinc
carbonate and many other similar salts.
In the production of oxides and peroxides the electrolytes require no addition
during electrolysis, but in the production of salts the used up acids or halogens
must naturally be replaced according to requirement and consumption. The
greater number of electrolytes employed, for instance, the sulphates, borates,
chlorates and chlorides regenerate themselves during the process and remain of the
same dilution constitution and reaction. It is preferred in order to protect the
cathodes to envelop them in thin bags of fine tissue.
The strength of the current employed to decompose the dilute solutions must
only be moderate but depends upon whether the anodes are to be changed into
oxides or peroxides, or whether they are to be dissolved and formed into salts
which are insoluble in the electrolyte.
In the first case, particularly if the oxides or peroxides are not required to
detach themselves from the anodes a very weak current of not
more than
1 ampere to each 2 or 3 square decimeters of one side of the anodes may be
employed, as a stronger current, although it increases the yield, does not increase
it in a degree proportional to the greater current required. The strength of the
current should be proportionate to the oxidising power of the electrolyte upon the
anode and attention must be paid that no free oxygen is developed upon the anode.
In the manufacture of peroxide of lead for example for example, the current can not
exceed the above limits without waste. The rate of dissolution of the anodes
increases in proportion to the strength of the curient employed, but it has been
found that the products are finer with the weaker currents.
The result of experiments has been to prove that the best current to employ
generally for the wholesale and commercial manufacture of salts is about 1 ampere
to each square decimeter of one side of the anodes. With a stronger current the
products suffer in fineness while with a weaker one the production is too slow.
The pressure of the current required depends on the conductivity of the electro-
lytes and the distance between the pairs of electrodes. With electrolytes
containing about 1.5 per cent. of anhydrous salts and with a distance between the
electrodes of from 12 to 15 millimeters the pressure required is, for weakly acid
solutions from 15 te 16 volts, for a neutral solution from about 17 volts, and for
a weakly alkaline solution about 2 volts.
The pressure of current in the cell does not increase as long as the anodes
remain bright but increases proportionately as they become coated with layers of
oxides or peroxides. For instance in the production of plates for secondary
batteries the pressure in the cells is increased to 3 to 3.5 volts owing to the layers
of peroxide on the anode.
A dynamo of 150 volts and 25 amperes will operate 75 to 100 couples in series
and in from 10 to 15 hours will precipitate or from about 100 kilograms of oxides
or salts.

page_text: As before stated, it is preferred to form both the anode and cathode of the same
metal so that when the anode is almost worn out the current may be reversed, the
former cathode becoming the anode until it in turn is worn away.
The worn
electrodes are then replaced by new ones. The products are placed in bags and
are filtered washed and slowly dried.
As electrolytes all those salts may be employed whose weak solutions on being
decomposed by the electric current leave no products at the positive pole which
might interfere with or hinder oxidation, and with which either no separation of
metal takes place at the negative pole or the separation may be prevented by the
addition of a small quantity of free acid. The electrolytes must be neutral or ouly
faintly acid or alkaline and must contain a very low percentage of salts.
The oxidising effect commences upon the passage of a current, and only upon
the anodes, when the electrolyte is in its proper condition. In general the
proportion of free acid or alkali present must not exceed 1-5 per cent. of the
volume of the solution if the oxidation is not to be interfered with. The quantity
of salts contained in the electrolytes varies according to their nature from between
0.3 per cent. to 3 per cent. The employment of these extremely weak solutions
is an important point in the invention.
The oxidation decreases rapidly as the solutions become more alkaline or more
acid.
If the electrolytes are too dilute the oxidation decreases in proportion to the
smaller capacity of the electrolyte and its greater resistance to the passage of
the current. It is peculiar also that the effect also decreases rapidly when the
electrolytes are concentrated beyond the above named limits.
In the more concentrated solutions, especially when they are too alkaline or too
acid, the current oxidises the anode at a rapidly decreasing rate and more super-
ficially and unequally; the produced oxides become more and more dirty and
hydrated and assume a crystalline form.
In
The very dilute and neutral or weakly acid or alkaline solutions however allow
the rapid production of pure amorphous and finely divided oxides and salts.
addition to the easily oxidisable soft lead, peroxides of most metals, for example
copper, may be produced by this process instead of obtaining them by treating
their respective hydroxides with very dilute peroxide of hydrogen.
The process is particularly valuable for the formation of plates for secondary
batteries, as strongly adhering layers of peroxide may be produced on metal plates.
As an example of the excessively fine division in which these products are
obtained I will instance the white oxide of zinc which easily penetrates the usual
filters be they double or treble, and can only be filtered in especial substances of
the finest and closest tissue.
The great advantage in the use of the extremely dilute electrolytes is that the
solution no longer contains the original salt, which is dissociated. The extreme
dilution overcomes the chemical affinity of the atoms and splits the molecules into
their constituent atonis.
For example in a strongly diluted solution of chloride of sodium the salt is no
longer present as such, but has changed to its constituents Na and Cl. With still
more facility is a solution of borax split up into its constituent parts. Upon the
concentration of the solution, the atoms combine eagerly to produce the former
molecules.
The proper degree of solution for each salt must therefore be decided with the
greatest pains. The addition of a little too much water increases the internal
resistance out of all proportion. The proper condition of the electrolyte is when
the dissociation has so far taken place that the component atoms are adhering
most loosely. This condition varies with the salt used and is only to be found
within very narrow limits.
The most generally useful degree of dilution is when the solution contains
between 1 and 2 per cent. of anhydrous salts, although the proportion may vary as
before stated between 0-3 and 3 per cent.

page_text: The strong acids such as sulphuric and hydrochloric and the strong bases such
as potassium and sodium combine in their salts with much greater affinity than the
weaker acids and bases, and therefore require a greater dilution to reach the same
state of impending dissociation.
With an excess of free acids or bases, the dissociation is rendered more difficult
as the acids and bases which are in solution as hydrates never, in the weakest
solution, approach that condition.
With an electrolyte in the favourable condition, the current has very little work to
do, as it simply directs the dissociated or weakly joined ions to their respective
poles, the acids or halogens appearing at the anodes.
Under these conditions it will be understood that the current exerts its entire
force upon the work which it has to do at the poles without any loss of energy.
Both the oxidation at the positive pole and the reduction at the negative pole
reach their highest possible efficiency and economy.
By this process and by the employment of the electrolytes hereinbefore described
it is thus possible to economically produce chemically pure oxides, peroxides and
salts which are anhydrous and insoluble in the electrolytes, and which are amorphous
and in a state of the finest possible division.
As anodes, any suitable plates masses or structures of the required metals or
such of their ores alloys or compounds as are suitable and available for the purpose
of this invention may be employed.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. The bereinbefore described process for the production of oxides and salts
which are insoluble or practically insoluble in the electrolyte, from very dilute
neutral or slightly acid or alkaline solutions, substantially as and by the means
set forth.
2. In the electrolytic production of oxides and salts which are insoluble or
practically insoluble in the electrolyte, the use in combination of an anode of or
containing the metal base and a very dilute neutral or faintly acid or alkaline
electrolyte, substantially as and for the purpose hereinbefore described.
Dated this 3rd day of August. A D 1895
W. E. HEYS & SON,
Agents for the Applicant.