IMPROVEMENTS THE MANUFACTURE OF CHLORINE, AND IN APPARATUS AND ARRANGEMENTS FOR THAT PURPOSE
Year: 1872

page_text: LETTERS PATENT to Walter Weldon, of 29, The Cedars, Putney, in
IN
the County of Surrey, for the Invention of “IMPROVEMENTS
THE MANUFACTURE OF CHLORINE, AND IN APPARATUS AND ARRANGEMENTS FOR
THAT PURPOSE."

page_text: 2. In describing the improvements which constitute my present
Invention, I will begin with the operation in which chlorine is generated
by the reaction of aqueous hydrochloric acid upon the mixture or com-
pound which will herein-after for convenience be called manganite of
magnesium. That mixture or compound consists essentially of peroxide
of manganese and magnesia, but may contain also more or less protoxide
of manganese and small quantities of sesquioxide of iron and other
bodies. All those of its constituents which neutralize hydrochloric acid
without liberating chlorine therefrom will be spoken of herein-after under
the general designation of "bases."
3. The first object of my present improvements is to obtain in the
operation aforesaid a residual liquor which shall be practically neutral.
The method by which hydrochloric acid and native oxides of manganese
are treated together, and by which hydrochloric acid and artificial oxides
of manganese peroxidized in the dry way have always hitherto been
treated together, necessarily yields a residual liquor containing more or
less free acid, and the presence of free acid in a liquor to be treated as
will be herein-after described, renders the pumping of the liquor trouble-
some and expensive, and renders impracticable the application to
it of those methods of evaporation which are most economical of fuel.
Moreover, the free acid in such a liquor must almost inevitably be
lost.
4. My present improvements begin then with so treating together
aqueous hydrochloric acid and manganite of magnesium as to obtain,
besides chlorine going off as gas, a practically neutral residual liquor.
To this end I prefer to put the acid into the still first, and to add the
manganite of magnesium thereto gradually. I thus secure that as long
as the acid continues to be capable of dissolving peroxide of manganese,
the whole of each portion of manganite of magnesium which is added
during that period, -that is to say, both the peroxide of manganese
which is contained in the said manganite of magnesium and the bases
which are contained therein,-shall dissolve completely. When the
stage has been reached at which the quantity of acid remaining un-
neutralized and undecomposed is so small, in proportion to the chlorides
in the solution of which it is diffused, that it can no longer dissolve
peroxide of manganese, I prefer to make a further addition of manganite
of magnesium, and this preferably in such quantity that the remaining
acid shall be completely neutralized by the bases in the further quantity

page_text: of manganite of magnesium so added, the peroxide of manganese in such
further quantity of manganite of course remaining undissolved. I thus
obtain a completely neutral residual solution, containing suspended in it
some undissolved peroxide of manganese. I prefer to allow this undis-
solved peroxide to deposit in the still, and then to draw off the supernatant
solution only. To the undissolved peroxide remaining in the still I then
add the next charge of acid, and thereafter proceed again as before, and
so on continually.
5. In order to permit the hydrochloric acid and the manganite of
magnesium to be treated together as above described. I either make the
manganite of magnesium into a fluid mud by grinding it either with
water or preferably with residual liquor from a previous operation, and
admit this fluid mud into the still by means of a hydraulic joint, as is
practised with the mud obtained in my process for regenerating by the
wet way oxides of manganese employed in the manufacture of chlorine,
or I charge the manganite of magnesium in the state of powder into a
hopper so placed and constructed and arranged that when it has been
charged with manganite of magnesium it can be so closed that air
cannot pass into it and that chlorine cannot pass out of it, while either
by opening a cock or otherwise unstopping a passage communicating
between the hopper and the still, the maganite of magnesium can be
admitted into the still in any quantity or at any rate which may be
desired.
}
6. When it is not convenient to proceed by either of the above
described methods, and when the residual liquor produced in the still
therefore contains some free acid, the acid residual liquor may be run
from the still into another vessel, and in that other vessel be treated with
manganite of magnesium, so that it shall become neutralized by the
bases therein. It is much better however to completely neutralize the
residual liquor in the still itself. When that is done the liquor can be
pumped from the well or other receptacle into which it is run out of the
still directly into one or other of the evaporating vessels, which will be
further spoken of below, and that receptacle can morcover be of iron,
which is greatly to be preferred, as minimizing liability to leakage; but
when the liquor has to be neutralized in such receptacle, it cannot well
be of iron, and the liquor has to be pumped from it into an intermediate
vessel placed above the evaporating vessels, in order that before
passing on into those vessels it may deposit in the said 'inter-
"

page_text: in it.
7. Having obtained either a neutral residual liquor, as directed in
paragraphs 4 and 5, or a neutralized residual liquor, as directed in para-
graph 6, the next step is to evaporate off from the said residual liquor
its surplus water. An acid residual liquor could be evaporated only in
brick furnaces by very wasteful methods of applying heat, and what
first came off from it would be an acid so dilute as to be of little or no
value; but by procuring either a neutral or a neutralized residual liquor
I am enabled to evaporate the said liquor by the cheapest of all methods,
and moreover in such wise that what first comes off from it shall be
water only.
I thus not only reduce to the absolute minimum the
cost of evaporating the liquor, but I also both avoid all need to lose
that portion of the chlorine in the liquor which is an acid residual
liquor exists as free bydrochloric acid, and which in treating an acid
liquor would usually have to be thrown away, and at the same
time secure that all the chlorine recovered from the residual liquor in
the state of acid shall be recovered under.conditions under which it may
be obtained at a maximum degree of concentration.
8. I evaporate the neutral or neutralized residual liquor in iron vessels
or pans, to whose under surfaces heat is directly applied; and I prefer
that the heat used should be the surplus or "waste" heat either of the
furnace or furnaces in which the chlorides in the said liquor will after-
wards be decomposed, or of any other furnace or furnaces whose surplus or
waste heat can conveniently be so utilized. The pans should nevertheless
be provided with fire-places of their own, to be used only when enough
surplus or waste heat is not available. I prefer to employ in each case
a series of several such vessels or pans, and so to connect them together
by pipes furnished with cocks or valves or moveable plugs, that when
a charge of concentrated liquor has been withdrawn from the final vessel
of the series that vessel may be re-filled to the proper point from the last
vessel but one, and then this vessel from the last vessel but two, and so
It may perhaps be an advantage to place the several vessels,
counting from the final vessel of the series, each successively at an
increased elevation, so as to admit of the last vessel being completely
replenished from the last vessel but one without anything being mean-
while admitted into that vessel from the next preceding vessel, and so
on throughout the series. When these evaporating vessels are of cast
on.

page_text: iron, as will usually be the case, they should of course never be emptied
in ordinary working below some point above which the heat applied to
them externally does not play; they may be either open or closed vessels
at pleasure.
9. In these vessels I evaporate the liquor down or nearly down to the
point at which the chloride of magnesium contained in it begins to
decompose, and at which hydrochloric acid accordingly begins to come
off. This usually happens when the liquor has attained a temperature
above 300 but below 350 degrees Fahrenheit. For its further treatment
I transfer the now concentrated mixed solution of ehloride of manganese
and chloride of magnesium to other apparatus. Its said further treat-
ment consists in continuing its evaporation to the point of dryness, and
then heating the residue with a certain access of air. The chlorine of
the two chlorides is thereby driven off partly as hydrochloric acid and
partly in the free state, and there is at the same time reproduced the
aforesaid mixture or compound which has herein-before been and will
herein-after be called manganite of magnesium..
10. During the evaporation of the concentrated liquor from the point
at which acid begins to come off to that of dryness a variable proportion
of the chlorine of the chlorides originally contained in it is driven off
éntirely in the state of hydrochloric acid. This part of the evaporation
must therefore be performed in an apparatus which shall permit of this
acid being caught and conveyed to a suitable condenser. The said
apparatus may be an iron pot covered in and otherwise arranged similarly
to an ordinary salt cake pot, or it may be almost any kind of muffle
furnace constructed in brick. A "close roaster," such as many manu-
facturers employ in the second stage of the manufacture of salt cake, is
very suitable. It is possible to use a reverberatory furnace for this
operation, but I very much prefer a muffle furnace.
11. The operation of evaporating to dryness the concentrated liquor
and that of heating with access of air the dried material so produced
may both take place in the same furnace, which in that case should
preferably have several beds, or they may be performed either in separate
furnaces or in distinct parts of a composite furnace. An apparatus of
the latter kind may consist of a long muffle furnace divided internally
into two parts, one of which we will call A and the other B. Such a
furnace may be called a double" furnace. In the wall separating the
two parts of it there should be an aperture furnished with a valve, or
66

page_text: door, or damper, or other appliance by means of which communication
between the two parts of the furnace may be opened or cut off at
pleasure. The furnace should preferably be fixed at both ends, the
products of combustion of both fires being led on, leaving the furnace
under the vessels in which the residual liquor is evaporated down to the
point at which acid begins to come off from it. These vessels should of
course be placed in all cases at such an elevation that concentrated
liquor can run from them into the furnace or other apparatus in which
its evaporation is to be completed.
1,
12. In one method of working such a double furnace the operator
will begin by running into part A of the furnace (the working door of
that part of the furnace and the aperture of communication between it
and the other part of the furnace having both been closed) a convenient
quantity of concentrated liquor. When this has been brought to
dryness he will run in a second quantity of liquor, and what that has
been brought to dryness he will run in a third quantity; and he will
proceed in this way time after time until he has accumulated in part A
of the furnace as much dried material as can be conveniently treated
therein at one time. He will then open the working door, break up the
dried mass into pieces of moderate size, and thereafter heat with access
of air until the reactions which are so caused to take place have been
carried sufficiently far. While he is thus treating in part A of the
furnace his first charge of dried material, in part B he will prepare a
second charge of dried material by drying down therein successive quan-
tities of concentrated liquor, and by the time he has thus accumulated a
sufficient quantity of dried material in part B of the furnace the charge
in part A will have become ready to draw. Having drawn that charge
he will now heat with access of air the charge of dried material accumu-
lated in part B, and meanwhile will dry down more concentrated liquor
in part A. Proceeding in this manner he will use each part of his
double furnace for both operations, now drying down concentrated liquor
in part B while heating with access of air a charge of dried material in
part A, then drying down liquor in part A while treating a charge of
dried material in part B, and alternating in this way continually.
13. In another and preferable method of working a double furnace
the evaporation to dryness of the concentrated liquor always takes place
in part A, and the treatment of the dried material always in part B. In
working by this method when a quantity of concentrated liquor has

page_text: been dried down in part A of the furnace, and the bed of that part of
the furnace has accordingly become covered with a thin layer of dried
material, this dried material is broken up and is pushed through the
aperture in the wall separating part A from part B into the other part
of the furnace where it is piled up as a heap of thin cakes, in which
state it of course occupies in part B a much smaller arca than that
which as a single thin layer it had occupied in part A. The aperture of
communication between the two parts of the furnace is then closed,
and a second quantity of liquor run into part A, producing therein a
second thin layer of dried material. The heap of thin cakes in part B
is now moved a certain distance forwards so as to make room for
a second heap, and then the second thin layer of dried material in
part A is broken up and pushed through into part B just as the first
had been: When a third layer of dried material has been produced in
part A the two heaps now in part B are both moved forwards sufficiently
to admit of this third layer being piled up therein as a third heap of
thin cakes, and as further quantities of liquor are successively dried
down in part A the whole of the contents of part B are each time
moved a stage further down to make room therein for a fresh heap
of thin cakes, until at length a certain quantity of finished product
is regularly withdrawn at certain intervals from one end of part B,
and a corresponding quantity of dried material added at the other end.
14. Instead of a furnace divided into two parts A and B, a furnace
divided into three parts, A, B, and C, may be employed. In that case
as liquor is dried down in the part A it may be pushed over into the
part B, and may there accumulate until there is sufficient for a full
charge for the part C, in which the heating with access of air is to take
place. A complete charge for the part C may thus be put thereinto,
and when finished be withdrawn therefrom all at once.
Or a large
drying down furnace may be associated with several furnaces for the
subsequent treatment of the dried material, these latter being preferably
so much smaller than the drying down furnace that a single operation
in the drying down furnace shall produce enough dried material for
a complete charge for any one of them. In such case when a charge
of dried material has been produced in the drying down furnace it
will be pushed through into whichever of the other furnaces may be
ready to receive it.
15
The treatment of the dried material by heating it with nonese of

page_text: air may be performed instead of in a horizontal furnace in a vertical
furnace or kiln heated externally. The fire should be under the bottom
of the kiln so as to make the lower part of it the hottest, and the flame
and products of combustion should then be led round its sides by a
spiral flue. The kiln must of course be closed at the top, but at its
upper part it should communicate with a muffle furnace for drying
down concentrated liquor in a manner similar to that in which part B
of a double horizontal furnace communicates with part A thereof, and
to permit of this without requiring that the said drying down furnace
should be unduly elevated, the lower part of the kiln should be sunk in
the ground to whatever distance may be requisite or convenient. The
kiln may either be of uniform dimensions from top to bottom, or it may
have more or less the shape of an inverted truncated cone, or it may
otherwise be wider at one part than at another. I prefer that its
horizontal section should be either a very flat, oval, or a narrow parallelo-
gram. At the lower part of the kiln should be a door by which the
manganite of magnesium produced in it may from time to time be
withdrawn. The method of working such a kiln will consist simply in
from time to time putting in dried material at the top and taking out
finished product at the bottom.
16. As the reactions which take place during the treatment of the
dried material by heating it with access of air produce not only
manganite of magnesium, but also hydrochloric acid and free chlorine,
both in the state of gas, there passes off from the furnace in which that
treatment is performed a mixture of those bodies diluted by the
nitrogen of that portion of the air entering the furnace, the oxygen of
which takes part in the said reactions, and by whatever air, if any, may
be admitted into the furnace in excess of the quantity strictly necessary
to supply oxygen to its charge. For some applications of the chlorine
contained in it, this mixture of gases may be employed without first
separating from it its hydrochloric acid, but ordinarily it will require to
be conveyed to an apparatus in which the hydrochloric acid contained
in it shall be condensed out, the remained of the mixture then passing
on to apparatus in which its chlorine may be applied to whatever
purpose it is intended for.
17. When thus condensing the hydrochloric acid out of the mixture of
gases which comes off from the furnace in which the dried material is
heated with access of air, the gas flue which conveys the said mixture

page_text: from the furnace to the condenser may either be the same as that which
conveys to the condenser the hydrochloric acid which comes off from the
furnace in which the concentrated liquor is evaporated to dryness, or it
may be a separate flue. When the same gas flue is made to serve both
furnaces, the two furnaces may either have each a separate communi-
cation with the one gas flue, or the gas or gases from one furnace may
pass into and through the other furnace, the gases from both furnaces
then entering the gas flue by a single channel. The arrangements
should be such that the furnace in which the gases mingle can be either
the one or the other at will. When the furnace in which the dried
material is heated with access of air is a vertical furnace or kiln, the
gases may pass from it to the gas flue either from the upper part of the
kiln or from its lower part, but I prefer that they should pass into the
gas flue from the lower part of the kiln. In such case the air required
in the kiln must of course be admitted at its upper part.
18. It is of very great importance that into the furnace in which it is
to be decomposed by heating with air the dried material should be
charged in pieces of moderate size. I believe that by far the best plan
is for it to be put into the said furnace in the state of thin cakes,
preferably piling these up in heaps as above described.
19. The heat employed during the treatment of the dried material
with air should never be sufficient to fuse the material, since it assumes
on fusion a state in which its decomposition by air is extremely difficult.
The dried material as it exists immediately after the completion of the
evaporation to dryness of the concentrated liquor is tolerably hard and
compact, but fusion so increases its hardness that the air can act only
on its surface, whereas when the heat is kept below the fusing point the
air gains access to every particle of the material, the cakes in which it is
charged into the furnace becoming gradually more and more porous,
until at last a very slight pressure will cause them to crumble to a fine
black powder.
20. Provided that the temperature be thus kept always below the
point of fusion the decomposition of the material proceeds however the
more rapidly the higher the temperature, and as the tendency to fuse
and the capability of fusing become less and less as the decomposition
becomes more and more nearly complete, it is hence desirable to raise
the temperature gradually as the decomposition of the material goes on.

page_text: It is for this reason that when treating the dried material in a vertical
furnace or kiln I prefer to make the lower part of such kiln the hottest,
and for the same reason when working in a horizontal furnace in the
manner described above in paragraph 13, I prefer that the hottest end
of such furnace should be that towards which the material is gradually
moved, and from which it is eventually withdrawn, being the end
furthest from that at which it enters the furnace. In other cases the
gradual increase of the temperature must be effected by suitable
regulation of the firing of the furnace employed.
21. The series of operations above described yields chlorine in two
conditions, strong chlorine being obtained by the reaction of hydro-
chloric acid upon manganite of magnesium, and weak chlorine by the
decomposition of atmospheric oxygen of the two chlorides which are a
secondary result of that reaction. When for the purposes for which the
chlorine is required, its dilution by inert gases is not a too serious dis-
advantage, it will be desirable to increase to the utmost the proportion
of that part of the chlorine of the two chlorides which in the operation
of regenerating manganite of magnesium therefrom comes off in the
free state, and to diminish as far as possible the proportion of that part
of their chlorine which comes off in that operation as hydrochloric acid,
requiring further treatment for its attainment as free chlorine. To do
this the evaporation to dryness of the concentrated solution of the two
chlorides must be so performed as to yield a dried material containing at
once a maximum of chlorine and a minimum of water, being in such
wise that as little chlorine as possible, but at the same time as much
water as possible, shall be driven off during the evaporation to dryness,
as much chlorine as possible being left in the dried residue, and a
maximum proportion thereof in the state of anhydrous chloride. To
this end advantage must be taken of the fact that if a concentrated
solution of the two chlorides be evaporated to dryness as rapidly as
possible in an apparatus at a high temperature much more of the water
in it will go off in the state of water without having reached upon
either of the chlorides than if the evaporation be performed more slowly
in an apparatus at a lower temperature.
22. On the other hand it will sometimes be desirable to minimize the
production of weak chlorine, and to recover as much as possible of the
chlorine of the two residual chlorides in the state of acid, from which
manganite of magnesium may liberate strong chlorine. In such case

page_text: on further experiment to answer best will be stated in my final
Specification.
27. Nearly all the methods of procedure, and all the arrangements
which are above described, are equally applicable when what is com-
menced with is a solution of chloride of manganese only, yielding
manganite of manganese, instead of a mixed solution of chloride of
magnesium and chloride of manganese, yielding manganite of mag-
nesium; but the performance of the process when employing manganese
compounds only is much more difficult and costly than its performance
when employing manganese and magnesium compounds together.
Nearly all that is said above is applicable also to the manufacture of
chlorine by means of perpetually regenerated chromate of magnesium.
28. Instead of air as directed above pure oxygen may of course be
used when cheap enough. It may be desirable to heat the air or
oxygen before admitting it into the furnace.
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 1872.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WALTER
WELDON, of 29, The Cedars, Putney, in the County of Surrey, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the First day of February, in the year
of our Lord One thousand eight hundred and seventy-two, in the thirty-
fifth year of Her reign, did, for Herself, Her heirs and successors, give
and grant unto me, the said Walter Weldon, Her special licence that I,
the said Walter Weldon, my executors, administrators, and assigns, or
such others as I, the said Walter Weldon, my executors, administrators,
and assigns, should at any time agree with, and no others, from time
to time and at all times thereafter during the term therein expressed,
should and lawfully might make, use, exercise, and vend, within the
United Kingdom of Great Britain and Ireland, the Channel Islands,
and Isle of Man, an Invention for "IMPROVEMENTS IN THE MANUFACTURE

page_text: OF CHLORINE, AND IN APPARATUS AND ARRANGEMENTS FOR THAT PURPOSE," upon
the condition (amongst others) that I, the said 'Walter Weldon, my
executors or administrators, by an instrument in writing under his, or
their, or one of their hands and seals, should particularly describe and
ascertain the nature of the said Invention, and in what manner the
same was to be performed, and cause the same to be filed in the Great
Seal Patent Office within six calendar months next and immediately
after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Walter Weldon, do hereby declare
the nature of my said Invention, and in what manner the same is to
be performed, to be particularly described and ascertained in and by
the following statement :-
I. This Invention relates to the manufacture of chlorine by means of
manganite of magnesium. It is equally applicable to the manufacture
of chlorine by means either of chromate of magnesium or of manganite
of manganese.
II. By "manganite of magnesium" I mean any compound or mixture
of magnesia and peroxyde of manganese such as is produced by heating
in contact with air any mixturè either of chloride of manganese and
chloride of magnesium, or of chloride of manganese and magnesia, or of
chloride of manganese and carbonate of magnesium. By "chromate of
magnesium " I mean any corresponding compound or mixture, similarly
produced, of chromic acid and magnesia; and by "manganite of man-
ganese" any corresponding compound or mixture, produced by the like
method, of peroxyde of manganese, and protoxyde of the same metal.
III. Of these bodies the one first mentioned has many advantages over
the other two so far as concerns the manufacture of chlorine by means
of it. I shall therefore, in what follows, speak only of the manufacture
of chlorine by means of manganite of magnesium. Nearly all that will
be said, however, with respect to the manufacture of chlorine by means
of that compound will apply equally to its manufacture by means either
of chromate of magnesium or of manganite of manganese.
IV. The manufacture of chlorine by means of manganite of mag-
nesium commences with a mixed solution of chloride of manganese and
chloride of magnesium. This is evaporated to dryness, and the dry
residue is then heated with access of air. Chlorine and hydrochloric acid

page_text: are disengaged and pass off in admixture with the nitrogen of that
portion of the air which has entered the furnace the oxygen of which has
taken part in the reactions going on therein, and also with whatever
excess of air may have entered, and there remains in the furnace man-
ganite of magnesium. This is then treated in a still with aqueous
hydrochloric acid, from which it liberates pure chlorine, at the
same time, producing a mixed solution of chloride of manganese and
chloride of magnesium exactly similar to that which the series of
operations began with. With this reproduced solution the series of
operations recommences, and so on time after time indefinitely.
V. Such is the general plan of the system of manufacturing chlorine
to which my present Invention relates. A crude form of this method of
manufacturing chlorine constitutes the second part of an Invention for
which Letters Patent numbered 662, and bearing date the Twenty-
seventh of February 1868, have been granted to me. My present
Invention consists in certain improvements upon the said second part
of the said former Invention, whereby I am better enabled to carry the
said method of manufacturing chlorine into practical and economical
effect.
VI. The object of the improvement which I will describe first is that
of obtaining as residue of the operation in which manganite of mag-
nesium reacts upon aqueous hydrochloric acid, a liquor which shall be
neutral, or practically so.
VII. The product of which I shall speak in this Specification by the
name of "manganite of magnesium" will only rarely consist simply of
a compound of peroxyde of manganese and magnesia, but will usually
contain also some portion of manganite of manganese, and perhaps
some free magnesia, besides small quantities of such foreign bodies as
oxide of iron, silica, and certain sulphates. All the bodies contained in
it which neutralize hydrochloric acid without liberating chlorine there-
from, that is to say, the magnesia existing in combination with peroxyde
of manganese as manganite of magnesium, the protoxide of manganese
existing similarly combined as manganite of manganese, and the free
magnesia, if any, I shall designate by the general name of "bases.”
VIII. The method by which aqueous hydrochloric acid and native
oxides of manganese are treated together, and by which hydrochloric
acid and artificial oxides of manganese peroxidized in the dry way have

page_text: always hitherto been treated together, necessarily yields a residual liquor
containing more or less free acid. Such a liquor is difficult and costly
to pump, and cannot be evaporated by the methods most economical of
fuel. Moreover, in evaporating such a liquor the free acid contained
therein goes off associated with so much water that when condensed it is
of little or no practical value.
IX. The method by which aqueous hydrochloric acid and native oxides
of manganese are treated together, and by which aqueous hydrochloric
acid and artificial oxides of manganese peroxidized in the dry way have
always hitherto been treated together, consists in putting the oxides first
into the still, and then adding thereto the hydrochloric acid. When this
method is followed with manganite of magnesium the acid dissolves out
all the bases contained in that product before touching the peroxide of
manganese contained in it, and is thus greatly enfeebled before beginning
to act upon the latter. Under no circumstances can peroxide of
manganese by itself completely neutralize aqueous hydrochloric acid,
and the weaker the acid it is treated with the smaller is the proportion
of the acid which it can neutralize. Hence when manganite of magne-
sium and hydrochloric acid are treated together by the method just
stated the quantity of the acid which is left unneutralized is very
considerable indeed.
X. The improved method of treating together aqueous hydrochloric
acid and manganite of magnesium, by which I am enabled to obtain a
practically neutral residual liquor, is as follows:-I put the acid into
the still first, and I add the manganite of magnesium thereto gradually
or by more portions than one, and preferably in such wise that as long
as the acid continues strong enough to be capable of dissolving peroxide
of manganese the whole of the manganite of magnesium which enters
the still, that is to say, the peroxide of manganese which is contained
in such manganite of magnesium, as well, as the bases which are also
contained in it, shall dissolve completely or very nearly so, and this as
fast or almost as fast as it enters the still. It may enter either in a
continuous stream or intermittently, but the greater portion of what has
previously entered should always have dissolved before any subsequent
portion is added. When the stage is at length reached at which what
acid remains free is no longer strong enough to dissolve peroxide of
manganese I make a further addition of manganite of magnesium, and
I thus neutralize the remaining acid completely, or very nearly so, by.

page_text: the bases in the further quantity of manganite of magnesium thus
added. I thus obtain a neutral or practically neutral residual liquor,
containing in suspension more or less undissolved peroxide of manganese.
I prefer to allow this to settle in the still itself, after which I draw off
the supernatant solution only. To the undissolved peroxide of manga-
nese remaining in the still I then add the next charge of acid, and when
it has dissolved this peroxide I proceed with the addition of manganite
of magnesium as before. When economy of still space is important
the residual liquor produced in the still may be run off therefrom the
moment it is neutral, and be allowed to deposit its undissolved peroxide
in another vessel instead of in the still itself. In such case the undis-
solved peroxide after it has deposited and the clear liquor has been
decanted from it must be returned to the still either by itself or in
admixture with a mud of manganite of magnesium. When it goes into
the still by itself it should preferably be put in upon a charge of fresh
acid, the addition of manganite of magnesium not commencing until
this peroxide is all dissolved or nearly so.
XI. In order to permit the bydrochloric acid and the manganite
of magnesium to be treated together as I have just described, I employ
for their reaction upon each other a still, which is closed during the
admission into it of the manganite of magnesium, and I make the man-
ganite of magnesium into a fluid mud by grinding or otherwise mixing
it with some residual solution produced in a previous operation, and I
admit this fluid mud into the closed still by an aperture or passage pro-
tected against the exit through it of gas from the still by a hydraulic
lute, or other equivalent arrangement, as will be well understood. I
prefer to use such stills, and such method of admitting into them a mud
of manganite of magnesium as are commonly employed for the mud
obtained in my process for the manufacture of chlorine by means of
compounds of manganese regenerated in the wet way. The manganite
of magnesium might be made into mud with water, but the use for this
purpose of residual liquor from a previous operation is far preferable.
XII. It is also practicable to admit, either intermittently or in a
nearly regular and continuous current, as may be desired, manganite of
magnesium in powder into a still kept closed during the admission of it,
by charging the powder into a hopper communicating with the interior
of the still by a tube or other passage provided with a cock or valve, or
other means of allowing the powder of manganite. of magnesium to enter

page_text: the still through the said tube or passage without permitting the exit
of gas thereby.
XIII. In another method of treating together manganite of mag-
nesium and hydrochloric acid in such wise as to obtain a practically
neutral residual liquor, an acid liquor is allowed to leave the still, and is
then treated in another vessel with manganite of magnesium until its
free acid has become neutralized by the bases thereof. This other vessel
should be placed below the still, and should preferably be furnished with
a mechanical agitator. The manganite of magnesium should preferably
be put in this vessel first, and in such quantity that the bases in it shall
be rather more than equivalent to the free acid in the liquor it is to
neutralize. That the manganite of magnesium should be put into this
vessel first is not essential, but has two advantages; it avoids the risk
which there would otherwise be of the generation of chlorine in this
vessel, and it permits the vessel to be made of cast iron. The result of
the treatment in this vessel of an acid liquor from the still by a slight
excess of manganite of magnesium, is a neutral solution of chloride of
manganese and chloride of magnesium, having suspended in it a con-
siderable quantity of pure peroxide of manganese and a small quantity
of manganite of magnesium which has not been acted upon. These
bodies must be allowed to settle, and then, when the supernatant clear
liquor has been removed from above them, they will be in a suitable
state for admission into the still as mud. They may be admitted there-
into, either before the acid, or as is described above in paragraph X.
They will require to be treated with a considerable excess of acid, giving
a strongly acid residual liquor, which must be treated as before, and so on
time after time continually. The deposition from the neutralized liquor
of the bodies at first suspended in it may take place in the vessel in
which the neutralization is effected, but it should preferably take place
in another vessel, placed at such an elevation that the clear liquor which
forms in it may, run from it into the vessel or vessels in which the next
operation is performed, and the deposit of peroxide of manganese and
manganite of magnesium into the still.
XIV. Having obtained a neutral residual liquor by either of the
methods described above, the next step is to concentrate it by evapo-
ration. An acid residual liquor could be evaporated only in brick
furnaces, which would rapidly wear out, besides being very expensive
for fuel, while all through its evaporation such a liquor would give off
B

page_text: an acid vapour which would have to be condensed, although the re-
sulting aqueous acid would be too weak to be capable of being turned
to any practical account. By obtaining a neutral residual liquor I avoid
these disadvantages, and am enabled to evaporate my liquor by the
cheapest of all methods, and in such wise that during the evaporation
from it of its excess of water it shall give off only steam, while I at the
same time secure that none of the chlorine contained in the liquor shall
be disengaged except under conditions under which it can be utilized.
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XV. Although I do not confine myself to such method, I prefer to
evaporate my neutral or neutralized liquor in iron vessels or pans, heated
from below. I also prefer that the heat used, or as much as possible of
it, should be the surplus or waste heat either of the furnace or fur-
naces in which the chlorides in the said liquor will afterwards be
decomposed, or of any other furnace or furnaces whose surplus heat can
conveniently be so applied. The evaporating vessels should nevertheless
be furnished with fire-places of their own, to be used when enough
waste heat is not available. I prefer to employ in each case two or
more evaporating vessels, and so to connect and arrange them that when
a charge of concentrated liquor has been drawn off from the final vessel
of the series one may run into that vessel partially concentrated liquor
from the next preceding vessel, and so on throughout the series, if it
consist of more vessels than two. The vessels may be either open or
closed. When they are of cast iron, as will usually be the case, they
should of course never be emptied, in ordinary working, below some
point above which the heat applied to them externally does not play.
XVI. In these vessels I evaporate the liquor down very nearly to the
point at which the chloride of magnesium contained in it would begin to
decompose, and at which hydrochloric acid would accordingly begin to
come off from it. With some mixtures of chloride of manganese and
chloride of magnesium this happens when the solution has attained a
temperature of about 280 degrees Fahrenheit. With other mixtures
decomposition does not begin until the solution has reached a tem-
perature of nearly 350 degrees. Ordinarily the temperature at which
acid would begin to come off will be between these limits.
XVII. When the liquor has been concentrated in the evaporating
vessels as far as it can be without evolution of acid, or nearly so, the next
step is to complete its evaporation to dryness. During this completion.

page_text: of the evaporation of the concentrated liquor a certain amount of decom-
position takes place, causing a considerable quantity of hydrochloric acid
gas to be given off. This operation must therefore be performed in an
apparatus which shall permit of this gas being collected and conveyed to
5 a suitable condenser. Such apparatus may consist of a cast-iron pot,
similar to an ordinary salt cake pot, and similarly covered in and con-
nected with a condenser; or it may be almost any kind of muffle
furnace constructed in brick. A "close roaster," such as many manu-
facturers employ in the second stage of the manufacture of salt cake, is
very suitable. It is possible to use a reverberatory furnace for this
operation, but I very much prefer a muffle furnace.
XVIII. The evaporation to dryness of the concentrated liquor leaves
upon the bed of the furnace in which it is performed a thin layer of dried
material consisting of a mixture of chloride of manganese, probably
anhydrous, and chloride of magnesium, partially hydrated, with more or
less magnesia, and perhaps a little protoxide of manganese. The final
operation of the process consists in heating this material with access of
air, thereby converting it into manganite of magnesium, its chlorine
being at the same time disengaged mainly in the free state, but partly as
hydrochloric acid.
XIX. The operation of evaporating to dryness the concentrated liquor,
and that of heating with access of air the dried material so produced,
may both take place in the same furnace, or they may be performed
either in separate furnaces or in distinct parts of a composite furnace.
An apparatus of the latter kind may consist of a long muffle furnace,
divided internally into two compartments A and B. Such a furnace
may be called a
"double furnace." In the partition between the two
parts of it should be an aperture furnished with a valve, or door, or
damper, or other appliance, by means of which communication between
the two parts of it may be opened or closed at pleasure. The furnace
should preferably be fired at both ends, the products of combustion from
both fires being led on leaving the furnace under the evaporating vessels.
These last should of course be placed in all cases at such an elevation
that concentrated liquor can run from them into the furnace or other
apparatus in which its evaporation is to be completed.
The method by which I nmfan
}
The method by which I prefer to work such a double furnace is
as follows: A suitable quantity of concentrated liquor is run into
B 2

page_text: :
part A of the furnace, the working doors of that part of the furnace,
.and also the aperture of communication between it and the other part of
the furnace, having first been closed. When this first charge of concen-
trated liquor has been dried down, and the bed of part A of the furnace
has accordingly become covered with a thin layer of dried material, the
-working doors of part A of the furnace and the aperture of communi-
cation with part B are both opened, and the thin layer of dried material
.covering the bed of part A is broken up into small pieces and pushed
through on to the bed of part B. There it is piled up as a heap of thin
cakes, occupying only a small portion of the bed of part B, at the end of
part B nearest to part A. The aperture of communication between the two
parts of the furnace is then closed, and a second quantity of liquor run
into part A, producing therein a second thin layer of dried material.
The heap of thin cakes in part B is now moved a certain distance
towards the other end of that part of the furnace, so as to make room
for a second heap, and then the second thin layer of dried material in
part A is broken up and pushed through into part B, and there piled up
in a heap just as the first had been. When a third layer of dried
material has been produced in part A the two heaps now in part B are
both moved downwards sufficiently far for this third layer of dried
material to be pushed through into part B as the first and second had
been; and as further quantities of concentrated liquor are successively
reduced to dryness in part A the whole of the contents of part B are
each time moved a stage further down, thereby making room for the
admission into part B of a fresh heap of thin cakes from part A until at
length the whole of the bed of part B is occupied. Thereafter, every
time a fresh charge of concentrated liquor has been dried down in
part A, the whole of the contents of part B are moved downwards as
before, a certain quantity of manganite of magnesium being first
withdrawn from the end of part B which is furthest from part A, and
a fresh charge of dried material being afterwards added at the other end.
XXI. From part A of such a double furnace worked as just described
hydrochloric acid will be given off, as has been said above, and from
part B a mixture of hydrochloric acid and free chlorine. Both parts of
the furnace must therefore be connected with apparatus for the con-
densation of hydrochloric acid, as is well understood. In the condensers
employed for part A of the furnace everything which passes off from
that part of the furnace will condense, except the air which gets into it

page_text: it may otherwise be wider at one part than at another. I prefer that its
horizontal section should be either a very flat oval or a narrow paral-
lelogram. Air must enter the kiln at one of its extremities, and
from its other extremity will pass off the same mixture of gases as from
the part B of the double furnace described above.
XXIV. The advantage of the method of drying down the concentrated
liquor in one furnace or part of a furnace, and then for its treatment
by heating it with access of air, transferring the dried material so pro-
duced into another furnace or part of a furnace, down the whole length
of which it shall pass gradually, entering at one end in the state of thin
cakes having the constitution stated above in paragraph XVIII., and
being withdrawn from the other end as manganite of magnesium, more
or less completely in the state of powder, is owing to the quantity of
dried material which can be produced in one operation, in cakes thin
enough for their subsequent treatment not to require an excessively long
time, being much too small to form a full charge as regards the next
operation for such a furnace as it was produced in. It may be possible
however to perform in a single furnace both the evaporation to dryness
of the concentrated liquor and the subsequent heating with access of air
without unduly wasting furnace space by drying down a charge of con-
centrated liquor, then adding another charge of concentrated liquor, and
when it is dry adding a third charge, and after that as many more
charges as may be necessary, and then when the furnace is at length
sufficiently full breaking up the mass into pieces of as moderate size as
possible, and thereafter proceeding with the heating with access of air.
It will be better in such case to break up the product of the evaporation
to dryness of each charge of concentrated liquor, and if possible. to pile
it up at one end or at one side of the furnace before adding the next
charge of concentrated liquor. There will otherwise be risk of the dried
material being in too thick cakes. When thus performing both opera-
tions in the same furnace it will still be desirable to employ two
furnaces, using each alternately to dry down concentrated liquor, while
the other is being devoted to the further treatment of the dried
material.
XXV. The temperature of the furnace in which the dried. material is a
heated with access of air should never be sufficient to fuse the material,
since the material assumes on fusion a condition in which its decom.
13

page_text: immediately after the completion of the evaporation to dryness of the
concentrated liquor is tolerably hard and compact, but fusion so increases
its hardness that the air can act only on its surface; whereas when the
heat is kept below the fusing point the air gains access to every particle
5 of the material, what are at first hard white cakes becoming gradually
more and more porous, and at the same time darker in colour, until at
last an extremely slight pressure will cause them to crumble into a very
fine black powder.
XXVI. Provided however that the temperature be kept always below
the point of fusion, the decomposition of the material proceeds the more
rapidly the higher the temperature, and as the tendency to fuse, and the
capability of fusing become less and less as the decomposition becomes
more and more nearly complete, it is hence desirable to raise the
temperature as the decomposition of the material advances. It is for
this reason that when treating the dried material in a vertical furnace or
kiln I prefer to make the lower part of such vertical furnace the hottest;
and for the same reason when working a double horizontal furnace as
described above in paragraph XX., I prefer that the part of such furnace
in which the dried material is heated with access of air should be hotter
at the end towards which the material is gradually moved than'at the
end at which it enters. In other cases the gradual increase of the
temperature must be effected by suitable regulation of the firing of the
furnace employed.
XXVII. Instead of employing a still for the reaction of hydrochloric
acid and manganite of magnesium upon each other, it may be possible to
effect that reaction in the furnace in which the manganite of magnesium
is produced, the acid being admitted thereinto either in the liquid state
or as vapour. Air being excluded, there would thus be produced
strong chlorine and a residue of chloride of manganese and chloride of
magnesium. This residue might be decomposed by steam, and the
product of its decomposition be then treated with air, thereby repro-
ducing the manganite of magnesium. The treatment with acid might
then be repeated, and thereafter the treatment first with steam and then'
with air, and so on time after time continually.
XXVIII. To avoid loss of material in the solid state, as dust, the .
apparatus for the performance of the operations above described' should
be well enclosed and fenced in; and to avoid loss of any material in the

page_text: state of solution,, all parts of the flooring upon when solution coutu
possibly be spilt should be made impervious to liquid, and should slope
towards a well or other receptacle, into which shall run whatever may be
spilt upon it.
XXIX. The sulphuric acid which is contained in ordinary hydro-
chloric acid will accumulate in the manganite of magnesium as sulphate
of magnesium, which from time to time must be dissolved out there-
from.
XXX.. In commencing the manufacture of chlorine by the series of
operations above described, the first charge of manganite of magnesium
may perhaps be most conveniently produced by neutralizing with either
magnesia or carbonate of magnesium a strongly acid solution of chloride
of manganese; or one may first obtain chloride of magnesium and add
that to chloride of manganese. I prefer that the magnesium should be
to the manganese in the proportion of equivalent per equivalent, or very
nearly; but I have obtained good results with one of magnesium to two
of manganese, with two of magnesium to one of manganese, and with all
intermediate proportions.
XXXI. Instead of air as directed above, pure oxygen may of course
be used when cheap enough;' and it is a great advantage to heat the air
or oxygen before admitting it into the furnace or other apparatus in
which it is to react on the product of the evaporation to dryness of the
concentrated liquor.
XXXII. In what precedes I have described my present Invention
only as it is applied to the manufacture of chlorine by means of man-
ganite of magnesium. All that I have described is equally applicable
however to the manufacture of chlorine by means of either chromate of
magnesium or manganite of manganese, except that when employing
chromate of magnesium the hydrochloric acid on which it is made to
react can be neutralized without employing an excess, or more than a
'very slight excess, of the chromate, and that when employing manganite
of manganese no magnesia has to be used. The treatment of a mixture
of chloride of chromium and chloride of magnesium as I have described
above for mixtures of chloride of manganese and chloride of magnesium
results in the production of chromate of magnesium, which is a com-
pound closely resembling manganite of magnesium, but having trioxide
of chromium instead of binoxide of manganese for its acid constituent..

page_text: The similar treatment of chloride of manganese by itself produces a com-
pound still more nearly resembling manganite of magnesium, having
the same acid constituent as that compound, but having protoxide of
manganese as its basic oxide instead of magnesia.
Having now described and particularly ascertained the nature of my.
said Invention, and in what manner the same is to be performed,
I would state in conclusion that what I claim as my Invention, and
desire to have secured to me by the herein-before in part recited Letters
Patent, is as follows:-
:-
First. Treating together aqueous hydrochloric acid and either man-
ganite of magnesium or manganite of manganese in such wise as to
neutralize the acid completely, or practically so, by the manganite itself,
by the method of putting the acid first into the still employed for the
said treatment and then adding the manganite, thereto gradually, and
ultimately in excess, to the end that until a certain stage of neutra-
lization of the acid has been reached the whole of the constituents of the
manganite employed shall dissolve completely or very nearly so, and as
fast or very nearly as fast as it enters the still, and that the acid which
remains free at that stage shall then be neutralized by the bases in a
further quantity of manganite, as is described above in paragraph. X.,
Second. Treating together aqueous hydrochloric acid and chromate of
magnesium by putting the acid into the still first, and then adding the
chromate of magnesium thereto gradually.
Third. Admitting the manganite or chromate into stills which are
closed during its admission into them, and enabling it to enter in a more
or less regular and continuous stream, by making the said manganite or
chromate into a fluid mud by grinding or otherwise mixing it with some
portion of a solution obtained as residue of the treatment together of
aqueous hydrochloric acid and a previous charge of the same compound,
and then sending this mud into the stills by means of passages so pro-
tected by ordinary hydraulic lutes or otherwise that while mud can go in
through them gas cannot come out through them, as is described above
in paragraph XI.

page_text: Finally. I claim the application to the manufacture of chlorine of all
or any of the improvements which my foregoing Specification describes.
In witness whereof, I, the said Walter Weldon, have hereunto
set my hand and seal, this Twenty-fourth day of July, in the
year of our Lord One thousand eight hundred and seventy-
two.
WALTER WELDON. (L.S.)