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."
ealed the 28th May 1878, and dated the 11th January 1878.
PROVISIONAL SPECIFICATION left by the said Walter Weldon at the
Office of the Commissioners of Patents on the 11th January 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 in suitable proportions of sulphate of soda, coal, and car-
bonate 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 carbonate of soda. Towards the end of the operation
however another re-action takes place, in part owing to the furnace in which it is
performed being now hotter than at any previous stage of the operation. Some of
the carbonate of soda thereby becomes reconverted into sulphide of sodium, the
presence of which body in the product ultimately drawn from the furnace is
extremely disadvantageous.
The object of the present Invention is to diminish the proportion of sulphide of
sodium in the said product, commonly known as "black ash." The said Invention
consists in adding to the charge in the furnace and very intimately mixing there-
with a further quantity of carbonate of lime, this addition being made at or about
or a little after that stage of the operation at which the prejudicial inverse re-
action above referred commences to take place. This additional carbonate of lime
then acts in two ways. It so lowers the temperature of the furnace that the
said inverse re-action can no longer take place, and it converts into carbonate of
soda any sulphide of sodium already existing in the charge. There is thus obtained
a black ash, which yields on lixiviation at a suitably low temperature liquors
Paine A71

page_text: containing very much less sulphide of sodium, and consequently very much less iron,
than black ash liquors ordinarily contain at present.
The use of a further quantity of carbonate of lime, to act as above set forth, may
be combined with the use of the additional sulphate of soda for the destruction of
cyanides in black ash, which is prescribed in the Specification of an Invention com-
municated to me from abroad by Alfred Rangoon Péchiney, of Salindres, in the
Republic of France, which Specification was filed on the 24th of December last, and
bears the number 4880, that is to say, the said further quantity of carbonate of
lime may either be added after the said sulphate of soda, or may be mixed there-
with and added at the same time.
The Invention above described is equally applicable to the manufacture of
potash.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Walter Weldon in the Great Seal Patent Office on the 10th July
1878.
WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey. " AN
IMPROVEMENT 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 product
of this operation is crude soda or "black ash." The present Invention consists,
firstly, in adding to the charge in the black ash furnace near the end of the said
operation a further quantity of carbonate of lime; and, secondly, in combining the
use, as just stated, of additional carbonate of lime with the use of the addi-
tional sulphate of soda, which is prescribed in the Specification of an Invention
communicated to me from abroad by Alfred Rangod Pechiney, of Salindres,
in the Republic of France, for which Her Majesty's Letters Patent, bearing
date the Twenty-fourth day of December last, have been granted to me.
The object of the present Invention is to obtain a black ash containing less
sulphide of sodium than is usually contained in black ash as ordinarily hitherto
manufactured. Although the proportion of sulphide of sodium in ordinary black
ash is usually under one per cent., it is extremely prejudicial to the quality of the
commercial products manufactured therefrom, carrying iron into those products, and
also during the processes of their manufacture being itself reconverted into sulphate.
By my present Invention the sulphide of sodium, which would otherwise be con-
tained in the black ash as drawn from the furnace, is placed and maintained for a
suitable time before the charge leaves the furnace in contact with a relatively large
quantity of carbonate of lime, whereby a large part, and often the whole of it, is
converted into carbonate of soda.
In carrying out the present Invention, the additional carbonate of lime, associated
or not with additional sulphate of soda, is put into the furnace at or about or a little
before the moment at which the charge would otherwise be considered finished, and
would accordingly be withdrawn. It must be mixed with the charge as intimately as

page_text: possible, and the charge must remain in the furnace some little time after it has
been added.
In the only factory in which the present Invention is as yet employed, per thirty
parts of carbonate of lime contained in the mixture charged into the furnace at the
commencement of the operation, four parts of additional carbonate of lime are added
two and a half minutes before the charge is drawn. It will be well understood
however the proportion of sulphide of sodium to be destroyed by the additional
carbonate of lime will differ in different works, and that the proportion of additional
carbonate which must be used, and the length of time the charge must remain in
the furnace after it is added, will vary accordingly.
The Invention above described is equally applicable to the manufacture of potash
by the Leblanc process.
Having now described and particularly ascertained the nature of the said In-
vention, 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,-
Firstly. The use of additional carbonate of lime in the manufacture of soda and
potash by the Leblanc process, substantially as is above described.
And, Secondly. The combination of additional carbonate of lime, as aforesaid, for
the purpose of destroying wholly or in part the sulphide of sodium contained in
crude soda and the sulphide of potassium contained in crude potash, with the use
of additional sulphate of soda or sulphate of potash for the purpose of similarly
destroying in crude soda cyanide of sodium and in crude potash cyanide of
potassium.
In witness whereof, I, the said Walter Weldon, have hereunto set my hand
and seal, this eighth day of July, in the year of our Lord One thousand
eight hundred and seventy-eight.
WALTER WELDON. (L.S.)