Improvements connected with the Electrical Deposition of Zinc and other Metals.
Year: 1894

page_text: Date of Application. 23rd Aug., 1894
Complete Specification Left, 17th May, 1895-Accepted, 17th Aug., 1895
TRUVIDIONAL DI
Improvements connected with the Electrical Deposition of Zinc and
other Metals.
RICHARD Heathfield of 1 Leadenhall Street London E.C. Merchant and
WILLIAM STEPNEY RAWSON of 86 York Street Westminster London S.W.
Electrical Engineer do hereby declare the nature of this invention to be as
follows:-
Articles may be covered with a thin coating of mercury by making them the
cathode in an acid solution of a salt of mercury such as the sulphate.
We find that in the case of articles of iron & steel which resist the formation of
an alloy with mercury the formation of the coating of mercury is facilitated by
adding to the mercury solution a small quantity of the corresponding salt of zinc
or other metal which is both freely dissolved in the acid of the solution and also
forms an alloy with mercury.
The same result may be less conveniently attained by depositing a thin coating
of zinc and afterwards alloying this with a small amount of mercury by means of
the current in a solution of a salt of mercury & finally dissolving out the zinc in
strong acid.
The coating of mercury may be used for the preparation of iron & steel articles
before coating them with other metals than zinc.
We find that when using the solutions of zinc formed by dissolving the
hydrated oxide of zinc in caustic alkalis it is advantageous to wash the oxide
free of the neutral salt formed during precipitation before adding the excess of
alkali.
Also there is a difficulty in getting enough metal into solution to enable deposi-
tion to be carried on with a sufficiently great current density without the formation
of an objectionable amount of hydrogen.
We find we can increase the amount of metal in solution by suspending in the
liquid plates of zinc electrically connected to iron plates or to the metal of the iron
containing vessel.
Or scrap zinc may be hung in a basket of iron ganze suspended in the liquid.
An electrical action is set up which rapidly attacks the zinc which passes into
solution to a far greater extent than the ordinary hydrated oxide.
The same method may be employed to supplement the amount of metal dissolved
from the anode which in these solutions is generally less than the amount
deposited.
By properly proportioning the surfaces immersed to the current the density of
the solution may be kept constant.
£ A van 1904
RICHARD HEATHFIELD.
W. STEPNEY RAWSON.

page_text: Improvements connected with the Electrical Deposition of Zino and
other Metals.
We, RICHARD HEATHFIELD, of 1 Leadenhall Street, London, E.C. Merchant,
and WILLIAM STEPNEY RAWSON of 86 York Street, Westminster, London, S. W.
Electrical Engineer, 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 :-
Articles may be covered with a thin coating of mercury by making them
the cathode in an acid solution of a salt of mercury such as the sulphate.
We find that in the case of articles of iron and steel which resist the formation
of an alloy with mercury, the formation of the coating of mercury is facilitated
by adding to the mercury solution a small quantity of the corresponding salt
of zinc.
The coating of mercury may be used for the preparation of iron and steel
articles before coating them with metals, other than zinc, such as amalgamate with
mercury.
When, for depositing zinc, the solution employed is that formed by dissolving
hydrated oxide of zinc in caustic alkali, it is advantageous first to wash the oxide
free of the neutral salt formed during its precipitation and then to add the excess
of alkali for its solution.
The amount of metal in solution in the electrolyte can be increased by suspending
in it plates of zinc electrically connected to iron plates or to the metal of the iron
vessel containing the electrolyte. Or scrap zinc may be hung in baskets of iron
gauze suspended in the liquid.
By this means an electrical action is set up which rapidly attacks the zinc
rendering the solution rich in zinc to a far greater extent than that obtained from
the hydrated oxide.
By thus enriching the solution, deposition can be carried on with a sufficiently
great current density without the formation of an objectionable amount of
hydrogen.
In like manner, zinc in contact with iron may be employed to make up for that
part of the zine which is deposited but which is not dissolved from the anode. The
surfaces of the zinc and iron immersed may be so proportioned to the current
that the density of the solution may be kept constant. The zinc in contact
with iron is liable after a time to become coated with a film which impedes its
solution.
It should therefore from time to time be removed from the cell and washed with
dilute acid.
In employing zinc in contact with iron for enriching the electrolyte as above
described, care should be taken to prevent the temperature in the bath from
exceeding 80° F., and to prevent the electrolyte from attaining complete saturation
with zinc.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
―
1. The herein described method of preparing metal surfaces for electrolytic
deposit thereon of zinc and the like, by first depositing on these surfaces a coating
of mercury.

page_text: 2. The herein described method of enriching the alkaline solution employed for
electrolytic deposit of zinc, by placing in the solution zinc in contact with iron.
Dated this 17th day of May 1895.
ABEL & IMRAY,
Agents for the Applicants.