Improvements in the Manufacture. of Chlorine and Hydrochloric Acid from Chloride of Magnesium.
Year: 1884

page_text: Improvements in the Manufacture. of Chlorine and Hydrochloric
Acid from Chloride of Magnesium.
PROVISIONAL SPECIFICATION.
I, WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey, Fellow
of the Royal Society, President of the Society of Chemical Industry, do
hereby declare the nature of the said Invention for "IMPROVEMENTS IN THE
MANUFACTURE OF CHLORINE AND HYDROCHLORIC ACID FROM CHLORIDE OF
MAGNESIUM," to be as follows:—
This invention relates to the manufacture of chlorine and hydrochloric acid from
chloride of magnesium.
Chloride of magnesium crystallises with six equivalents of water, and when
crystals of it containing that quantity of water are heated, much of the chlorine of
the chloride of magnesium is evolved as vapour of hydrochloric acid. If the heating
be performed in presence of air, some free chlorine is evolved in addition to the
said vapour of hydrochloric acid. But the evolution of free chlorine requires that
the chloride of magnesium be heated in presence of air to a high temperature, and
the proportion of free chlorine in the mixture of free chlorine and vapour of
hydrochloric acid which is evolved during the operation of so heating hydrated
chloride of magnesium in presence of air is greater the less the proportion of water
present with the chloride of magnesium at the commencement of the operation.
The present invention therefore consists in heating hydrated chloride of mag-
nesium, whether such hydrated chloride of magnesium be crystallized or not, to a
low temperature, before heating it in presence of air to the higher temperature
necessary to the reaction of oxygen upon it. My correspondents who have
communicated to me this invention have found that by heating hydrated chloride
of magnesium to a temperature of from 150 degrees to 200 degrees Centigrade,
the quantity of water remaining with the chloride of magnesium can be reduced
to about two equivalents. This invention is not confined to the use of such
temperatures, but the temperatures stated are indicated as having given good
results. After having diminished by such heating to a low temperature the
quantity of water present with the magnesium chloride, on then heating the residue
[Price Ad 1

page_text: in contact with air vapour of hydrochloric acid and free chlorine are evolved, but
the latter in much greater proportion than if the hydrated chloride of magnesium
had not been previously heated to a low temperature as aforesaid. During the
preliminary heating at a low temperature a very small proportion of the chlorine
of the chloride of magnesium is driven off as vapour of hydrochloric acid. In the
experiments of my correspondents in which that preliminary heating was performed
at a temperature not exceeding 200 degrees Centigrade, the proportion of the
chlorine of the chloride of magnesium so driven off as vapour of hydrochloric acid
has not exceeded one and a half per cent.
The said preliminary heating of the hydrated chloride of magnesium, for the
purpose of driving off a portion of its water, before treating it for the obtainment
of free chlorine from it, may be performed either in close vessels or apparatus, or
in vessels or apparatus into which air shall be admitted during the operation, and
the said vessels or apparatus may be either those in which the residual product of
the said preliminary heating is afterwards heated to a higher temperature in contact
with air, or the said preliminary heating to a low temperature may be performed
in apparatus specially affected thereto.
What is new in this invention thus consists in obtaining free chlorine and vapour
of hydrochloric acid from chloride of magnesium associated with water by first
heating such chloride of magnesium to a low temperature in order to drive off some
of its water and then heating the residue of that operation to a higher temperature
in contact with air.

page_text: I, WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey Fellow
of the Royal Society, do hereby declare the nature of the said Invention for
IMPROVEMENTS IN THE MANUFACTURE OF CHLORINE AND HYDROCHLORIC ACID
FROM CHLORIDE OF MAGNESIUM, and in what manner the same is to be performed,
to be particularly described and ascertained in and by the following statement :-
The present invention consists in performing upon solid hydrated magnesium
chloride, whether such solid hydrated magnesium chloride be in the state of crystals
or otherwise, two successive operations, the object of the first of which is to partially
dehydrate the said chloride of magnesium; its partial dehydration being accompanied
by the evolution of some of its chlorine as vapour of hydrochloric acid, and the
object of the second of which two operations is to drive off the chlorine, or some
of the chlorine, of the solid residue of the first operation, partly as vapour of
hydrochloric acid and partly in the free state.
My correspondents who have communicated to me this invention have found that
by heating hydrated chloride of magnesium to a temperature of from 150 degrees
to 200 degrees Centigrade, the quantity of water remaining with the magnesium
chloride can be reduced to about two equivalents. Their said invention is not
confined to the use, in the first of the two operations together constituting the said
invention, of the said temperatures and degree of dehydration; but those
temperatures, and that degree of dehydration, are indicated as having given good
results. Solid hydrated magnesium chloride may be heated to the said temperatures,
and be so. dehydrated to the degree above mentioned, without undergoing fusion,
and without evolution of more than a very small proportion of its chlorine. The
chlorine evolved during such partial dehydration is evolved chiefly or exclusively as
vapour of hydrochloric acid.
After having diminished by the aforesaid heating to a low temperature the
quantity of water present with the magnesium chloride, on then heating the solid
residue to a higher temperature, in contact with air, vapour of hydrochloric acid
and free chlorine are evolved, but the latter in much greater proportion to the
former than if the hydrated magnesium chloride commenced with had not previously
been heated to a low temperature as aforesaid.
The said preliminary heating of the hydrated magnesium chloride, for the
purpose of driving off a portion of its water, before treating it for the obtainment
of free chlorine from it, may be performed either in close vessels or apparatus, or in
vessels or apparatus heated externally into which air or gases shall be admitted
during the operation; or by passing over the hydrated chloride air or gases heated
to the requisite temperature, and the said vessels or apparatus may be either those
in which the residual product of the said preliminary heating to a low temperature
is afterwards heated to a higher temperature in contact with air, or the said
preliminary beating to a low temperature may be performed in one apparatus, and
the subsequent heating to a higher temperature in another apparatus. There are

page_text: many kinds of apparatus in which the two operations may be performed, as will be
well understood by practical men, and no particular kind of apparatus for either of
them constitutes any part of the present invention; but my correspondents prefer
to perform the first of the two operations which together constitute their present
invention by passing over solid hydrated chloride of magnesium air or gases which
have been previously heated to the requisite temperature, and the second of the
said two operations either in muffle furnaces or in apparatus such as is the subject
of the patent numbered 9304, of the 23rd. June, 1884.
Having now particularly described and ascertained the nature of the said
Invention, and in what manner the same is to be performed, I declare that what
I claim is
Treating solid hydrated magnesium chloride, crystallized or not, by first heating
it to a temperature which will drive off a part of its water without driving off
more than a small part of its chlorine, and then treating the solid residue of
this first operation by heating it in a current of air or oxygen to such temperature
that some of its chlorine shall be thereby driven off in the free state.
D
1 11
.
OL
....
1.