Improvements in or connected with Electrolytical Condensers and Electric Current Directing Devices.
Year: 1898

page_text: Date of Application, 5th Sept., 1898
Complete Specification Left, 5th June, 1899-Accepted, 2nd Sept., 1899
PROVISIONAL SPECIFICATION.
Improvements in or connected with Electrolytical Condensers and
Electric Current Directing Devices.
I, CHARLES POLLAK, of No. 253, Mainzer Landstrasse, Frankfurt-on-the-Maine,
in the German Empire, Managing Director to the Akkumulatoren Werke System
Pollak, do hereby declare the nature of this invention to be as follows:―
This invention has reference to a previous invention of mine described in
the Specification of Letters Patent No. 1069 of 1896 in which the aluminium
electrode of an electrolytical cell connected to the positive pole of the source of
electricity, becomes coated with an insulating polarizing layer, which when the
current passes through in an opposite direction, undergoes an alteration, so that
the electrode will not then oppose any appreciable resistance to the current
passing in this direction, whilst when the direction of the current is again changed
the said electrode will instantly return to its original state, in which it does not
allow the current to pass.
By further experiments I have found that for the purpose of rapidly forming
and altering the condition of the polarizing layer, the presence of an alkali in
the electrolyte is necessary and that it is immaterial whether this alkali in the
electrolyte be combined with a weak or a strong acid, and whether it be of an
alkaline, neutral or acid reaction, that even the solution of a salt may be advan-
tageously employed as electrolyte. This is due to the fact, that when a current
passes, owing to the electrical decomposition taking place on the electrode, so
much alkali is eliminated from the salt solution as is required for the purpose
of causing a change of the insulating layer.
Solutions of the following salts I have found to be advantageous:
1) Acid or neutral alkalines of phosphoric acids;
2) Alkalines of organic acids of the fatty group, which contain two or more
carboxyl groups for instance oxalic acid, or, beside a carboxyl group, or groups,
an oxy group or groups, for instance malic acid or tartaric acid; or a keto group
or groups for instance acetic acid, or aldehyde groups, for instance glyoxalic acid.
3) Alkalines of organic acids of the aromatic group, which contain two or more
carboxyl groups for instance phthalic acid or beside a carboxyl group or groups
one or more than one of the groups mentioned in the second clause such for
instance as salicylic acid, gallic acid.
Dated this 5th dow of Cantambon 1000
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.

page_text: COMPLETE SPECIFICATION.
Improvements in or connected with Electrolytical Condensers and
Electric Current Directing Devices.
I, CHARLES POLLAK, of No. 253, Mainzer Landstrasse, Frankfort on the Main,
in the German Empire, Managing Director to the Akhumulatoren Werke System
Pollak, 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:
Electrolytic cells of a certain kind may be used as transformers, or rectifiers,
of alternating into direct currents, as static condensers, spark arresters, and so on.
The principles of such cells are known already and improved methods for the
arrangement and preparation of the electrodes in suitable electrolytes are described
in my British Patents: No. 234421897 and No. 9331818
If used for the purpose of rectifying alternating currents, i.c. of changing them
into direct currents the cells are provided with two different electrodes.
One electrode must consist of such a metal or body, that is capable of receiving
an insulating coating by electrolytic action, if connected to the positive current
conductor (as anode); but the said insulating coating must disappear or be
changed rapidly, as soon, as the current direction is reversed and the electrode
becomes a cathode, when the current may pass through the cell, without any
considerable resistance.
The second electrode of the cell consists of an indifferent body but does not
oppose the passage of the current in either direction.
Thus, taking for instance aluminium, magnesium or similar substances as
the insulating, and lead or copper, etc., as the indifferent electrode we get a
cell, which may be passed easily by currents in the direction from lead to
aluminium, but not from the aluminium to the lead electrode, the aluminium
now being the anode or positive part and being covered immediately with an
insulating layer, capable of withstanding the action of even high voltages.
One part only of an alternating current wave can pass such a cell, but by
means of a combination of 2 or 4 cells all parts of an alternating current wave
can be rectified.
In the other case, when the cell is to be used as a static condenser and to be
connected in series or parallel with an alternating current system, both electrodes
must belong to the insulating class, as the current should not pass the condenser
in any direction and the specific static capacity of the cell is only made use of.
The capacity of the electrolytic condensers is very considerable and can still
be increased by using electrodes with porous surfaces.
The action of the electrodes during the passage of alternating current waves
is similar to that described in the first case, as the electrode connected to the
instantly positive conductor stops the current, while the other electrode does
the same for the opposite current impulse, the leakage being very small in good
cells.
Having explained the general principles of electrolytic rectifiers and condensers
of this class I give below the description of the present improvement.
In the course of studies made with electrolytic transformers I have noticed.
that their perfect action depends largely on the electrolyte used. The strain
put on such cells for technical purposes is very great, especially with regard to
the high frequencies employed in alternating current plants.
If the losses due to leakage have not to be excessive the action of the electrolyte
on the insulating electrodes must be very rapid and perfect, both as regards the
formation and the destruction (or change) of the insulating coating.

page_text: The following.combinations have given most satisfactory results and must be
considered as a notable improvement over those hitherto known.
As active electrodes I use any substance, capable of receiving an insulating
coating as an "anode" and of losing it as a cathode," preferably aluminium,
magnesium and other metals.
As electrolytes I employ,
1. Alkaline salts of phosphoric acids, either of acid or neutral character;
2. Alkaline salts of organic acids belonging to the fatty series which contain
either:
(a) two or more groups of carboxyle (for instance oxalic acid) or (b) combined
with one or more groups of carboxyle one or more
oxy groups (for instance malic acid or tartaric acid)
keto
aceto-acetic acid)
aldehyde (
glyoxalic acid).
"
"
"
"
3. Alkaline salts of organic acids belonging to the aromatic series, which also
contain the groups mentioned sub. 2" and 2b (for instance phtalic, and salicylic,
and gallic acid and the like).
4. Organic acids of the sebacic or aromatic series containing the groups men-
tioned sub. 2ª and 2b, but without alkalis.
It can be easily found by experiment, that the presence of acids or acid ions
in the electrolyte favourably influences the rapid formation of the insulating
layer, whilst alkaline ions contribute to the rapid removal of this layer, as soon
as the current begins to flow in opposite direction and renders that electrode
negative (cathode).
Consequently the electrolytes cited sub. (4) are best suited for condensers, where
a rapid formation is essential, whilst the compounds enumerated sub. (1), (2), (3),
which contain alkaline and acid ions are especially adapted for current rectifiers,
where both rapid formation and rapid removal of the insulating coating are of
equal importance.
It is advisable to prepare the electrodes before use and this is best effected
by means of high voltage continuous currents, of say 500, or more, volts in any
of the electrolytes enumerated before. The plates to be prepared are inserted
in the circuit as anodes and at first a suitable resistance is interposed to prevent
too great a rush of the current; but as the insulating layer on the electrode is
soon formed the resistance can be diminished and finally cut out entirely, while
the electrode is still left for some time under the action of the full voltage, and
is afterwards ready for use.
In practical service the best results are obtained with electrolytic condensers
and rectifiers, if the cells are kept at a uniform and low temperature.
Having now particularly described and ascertained the nature of this inven-
tion, and in what manner the same is to be performed, I declare that what
I claim is:-
Electrolytic condensers and current rectifiers, having one, or both, electrodes
covered with an insulating layer, when acting as the anodes of a cell, but which
do not oppose the passage of the current as cathodes, in an electrolyte composed
of solutions of alkaline salts of phosphoric acids, or of organic acids, which belong
to the sebacic or aromatic series and contain either two or more groups of car-
boxyle, or in combination with one or more groups of carboxyle, one, or more,
oxy-, keto-, or aldehyde groups,—or in electrolytes composed of solutions of said
organic acids only, without alkalis.
Dotad this 5th day of Tune 1800
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.