IMPROVEMENTS IN THE MANUFACTURE OF CHLORATE OF SODA, PARTLY APPLICABLE ALSO TO THE MANUFACTURE OF CHLORATE OF POTASH
Year: 1881

page_text: LETTERS PATENT to Walter Weldon, of Rede Hall, Burstow, in the County
of Surrey, for an Invention of "IMPROVEMENTS IN THE MANUFACTURE OF
CHLORATE OF SODA, PARTLY APPLICABLE ALSO TO THE MANUFACTURE OF
CHLORATE OF POTASH." A communication from abroad by Alfred Rangod
Pechiney, of Salindres, in the Republic of France.
PROVISIONAL SPECIFICATION left by the said Walter Weldon at the
Office of the Commissioners of Patents on the 1st February 1881.
WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey. " IMPROVE-
MENTS IN THE MANUFACTURE OF CHLORATE OF SODA, PARTLY APPLICABLE ALSO
TO THE MANUFACTURE OF CHLORATE OF POTASH." A communication from abroad
by Alfred Rangod Pechiney, of Salindres, in the Republic of France.
Chlorate of soda is at present always manufactured from chlorate of potash. By
the present Invention it is obtained by reaction of sulphate of soda upon the
chlorate of lime of the product formed by treating milk of lime by chlorine gas
after removal from that product of more or less of its chloride of calcium by the
means which will hereinafter be described.
The product of the treatment of milk of lime by chlorine gas should consist
theoretically of one equivalent of chlorute of lime and five equivalents of chloride
of calcium. As produced industrially it ordinarily contains from five and a half
to six equivalents of chloride of calcium. To convert the chlorate of lime of such
a solution into chlorate of soda by means of sulphate of soda, there must be added
to it from six and a balf to seven equivalents of sulphate of soda, the products
being from six and a half to seven equivalents of solid but very bulky sulphate of
lime, one equivalent of chlorate of soda, and five and a half to six equivalents
of chloride of sodium. It would be very inconvenient to wash so much sulphate of
lime, and both costly and difficult to separate the chlorate of soda from so much
chloride of sodium. Under the Invention communicated to me by my corre-
spondent the product of the treatment of milk of lime by chlorine gas, before being

page_text: treated by sulphate of soda, is therefore first treated for the separation from it of a
portion of its chloride of calcium.
My correspondent has found that if the ordinary product of the treatment of
milk of lime by chlorine gas be evaporated until it attains a certain degree of
concentration and then cooled, more than seventy-five per cent. of its chloride
of calcium will separate out in crystals susceptible of being almost completely
freed from adherent liquor by means of a hydro-extractor or other efficient
appliance for separating liquids from solids, leaving a mother-liquor containing,
per equivalent of chlorate of lime in it, only 12 (one and two-tenths) equivalents
of chloride of calcium. It is preferable not to push the evaporation beyond the
point at which the boiling liquor attains a specific gravity of 1485, or thereabout,
and then not to cool it much below 50 degrees Fahrenheit. My correspondent has
also found that if the mother-liquor remaining after the separation of crystals of
chloride of calcium, as just set forth, have now added to it its own volume of water
and as much lime, preferably hydrated, as corresponds to about three equivalents
upon the chloride of calcium remaining in the liquor, heating to about 80 degrees
ceutigrade, corresponding to about 176 degrees Fahrenheit, will determine the
formation of oxychloride of calcium, which on cooling will separate out as a
crystalline mass, leaving a mother-liquor now containing only about three-tenths
of an equivalent of chloride of calcium. To convert into chlorate of soda the
chlorate of line of such a liquor will require only 13 (one and three-tenths)
equivalents of sulphate of soda, while per equivalent of chlorate of soda in the
product there will be only 1-3 (one and three-tenths) equivalents of sulphate of
lime, and only three-tenths of an equivalent of chloride of sodium.
Instead of treating the product of the treatment of milk of lime by chlorine
gas for the separation of chloride of calcium from it, tirst by the above described
method of separating chloride of calcium as hydrated crystals of that compound
itself, and then by the further above described method of separating more chloride
of calcium as oxychloride, either of these methods of separating chloride of calcium
may be used without the other, and sulphate of soda then added to the resulting
mother liquor. When, however, only the method of separating chloride of calcium
as oxychloride is employed, it will usually not be necessary to dilute the crude
liquor, since that liquor will not have been previously subjected to concentration
by evaporation.
After having added sulphate of soda to a mother-liquor obtained by separating
chloride of calcium, as above described, from the product of the treatment of milk
of lime by chlorine gas, my correspondent prefers to precipitate by carbonate of
soda any calcium salts still remaining in solution. Having separated the precipitate
he then evaporates the mother-liquor, and fishes out the chloride of sodium which
falls during such evaporation. When the liquor has been evaporated to the point
at which its density becomes about 1-485, or about 48 degrees Beaumé, it is ready
to be cooled and crystallized, as will be well understood.
As the chloride of sodium which is separated by evaporation from a mixed
solution of chlorate of soda and chloride of sodium has always some chlorate of
soda associated with it, it is necessary to wash the said chloride of sodium. Various
other methods of utilizing the resulting wash-waters will be obvious to practical
men, but my correspondent has found that a very good method is to add to such
wash-waters chloride of potassium, and so convert their chlorate of soda into the
much less soluble salt chlorate of potash, which can be then separated by
crystallization, as will be well understood. My correspondent prefers to treat in
this way also the sulphate of lime precipitated when sulphate of soda is added to
solutions of chlorate of lime, and thus in the same series of operations to produce
both chlorate of soda and chlorate of potash. He also in some cases treats by
chloride of potassium the waters obtained by washing the oxychloride of calcium
produced when the product of the treatinent of milk of lime by chlorine gas is
treated by addition of lime followed by beating and cooling, as above set forth.

page_text: My correspondent does not confine himself to the exact temperatures and
densities above indicated, though he believes them to be best, but what he regards
as his Invention is the manufacture of chlorate of soda by reaction of sulphate of
soda upon the product of the treatment of milk of lime by chlorine gas, from
which product chloride of calcium has first been separated either by simple
evaporation and cooling, or by addition of lime followed by heating and
cooling, or by a combination of both these methods used one after the
other, substantially as is above described, by then precipitating all calcium
salts by carbonate of soda and then evaporating the mother-liquor and separating
chloride of sodium, as above set forth, and in further manufacturing at the same
time chlorate of potash by adding chloride of potassium to the wash-waters
containing chlorate of soda or chlorate of lime as aforesaid.

page_text: SPECIFICATION in pursuance of the conditions of tho Letters Patent filed
by the said Walter Weldon in the Great Seal Patent Office on the 29th July
1881.
WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey. "IMPROVE-
MENTS IN THE MANUFACTURE OF CHLORATE OF SODA, PARTLY APPLICABLE ALSO
TO THE MANUFACTURE OF CHLORATE OF POTASII." A communication from Alfred
Rangod Pechiney, of Salindres, in the Republic of France.
Chlorate of soda is at present always manufactured from chlorate of potash. By
the present Invention it is obtained by reaction of sulphate of soda upon the
chlorate of lime of the product formed by treating milk of limo by chlorine gas,
after removal from that product of more or less of its chloride of calcium by the
means which will hereinafter be described.
The product of the treatment of milk of lime by chlorine gas should consist
theoretically of one equivalent of chlorate of lime, and five equivalents of chloride
of calcium. As produced industrially, it ordinarily contains from five and a half to
six equivalents of chloride of calcium. To convert the chlorate of lime of such
a solution into chlorate of soda by means of sulphate of soda, there must be added
to it from six and a half to seven equivalents of sulphate of soda, the products
being from six and a half to seven equivalents of solid but very bulky sulphate of
lime, one equivalent of chlorate of soda, and five and a half to six equivalents of
chloride of sodium. The object of the Invention communicated to me by my
correspondent is to avoid the necessity to use so much sulphate of soda, to avoid
the inconvenience of washing so much sulphate of lime, and to avoid the cost and
difficulty of separating the chlorate of soda from so much chloride of sodium.
Under the said Invention the product of the treatment of milk of lime by chlorine gas,
before being treated with sulphate of soda, is therefore first treated for the
separation from it of a portion of its chloride of calcium.
My correspondent has found two methods by which appreciable quantities of
chloride of calcium may be separated from the product of the treatment of milk of
lime by chlorine gas, and either both these methods may be used in combination or
one of them may be used without the other.
My correspondent has found that if a liquor containing from five to six
equivalents of chloride of calcium per equivalent of chlorate of lime in it bo
evaporated to a certain degree of concentration, and be then cooled to a certain
point it will deposit a considerable part of its chloride of calcium as hydrated
crystals, which by means of a hydro-extractor or other suitable appliance for
separating solids from liquids, can be freed from mother-liquor so far as to retain
only a very small proportion of chlorate. The evaporation should be carried on
until the boiling liquor has a density of about forty-eight degrees Beaumé,
corresponding to a specific gravity of about 1.485. The subsequent cooling should be
carried to fifty degrees Fahrenheit or a little lower, but should not be carried
below forty-seven degrees Fahrenheit. At above fifty degrees Fahrenheit a
maximum separation of chloride of calcium would not be obtained, while at about
forty-seven degrees Fahrenheit chlorate of lime would begin to crystallize out also.
When the liquor before cooling has a specific gravity of about 1-485, and it is
cooled to fifty degrees Fahrenheit or a little below, the quantity of chloride of
calcium which crystallizes out is such that when these crystals have been separated
from their mother-liquor by suitable means of filtration or otherwise, their mother-
liquor will contain per equivalent of chlorate of lime in it only about 1-2 (or one and
two-tenths) equivalents of chloride of calcium. On adding to this liquor 2.2 (two
and two-tenths) equivalents of sulphate of soda, there will be formed one equivalent
of chlorate of soda, 12 (one and two-tenths) equivalents of chloride of sodium,
and 2.2 (two and two-tenths) equivalents of sulphate of lime.

page_text: My correspondent has also found that a large part of the chloride of.calcium
contained in the product of the treatment of milk of lime by chlorine gas, may be
separated therefrom as oxychloride of calcium by adding to the said product free
lime, heating to a suitable temperature, and then allowing to cool to ordinary
temperatures. He has found, for example, that a liquor containing 56 (five and
six-tenths) equivalents of chloride of calcium, per one equivalent of chlorate of lime,
and of a density of about 25 degrees Beaumé, corresponding to a specific gravity of
about 1-205, can have removed from it about 3-6 (three and six-tenths) equivalents
of chloride of calcium by adding to it free lime, and then heating and subsequently
cooling as aforesaid. The quantity of lime to be added, if a maximum separation
of chloride of calcium is to be effected by this method, should be the quantity equal
to about three equivalents for each equivalent of chloride of calcium in the liquor.
It is convenient to add the lime in the state of hydrate; if it be added in the
anhydrous state, water equal to the quantity required for its hydration must be
added also. The liquor to which lime has thus been added must be heated to at
least 170 degrees Fahrenheit, but it is better to heat it to ebullition. On cooling to
ordinary temperatures oxychloride of calcium will then crystallize out.
resulting mixture of oxychloride of calcium, with any excess of lime which may
have been employed, and with nother liquor must then be submitted to efficient
filtration, by means either of the centrifugal hydro-extractor or of any other suitable
appliance for separating liquids from solids. The filtrate will be a liquor
containing, for each equivalent of chlorate of lime in it, about two equivalents only
of chloride of calcium. Addition to this filtrate of three equivalents of sulphate of
soda will give a solution containing one equivalent of chlorate of soda and three
equivalents of chloride of sodium, this solution holding in suspension three
equivalents of sulphate of lime.
The
My correspondent has further found that by employing successively first one and
then the other of the above described methods of separating chloride of calcium
from the product of the action of chlorine gas on milk of lime, he can obtain a
solution containing, per equivalent of chlorate of lime in it, only about three-tenths
of an equivalent of chloride of calcium. When he thus combines the said two
methods, he first evaporates the crude liquor until its density, while boiling, is
about 1485, as aforesaid; he then cools to or a little below fifty degrees Fahrenheit.
He then filters to separate the chloride of calcium which has crystallized out, and
then to the mother-liquor he adds either its own volume of water and three
equivalents of hydrate of lime, per equivalent of chloride of calcium in it, or a little
more than its own volume of water, and per equivalent of chloride of calcium in it
three equivalents of anhydrous lime. He then heats the mixture to not less than
176 degrees Fahrenheit, but preferably to ebullition, and thereby determines the
formation of oxychloride of calcium. He then allows the product to cool to
ordinary temperatures, and when it has done this he submits it to efficient filtration
by means of either a centrifugal hydro-extractor or any other suitable appliance.
The filtrate is a solution of chlorate of lime containing only about three-tenths of
an equivalent of chloride of calcium for each equivalent of chlorate of lime in it.
By addition to this filtrate of 13 (one and three-tenths) equivalents of sulphate of
soda he obtains a solution of one equivalent of chlorate of soda, together with 1.3
(one and three-tenths) equivalents of chlorate of sodium, this solution holding in
suspension 13 (one and three-tenths) equivalents of sulphate of lime.
After having added sulphate of soda to a liquor obtained by separating chlorido
of calcium, as above described, from the product of the treatment of milk of lime by
chlorine gas, my correspondent separates the resulting sulphate of lime from the
mixed solution of chlorate of soda and chloride of sodium, which is formed at the
same time by means of a centrifugal hydro-extractor or any other efficient means
of separating solids from liquids. He then adds to the filtrate enough carbonate
of soda to precipitate any calcium salts still remaining in solution therein. Having
separated the resulting precipitate by filtration, or otherwise, he then evaporates
the mother-liquor and fishes out the chloride of sodium which falls during such

page_text: evaporation. When the liquor has been evaporated to such a point that its
density is about forty-four degrees Beaumé, corresponding to a specific gravity of
about 1.428, it is ready to be cooled and crystallized, as will be well understood.
As the chloride of sodium which falls during the evaporation of the mixed
solution of chlorate of soda and chloride of sodium and is fished out during such
evaporation has always some chlorate of soda associated with it, it is necessary to
wash such chloride of sodium. It is also necessary to wash the sulphate of lime
formed at a previous stage of the process, and it is likewise necessary to wash the
precipitate formed by addition of carbonate of soda to the liquors from which the
said sulphate of line has been separated. A simple method of utilizing the chlorate
of soda in the wash-waters so obtained is to employ those wash-waters for making
milk of lime to be treated by chlorine gas for the production of more crude
chlorate liquor. But the chlorate of soda in the said liquors may also be utilized
by adding to the said liquors chloride of potassium, and so converting their
chlorate of soda into the much less soluble salt, chlorate of potash. The same
series of operations will thus yield both chlorate of soda and chlorate of potash.
My correspondent does not confine himself to the exact proportions, temperatures,
and densities above set forth, since these may be varied without departing from or
interfering with the substance of his Invention, though he believes those above
given to be best; but what he regards as his Invention is the manufacture of
chlorate of sola by the reaction of sulphate of soda upon the solution remaining
after separation of chloride of calcium from the crude product of the treatment of
milk of lime by chlorine gas, such separation of chloride of calcium from the said
crude product having been made, substantially as is above set forth; the sub-
sequent decomposition by carbonate of soda of any calcium salts not precipitated
by the said sulphate of soda, and the utilization of the chlorate of soda in the
above specified wash-waters by its reaction upon chloride of potassium.
In witness whereof, I, the said Walter Weldon, have hereunto set my hand
and seal, this
day of July, in the year of our Lord One
thousand eight hundred and eighty-one.
WALTER WELDON. (L.S.)