Improvements relating to the Coating of Articles with a New Metallic Alloy by Electro-deposition.
Year: 1892

page_text: Date of Application, 23rd Jan., 1892-Accepted, 27th Feb., 1892
COMPLETE SPECIFICATION.
Improvements relating to the Coating of Articles with a New
Metallic Alloy by Electro-deposition.
We, THE LONDON METALLURGICAL COMPANY LIMITED and SHERARD
OSBORN COWPER-COLES, Engineer, both of 80 Turnmill Street, in the City of
London, 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 coating by electro deposition of articles of metal or
other suitable material with a new metallic alloy, and its object is to produce upon
the said articles a brilliant coating or plating resembling silver but which is better
adapted than silver to resist the tarnishing influences of the atmosphere.
For this purpose we deposit upon the said articles by electrolysis an alloy of
cadmium and silver, or zinc cadmium and silver. We find that to protect the silver
from being so rapidly tarnished by the atmosphere, about from thirty five to
twenty five per cent. or even less cadmium is sufficient. When however we desire
to produce less costly coatings, we employ say from forty per cent. to ninety per cent.
of the baser metal or metals.
Our said invention, moreover comprises a method or process of electro-depositing
the aforesaid alloy, whereby we are enabled to obtain a homogeneous coating, that
is to say a coating which consists throughout of a perfect intermixture of the metals
constituting the alloy.
In carrying on our improved method of electro-deposition we proceed as follows,
that is to say, we prepare an electrolytic bath by dissolving a suitable quantity of
cyanide of cadmium in a solution of cyanide of potassium so as to form a double
salt having a slight excess of cyanide of potassium. To this solution we add a
small quantity of the double salt of the cyanides of potassium and silver, the two
together forming the electrolyte or electrolytic bath which is introduced into any
suitable electro-plating or electro-typing apparatus; we employ an anode composed
of an alloy of cadmium and silver in the same or approximately the same propor-
tions as are desired in the alloy to be deposited; for example, for the deposition of
an alloy composed of equal parts by weight of silver and cadmium we use an anode
composed of equal or about equal parts of the said metals.
After the cathodes, that is to say, the articles upon which it is desired to form
the deposit, have been placed in the electrolytic bath and the current caused to
flow, the metals are deposited thereon as an alloy of the desired composition.
The electrolytic bath may be used either hot or cold and the hardness of the
deposit can be increased or diminished by varying the proportions of the metals in
the alloy.
We wish it understood that we do not limit ourselves to any special proportions
of the metals, as such proportions may be varied according to the purpose for
which the alloy is required without departing from the nature of our invention.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed, we declare that what we
claim is :-
1. The method of depositing by electrolysis an alloy of silver and cadmium, or
silver zinc and cadmium, on metal and other suitable articles, substantially as
described.
2. An article of metal or other suitable article that has been coated with an alloy

page_text: of silver and cadmium, or silver. zinc and cadmium by electro deposition, for the
purpose specified.
Dated this 23rd day of January 1892.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicants.