IMPROVEMENTS IN COATING METALS AND IN APPARATUS EMPLOYED THEREIN AND FOR LIKE PURPOSES
Year: 1867

page_text: LETTERS PATENT to Gustav Bischof, junior, of 14, Poppelsdorfer Allée,
Bonn, in the Kingdom of Prussia, for the Invention of "IMPROVEMENTS
IN COATING METALS AND IN APPARATUS EMPLOYED THEREIN AND FOR LIKE
PURPOSES."
Sealed the 17th September 1867, and dated the 20th March 1867.
PROVISIONAL SPECIFICATION left by the said Gustav Bischof at the
Office of the Commissioners of Patents, with his Petition, on the
20th March 1867.
I, GUSTAV BISCHOF, junior, of 14, Poppelsdorfer Allée, Bonn, in the
Kingdom of Prussia, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN COATING METALS AND IN APPARATUS EMPLOYED THEREIN, AND
FOR LIKE PURPOSES," to be as follows:-
One part of my improvements consists in a method by which wrought-iron
baths in which the coating is fused are protected against the destroying action
of such metals; to effect this I out the interior sides of such baths in like
manner to rough files. The plates so prepared are coated with a good fire-
clay in the usual manner, or by preference with a mixture of about 26 parts of
sand, 13 parts of fire-clay, both finely ground; 12 parts of a solution of water
glass of specific gravity about 1'44. The bath is then allowed to stand until
air dry, when it is exposed to a gradually increased heat until perfectly dry.
Another part of my improvements consists in dipping the plates or other
articles in a boiling or nearly boiling solution of sal ammoniac before intro-

page_text: ducing them into the fused coating metal. The beat thus imparted to the
plates or other articles is sufficient instantaneously to evaporate the water
contained in such solution, leaving them covered with a dry or nearly dry film
of sal ammoniac. The use of an oven for drying the plates and articles can
thus be dispensed with, whilst the plates or articles treated by my method
take the coating metal instantaneously and completely. In using this method
no further flux is required on the bath.
Another part of my improvements consists in a pyrometer, or apparatus by
means of which the temperature of the fused coating metal can be regulated.
This is composed of a cylindrical fire-clay crucible, the top of which is luted
to a small plate of the same material; through the bottom of such crucible
and likewise through the centre of the plate a hole is bored; this plate forms
the basis of the pyrometer, and floats on the top of the fused coating metal.
If then a common thermometer constructed for high temperatures be intro-
duced through the hole made in the bottom of the crucible, which bottom
now forms the top, as the crucible is inverted, the interior of the crucible is
in direct communication with the fused coating metal on which the pyrometer
is kept floating, and the thermometer is held at a fixed distance from the
surface of such metal, such that it cannot burst through the heat; the
thermometer then indicates a certain temperature, which remains the same as
long as the temperature of the fused coating metal does not change; thus by
using such a pyrometer the temperature of the coating metal can be exactly
regulated so as to suit any required purpose if once by a few practical trials
the temperature or height of the thermometer required for any purpose be
ascertained and that height be maintained by either increasing or diminishing
the fire, as the case may be. The temperature indicated by the thermometer
is lower than the actual temperature of the fused metal; so, for instance, that
one degree of the thermometer may be equal to two degrees of the metal.
When using the pyrometer for other purposes than for ascertaining the
temperature of fusel metals, for instance, for regulating the beat of furnaces
and the like, an iron plate is fixed in any convenient place so as to be exposed
on one side to the direct heat of such furnace or source of heat. On the
other side of the plate two concentric rings are fixed, so that the top of the
before-mentioned crucible can be inserted between them. The space remaining
between the rings and the crucible being filled with fine sand the pyrometer
indicates the temperature of such furnace and the like, much in the same
manner as in the case of fused metals.
A fourth part of my improvements refers to the production of galvanized
tinned iron. Instead of tinning the plates by the wet way previous to their

page_text: being galvanized, as was bitherto customary, I add to the fused zinc about
to per cent. of tin, thus saving the operation of tinning, and producing in
one operation the same result.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Gustav Bischof in the Great Seal Patent Office on the
19th September 1867.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, GUSTAV
BISCHOF, junior, of 14, Poppelsdorfer Allée, Bonn, in the Kingdom of Prussia,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twentieth day of March, in the year of our Lord
One thousand eight hundred and sixty-seven, in the thirtieth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me, the
said Gustav Bischof, Her special licence that I, the said Gustav Bischof, my
executors, administrators, and assigns, or such others as I, the said Gustav
Bischof, my executors, administrators, and assigns, should at any time agree
with, and no others, from time to time and at all times thereafter 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 "IMPROVEMENTS IN COATING
METALS AND IN APPARATUS EMPLOYED THEREIN, AND FOR LIKE PURPOSES," upon the
condition (amongst others) that I, the said Gustav Bischof, my executors or
administrators, by an instrument in writing under my, or their, or one of
their bands 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 the said Letters
Patent.
NOW KNOW YE, that I, the said Gustav Bischof, 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 :-
One part of my improvements consists in a method by which wrought-iron
baths in which the coating metal is fused are protected against the destroying
action of such metals; to effect this I cut the interior sides of such baths
similarly to rough files, but so that the jags thus produced are not raised at

page_text: right angles to the plates, but remain in an inclined position. On every
square foot I make some 900 cuts, each being about of an inch wide, of
an inch long, and of an inch deep. They are cut in rows, one row towards
the top, the next towards the bottom of the bath, and so on. In case the
plates thus prepared cannot be lined at once in the manner herein-after
described they may be protected against oxidation by a mixture of 9 parts of
good fire-clay of the same composition as is used for fire-bricks, and 5 parts
of a solution of water glass of a specific gravity of 1.44. This coating is laid
on as thin as possible by means of a stiff brush. The plate may then be
lined with fire-clay and water, but I prefer using a mixture of 13 parts of
fire-clay of the same quality as above; 26 parts of sand, both finely sifted ; and
12 parts of a solution of water glass of the same gravity as above. The
mixture is to be kneaded in quantities of from 1 to 2 lbs. until plastic. The
plate having been first moistened with water glass, about 20 ozs. of the mixture
are spread on every square foot, taking care that it is firmly pressed into the
cuts; the bath is then allowed to stand until air dry, which in dry weather
requires about a fortnight, and finally exposed to a gradually increased heat
until perfectly dry. To effect the latter I place into a basket made up of iron
bars, and a little shorter and narrower than the bath to be dried, a plate of
sheet iron of the same length as the basket, and bent so as to form a lining to
the basket, or to the shape of a so-called Liebig's furnace, and provided with
holes at the bottom; the basket is then lowered to about one-third of the
height of the bath from the bottom, burning charcoal is introduced, and the
lining exposed during 24 hours to a gradually increased temperature of from
80 to 250° centigrade; the latter temperature being reached the bath is
gently heated from without, first with charcoal, and afterwards with coke ;
the basket is raised, and the coating metal to be fused cautiously and
gradually introduced.
Another part of my improvements consists in dipping the plate or other
articles in a boiling or nearly boiling solution of sal ammoniae before in-
troducing them into the fused coating metal. I heat this solution in a
wooden tank by means of steam which passes through a tin worm in the
tank. The boiling point of such a solution being about 110° centigrade,
the heat imparted to the plates or other articles by immersing them into
it is sufficient rapidly to evaporate the water contained in such solution,
leaving them covered with a dry or nearly dry film of sal ammoniac. I
prefer this method, as the use of an oven for drying the plates and other
articles as hitherto customary can thus be dispensed with. Furthermore, the
plates and other articles to be coated are apt to be oxidized, and not to take

page_text: the coating metal so rapidly and completely when using a cold solution of
sal ammoniac and afterwards drying them in an oven as when using ny
method. I also by my process obtain a thicker film of sal ammoniac on the
iron than when using a cold solution. I do not use any flux on the bath.
When galvanizing large and heavy plates I immerse them into the fused
metal by placing them vertically in a kind of iron basket suspended on a
chain, which can be lowered or raised by means of a winch. Before raising
the plate the surface of the zinc is skimmed off. Lighter plates I, as a rule,
carry through the fused zinc by means of rollers.
Another part of my improvements consists in a pyrometer, or apparatus by
Deans of which the temperature of the fused coating metal can be regulated.
The accompanying Drawing represents a full-size vertical section of this
pyrometer.
- a, a, a, a, is a cylindrical fire-clay crucible, the top of which is luted to a
slightly arched plate of fire-clay c, c. Through the bottom b, b, of the
crucible, and likewise through the centre 9, 9, of plate c, c, a hole is bored.
Through b, b, a glass tube d, d, d, d, is introduced, which serves as a guide
for an ordinary thermometer e, e, constructed for high temperatures.
At the
top and bottom of the cylinder two small holes h are bored in order to cause
a slight circulation of the air in its interior. The plate c, c, forms the basis of
the pyrometer, and floats on the top of the fused coating metal, which latter
is consequently in direct communication with the mercury of the thermometer.
The thermometer being only so much approached to the fused metal that it
cannot burst through the heat indicates a certain temperature, which remains
the same as long as the temperature of the fused coating metal does not
change. At f, f, a brass wire spirally wound round the thermometer (which
wire is not represented in the Drawing) prevents its falling through the glass
tube d, d, d, d, allowing at the same time by moving it up or down to
approach the thermometer more or less to the fused metal. By using such
a pyrometer the temperature of the fused coating metal can be exactly
regulated, so as to suit any required purpose, if once by a few practical trials
the temperature necessary for the thermometer to indicate be ascertained, and
that indication maintained by increasing or diminishing the fire, as the case
may be.
The advantage of such an apparatus in regard to the regular working of
It enables, for instance,
the process of coating will readily be understood.
workmen to regulate the thickness of the coating to prevent loss through
oxidation of the coating metal if the temperature be raised too high; it allows
the utmost economy in fuel; and particularly in the case of galvanizing iron it

page_text: will be found that it is at a certain temperature within small limits that the
zinc adheres best to the iron, and is most ductile, which temperature can easily
be maintained by aid of the said pyrometer. It is advisable to use the
pyrometer always in the same place, and to select such a one as is least
exposed to draughts. If several pyrometers are used they ought to be regulated
after one which niay be selected as the normal pyrometer by either raising or
lowering the thermometers in the respective glass tubes d, d, d, d, until they
give the same indication when placed side by side on a bath of fused metal.
The nearer the thermometer to the fused metal the higher is the temperature
it indicates, and the more sensitive is the instrument. The degrees of the
ordinary thermoter to which the degrees indicated by the pyrometer corre-
spond can if desirable be ascertained by placing the latter on a bath whilst
gently fusing the coating metal, or still more accurately placing it
successively on different baths whilst fusing different metals, and then com-
paring the temperatures indicated with those of the known melting points of
these metals.
The pyrometer will amongst other applications likewise be found very useful
in the process of separating silver from lead, or from lead and zinc, rendering
a much more regular working, and a more complete separation of the silver
than hitherto feasible. When using the pyrometer for other purposes than
for ascertaining the temperature of fused metals, for instances, for regulating
the heat of furnaces, retorts, gases, and the like, an iron plate is fixed in any
convenient place so as to be exposed on one side to the direct heat of such
furnaces and the like. On the other side of the plate two concentric rings
are fixed, so that a, a, a, a, (instead of being luted to c, c,) can be inserted
between them; the space remaining between the rings and the crucible being
filled with fine sand the pyrometer indicates the temperature of such furnaces,
and the like, much in the same manner as in the case of fused metals.
A fourth part of my improvements refers to the production of galvanized
tinned iron. Instead of tinning the plates by the wet way previous to their
being galvanized, as was hitherto customary, I add to the fused zinc a small
per-centage, about to 1 per cent. of tin. If as to the rest the way herein-
before described be followed the operation of tinning is saved, and the same
result produced in one operation.
Having thus described the nature of my Invention, I claim,-
Firstly, the method of lining wrought-iron baths in order to protect them
against the destroying action of the coating metal.
Secondly, the dipping iron plates and other articles into a hot bath of
sal ammoniac, and then immersing them into fused coating metal, as described.

page_text: Thirdly, the construction of the pyrometer or apparatus for ascertaining
and regulating the temperature of fused metals, furnaces, retorts, gases, and
the like, as described.
Fourthly, the manner of producing galvanized tinned iron in one operation
without previous tinning by the wet way by employing an alloy of zinc in the
proportions herein-before set forth.
In witness whereof, I, the said Gustav Bischof, have hereunto set my
hand and seal, this Fifth day of September, in the year of our Lord
One thousand eight hundred and sixty-seven.
GUSTAV BISCHOF, JUNIOR. (L.S.)