AN IMPROVED METHOD OF HARDENING AND TEMPERING STEEL
Year: 1856

page_text: LETTERS PATENT to George Cummins Thomas, of Washington City,
United States, but now of 67, Gracechurch Street, London, for the
Invention of "AN IMPROVED METHOD OF HARDENING AND TEMPERING
STEEL "A communication.
Sealed the 11th April 1856, and dated the 5th February 1856.
PROVISIONAL SPECIFICATION left by the said George Cummins Thomas
at the Office of the Commissioners of Patents, with his Petition,
on the 5th February 1856.
I, GEORGE CUMINS THOMAS, of Washington City, United States, but
now of 67, Gracechurch Street, London, do hereby declare the nature of
the said Invention for "AN IMPROVED METHOD OF HARDENING AND TEMPERING
STEEL" a communication from a foreigner residing abroad, to be as follows:-
It consists in applying to steel, heated to a greater or less degree, according
to the character of the article to be tempered, a pulverized composition, formed
by mixing chloride of sodium with the bichromate or prussiate of potash, in
proportions varying with the kind of work to be done; and when the said
composition is melted, producing a sudden cooling in the usual way.
The bicromate and prussiate of potash may be used either separately or
together, in combination with the chloride of sodium, or other materials, having
similar chemical properties, may be substituted for them.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said George Cummins Thomas in the Great Seal Patent Office
on the 5th August 1856.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, GEORGE
CUMMINS THOMAS, of Washington City, United States, but now of 67, Grace-
church Street, London, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Fifth day of February, in the year of our Lord
One thousand eight hundred and fifty-six, in the
year of Her reign,
did, for Herself, Her heirs and successors, give and grant unto me, the said
George Cummins Thomas, Her special licence that I, the said George
Cummins Thomas, my executors, administrators, and assigns, or such others
as I, the said George Cummins Thomas, 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 law-
fully might make, use; exercise, and vend, within the United Kingdom of
Great Britain and Ireland, the Channel Islands, and Isle of Man, an In-
vention for "AN IMPROVED METHOD OF HARDENING AND TEMPERING STEEL," a
communication, upon the condition (amongst others) that I, the said George
Cummins Thomas, my executors or administrators, by an instrument in
writing under me, or their, or one of their hands and seals, should par-
ticularly 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 George Cummins Thomas, do hereby
declare the nature of my said 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 consists in hardening, tempering, and restoring steel, `by
applying to it, when heated, a finely pulverized compound of chloride of sodium,
bichromate of potash, and prussiate of potash. For ordinary purposes the
ingredients should be combined in the proportions of 21 parts of the chloride of
sodium, 8 of bichromate of potash, and 8 of prussiate of potash. Variations
in these proportions may be required by the differences in the qualities of the
steel operated upon; but the degree of modification must be learned by
experience.
The chloride of sodium may be used in combination with the bichromate of

page_text: potash alone, as well as with the bichromate & prussiate. It may also be
combined with any other material having the same chemical properties as
these. In this case the proportions will be about 21 parts of the chloride of
sodium to 16 parts of the other ingredients; the exact proportions varying, as
in the first case, with the nature of the material operated upon.
The process of applying the compound differs according to the hardness and
temper it is desired to impart, and also to the size and form of the article
subjected to it. To illustrate the manner in which it is to be applied, I will
describe the treatment adapted to the class of tools having a square or nearly
square cutting edge, such as taps, reamers, turning and planing tools for iron,
cold chisels, drills, dies; &c. used for working iron and steel. The steel is
evenly and slowly heated to a color that would look red in the dark;; it is then
sprinkled evenly and freely with the composition; or in some cases (as in
turning & planing tools for iron, cold chisels, drills, &c.) dipped, in the
compound, and then replaced in the fire and brought slowly to a moderate
cherry red, or a high cherry red, according to the temper required. The
higher the heat, and the greater the quantity of the fluid employed, the harder
the tool can be made; and the more slowly and evenly the heat is applied
the more perfectly will the flux be absorbed. The heating is continued until
the flux has nearly dried off. The tool points should be kept rather out of the
fire, in order that they may more perfectly absorb the compound. For the
same reason, gear cutter teeth should not be heated too much, and should
receive such a quantity of the flux that it may run in freely between the teeth.
As a general rule, the part of the tool that is longest in coming to a given heat
is benefitted by the longer time the flux is being absorbed. The time may in
some measure be regulated by the quantity of the powder applied. After
having been sufficiently heated, and having absorbed its proper portion of the
flux, the tool is removed from the fire, cleaned by a broom or otherwise, &
plunged into cold water and finished. If more than one heating is required,
as may be the case with large reamers and the like, a second application of
the flux takes place after the tool has been heated rather hotter than before,
but not so much as completely to dry up the flux. The process may again
be repeated, if required, until the article has acquired the proper condition
(which can only be known by experience), when it is plunged into cold water
and finished.
The same treatment substantially is adopted in the case of that class of tools
having beveled edges on one or both sides, or thin edges, as drawing knives,
double plane irons, and scythes. The compound is applied with greater care,
and only to the side or sides where the steel is; and the second heat should not

page_text: exceed a dark blood red, reached slowly, so that the fluid may be gradually
and perfectly absorbed.
With regard to thin edged tools, I consider it best not to heat them above
blood red, and then to dip them into salt and oil (say lb. of the former to
a gallon of the latter), instead of water. If the tools prove too hard they
should be held over the fire until a slight change takes place in their color.
In light hardening steel, the composition is sprinkled on one or both sides
where the hardening is required. Burnt steel is restored by the application of
the same materials in a similar way.
Having given the above general rules and examples to enable others skilled
in the art to make use of my Invention, what I claim is the use of the chloride
of sodium in combination with the bichromate of potash, with or without the
prussiate of potash, for hardening & tempering steel in the mode substantially
as herein described.
In witness whereof, I, the said George Cummins Thomas, have hereunto
set my
hand and seal, this Fifth day of August, in the year of our
Lord Eighteen hundred and fifty-six.
GEORGE C. THOMAS. (L.8)