IMPROVEMENTS IN THE MANUFACTURE OF CHLORATE OF POTASп
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 POTASп." 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.
"IMPROVE-
A communication from
WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey.
MENTS IN THE MANUFACTURE OF CHILORATE OF POTASH.'
abroad by Alfred Rangod Pechiney, of Salindres, in the Republic of France.
Chlorate of potash is at present manufactured by the reaction of chloride of
potassium upon the chlorate of lime in a solution containing for each equivalent
of chlorate of lime in it five or more equivalents of chloride of calciun, being the
solution obtained by treating milk of line by an excess of chlorine gas. The said
reaction gives rise to a solution containing six or inore equivalents of chloride of
calcium for each equivalent of chlorate of potash in it. This solution is evaporated
to a certain point, and then on cooling a portion of its chlorate of potash crystallizes
out. A portion however remains in the mother-liquor, and cannot practically be
turned to any useful account. If the mother-liquor were further concentrated by
evaporation and then again cooled, some of its chlorate of potash would crystallize
out, but what did so would be so contaminated by chloride of calcium which would
crystallize out with it as to be useless. The mother-liquor, though containing a
considerable proportion of chlorate of potash, has therefore to be thrown away.
The presence of so much chloride of calcium with the chlorate of lime used in the
manufacture of chlorate of potash thus occasions a considerable loss of a very
valuable commodity.
The object of the present Invention is to diminish this loss in the manufacture
of chlorate of potash. My correspondent, who has communicated to me the present
Invention, has discovered certain methods of separating very important proportions

page_text: of chloride of calcium from the mixed solution of chlorate of lime and chloride of
calcium, which is produced by treating milk of lime by chlorine gas, and the
present Invention consists in first treating such solution for the separation of
chloride of calcinm from it before employing its chlorate of lime for the manu-
facture of chlorate of potash, and in-then obtaining chlorate of potash by adding
chloride of potassium or other suitable potassium salt to a solution of chlorate of
lime, containing much less than the five to six equivalents of chloride of calcium
contained in the solution of chlorate of lime which manufacturers of chlorate of
potash have always employed hitherto.
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 he prefers to combine both methods, though either
of them may be used without the other. When both methods are combined the
first step is to evaporate the product of the treatment of milk of lime by chlorine
gas until its density while boiling is about forty-eight degrees Beaumé, corre-
sponding to a specific gravity of about 1485, and then to cool to about 10 degrees
centigrade, corresponding to about 50 degrees Fahrenheit. There will thus be
determined an abundant formation of hydrated crystals of chloride of calcium,
susceptible of heing easily separated from their mother-liquor. After having been
submitted to the action of a hydro-extractor or other efficient means of filtration
these crystals will retain barely more than merely traces of chlorate. If the liquor
did not contain originally more than about five and a half equivalents of chloride
of calcium, the liquor remaining after separation of theso crystals will contain only
about one and two-tenths equivalents of chloride of calcium.
The next step is to add to this liquor its own volume of water and a quantity of
line, preferably hydrated, equal to about three equivalents for each equivalent of
chloride of calcium present. The liquor must now be heated to about 80 degrees
centigrade, corresponding to about 176 degrees Fahrenheit, whereby will be
determined the conversion of the larger part of its chloride of calcium into
oxychloride, which on cooling will separate out mixed with any excess of lime
which may have been used. The mother-liquor will now contain only about
three-tenths of an equivalent of chloride of calcium. If to this liquor chloride of
potassium be now added, a solution will be obtained containing one equivalent of
chlorate of potash, and only one equivalent and three-tenths of chloride of calcium,
from which solution a very much larger proportion of the chlorate of potash
contained in it can be separated by the usual methods than can possibly be
separated from the ordinary solutions of one equivalent of chlorate of potash with
six or seven equivalents of chloride of calcium.
To economise however a very large part of the chlorate of potash lost by the
method of manufacture at present in use, it is not essential to employ both of the
above described methods of separating chloride of calcium from the solution
containing the chlorate of lime by reaction of chloride of potassium upon which
the chlorate of potash is to be produced, but either of the said methods may be
employed separately and alone. When only one of the said methods is employed,
it will usually be best to choose that which is first above described. The manner
of proceeding will then consist in evaporating the product of the treatment of milk
of lime by chlorine gas until its density at its boiling point is about 1-485, cooling
until crystals of hydrated chloride of calcium have formed, submitting these to
filtration, and then adding chloride of potassium to the mother-liquor, whereby
there will be obtained a solution containing, per equivalent of chlorate of potash in
When the
it, only about one-third of the usual proportion of chloride of calcium.
other method of separating chloride of calcium is used by itself, it will usually not
be necessary either to concentrate or to dilute the crude clilorate of lime and
chloride of calcium liquor. Lime may be added directly to that liquor as it comes
from the apparatus in which it is produced if the density of that liquor, as is
usually the case, be about 25 degrees Beauté, corresponding to a specific gravity of
about 1205. The liquor to which lime has thus been added must now be heated

page_text: to about 176 degrees Fahrenheit, and then allowed to cool, after which what has
separated in the solid state must be submitted to efficient filtration. by adding
chloride of potassium to the liquor from which chloride of calcium has thus been
separated as oxychloride, a solution will be obtained containing, per equivalent of
chlorate of potash in it, about half as much chloride of calcium as is contained in
the crude chlorate of potash liquors produced by the method at present in use.
To utilize oxychloride of calcium produced as above described, my correspondent
treats it by hot water, whereby it is decomposed into lime and chloride of calcium.
Having separated the lime by subsidence and decantation or otherwise, and having
suitably washed it, he uses the lime for the production of more chlorate liquor, or
applies it to any other more convenient use." The solution from which it has been
separated, and also the waters with which it has been washed, may contain an
appreciable quantity of chlorate of lime, in which case the said solution and wash-
waters should afterwards be treated for the separation of chloride of calcium from
them by the first of the two methods above described.
My correspondent's Invention thus consists in obtaining chlorate of potash by
adding chloride of potassium to solutions produced by treating milk of lime by
chlorine gas, but from which a large part of their chloride of calcium has been first
separated, either as crystals of that compound caused to separate by evaporation
and cooling, or as oxychloride of calcium, caused to form and then to separate by
adding lime, and then heating and cooling, or by a combination of both these
methods used one after the other, substantially as above described, and in utilizing,
as above set forth, such oxychloride of calcium as may be produced as aforesaid.

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 29th July
1881.
"IMPROVE
WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey.
MENTS IN THE MANUFACTURE OF CHILORATE OF POTASH." A communication from
abroad from Alfred Rangod Pechiney, of Salindres, in the Republic of France.
Chlorate of potash is at present manufactured by the reaction of chloride of
potassium upon the chlorate of lime in a solution containing for each equivalent of
chlorate of line in it five or more equivalents of chloride of calcium, being the
solution obtained by treating milk of lime by an excess of chlorine gas. The said
reaction gives rise to a solution containing six or more equivalents of chloride of
calcium for each equivalent of chlorate of potash in it. This solution is evaporated
to a certain point, and then on cooling a portion of its chlorate of potash crystallizes
out. A portion however remains in the mother-liquor, and cannot practically be
turned to any useful account. If the mother-liquor were further concentrated by
evaporation, and then again cooled, some of its chlorate of potash would crystallize
out, but what did so would be so contaminated by chloride of calcium, which would
crystallize out with it, as to be useless. The mother-liquor though containing a
considerable proportion of chlorate of potash has therefore to be thrown away.
The presence of so much chloride of calcium with the chlorate of lime used in the
manufacture of chlorate of potash thus occasions a considerable loss of a very
valuable commodity.
The object of the present Invention is to diminish this loss in the manufacture
of chlorate of potash. My correspondent, who has communicated to me the present
Invention, has discovered certain methods of separating very important proportions
of chloride of calcium from the mixed solution of chlorate of lime and chloride of
calcium, which is produced by treating milk of line by chlorine gas; and the present
Invention consists in first treating such solution for the separation of chloride of
calcium from it before employing its chlorate of lime for the manufacture of chlorate
of potash, and in then obtaining chlorate of potash by adding chloride of potassium
or other suitable potassium salt to a solution of chlorate of lime containing much
less than the five to six equivalents of chloride of calcium contained in the solutions
of chlorate of lime, which manufacturers of chlorate of potash have always employed
hitherto.
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 the 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 one equivalent of chlorate of lime be evapo-
rated 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 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
When the liquor
Fahrenheit chlorate of lime would begin to crystallize out also.

page_text: 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 12 (or one and two tenths),
equivalents of chloride of calcium. On adding an equivalent of chloride of
potassium to such a liquor, one obtains a solution of one equivalent of chlorate of
potash, and only about two and two-tenths equivalents of chloride of calcium, from
which solution a very much larger proportion of the chlorate of potash in it can be
crystallized out by the ordinary methods, as will be well understood, than can be
crystallized out from the ordinary solutions containing three times as much chloride
of calcium per equivalent of chlorate of potash in them.
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 36 (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 176 degrees Fahrenheit, but it is better to heat it to ebullition. On cooling
to ordinary temperatures, oxychloride of calcium will then crystallize out. The
resulting mixture of oxychloride of calcium with any excess of lime which may
have been employed, and with mother-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 an equivalent of chloride of
potassium will give a solution containing about three equivalents of chlorate of
potash for each equivalent of chloride of calcium in it.
When either of the above described methods of separating chloride of calcium
from crude chlorate liquor before adding chloride of potassium thereto is employed
by itself, the method adopted should preferably be that which is first above
described. My correspondent finds it more advantageous however to combine both
methods. He finds that by employing both the said methods succesively, he can
remove so much chloride of calcium as to obtain a solution containing per
equivalent of chlorate of lime in it only about three-tenths of an equivalent of
chloride of calcium. To this end 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 calciuin which
las 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 forination 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 centrifngal hydro-extractor, or any
other suitable appliance. The filtrate is a solution of chloride of lime containing
only about three-tenths of an equivalent of chloride of calcium for each equivalent

page_text: of chloride of lime in it. By addition of chloride of potassium to this filtrate be
obtains a solution of chlorate of potash containing, per equivalent of chlorate of
potash in it, only about 13 (one and three-tenths) equivalents of chloride of
calcium.
It will of course be understood that other potassium salts than the chloride of
potassium may be used under this Invention for the decomposition of the chlorate
of lime contained in the solutions obtained by treating milk of lime by chlorine
gas, and separating chloride of calcium from the resulting product by either of the
methods above set forth. In most cases however the use of chloride of potassium
for this purpose will be more advantageous than that of any other potassium
salt.
When the above described method of separating chloride of calcium as oxy-
chloride is employed, either separately or combined with the method of separating
chloride of calcium as such, the oxychloride will retain after filtration an appreciable
quantity of chlorate of lime. It will be necessary to utilize this chlorate, and also
to utilize the lime of the oxychloride. My correspondent treats the oxychloride by
hot water, and so decomposes it into lime and a solution of chloride of calcium,
which solution will contain also chlorate of lime. This solution and the line mixed
with it may be used as milk of lime for the preparation of more crude chlorate
liquor by treatment with chlorine gas. Or the line may be separated from the
solution by filtration by means of a hydro-extractor or otherwise, and the filtrate
may be boiled down till its density is such that chloride of calcium will crystallize
out from it on cooling, as above set forth. The lime thus separated by filtration
may be used for the preparation of more chlorate liquor, or after suitable washing
if need be may be applied to any other purpose which may be preferred.
My correspondent's Invention thus consists in obtaining chlorate of potash by
adding chloride of potassium or other suitable potash salt to solutions obtained by
treating milk of lime by chlorine gas, but from which a large part of their chloride
of calcium has been first separated either as crystals of that compound, caused to
separate by evaporation and cooling, or as oxychloride of calcium, caused to forin
and then to separate by adding lime, and then first heating and afterwards cooling,
or by a combination of both these methods, used one after the other, substantially
as is above set forth.
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.)