IMPROVE- MENTS IN THE MANUFACTURE OF SODA AND POTASH
Year: 1865

page_text: LETTERS PATENT to Andrew George Hunter, of Rockcliff Hall, near
Flint, in the County of Flint, Chemist, for the Invention of "IMPROVE-
MENTS IN THE MANUFACTURE OF SODA AND POTASH."
Sealed the 6th October 1865, and dated the 8th April 1865.
PROVISIONAL SPECIFICATION left by the said Andrew George Hunter at
the Office of the Commissioners of Patents, with his Petition, on the
8th April 1865.
I, ANDREW GEORGE HUNTER, of Rockcliff Hall, near Flint, in the County
of Flint, Chemist, do hereby declare the nature of the said Invention
for "IMPROVEMENTS IN THE MANUFACTURE OF SODA AND POTASH," to be as
follows:-
The object of my Invention is to effect the conversion of sulphate of soda
into caustic soda or of sulphate of potash into caustic potash by decomposing
sulphate of soda or sulphate of potash by mixing therewith caustic lime to
combine with the sulphuric acid it contains, and subjecting the mixture to
pressure (either hydraulic, steam, or mechanical pressure) whereby sulphate
of lime is formed and caustic soda or caustic potash liberated. I conduct
this process by mixing a solution of the sulphate of soda or sulphate of potash
(herein-after called alkaline sulphates) which is to be operated upon with
caustic lime, and I subject the mixture to pressure, and by agitation keep the
lime in contact with the alkaline sulphate until a sample when tested shews
that the alkaline sulphate under treatment is sufficiently converted into caustic
soda or potash.

page_text: I find it advantageous to boil the mixture of the alkaline sulphate and lime
while under pressure, also to use a weak solution of the alkaline sulphate, and
to slake the lime and convert it into milk of lime before introducing it to the
solution of the alkaline sulphate. It is also advantageous to use an excess of
lime, and when it is desired to obtain a pure sulphate of lime, the mixture of
caustic lime and sulphate of lime produced by one operation with the alkaline
sulphate may be treated with a second quantity of alkaline sulphate, which
can be afterwards further causticized by treatment with a second or fresh
quantity of lime, which in its turn can be further sulphated by a second
quantity of alkaline sulphate. The degree of pressure necessary varies
according to the alkaline sulphate and lime used, the temperature employed,
and the time in which it is desired to accomplish the operation.
Sulphate of potash requires more pressure, and is more difficult to decom-
pose than sulphate of soda; some varieties of lime being less chemically
active than others require more pressure. I have obtained good results with
sulphate of soda by boiling at a pressure of from 40 to 50 pounds per
inch, and with sulphate of potash by boiling at a pressure of from 80 to 90
pounds per inch, and have found that the process is hastened by greater
pressure. When the alkaline sulphate is sufficiently causticized I separate
the undissolved sulphate of lime from the liquor by filtration or subsidence
and decantation, and after washing it to free it from adhering soda or potash
it may be used as a manure, or if sufficiently freed from caustic lime, either
by the process described above, or washing with sulphuric or hydrochloric
acid, it may be converted into plaster of paris or applied to any other purpose
for which sulphate of lime is used.
From the liquor I manufacture marketable caustic soda or caustic potash,
or I carbonate the liquor and manufacture from it carbonate or bicarbonate
of soda or carbonate or bicarbonate of potash. The liquor may be carbonated
either by exposure to or injection of carbonic acid, or by concentrating the
caustic alkaline liquor in contact with a carbonate of lime which yields its
carbonic acid to concentrated caustic soda or potash, and the caustic lime thus
produced may be used to causticize sulphate of soda or sulphate of potash, or
if it has been produced by carbonating caustic potash it may be saturated
with chlorine and used for making chlorate of potash. The proportions of the
chemical ingredients mentioned vary according to their equivalents, or
according to their respective chemical affinities.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Andrew George Hunter in the Great Seal Patent Office ou
the 7th October 1865.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ANDREW
GEORGE HUNTER, of Rockcliff Hall, near Flint, in the County of Flint,
Chemist; send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Eighth day of April, in the year of our Lord One
thousand eight hundred and sixty-five, in the twenty-eighth year of Her reign,
did, for Herself, Her heirs and successors, give and grant unto me, the said
Andrew George Hunter, Her special licence that I, the said Andrew George
Hunter, my executors, administrators, and assigns, or such others as I, the said
Andrew George Hunter, 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 THE
MANUFACTURE OF SODA AND POTASH," upon the condition (amongst others) that I,
the said Andrew George Hunter, my executors or administrators, by an instru-
ment 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.
NOW KNOW YE, that I, the said Andrew George Hunter, 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:-
The object of my Invention is to effect the conversion of sulphate of soda
into caustic soda or of sulphate of potash into caustic potash by decomposing
sulphate of soda or sulphate of potash by mixing therewith caustic lime to
combine with the sulphuric acid it contains, and subjecting the mixture to
sufficient pressure (either hydraulic, steam, or mechanical pressure) whereby
sulphate of lime is. formed and caustic soda or caustic potash liberated. I
conduct this process by mixing a solution of the sulphate of soda or sulphate
of potash (herein-after called alkaline, sulphates), which is to be operated upon
with caustic lime, and I subject the mixture to sufficient pressure, and by
agitation keep the lime in contact with the alkaline sulphate until a sample

page_text: when tested shews that the alkaline sulphate under treatment is sufficiently
converted into caustic soda or potash. I find it advantageous to boil the
mixture of the alkaline sulphate and lime while under pressure, also to use a
weak solution of the alkaline sulphate, and to slake the lime and convert it
into milk of lime before introducing it to the solution of the alkaline
sulphate.
It is also advantageous to use an excess of lime, and when it is desired
to obtain a pure sulphate of lime, the mixture of caustic lime and sulphate of
lime produced by one operation with the alkaline sulphate may be treated
with a second quantity of alkaline sulphate, which can be afterwards further
causticized by treatment with a second or fresh quantity of lime, which in its
turn can be further sulphated by a second quantity of alkaline sulphate. The
degree of pressure necessary varies according to the alkaline sulphate and
lime used, the temperature and strength of solution employed, and the time in
which it is desired to accomplish the operation.
Sulphate of potash requires more pressure, and is more difficult to decom-
pose than sulphate of soda; some varieties of lime being less chemically
active than others require more pressure. I have obtained good results with
sulphate of soda by boiling a solution of specific gravity 1-100 at a pressure of
from 40 to 50 pounds per inch, and with sulphate of potash by boiling a solu-
tion of specific gravity 1-100 at a pressure of from 80 to 90 pounds per inch,
and have found that the process is bastened and improved by greater pressure.
When the alkaline sulphate is sufficiently causticized I separate the undis-
solved sulphate of lime from the liquor by filtration or subsidence and decan-
tation, and after washing it to free it from adhering soda or potash, it may be
used as a manure, or if sufficiently freed from caustic lime, either by the
process described above, or washing with sulphuric or hydrochloric acid, it
may be converted into plaster of paris or applied to any other purpose for
which sulphate of lime is used. I have found it advantageous to filter or
settle the sulphate of lime under pressure in order to prevent the caustic soda
or potash reacting on it. From the liquor I manufacture marketable caustic
soda or caustic potash, or I carbonate the liquor and manufacture from it
carbonate or bicarbonate of soda, or carbonate or bicarbonate of potash.
The liquor may be carbonated either by exposure to or injection of carbonic
acid, or by concentrating the caustic alkaline liquor in contact with a car-
bonate of lime which yields its carbonic acid to concentrated caustic soda or
potash, and the caustic lime thus produced may be used to causticize sulphate
of soda or sulphate of potash; or if it has been produced by carbonating

page_text: caustic potash, it may be saturated with chlorine, and used for making chlorate
of potash.
The proportions of the chemical ingredients mentioned vary according to
their equivalents, or according to their respective chemical affinities, which are
well known to chemists.
Having now described the nature of my said Invention, and the manner in
which the same is to be performed, I claim as my Invention, and desire to
be secured to me by the herein in part recited Letters Patent, the improve-
ments in the manufacture of soda and potash by converting the sulphate of
soda or sulphate of potash into caustic soda or caustic potash by means of
caustic lime under pressure, and the production of marketable caustic soda or
potash, or of the carbonates or bicarbonates of soda or potash, and the pro-
duction and utilization of the sulphate of lime, substantially as herein
specified.
In witness whereof, I, the said Andrew George Hunter, have hereunto
set my hand and seal, this Fifth day of October, in the year of our
Lord One thousand eight hundred and sixty-five.
D
Witness,
ALFRED T. KEENE,
Solr.,
Mold.
A. G. HUNTER. (L.S.)