AN IMPROVEMENT IN THE MANUFACTURE OF SODA AND POTASH BY THE LEBLANC PROCESS
Year: 1878

page_text: LETTERS PATENT to Walter Weldon, of Rede Hall, Burstow, in the County.
of Surrey, for the Invention of "AN IMPROVEMENT IN THE MANUFACTURE
OF SODA AND POTASH BY THE LEBLANC PROCESS."
Sealed the 6th December 1878, and dated the 11th July 1878.
PROVISIONAL SPECIFICATION left by the said Walter Weldon at the Office
of the Commissioners of Patents on the 11th July 1878.
WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey. "AN IM-
PROVEMENT IN THE MANUFACTURE OF SODA AND POTASH BY THE LEBLANC
PROCESS."
The essential operation of the manufacture of soda by the Leblanc process consists
in calcining a mixture of sulphate of soda, coal, and carbonate of lime. The chief
re-actions which take place in this operation consist in the reduction of the sulphate
of soda to the state of sulphide of sodium, and the decomposition of this sulphide of
sodium by the carbonate of lime, with production of sulphide of calcium and car-
bonate of soda. For this last-mentioned re-action the quantity of carbonate of lime
chemically equivalent to the sulphate of soda employed is theoretically sufficient,
but it has been the practice till recently to employ, instead of a single equivalent of
carbonate of lime, from one and a half to two equivalents. Recently, Mr. Mactear
has reduced to the theoretical quantity the quantity of carbonate of lime employed,
with very great advantage as regards the quantity of sulphate of soda which a given
furnace can be made to decompose in a given time, but with the disadvantage that
the product contains an increased amount of that exceedingly prejudicial impurity,
sulphide of sodium.
The object of the present Invention is to provide a mode of working whereby the
advantages resulting from the use of merely the theoretical quantity of carbonate of
lime may be retained, while at the same time the proportion of sulphide of sodium
in the product, instead of being greater, as in Mr. Mactear's product, shall be less
than the proportion of sulphide of sodium contained in the product of the old method

page_text: of working. That very important object it accomplishes by combining with the
employment of an initial mixture of sulphate of soda, coal, and carbonate of lime
containing a proportion of carbonate of lime merely or about or not quite equivalent
to the quantity of sulphate of soda contained therein, the employment of a small
additional quantity of carbonate of lime added separately, and, instead of at the
commencement of the operation, at or near the end of it. This additional carbonate
of lime I add at, or about, or a little before the moment at which the charge would
otherwise be considered to be finished, and would accordingly be withdrawn from
the furnace. I mix it with the charge as intimately as possible, and after it is added
I allow the charge to remain in the furnace long enough to enable the additional
carbonate of lime to re-act upon the sulphide of sodium contained in the charge at
the moment of its addition thereto.
In performing the present Invention I find it desirable that the proportion of coal
in the initial mixture of sulphate of soda, coal, and carbonate of lime should be less
than any of the proportions ordinarily used. Those proportions vary from forty-five
or fifty parts of coal per one hundred parts of sulphate of soda to one hundred parts
of coal per one hundred parts of sulphate of soda. I find that from twenty-five to
thirty-five parts of coal per one hundred parts of sulphate of soda give very much
better results.
The present Invention is equally applicable to the manufacture of potash by the
Leblanc process.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Walter Weldon in the Great Seal Patent Office on the 6th January
1879.
WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey.
"AN IM-
IN THE MANUFACTURE OF SODA AND POTASH BY THE LEBLANC
PROVEMENT
PROCESS."
The essential operation of the manufacture of soda by the Leblanc process consists
in calcining a mixture of sulphate of soda, coal, and carbonate of lime. The chief
re-actions which take place in this operation consist in the reduction of the sulphate
of soda to the state of sulphide of sodium, and the decomposition of this sulphide of
sodium by the carbonate of lime, with production of sulphide of calcium and car-
bonate of soda. For this last-mentioned re-action the quantity of carbonate of lime
chemically equivalent to the sulphate of soda employed is theoretically sufficient,
but it has been the practice till recently to employ, instead of a single equivalent of
carbonate of lime, from one and a half to two equivalents. Recently, Mr. Mactear
has reduced to the theoretical quantity the quantity of carbonate of lime employed,
with very great advantage as regards the quantity of sulphate which a given furnace
can be made to decompose in a given time, but with the disadvantage that the pro-
duct contains an increased amount of that extremely prejudicial impurity, sulphide
of sodium.
The object of the present Invention is to provide a mode of working which shall
permit the use of only or even less than the theoretical quantity of carbonate of
lime, and yet yield a product of satisfactory quality. That object it accomplishes
by combining with the employment of an initial mixture of sulphate of soda, coal,
and carbonate of lime containing a proportion of carbonate of lime merely or about
or not quite equivalent to the quantity of sulphate of soda contained therein, the
employment of an additional quantity of carbonate of lime, added separately near
the end of the operation. This additional carbonate of lime I add at, or about, or a
little before the moment at which the charge would otherwise be considered _to_be_
finished, and would accordingly be withdrawn from the furnace. I mix it with the
charge as intimately as possible, and after it is added I allow the charge to remain
in the furnace long enough to enable the additional carbonate of lime to re-act
sufficiently upon the sulphide of sodium contained in the charge at the moment. of
its addition thereto.
I prefer, though this is not essential, that the additional carbonate of lime should
be in the state of powder or dust. The quantity of it to be used will vary, as will
be well understood, with all the conditions influencing the proportion of sulphide of
sodium present in the charge at the moment of its addition thereto; but the quan-
tities I have hitherto employed have varied between five per cent. and twenty per
cent., reckoned on the sulphate in the initial mixture.
This Invention is equally applicable to the manufacture of potash by the Leblanc
process.
Having now described the nature of the said Invention, and in what manner the
same is to be performed, I claim as the Invention to be secured to me by the herein-
before in part recited Letters Patent the combination, in the manufacture of soda
and potash by the Leblanc process, of from less than an equivalent to not much more
than an equivalent of initial carbonate of lime with the employment of an additional

page_text: quantity of carbonate of lime, such additional quantity of carbonate of lime being
added near the end of the operation, substantially as is above described.
In witness whereof, I, the said Walter Weldon, have hereunto set my hand
and seal, this Fourth day of January, in the year of our Lord One thousand
eight hundred and seventy-nine.
WALTER WELDON. (L.S.)