IMPROVEMENTS IN THE CONSTRUCTION OF ZINCING BATHS
Year: 1868

page_text: PROVISIONAL SPECIFICATION left by John Henry Johnson at the
Office of the Commissioners of Patents, with his Petition, on the
15th June 1868.-A communication from abroad by Frederick
Adam Kraft and Frederic Chase, both of Philadelphia, Pennsyl-
vania, United States of America.
I, JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County
of Middlesex, Gentleman, do hereby declare the nature of the said
Invention for "IMPROVEMENTS IN THE CONSTRUCTION OF ZINCING BATHS," a
communication to me from abroad by Frederick Adam Kraft and
Frederic Chase, both of Philadelphia, Pennsylvania, United States of
America, to be as follows:-
This Invention relates to the zincing of articles of iron or other metal
by immersing them in molten zinc, and consists of a zincing bath
composed of an outer casing of iron lined with copper or equivalent
material for preventing the formation of a dross from the iron and zinc,
which tends to destroy the iron vessel and renders a great portion of the
zinc unfit for coating purposes. In conducting the process of coating iron
with zinc it has been usual to employ cast or wrought iron vessels for
containing the zinc, which is maintained in a molten condition by the

page_text: application of external heat. Vessels of the smaller size are occasionally
made of cast iron, but those of larger size of thick wrought-iron plates.
For a vessel twelve feet long, twenty-six inches wide, and forty inches
deep, for instance, wrought-iron plates one inch in thickness are
necessary to withstand the pressure of the zinc, a coke fire contained
in a recess continued on all sides of the vessel being used for main-
taining the zinc at or about the temperature of 750 degrees Fahrenheit.
Owing to the intimate contact of the zinc with the iron and to the
heat to which both are subjected the two metals alloy, forming what is
known as "Spelter dross" which settles on the bottom of the vessel, and
the greater the heat the faster does this so-called dross accumulate.
In order to obviate this and other evils it is proposed to line the cast
or wrought iron vessel with a material which at the temperature to
which it is usually subjected will not be affected by or form an alloy
with the zinc, or which will not so readily form an alloy with the
latter as iron. It is not necessary in order to maintain the zinc in a
proper molten condition to heat it above 750° or 800°, and as at
this temperature no combination can be effected between copper and
zinc the formation of dross in a vessel lined with copper cannot take
place. Through carelessness however the vessel may be heated to such
an extent that the copper would form an alloy with the zinc, but as a
provision against such accidents the surface of the copper exposed to
the zinc may have a thin coating of silver, which although it can be
melted at a less heat than copper has not such an affinity as the latter
for zinc. The interior of the vessel may be lined with thin fire-tiles in
place of copper, the tiles being secured by copper or other fastenings, or
slabs of slate or glass or earthenware may be used for lining purposes
with good results as regards preventing the formation of the above-
mentioned dross; or the interior of the vessel may be lined at the sides
with copper and at the bottom with fire-tiles, slate, glass, and other like
substances.