AN IMPROVEMENT IN COATING IRON AND STEEL WITH ZINC
Year: 1855

page_text: LETTERS PATENT to Alexander Watt, of 83, Dean Street, Solo, Electro-
Metallurgist, for the Invention of "AN IMPROVEMENT IN COATING IRON AND
STEEL WITH ZINC."
Sealed the 20th May 1856, and dated the 3rd December 1855..
PROVISIONAL SPECIFICATION left by the said Alexander Watt at the
Office of the Commissioners of Patents, with his Petition, on the 3rd
December 1855.
I, ALEXANDER WATT, of 83, Dean Street, Soho, Electro-Metallurgist, do
hereby declare the nature of the Invention for "AN IMPROVEMENT IN COATING
IRON AND STEEL WITH ZINC ".to be as follows:-
My process consists in forming and employing a solution of zinc in the
following manner-I dissolve a quantity of cyanide of potassium in water; I
then nearly fill a porous cell or other suitable diaphragm with some of this
solution, the remainder I place in a stone or other suitable vessel. The porous
cell is then placed in this solution, allowing the solution in cach vessel to be
at about the same height. I attach a piece or soveral pieces of copper or other
suitable metal to the positive wire of a battery or other apparatus for generating
the current of electricity, and these pieces of copper or other. metal I put into
the porous cell; I then attach a piece of zinc to the negative wire' of a battery
or other apparatus, and immerse this. zinc in the solution in the larger vessel;

page_text: I then add a given quantity of liquid ammonia to the solution in the larger
vessel, and allow the whole to remain under the influence of the current until
enough of the zinc is dissolved to form a good solution. When the required
amount of zinc is dissolved, I remove the porous cell and its contents, and
add to the solution in the larger vessel a quantity of carbonate of potassa.
This solution is to be worked with a zinc anode and brisk battery power when
depositing on iron or steel.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Alexander Watt in the Great Scal Patent Office on the
3rd June 1856.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ALEXANDER
WATT, of 83, Dean Street, Soho, Electro-Metallurgist, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Third day of December, in the year of our Lord
One thousand eight hundred and fifty-five, in the nineteenth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto
me, the said Alexander Watt, Her special licence that I, the said Alexander
Watt, my executors, administrators, and assigns, or such others as I, the
said Alexander Watt, my executors, administrators, and assigns, should at any
time agree with, and no others, from time to time and at all times there-
after during the term therein expressed, should and lawfully might make,
use, exercise, and vend, within the United Kingdom of Great Britain and
Ireland, the Channel Islands, and Isle of Man, an Invention for AN IMPROVE-
MENT IN COATING IRON AND "STEEL WITH ZINC," upon the condition (amongst
others) that I, the said Alexander Watt, my executors or administrators, by
an instrument in writing under my, or their, or one of their hands and seals,
should particularly describe and ascertain the nature of the said Invention,
and in what manner the same was to be performed, and cause the same to be
filed in the Great Seal Patent Office within six calendar months next and
immediately. after the date of tlie said Letters Patent.
NOW KNOW YE, that I, the said Alexander Watt, do hereby declare
the nature of the said Invention, and in what manner the same is to be per-
formed; to be particularly described and ascertained in and by, the following
statement thereof, that is to say:-
My Invention consists, firstly, in forming a solution for the purpose of

page_text: coating iron or steel with zinc by galvanic agency. To form the solution I
proceed as follows:-I dissolve 200 oz. of commercial cyanide of potassium in
twenty gallons of water (rain water or distilled water being preferable) in a
suitable vessel; I then pour into this solution 80 ounces by measure of strong
liquid ammonia (of the specific gravity of 880 I prefer). Having stirred these
compounds together, I place several large porous cells, such as those used in
forming Daniell's batteries, in this solution, and pour into each of these porous
cells as much of a strong solution of a cyanide of potassium (say, about 16 ozs.
to the gallon, as will be equal to the height of the solution in the larger vessel;
I then attach several pieces of metal, copper or iron by preference, to pieces of
copper wire, which are then to be attached to the negative pole of a galvanic
battery. These pieces of copper or iron are to be placed in the porous cells.
I next attach a piece or several pieces of zinc to the positive pole of the
battery, and I then immerse these pieces of zinc in the solution of cyanide of
potassium and ammonia. For the above purpose I prefer using good milled
zine, the weight of which is to be ascertained before immersion; and I think it
better to "pickle" the zinc slightly previous to immersion in the cyanide
solution with dilute hydrochloric acid, after which process it should be well
rinsed in clean water. The galvanic battery is now to be set in action, and
allowed to continue in action on the abovo materials until the solution of
cyanide of potassium and ammonia has taken up about sixty ounces of zinc,
that is to say, about three ounces to the gallon of solution.
As soon as the pieces of zinc have been weighed to determine the amount
dissolved into the cyanide solution, I dip them into dilute hydrochloric acid,
and then rinse them, when they are placed aside for future operations, if
necessary; the porous cells are then to be removed. I now dissolve 80 ozs.
of a carbonated alkali (I prefer the carbonate of potassa) in a portion of the
above solution, and when dissolved I add it to the original solution, and stir
the whole together for a few moments, after which I allow the solution to
stand undisturbed until the sediment formed has subsided; I then transfer the
clear solution to another vessel, when it is ready for use.
The above solution may be made in a more concentrated form, if required;
say, with half the quantity of water, and it may be diluted down to the required
strength by adding more water when wanted to be worked. I prepare cast or
wrought iron or steel to be coated with the above solution in the following
manner, having first made a pickle composed of, say,-

page_text: The articles to be coated are first plunged into the above pickle, and allowed
to remain until the oxide of iron is easily removeable with a brush, sand, and
water. As soon as the articles are sufficiently pickled, they are to be rinsed in
clean water, and are then to be cleaned with a hard brush, sand, and water;.
and any oxide which may not, have been quite removed by the pickle may. be
scraped or otherwise removed, or the article be returned to tho pickling bath
until these parts yield to the brush and sand; or the iron or steel may be
cleaned by the processes ordinarily used at the "galvanized iron works."
When the articles to be coated are quite free from oxide, they are to. be
well rinsed in clean water, and immediately placed in the zincing bath, in
connection with the negative pole of the battery.
A's soon as the articles have received a slight coating they should be removed
from the bath and examined, in order to ascertain if there are any parts
remaining unclean, in which case those parts should be cleaned, and the whole
article to be once more brushed all over as before and then returned to the bath;
where it is to remain until sufficiently coated. It is as well, however, to move
the article about in the solution occasionally, in order to insure an uniformi
deposit. As soon as the articles are sufficiently coated they are to be removed
from the bath and rinsed in clean water (hot water being preferable), and they
may then be placed in sawdust to dry them. The articles may be rendered
bright either by means of the scratch brush, or by gently scouring with silver
sand, water, and a soft brush. When the above solution has been in use some
time it will be necessary to add occasionally a little cyanide of potassium and
liquid ammonia, so as to keep the solution at as near as possible the original
strength; and if the solution, from being worked with too small a surface of
positive electrode, or if from other causes it has become deprived of a portion
of its zinc, I place in the solution (by suspension or otherwise) several: porous
cells, which I fill with strong solution of cyanide of potassium, and into which
I place pieces of copper or iron as before, in connection with the negative pole
of the battery, and the zinc electrodes 1 attach to the positive pole of the
battery, by which means I am enabled to keep up the strength of the solution:
The above solution is to be worked with zinc electrodes (milled: zinc. being
preferable), and it will be necessary in coating flat surfaces, especially.to place
a piece of zinc on each side of the article to be coated; for instance, if sheets
of iron are to be coated, they are to be placed in the solution alternately, that
is to say, sheet zinc, sheet iron," sheet zinc, and so on, (the sheets of iron and
zine exposing about the same area of surface,) otherwise the surface opposite
the zinc electrode will receive the greatest amount of deposit. I prefer using a
battery which yields a considerable-quantity of electricity, and the action of

page_text: which can be maintained for a considerable time without losing its power,
by which means I not only secure a good deposit but uniform results. The
battery which I prefer is that known as Buusen's battery, or a battery
composed of carbon and zinc elements. Two or more 4-gallon cells of this
battery may be used when large articles are to be coated, or when a con-
siderable quantity of work is to be done in the bath at one time. When cast
or wrought iron or steel has become much rusted, it may be cleaned with
strong hydrochloric acid, or with a strong pickle composed of hydrochloric acid
and water, but it must not be allowed to remain too long in this pickle, or the
iron or steel will be acted upon.
Articles of cutlery may be coated by the above process to preserve them
from oxidation or rust in damp climates or during sea voyages, &c., and as
they will only require a slight coating for this purpose they will not require to
remain long in the bath. In pickling bright
In pickling bright steel articles I should not
recommend the use of any hydrochloric acid.
Having thus described the nature of my Invention, and the manner of
performing the same, I would have it understood that I do not confine myself
to the exact details or quantities described; but what I claim is, the method
of preparing a solution of zinc (suitable for coating iron and steel with zinc) by
means of electricity, as herein described.
In witness whereof, I, the said Alexander Watt, have hereunto set my
hand and seal, this Third day of Junc, in the year of our Lord One
thousand eight hundred and fifty-six.
5 Witness,
S. CARPMAEL.
ALEXANDER WATT. (L.S.)