An Improved Electro-plating Bath.
Year: 1896

page_text: Date of Application, 6th Mar., 1896-Accepted, 11th Apr., 1896
COMPLETE SPECIFICATION.
An Improved Electro-plating Bath.
I, SYDNEY PITT of Sutton in the County of Surrey, Gentleman, do hereby
declare the nature of this invention (which has been communicated to me from
abroad by William Barnum Hollingshead, of Bronxville, East Chester, in the
County of West Chester, State of New York, U.S.A., Electro-Metallurgist)
and in what manner the same is to be performed to be particularly described and
ascertained in and by the following statement :-
The invention consists in an improved electro-plating bath to be used in electrically
depositing copper from an anode upon plates or objects of another metal placed in
the bath in the ordinary manner.
The primary and distinguishing feature of the bath hereinafter described is that
in active operation it is not appreciably or materially depleted of its copper, but on
the contrary its strength remains practically constant, while it serves as a vehicle
for conveying the copper from the anode to the cathode or object upon which it
is deposited. Because of this stable quality of the bath I call it a conveyor.
In compounding the bath I may proceed as follows, using substantially the
proportions hereinafter stated-the proportions being such as to produce a bath
having the characteristic above mentioned:
I take (1) twelve (12) parts by weight of ammonium cyanide and dissolve it in
about three times its bulk of water at a temperature of from one hundred to
one hundred and ten! degrees Fahrenheit; (2) sixty-one (61) parts by weight of
potassium tartrate (neutral) and dissolve it in about three times its bulk of water at
a temperature of about 110 degrees Fahrenheit; (3) twenty-seven (27) parts of a
mixture of oxide of copper and water mixed to a pasty consistency; the last two
ingredients are then mixed, the potassium tartrate forming the solvent for the
cupric hydrate; the first named ingredient, ammonium cyanide is then added to
the mixture, and then a quantity of water, equal in bulk to about three times that
of the other two ingredients, is added to reduce the bath to a proper strength
for use.
I have found that Rochelle salts can be used in place of the potassium tartrate in
substantially the same proportions, and I consider it, for the purpose of the
invention and the claim herein, an equivalent of potassium tartrate, that may be
substituted in the compound for the latter element-in which case the ingredients
would be prepared and mixed in the manner above stated.
The bath or conveyor above described is stable, constant and active because it.
contains no ingredients that will be decomposed on the passage of the electric
current through the bath to form insoluble salts of copper that will be precipitated
in the bath and not again taken up or redissolved. The supply of metal deposited
is taken from the anode and not from the oxide of metal or salt of metal con-
tained in the solution bath or conveyor. This is caused by the solution bath or
conveyor having a salt which oxidizes the anode and is also a solvent or an
absorbent for said oxide and also a conveyor. The bath is therefore not depleted
of its copper, but remaining practically constant serves as a vehicle or conveyor by
or through which the copper is transferred from the anode to the cathode. I may
give as a further explanation of the fact that there is no material precipitation of
insoluble copper from this bath-the presence in the bath of a salt that oxidizes
the anode during the passage of the current and also acts as a solvent for the
oxide.

page_text: As a result of this characteristic, viz. :-practical constancy or uniformity of
strength of the bath I employ; the deposition of the copper is regular, uniform and
far more perfect and dense than can be obtained from the use of baths varying in
strength during operation.
The specific proportions of the constituents of the bath, may no doubt be varied
to some extent, and yet produce substantially the same results. The proportions
stated are, however, productive of the advantageous conditions described, as I have
by practical operation fully demonstrated.
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 herein described bath for copper electro-plating composed of 12 parts of
ammonium cyanide, 61 parts of potassium tartrate (neutral), 27 parts of a mixture
of water and oxide of copper mixed to a paste, and water, compounded substan-
tially as set forth.
2. A bath for copper electro-plating, substantially such as that herein described
and having the characteristics set forth.
Dated this 6th day of March 1896.
SYDNEY PITT.