IMPROVEMENTS IN ELECTRO-PLATING
Year: 1881

page_text: LETTERS PATENT to Frank Wirth, of the Firm of Wirth and Company,
Patent Solicitors, at Frankfort on the Main, in the Empire of Germany, for
an Invention of "IMPROVEMENTS IN ELECTRO-PLATING." A communication
from Alexander Classen. Doctor of Philosophy and Professor of Chemistry.
PROVISIONAL SPECIFICATION left by the said Frank Wirth at the Office
of the Commissioners of Patents on the 11th November 1881.
FRANK WIRTH, of the Firm of Wirth and Company, Patent Solicitors, at
Frankfort on the Main, in the Empire of Germany. "IMPROVEMENTS IN ELECTRO-
PLATING." [A communication from Alexander Classen, Doctor of Philosophy and
Professor of Chemistry, of Aix-la-Chapelle, in the Empire of Germany.]
This Invention relates to an improved process for the electro-deposition of metals,
and in carrying the same into practice I use, especially for copper, iron, cobalt,
nickel, zinc, cadmium, bismuth, lead, tin, and antimony, the solution of chlorides
or sulphates (for iron and tin it is immaterial whether a protoxide or an oxide bo
used) of the said metals are transformed by means of a solution of neutral potassium
oxalates into soluble potassium double salts; the solution becomes hot, and in it
is dissolved an excess of ammonium oxalate. Later on a small quantity of sodium
carbonate is added. The object to be covered or coated is connected with the zine
pole of a battery, and dipped in the bath. The other pole of the battery is con-
nected with a plate of platinum; which is also dipped in the bath. The solutions
are then made hot, and the current allowed to pass freely.
The property of the galvanic current to precipitate metals in solution is especially
applied to the production of metallic precipitates of copper, silver, gold, and nickel.
Iron could not hitherto be precipitated under the action of the galvanic current in
a compact bright form. The reduction of the zinc iron from its solution in cyanide
of potassium was set forth a few years ago by Beilstein and Tawein, who investi-.
gated the case to ascertain the quantitative analysis of that metal. The separation
of this metal has found no favour in the arts by reason of the strong currents

page_text: which are required, and the necessity for the use of cyanide of potassium. The
methods hitherto employed to obtain by means of galvanic currents metallic
precipitates are generally deficient in many respects, principally from the fact that
either cyanide of potassium must be used, or that the solutions offer too great a
resistance to the currents. So, for example, to precipitate cobalt or nickel, chloride
solutions of these metals with hydrochlorate of ammonia, or sulphate solutions
with an excess of ammonia are employed, both of which fluids, on account of the
products of the resulting decomposition, as also on account of the great resistance
which they offer to the current, seem altogether unfit, not taking into consideration
the fact that the obtained precipitates are not compact and do not posses the color
of the pure metals.
•
The importance of precipitating iron by means of the galvanic current in a
compact and bright form is self evident; it need only be mentioned that a
precipitate of iron on blocks for printing purposes perfectly insures their
durability.
It seemed natural that the separation of metals should generally take place
most advantageously when the metal is combined with an acid, which will easily
be decomposed by the current in such a manner that the said acid cannot be
reformed in a secondary, as is the case with sulphuric acid. Now oxalic acid is
such an acid; it can easily and gently be decomposed by the current into carbonic
acid and hydrogen gas. A solution of the metals in question, or metal oxides, in
pure oxalic acid, could not be made use of for the purpose in view, as several
metals form, with this acid, insoluble, or but slightly soluble, salts; as, for example,
copper, zinc, lead, nickel, and the like; but the_metals-mentioned-form,-with-the-
alkaline oxalates, double salts, which are themselves most easily decomposed by
weak currents; what then takes place is, for instance, that in the electrolysis of
the alkaline oxalate of zinc the zinc oxalate is decomposed into zinc and carbonic
acid, and oxalate of potassium in carbonic acid and potassium. Potassium acts
secondarily upon the water, in consequence of which the hydrogen goes to the
negative, the carbonic acid to the positive pole; the latter combines with the
potassium hydroxide to form potassium hydro carbonate. If one employs, instead
of potassium, oxalate of zinc, the ammonium oxalate of zinc, the decomposition of
the zinc oxalate follows, just in the same way, into zinc and carbonic acid, and
that of the ammonium oxalato into ammonium and carbonic acid, which latter
combine again into ammonium hydrocarbonate. Now to obtain compact bright
metals is in no way an indifferent matter, whether one uses for the reduction
double salts of potassium or of ammonium. If, for example, the latter salts are
used the reduction indeed goes on smoothly, but the reduced metals are but slightly
compact, and do not possess the color and properties of the said metals in the
forged or rolled state. So, for instance, cobalt, nickel, and zinc are obtained grey
from the ammonium chemical combinations, copper in a dark spongy form.
Appearance and properties become actually different when one transforms the
precipitated metals by the addition of neutral oxalate of potassium into double
salts of potassium. But the pure double salts of potassium are not adapted for
reduction, because through the electrolysis the potassium hydrocarbonate which
is formed occasions insoluble carbonate precipitate of the metals, which sometimes
react upon the reduced metal, but in any case frustrate a complete reduction.
Now if one transforms the metal to be reduced by the addition of neutral
potassium oxalate into a soluble oxalate double salt, and then adds an excess of
ammonium oxalate, the reduction then goes on quickly and very easy without
the appearance of a precipitate. The reduced metal is most compact, and possesses
the color and the brilliancy of the pure metal obtained in some other way. From
the experiments of the discoverer of this Invention, it is found that the brilliancy
of the metal is still further enhanced by the addition of carbonate of sodium to
the liquid which is to be reduced.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Frank Wirth in the Great Seal Patent Office on the 11th May
1882.
FRANK WIRTH, of the Firm of Wirth and Company, Patent Solicitors, at
Frankfort-on-the-Main, in the Empire of Germany. "IMPROVEMENTS IN ELECTRO-
PLATING." A communication from Alexander Classen, Doctor of Philosophy and
Professor of Chemistry, of Aix-la-Chapelle, in the Empire of Germany.
"
The property of the electric current of precipitating metals in solution on
metallic surfaces is especially applied to the production of metallic precipitates of
copper, silver, gold, and nickel. Iron could not hitherto be so precipitated under
the action of the electric current in a compact bright form. The reduction of zinc
from its solution in cyanide of potassium was accomplished a few years ago by
Beilstein and Tawein, who investigated the matter to ascertain the quantitative
analysis of that metal. The precipitation of this metal has found no favor in the
arts by reason of the strong currents which have been required for that purpose,
and also of the necessity for the use of cyanide of potassium. The methods hitherto
employed for obtaining, by means of electric currents, the said metallic precipitates,
have been generally inefficient in many respects, either from the fact that cyanide
of potassium must be used, or that the solutions used offered too great a resistance
to the electric currents. For example, for precipitating cobalt or nickel, chloride
solutions of these metals with hydrochlorato of ammonia, or sulphate solutions
with an excess of ammonia are employed, both of which fluids, on account of the
products of the resulting decomposition, as also on account of the great resistance
which they offer to the electric current, seem altogether unsuitable for the purpose,
not taking into consideration the fact that the obtained precipitates are not
compact and do not possess the color of the pure metals.
The importance of precipitating iron by means of the electric current in a
compact and bright state is self evident, and it need only be mentioned that a
precipitate of iron on blocks. for printing purposes would ensure their durability.
It seemed natural that the precipitation of metals should generally take place
most advantageously when the metal was combined with an acid, which com-
bination would be easily decomposed by an electric current in such a manner that
the said acid could not be re-formed into a secondary compound, as is the case with
sulphuric acid. Now oxalic acid is such an acid. It can easily be decomposed by
the electric current into carbonic acid and hydrogen gas.
A solution in pure
oxalic acid of the metals in question, or of metal oxides, could not be made use of
for the purpose in view, as several metals form with this acid insoluble, or only
partially soluble salts, as, for example, copper, zinc, lead, nickel, and the like.
But the metals mentioned form, with the alkaline oxalates, double salts, which
are themselves easily decomposed by weak electric currents. What then takes
place is, for instance, that in the electrolysis of the alkaline oxalate of zinc the
zinc oxalate is decomposed into zinc and carbonic acid, and oxalate of potassium
into carbonic acid and potassium. Potassium acts secondarily upon the water,
in consequence of which the hydrogen goes to the negative pole, and the carbonic
acid to the positive pole of the source of electricity. The latter combines with the
potassium hydioxide to form potassium hydrocarbonate. If, instead of potassium
oxalate of zinc the ammonium oxalate of zinc is employed, the decomposition of
the zinc oxalate follows, just in the same way, into zinc and carbonic acid, and
that of the ammonium oxalate into ammonium and carbonic acid, which latter
combine again into ammonium hydrocarbonate. Now to obtain compact bright
metals is in no way an easy matter, whether one uses for the reduction double

page_text: salts of potassium or those of ammonium.
If, for example, the latter salts are
used, the deposit of metal is thin and smooth, but the deposited metal is not close
grained, and does not possess the color and properties of the said metal in the
forged or rolled state. Thus, for instance, cobalt, nickel, and zinc are obtained of a
grey color from the ammonium chemical combinations, and copper in a dark
spongy form. The appearance and properties become actually different when one
transforms the precipitated metals by the addition of neutral oxalate of potassium
into double salts of potassium. But the pure double salts of potassium are not
adapted for deposition, because through the electrolysis the potassium hydro-
carbonate which is formed occasions insoluble carbonate precipitates of the metals,
which sometimes react upon the deposited metal, but in any case prevent a complete
deposition.
Now if one transforms the metal to be reduced, by the addition of neutral
potassium oxalate, into a soluble oxalate double salt, and then adds an excess of
ammonium oxalate, the deposition takes place very rapidly, and without the
appearance of a precipitate. The deposited metal is most compact, and possesses
the colour and the brilliancy of the pure metal obtained in any other way. From
the experiments of the inventor of this process it is found that the brilliancy of
the metal deposited is still further enhanced by the addition of carbonate of sodium
to the solution from which it is to be obtained.
In the process which the inventor uses to obtain platings of the different metals,
especially of copper, iron, cobalt, nickel, zinc, cadmium, bismuth, lead, tin, and
antimony, the solutions of chlorides or sulphates (for iron and tin it is immaterial
whether a protoxide or an oxide be used) of the said metals are transformed by
means of a solution of neutral potassium oxalates into soluble potassium double
salts ;
the solution is made hot, and in it is dissolved an excess of ammonium
The articlo
oxalate. Later on a small quantity of sodium carbonate is added.
to be electro-plated or coated is connected with the zinc pole of a battery and
dipped in the bath. The other pole of the battery. is connected with a plate of
platinum, which is also dipped in the bath. The solutions are then made hot, and
the current allowed to pass freely.
Having thus fully described the said Invention and the manner of performing
the same, I wish it understood that I claim,-
The improved process for obtaining, by means of electric currents, compact,
brilliant, and polishable platings or coatings of metal, substantially as hereinbefore
described.
In witness whereof, I, the said Frank Wirth, have hereunto set my hand
and seal, this Eighteenth day of April, in the year of our Lord One thousand