AN IMPROVEMENT IN THE MANUFACTURE OF SODA AND POTASH BY THE LEBLANC PROCESS
Year: 1877

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." A communication from abroad
by Alfred Rangod Pechiney, of Salindres, in the Republic of France.
Cooled to
841 T
PROVISIONAL SPECIFICATION left by the said Walter Weldon at the
Office of the Commissioners of Patents on the 24th December 1877.
WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey. "AN IM-
PROVEMENT IN THE MANUFACTURE OF SODA AND POTASH BY THE LEBLANC PRO-
CESS." A communication from abroad by Alfred Rangod Pechiney, of Salindres, in
the Republic of France.
Soda makers' "vat liquors" being the solutions obtained by the lixiviation of
crude soda or "black ash" always contain iron, which renders difficult the manu-
facture from such liquors of commercial products of the best quality.
Of the iron in the said liquors a considerable proportion exists as ferrocyanide of
sodium, formed during the lixiviation of the black ash by the reaction upon each
other of cyanide of sodium and sulphide of iron, both of which bodies black ash as
at present manufactured always contains.
The object of the present Invention is to prevent the presence of ferrocyanides
in the said vat liquors, or to greatly diminish the quantity thereof by destroying,
completely or partially the cyanide of sodium in the black ash before its lixi-
viation.
This object is accomplished by an improvement in the method of manufacturing
black ash, which improvement consists in adding to the charge in the black ash
furnace, at or somewhat before the moment at which the charge would otherwise

page_text: be finished, and would therefore ordinarily be drawn, a certain additional quantity
of sulphate of soda, and then mixing the whole very intimately. The sulphate of
soda thus added to and intimately mixed with the charge of black ash destroys by
oxidation the cyanide of sodium therein, and if the charge at the moment of its
addition thereto contains a sufficient excess of limestone is itself at the same time
converted into carbonate of soda.
The quantity of additional sulphate of soda to be thus added to each nearly
finished charge of black ash should be in somewhat considerable excess of the
quantity equivalent to the quantity of cyanide of sodium therein. As the pro-
portion of cyanide of sodium in black ash differs in different factories the pro-
portion of additional sulphate of soda to be used will also differ in different factories.
For such black ash as the experiments upon which this Invention is based have
been made with the proportion of additional sulphate of soda which has been found
to answer best is six per cent. of the quantity used for the charge of black ash.
The simplest rule however will be to use as much additional sulphate of soda as the
charge of black ash can decon pose without giving liquors containing too much
sulphide.
This Invention is equally applicable to the manufacture of potash, as regards
which it consists in using additional sulphate of potash, in the same manner as is
set forth above for additional sulphate of soda.

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 22nd June
1878.
WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey.
" "AN IM-
IMPROVEMENT IN THE MANUFACTURE OF SODA AND POTASII BY THE LEBLANC PRO-
CESS.' (A communication from abroad by Alfred Rangod Pechiney, of Salindres, in
the Republic of France.)
"
Soda makers' "vat liquors" being the solutions obtained by the lixiviation of
crude soda or "black ash".always contain iron, which renders difficult the manu-
facture fioin such liquors of commercial products of the best quality and colour.
Of the iron in the said liquors a considerable proportion exists as ferrocyanide of
sodium, formed during the lixiviation of the "black ash" by the reaction upon
each other of cyanide of sodium and sulphide of iron, both of which bodies black
ash, as ordinarily manufactured, always contains.
The object of the present Invention is to prevent the presence of ferrocyanide
in the said vat liquors, or to greatly diminish the quantity of ferrocyanide con-
tained therein by destroying, completely or partially, the cyanide of sodium in the
black ash before the black ash is lixiviated
This object is accomplished by an improvement in the method of manufacturing
black ash, which improvement consists in adding to the charge in the black ash
furnace, at or somewhat before the moment at which the charge would otherwise
be finished, an additional quantity of sulphate of soda, and then mixing the whole
very intimately. The additional sulphate of soda thus added to and intimately
mixed with the charge of black ash destroys the cyanide of sodium therein,
apparently by a reaction in which sulphate of soda is reduced by the cyanide of
sodium to the state of sulphide, the oxygen of the sulphate of soda combining with
the carbon of the cyanide of sodium, and the cyanide of sodium being thus con-
verted into carbonate of soda, with liberation of free nitrogen. While the
additional sulphate of soda thus converts the cyanide of sodium into carbonate of
soda, if at the moment of adding the additional sulphate there be present in the
charge a sufficient excess of carbonate of lime, or if, in the event of such an excess
of carbonate of lime not being then present, a suitable further quantity of carbonate
of lime be added, either with the additional sulphate or after it, the additional
sulphate is also itself converted into carbonate of soda.
The quantity of additional sulphate to be thus added to the nearly finished
charge of black ash should be in somewhat considerable excess of the quantity
equivalent to the quantity of cyanide of sodium therein. The quantity used
by Monsieur Pechiney, who has communicated to me the present Invention, is
about six per cent. of the initial quantity of sulphate employed for the charge. I
believe that five or six parts of additional sulphate per hundred parts of initial
sulphate will usually be a good working proportion in this country. For obvious
reasons however the proportion, which is the best in one work where the black ash
is of one quality, may not be the best in another work where the black ash may be
of another quality; but I believe that six per cent. of additional sulphate will
rarely be too much, and that still more rarely will it be too little Less will often
suffice to destroy completely, or reduce to traces only, the cyanide of sodium in the
black ash, and more will scarcely ever be needed for that purpose, but it should be
borne in mind that additional sulphate not only improves the quality of the black
ash by destroying, more or less completely, the cyanide of sodium therein, but also
that when not used in too great excess it is itself converted into more black ash
free of cost. It will therefore usually be a good rule to use as much additional
sulphate as the charge can decompose consistently with the production of balls
yielding liquors not containing too much sulphide of sodium.
The Invention above described is equally applicable to the manufacture of potash
by the Leblanc process.

page_text: Having now described and particularly ascertained the nature of the said Inven-
tion 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 addition
to crude soda of sulphate of soda, and the addition to crude potash of sulphate of
potash, near the end of the operation in the soda or potash furnace, as the case may
be, substantially as is above described.
In witness whereof, I, the said Walter Weldon, have hereunto set my hand
and seal, this Twentieth day of June, in the year of our Lord One thousand
eight hundred and seventy-eight.
WALTER WELDON. (LS.)