IMPROVEMENTS IN THE MANUFACTURE OF A Do AXED MINER PIAFROAD OF CHROMATES OF POTASH AND SODA AND THEIR BICHROMATES
Year: 1875

page_text: LETTERS PATENT to John White, of 166, Fleet Street, in the City of
London, for the Invention of “IMPROVEMENTS IN THE MANUFACTURE OF
A Do
AXED MINER PIAFROAD "
Sealed the 18th June 1875, and dated the 1st March 1875.
PROVISIONAL SPECIFICATION left by the said John White at the
Office of the Commissioners of Patents, with his Petition, on the
1st March 1875.
I, JOHN WHITE, of 166, Fleet Street, in the City of London, do hereby
declare the nature of the said Invention for "IMPROVEMENTS IN THE
MANUFACTURE OF CHROMATES OF POTASH AND SODA AND THEIR BICHROMATES,” to
be as follows:—
This Invention relates to improvements in the manufacture of
chromates of potash and soda and their bichromates, and consists in
slaking lime with sulphate of potash in solution, and adding chrome ore
to this mixture.
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page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said John White in the Great Seal Patent Office on
the 27th August 1875.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOHN
WHITE, of 166, Fleet Street, in the City of London, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the First day of March, in the year of
our Lord One thousand eight hundred and seventy-five, in the thirty-
eighth year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said John White, Her special licence
that I, the said John White, my executors, administrators, and
assigns, or such others as I, the said John White, my executors, ad-
ministrators, 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 THE MANUFACTURE OF CHROMATES OF POTASH AND SODA
CHROMATES, upon the condition (amongst others) that I, the said John
White, 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 the said Letters Patent.
"
AND THEIR BI-
NOW KNOW YE, that I, the said John White, 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 thereof, that is to say :-
The process at present in use for the manufacture of chromates of
potash and soda and their bichromates consists in the employment of a
mixture of chrome ore, lime, and carbonate of potash or caustic potash
(or soda), or a mixture or combination of both. The mixture is
subjected to heat in a furnace until the process is considered complete.

page_text: The object of the present Invention is to make the chromates of
potash and soda and their bichromates from the sulphates which are
cheaper than the carbonates. The fusibility of the mixture when these
salts are used has hitherto prevented manufacturers from using them in
the commercial production of chromates or bichromates, because by
fusion the oxidation at once ceased and the production of chromate was
thereby prevented. This Invention prevents fusion and allows oxidation
to proceed freely by the employment of a much larger quantity of lime
than has hitherto been used.
The proportion of lime may be reduced by the substitution of some
other infusible substance, such as metallic oxides, or even the refuse
from above mixture after lixiviation, but the proportion of lime or other
infusible substance must within certain limits bear a fixed proportion to
the amount of sulphate used. The amount of ore or the oxide used
varies according to its richness in chromium.
The salt may be mixed with the lime (dry or slaked) in powder or
granular, or mixed with sufficient water to slake the lime which is then
added, or a part of the salt may be dissolved in water and the lime
slaked therewith, and the rest of the salt added dry; or the lime may be
mixed with the dry salt and the mixture treated with water. In fact
the salt may be introduced in any manner, although the most advan-
tageous way is to dissolve as much as possible, adding the remainder of
the salt, and to slake the lime with the mixture and solution so
obtained.
The amount of lime required for the decomposition of 100 parts of
sulphate of potash is about 32 parts, whereas the present Invention
requires about 148 or about four and a half times the actual quantity
required for decomposition.
The amount of lime required for the decomposition of 100 parts of
sulphate of soda is about 39, whereas this Invention requires about 181,
that is also about four and a half times. Any greater proportion of lime
or other infusible oxide may be used, but the excess is nearly inert and
only renders the batch more infusible and powdery in the furnace.
Having now described the nature of my said Invention, and in what
manner the same has to be performed, I declare that I claim, the im-
provements in the manufacture of chromates of potash and soda and

page_text: described.
In witness whereof, I, the said John White, have hereunto set
my hand and seal, this Twenty-sixth day of August, One thou-
sand eight hundred and seventy-five.
JOHN WHITE. (L.S.)