IкPROVE- MENTS IN THE MANUFACTURE OF CARBONATE OF POTASH, AND THE RECOVERY OF CERTAIN PRODUCTS EVOLVED THEREIN
Year: 1869

page_text: LETTERS PATENT to Carl Friedrich Claus, of Middlesbro-on-Tees,
in the County of York, Chemist, for the Invention of "IкPROVE-
MENTS IN THE MANUFACTURE OF CARBONATE OF POTASH, AND THE RECOVERY
OF CERTAIN PRODUCTS EVOLVED THEREIN."
Sealed the 7th September 1869, and dated the 17th March 1869.
PROVISIONAL SPECIFICATION left by the said Carl Friedrich Claus
at the Office of the Commissioners of Patents, with his Petition,
on the 17th March 1869.
I, CARL FRIEDRICH CLAUS, of Middlesbro-on-Tees, in the County of
York, Chemist, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN THE MANUFACTURE OF CARBONATE OF POTASH, AND THE
RECOVERY OF CERTAIN PRODUCTS EVOLVED THEREIN," to be as follows:-
First. In the manufacture of carbonate of potash (in the manner
herein-after described) by the action of carbonic acid (either pure or
mixed with other gases, and from any available source) upon solutions
of sulphide of potassium, obtained either by the decomposition of
solutions of sulphate of potash by means of solutions of sulphide of
barium, herein-after referred to as process A," or by the reduction, at
a high temperature, of sulphate of potash by means of carbonaceous
Price & 3
<<

page_text: materials, such as coal, coke, or charcoal, and the like, and by dissolving
the sulphide of potassium, produced in water, herein-after referred to
as process B."
The carbonic acid which I employ for the above
process I produce either by the combustion of carbonaceous materials
in such a manner that it may be free from excess of oxygen, or by the
action of muriatic acid upon carbonate of lime.
Secondly. In the simultaneous concentration (evaporation) of weak
sulphide of potassium solutions, whilst undergoing the process of con-
version into carbonate in a tower, by means of impure and hot carbonic
acid gas derived from the combustion of carbonaceous matter, such
being accomplished by placing the furnaces producing the hot gases
close to the carbonating and evaporating tower and allowing the gases to
pass into the tower hot.
Thirdly. In the condensation of the vapours of sulphide of potassium,
produced in the "
process B," in a tower by means of solutions of
sulphide of potassium undergoing the process of conversion into carbonate
therein.
Fourthly. In the recovery of sulphur liberated from the sulphide of
potassium in the form of sulphuretted hydrogen, through the action of
carbonic acid upon the sulphide of potassium, by exposing the sul-
phuretted hydrogen to the action of solutions of per-salts of iron (such
as perchloride, persulphate, or pernitrate of iron, or mixtures of any of
these,) with or without free acid passing through them in a finely divided
state in a tower. And also in the re-oxidation of the solutions of proto-
salts of iron (produced by the action of sulphuretted hydrogen upon the
per-salts of iron) with their admixture of free acid by exposing them in a
tower, and in a finely divided state, to the oxidizing action of
atmospheric air.
In carrying out these processes I proceed as follows:-"Process A."--
When sulphide of potassium is to be produced by the decomposition of
sulphate of potash by sulphide of barium, I first of all manufacture the
sulphide of barium by any of the known methods, such as, for instance
by heating a mixture of sulphate of barytes (either native or the sul
phate of barytes recovered in a subsequent operation, or mixtures of the
two,) with small coal, in a reverberatory furnace until the analysis of a
sample shews that 70 to 75 per cent. of the mass of soluble sulphide of
barium has been formed. A furnace, the same or similar in con-
struction to a black-ash furnace will answer the purpose. Instead

page_text: of employing a reverberatory furnace for heating the balls of sulphate
of barytes mixture I use a deep kiln, but prefer one the horizontal
section of which has the form of a parallelogram.
About one-third
A'
of the kiln, from the bottom upwards, can be closed air-tight.
door on the bottom for withdrawing the finished sulphide is pro-
vided. The whole of the kiln and all connected with it are covered
with iron plates, so as to admit no air except where special openings
are left for that purpose.
In about the middle of one of the broader
sides is a large aperture or flue, extending across the whole width
of the kiln, the under side of which slopes from the inside towards the
outside in an upward direction, but so as to leave all the way a clear
flue space.
Into this flue a tube is inserted, through which flue and
tube the products of combustion are conveyed to the bottom of the
apparatus used in subsequent operations, and which is placed closely along-
side the kiln. In the opposite broad side of the kiln, about on a level
with the flue, is a row of holes, through which the air is admitted to
effect the combustion of the coke, the exact quantity of it being
regulated by stopping up or leaving open more or less of the air holes.
The kiln is closed on the top by an arch, having an aperture therein,
into which a lid is fixed, and through which the charge is thrown in.
When I employ a kiln of this construction for the manufacture of
sulphide of barium, I do so with the view of utilizing the heat and the
carbonic acid produced during the process. When in full working order
this kiln is kept charged with about equal bulk of coke and balls of
sulphate of barytes mixture until full. That part of the charge which
lies between the air or draught holes and the flue is in a high state of
incandescence. One of the objects I have in view in carrying the air
only through the middle of the kiln is that the film of carbonaceous
matter there passed through by the air remains of constant thickness.
The admission of the air is regulated so that no excess of oxygen
is
allowed to pass through the coke into the flue; at the same time a
maximum of carbonic acid and a minimum of carbonic oxide, as far as
practical, is formed. The indications for regulating the supply of air
are given with the greatest precision by the manner in which the gases
act in the subsequent stage of the process upon the sulphide of potassium.
If an excess of oxygen were passing into the sulphide of potassium
solution hyposulphite would be formed, and could be detected by analysis.
Less air should then be admitted until, by repeated tests and by practice,
the right quantity is fixed upon. Regularity in charging is also highly

page_text: necessary. The sulphide of barium produced in either way is thrown
into lixiviating vats and exhausted by boiling hot water, or weaker
liquors of the soluble sulphide. Simultaneously with this operation a
concentrated solution of sulphate of potash is made. The solution of
sulphide of barium is now added to the solution of sulphate of potash in
a closed vat and mixed together. As they become mixed a decompo-
sition takes place, sulphide of potassium is formed, which remains in
solution, and also sulphate of barytes, which is precipitated. The
addition of sulphide of barium solution to the other is continued until a
precipitate ceases to be formed; the precipitate is then allowed to settle
to the bottom and the solution of sulphide of potassium is drawn off
into an air-tight vessel; the precipitate of sulphate of barytes is washed
several times with hot water, or former wash waters, such wash water
being used for dissolving further quantities of sulphate of potash and
the sulphide of barium; or, if there be more wash water than necessary
for this purpose, it is used instead of water for feeding steam boilers, and
there concentrated. The precipitate of sulphate of barytes is run on
to a sand filter, and when sufficiently drained it is mixed with small
coal, formed into balls, and used again for the manufacture of sulphide
of barium.
"Process B." When sulphide of potassium is to be made directly by
heating sulphate of potash with carbonaceous matter, I do the same by
such an arrangement and in such a manner that I am able to obtain at
the same time carbonic acid gas free from excess of oxygen, and also to
utilize the vapours of sulphide of potassium volatilized in the operation
of heating. To effect the ignition I employ either a similar kiln, or a
similar general mode of operation to that described in reference to the
manufacture of sulphide of barium, except that I avoid in the construc-
tion of the kiln such materials as are likely to be acted upon by sulphide
of potassium; this I do by forming the kiln of a double iron tank, the
space between being filled with water or weak
The kiln is
charged with lump coke and sulphate of potash. The fused sulphide of
potassium is drawn from the bottom and dissolved in water; the solution
is then ready for the subsequent operation. The gases containing con-
densible vapours of sulphide of potassium should be free from oxygen
in order that they may be utilized as a source of carbonic acid in the
subsequent operation, viz., in the conversion of the sulphide of potassium
into the carbonate.
liquors.

page_text: Secondly. I effect the ignition of sulphate of potash and carbonaceous
materials also in a reverberatory furnace, in construction similar to
Siemens' gas blow-pipe puddling and steel furnace, only constructed of
different materials, but having no working door nor opening in it except
for the charging lid in the arch, which is fitted with a sand lute. This
furnace is charged, through the door hole in the arch, with a mixture of
finely pulverized and well washed coal, charcoal, pitch coke, or other
coke, and pulverized sulphate of potash, which, when fused and con-
verted into sulphide of potassium, is drawn off and dissolved in water.
The solution of sulphide of potassium, in whatever mode of manufacture
it may have been obtained, is now exposed in a tower in a finely divided
state to the action of carbonic acid from any source. I prefer a square
tower filled with angle irons placed close together and in layers, one
layer crossing the other at right angles. The distance of the angle irons
from one another in each layer should be arranged so that there is a
good draught. The tower is formed of a square air-tight tank, in the
bottom of which a flue or tube enters conveying the hot impure carbonic
and other gases into the tower, which is covered air-tight on the top.
The draught through this tower, the kiln, and the sulphur recovering
apparatus, and which are all connected together, is effected by means of
a flue leading out of the whole arrangement, and ultimately into a
chimney, or it is effected by the blast of the Siemens furnace. The sul-
phate of potassium solution pumped up to the top of the tower is
distributed, in a very finely divided state, over the large surface formed
by the angle irons, down which it runs. In its journey downwards it
meets the hot gases ascending, absorbs a portion of the carbonic acid,
and liberates an equivalent quantity of sulphuretted hydrogen, whilst, at
the same time, it becomes concentrated by the heat of the gases. The
vapours of sulphide of potassium, which may be volatilized in the direct
method of manufacturing, are then also condensed, and ultimately con-
verted into carbonate of potash. When arrived at the bottom the liquor
runs through a pipe back to the tank from whence it was pumped, and
is again pumped up as often as is necessary to complete its conversion
into carbonate of potash, and to evaporate it to the strength best suited
for the next operation. As soon as this result is attained, the liquor is
transferred to a boiling-down pan, boiled down to a crystaline salt, then
calcined thoroughly in a finishing furnace to convert all sulphides and
hyposulphites into sulphates. If required of a purer quality, it should
be dissolved again in the ordinary manner in which crude potashes from

page_text: other sources have been refined before. As a source of pure carbonic
acid I use that generated by the action of muriatic acid upon carbonate
of lime; as a source of carbonic acid mixed with other gases, that
generated in the manufacture of sulphide of barium and potassium, as
described before; but I also produce the same by burning coke or other
carbonaceous matter purposely, in a deep kiln of the same construction
as that above described in reference to the manufacture of sulphide of
barium and potassium. I use also the waste gases from blast furnaces
after they have been re-ignited, and either before or after the re-ignited
gases have been utilized for heating purposes (that is for heating boilers,
blast heating stoves, and the like), provided such precautions have been
taken before and after their re-ignition that no excess of oxygen exists in
them. I use also the waste gases from coke ovens after they have been
ignited in a properly constructed combustion chamber, so that they may
not contain any excess of oxygen.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Carl Friedrich Claus in the Great Seal Patent
Office on the 17th September 1869.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, CARL
FRIEDRICH CLAUS, of Middlesborough-on-Tees, in the County of York,
Chemist, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Seventeenth day of March, in the
year of our Lord One thousand eight hundred and sixty-seven, in the
thirty-second year of Her reign, did, for Herself, Her heirs and suc-
cessors, give and grant unto me, the said Carl Friedrich Claus,
Her special licence that I, the said
that I, the said Carl Friedrich Claus, my
executors, administrators, and assigns, or such others as I, the said
Carl Friedrich Claus, 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
THE MANUFACTURE OF
CARBONATE OF POTASH, AND THE RECOVERY OF CERTAIN PRODUCTS EVOLVED

page_text: THEREIN," upon the condition (amongst others) that I, the said Carl
Friedrich Claus, my executors or administrators, by an instrument in
writing under my, 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 Carl Friedrich Claus, 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, that is to say:-
My said Invention consists, firstly, in the manufacture of carbonate
of potash (in the manner herein-after described) by the action of
carbonic acid derived from the sources enumerated below, either pure
or mixed with other gases, upon solutions of sulphide of potassium,
obtained either by the decomposition of solutions of sulphate of potash
by means of solutions of sulphide of barium, herein-after referred to
as process A, or by the reduction at a high temperature of sulphate of
potash by means of carbonaceous materials (such as coal, coke, or
charcoal, or other analogous substances), and by dissolving the sulphide
of potassium produced in water, this process being herein-after referred
to as process B. The carbonic acid which I employ as above mentioned
I produce either by the combustion of carbonaceous materials in such
a manner that it may be free from excess of oxygen, or by the action
of hydrochloric acid upon carbonate of lime.
My said Invention consists, secondly, in the sinultaneous con-
centration (by evaporation) of weak solutions of sulphide of potassium
whilst undergoing the process of conversion into carbonate in a tower,
by means of impure hot carbonic acid gas derived from the combustion
of carbonaceous matter, the same being accomplished by placing the
furnaces producing the hot gases close to the carbonating and evapora-
ting tower, and allowing the gases to pass into the tower in a hot state.
The third portion of my said Invention consists in the condensation
of the vapours of sulphide of potassium produced in the process B
in the before-mentioned tower by means of solutions of sulphide of
potassium undergoing the process of conversion into carbonate therein.

page_text: The fourth part of my said Invention consists in the recovery of
sulphur liberated from the sulphide of potassium in the form of
sulphuretted hydrogen (through the action of carbonic acid upon the
sulphide of potassium) by exposing the sulphuretted hydrogen to the
action of solutions of per-salts of iron, such as perchloride, persulphate,
or mixtures thereof (either containing free acid or not) passing through
a tower in a finely divided state, and also in the re-oxidation of the
solutions of proto-salts of iron (produced by the action of sulphuretted
hydrogen upon the per-salts of iron) with their admixture of free acid
by exposing them in a tower, and in a finely divided state, to the oxidizing
action of atmospheric air.
In carrying out these processes I proceed as follows:-Process A.—
When sulphide of potassium is to be produced by the decomposition of
sulphate of potash by sulphide of barium, I manufacture in the first
instance the sulphide of barium by any of the known methods, such
as by heating mixture of sulphate of baryta (either native sulphate,
or the sulphate of. baryta recovered in a subsequent operation, or mixtures
of the two) with small coal or coal dust in a reverberatory furnace in
proportions according to the quality of the coal of 25 to 50 parts to
100 parts of sulphate of baryta, until the analysis of a sample shews
that from 70 to 75 per cent. of the mass of soluble sulphide of barium.
has been formed. This takes place after exposure of from one hour and
a half to three hours to red heat, according to the size of the charge,
which may vary from 10 to 20 hundredweight. If the recovered sulphate
of baryta is used, the mixture thereof with coal or coal dust should
first be dried before charging the furnace with the same, in the manner
herein-after described with reference to bricks and balls. A furnace
similar or analogous in construction to a black-ash furnace will be
well adapted for this purpose. The charges require to be turned during
the time of heating. In order to prevent the mixture of sulphate of
baryta and coal lying too closely and densely upon the bed of the
furnace, and thus preventing the heat from penetrating it, I prefer to
make the mixture of wet sulphate of baryta and coal or coal dust
into bricks or balls, and, after drying the same on stoves similar or
analogous to those used in brick-making, I charge the furnace with
such bricks or balls, and if the furnace be so charged therewith, the
charge requires very little turning as the heat easily penetrates the
charge, and if bituminous coal be used for the mixture the coking of
the same by reason of the heat to which it is subjected binds the

page_text: on the
materials together and prevents them from falling into dust. Instead of
employing a reverberatory furnace for heating the bricks or balls of baryta
mixture before referred to, I sometimes use a deep kiln or an apparatus
similar to a lime kiln, but I prefer that the section of the same should
have the form of a parallelogram of about the relative proportions
of 2' 9" x 4' 6" or thereabouts. About one-third of the kiln from the
bottom upwards may be closed in a perfectly air-tight manner
four sides. Air-tight doors are also provided on the bottom and in each
of the smaller sides of the kiln for withdrawing the finished sulphide
of barium. The whole of the kiln and the parts connected with it
may be covered with iron plates; so as to prevent the admission of air
through any part of the brickwork, except where it may be deemed
requisite to leave special openings for the purpose. In about the middle
of the kiln and in one of the broader sides thereof is a large aperture
or flue of about nine inches in depth extending across the whole width
of the kiln. This aperture or flue is arched over by a flat arch and
the under side thereof, which forms what may be called the furnace
bridge of the kiln, slopes from the inside of the kiln towards the outside
thereof in an upward direction for one or two feet past the arch, but
so as to leave all the way a clear flue space of at least six or nine
inches in depth. Into this long and shallow flue a brick-lined iron
tube. is inserted, the same being rendered air-tight by screwing its flanges
upon the coating plates of the kiln. Through the flue and tube the
hot gases and products of combustion are conveyed to the bottom of
the apparatus used in the subsequent operations, that is to say, the
carbonating tower, which is placed as closely as possible alongside the
kiln.
In the opposite broad side of the kiln, in the one opposite to
that in which the flue is placed and about on a level with the flue, is
a row of holes or apertures through which the air is admitted to effect
the combustion of coke, the exact quantity thereof being regulated
by stopping up or leaving open more or fewer of the air holes. The
kiln is closed on the top with an arch into which a lid is fixed through
which the charge is introduced. When I employ a kiln of the con-
struction last described for the manufacture of sulphide of barium; I
do so with the view of útilizing the heat and the carbonic acid produced
during the process.
Although the manufacture of sulphide of barium forms no part of

page_text: flue is in a high state of
heat generated, that part
of a contrivance similar to that described, and in the manner to be
herein-after explained, forms a link in or part of my process, inasmuch
as it enables me to use it as a producer of heat and carbonic acid free
from oxygen, and fit for the conversion of sulphide of potassium into
carbonate of potash, and the evaporation thereof, whilst at the same time
it prevents the re-oxidation of the sulphide of barium when once produced.
When in full working order, the kiln is kept charged through the lid in the
top with about an equal bulk of coke and bricks or balls of sulphate
of baryta mixture until completely full. That part of the charge which
lies between the air or draught holes and the
incandescence and in this part only is the
of the charge above this becoming prepared by the heat below, whilst
the coal in the mixture becomes coked and ready for ignition. That
part of the charge which lies below the hottest part having no draught
through it, and being almost excluded from contact with air and
retaining most of its heat, and being surrounded with an excess of
carbonaceous matter, is in a similar condition to that in which it would
be if it were in a crucible, and can therefore complete the conversion
of sulphate into sulphide of barium. When this stage is arrived at
the sulphide of barium should be quickly withdrawn, the doors closed,
and the kiln filled up again. One of the objects I have in view in
carrying the air only through the middle of the kiln is, that that part
can be more easily kept in a uniform condition of incandescence, whilst
no accumulation of inert masses of clinkers can take place, and the
film of carbonaceous matter thus passed through by the air remains
of constant thickness. The operation of the admission of the air is
controlled and regulated and carried out in such a manner by opening
and closing the air holes that no excess of oxygen is allowed to pass
out of the kiln into the flue, and at the same time through the coke,
and so as to form a maximum of carbonic acid and a minimum of
carbonic oxide, as far as is practicable. The indications for regulating
the supply of air are given with the greatest precision by the manner
in which the gases act in the subsequent stage of the process upon the
sulphide of potassium. If an excess of oxygen were passing through
the kiln into the sulphide of potassium solution hyposulphite would
instantly be formed, and could be detected by analysis, less air should
then be admitted until by repeated tests of the liquor and by practice
the right quantity is fixed upon. Regularity in charging the kiln and

page_text: in withdrawing the finished charges is also highly necessary, inasmuch
as by it the charge in the hot and gas producing zone is kept in the
same condition. The sulphide of barium produced in either of these
two ways and which when finished contains about 70 per cent. of soluble
sulphide is thrown into lixiviating vats similar to those used for the
lixiviation of black ash. In these it is exhausted by boiling water or
weaker liquors of all or nearly all the soluble sulphide. Simultaneously,
with this operation a concentrated solution of sulphate of potash is
made with boiling water. The solution of sulphide of barium is then
added to the solution of sulphate of potash in a vat covered with a
water luted lid to prevent access of air and mixed together by means
of an agitator. As soon as they become mixed a complete decomposition
instantly takes place, sulphide of potassium is formed which remains
in solution, and also sulphate of baryta which is precipitated. The
addition of sulphide of barium solution to the solution of sulphate of
potash is continued until a precipitate ceases to be formed. The
precipitate is then allowed to settle to the bottom, and the clear solution
of sulphide of potassium is drawn off into an air-tight vessel, the pipe
conveying the liquor being also fixed in an air-tight manner into the
vessel. The precipitate of sulphate of baryta is then washed several
times with hot water, or with former wash waters, such wash water
being used for dissolving further quantities of sulphate of potash and
the sulphide of barium, or if there be more wash water than necessary
for this purpose a portion of it is used instead of water for feeding steam
boilers and there concentrated to about 15° Twaddell. When it is
strong enough for the subsequent operation, namely, the conversion
into carbonate, the precipitate of sulphate of baryta is run on to a
sand filter, and when sufficiently drained is mixed with small coal in
a clay mill and formed into bricks or balls and used again for the
manufacture of sulphide of barium, as described.
When sulphide of
I will now proceed to describe process B.
potassium is to be made directly by heating sulphate of potash with
carbonaceous matter, I perform the same by such an arrangement and
in such a manner that I am enabled to obtain at the same time with
sulphide of potassium, carbonic acid gas free from excess of oxygen,
and also to utilize the vapours of sulphide of potassium volatilised in the
operation of heating sulphate of potash and coal together.

page_text: In order to effect the ignition of the sulphate of potash with
carbonaceous materials, I employ either a similar kiln or furnace, and
a similar general mode of operation to that described in reference
to the manufacture of sulphide of barium, but with the difference
that I make the heating zone of the same somewhat deeper,
and that I avoid in the construction of the kiln all such materials
as are likely to be acted upon by sulphide of potassium, or to
impart impurities to the same; this I do by forming the kiln of a
double iron tank, the space between the two parts being filled with
water or weak liquors. The water chills the fused sulphide of potassium
and prevents its acting upon the iron plates. The kiln is charged
through the door in the top with lumps of coke and sulphate of potash
(the former being largely in excess of the quantity required theoretically),
and the fused sulphide of potassium is withdrawn from the bottom of
the kiln, and kept as much as possible from contact with air, and as
soon as practicable is dissolved in water. The solution is then ready for
the subsequent operation. The coke used should be made of carefully
washed coal and free from sulphur. The gases containing condensible
vapours of sulphide of potassium, after passing out of the kiln, and
which with proper observance of the rules given with reference to the
manufacture of sulphide of barium, should be free from oxygen, in order
that they may be utilised as a source of carbonic acid in the subsequent
operation, namely, in the converson of sulphide of potassium into the
carbonate. I effect the ignition of sulphate of potash and carbonaceous
materials also in a reverberatory furnace of peculiar construction, and
fulfilling all the conditions enumerated above with regard to process B.
A furnace, in principle similar to Siemens' gas puddling and steel
furnace will answer the purpose, but it should be constructed of
different materials, and all access of air excluded by iron plating o
other suitable means, and by its having no working door or opening in
it excepting the charging lid in the arch, which is fitted with a sand lute
and a tapping hole, through which the finished charge is tapped, but
which can be stopped with a stopper. The arch of the furnace and the
flue leading away the gases is constructed of a water tank filled with
weak liquor, or the arch may consist of a hollow iron tank, through
which cold air is drawn for the purpose of keeping.it cool. The heated
air may be used in the combustion chamber, in which the gas is burni
or otherwise. The gas supplied to the Siemens' furnace for heating

page_text: should have no excess of air or oxygen in it, but rather some portion of
carbonic oxide in excess, and the necessary air should be admitted by a
valve. The inside of the arch or flue may be lined several inches thick
with a coating of calcined alum or similar substance to render it non-
conducting; and the bottom of the furnace may also consist of a water
tank, or be made of a mixture of ground pitch coke and pitch coke
together into a solid mass. This furnace is charged through the luted
hole in the arch with a mixture of finely pulverised and well washed
coal, charcoal, pitch coke, or other coke, or sawdust, and pulverised
sulphate of potash, which, when fused and converted into sulphide of
potassium is tapped and dissolved in water. A portion thereof is,
however, volatilised and condensed in the tower, and enters into solution
with the liquor and water in the tower. The solution of sulphide of
potassium, in whatever mode of manufacture it may have been obtained,
is now exposed in a tower in a finely divided state to the action of
carbonic acid (derived from the sources enumerated) which is allowed
to enter into the bottom of the same by allowing it to percolate down
through the tower. The tower may be filled with coke, flint, brick, or
tiles, or similar materials; but the arrangement which I prefer is a
square tower filled with angle irons placed close together and in layers,
one layer crossing the other at right angles, each one or two layers being
supported independently by iron bearing bars. The angle iron may be
lighter and of a sharper angle than ordinary angle iron. The distance
of the angle irons from one another in each layer should be arranged
so that the sum of the spaces left between them is about double that
of the area of the flue which leads the hot gases from the furnace
to the bottom of the tower, or of the tube which may lead the pure
carbonic acid there. The tower is formed of a square air-tight tank
made of iron plates bolted or riveted together, and is lined with
bricks. About a foot from the bottom the flue or tube enters, which
conveys into it the hot impure carbonic acid gas and other gases,
or the pure carbonic acid. The tower is covered in an air-tight manner
on the top, and the last-mentioned flue or tube is connected in an air-
tight manner to the tower and furnace, and above the flue the layers
of angle iron begin and fill up the tower up to the flue, which carries
away the waste gases and steam out of the tower. The draught through
this tower, the kiln, and the apparatus for recovering sulphur, and
which are all connected together, is effected by means of a flue leading
out of the whole arrangement, and ultimately into a large chimney.

page_text: The
There is a vacant space left equal in depth to the diameter of the flue,
and above it are two more layers of angle irons crossing each other.
These, in order to effect the distribution of the liquor in the form of
rain over the layers of angle irons below them, are placed very close
together, but at an equal distance, the edges being for this purpose
made perfectly straight. Over these two layers of angle iron there is a
so-called tumbling box, into which the solution of sulphide of potassium
is discharged from a pipe attached to a force pump, which carries the
liquor from the air-tight tank into which it had been run up to the top
of the tower. The tower is covered on top in an air-tight manner
by a water luted lid, which also covers the discharging pipe and tumbling
box, and protects the stream of liquor from contact with the air.
sulphide of potassium solution after being pumped up to the top of the
tower is distributed in a very finely divided state over the large surface
exhibited by the angle irons, down which it runs until it reaches the
bottom of the tower. In its journey downwards it meets the hot gases
ascending, absorbs a portion of the carbonic acid contained therein, and
liberates an equivalent quantity of sulphuretted hydrogen, whilst at the
same time it becomes concentrated by the heat of the gases. The
vapours of sulphide of potassium which may be volatilized in the direct
method of manufacturing are there also condensed and ultimately con-
verted into carbonate of potash. When arrived at the bottom the liquor
runs through a pipe back to the tank from whence it was pumped, and
is again pumped up as often as is necessary to complete its conversion
into carbonate of potash, and to evaporate it to the strength best suited
for the next operation. As soon as this point is arrived at the liquor is
transferred to a boiling-down pan, boiled down to a crystalline salt, and
then thoroughly calcined in a finishing furnace to convert all sulphides
and hyposulphites into sulphates. It can now be used at once as a
crude potash. If required of a purer quality it is dissolved again in the
ordinary manner in which crude potashes derived from other sources
have been refined previously. As a source of pure carbonic acid I use
that generated by the action of hydrochloric acid upon carbonate of
lime. As a source for carbonic acid mixed with other gases, that
generated in the manufacture of sulphide of barium and potassium, as
herein-before described; but I also produce the same by burning coke
or other carbonaceous matter purposely in a deep kiln of the same
construction as that described in reference to the manufacture of
sulphide of barium and potassium. I prefer in all these cases to

page_text: employ coke or fuel as free from sulphur and ashes as possible. When
I burn coke on purpose in the kiln I may also admit a regulated supply
of air from the bottom, where I also draw out any clinkers which may
have been formed. I, however, use also the waste gases from blast
furnaces after they have been re-ignited, and either before or after the
re-ignited gases have been utilised for heating purposes, that is, for
heating boilers or blast-heating stoves, provided such precautions have
been taken before, during, and after their re-ignition that no excess of
oxygen exists in them. I also use the waste gases from coke ovens after
they have been ignited in a properly constructed combustion chamber,
so that they may not contain any excess of oxygen. The sulphuretted
hydrogen which was evolved in the carbonating tower by the action of
the carbonic acid contained in the furnace gases, or by pure carbonic
acid, as carried by means of a tube along with the steam and other waste
gases into the bottom of another tower or set of towers, similar in con-
struction and arrangement to those described before, but constructed
and fitted in all parts with materials capable of resisting the action of
acid liquids. Through the tower or towers the sulphuretted hydrogen
is allowed to ascend, meeting on its way a fine shower of a liquid
containing in solution a persalt of iron, such as persulphate of iron,
with or without free acid. In order to condense the steam in this
mixture of waste gases before they enter the bottom of the tower (so
that it may not by condensation into water dilute the persalt of iron
solution) the tube conveying away the waste gases should take a long
circuitous route before entering the tower. A draught is created through
this tower, as was stated before, by the top of the same being connected
by means of a tube with a high chimney. The sulphuretted hydrogen
coming in contact with the persalts of iron becomes converted into free
solid sulphur, which falls to the bottom of the tower, whilst the persalts
of iron becomes a protosalt. The sulphur is collected at the bottom of
the tower, washed and filtered, or pressed, and can then be melted down
or used in the manufacture of sulphuric acid. In order that the sulphur
may not adhere to the angles or prisms (with which this tower is filled in
a similar manner to that in which the carbonating towers are filled with
angle irons), and thus choke up the draught through the same, they
should be of a sharp-pointed angle, and should be placed successively at
a greater distance from one another. The angles or prisms should be
The protosalts of iron (that is
made of stone, pottery ware, or glass.
to say, the proto-sulphate or proto-chloride of iron,) are re-oxidised as

page_text: far as practicable by being passed several times through another tower,
in which they come freely in contact with air, when they are again fitted
for recovering further quantities of sulphur, or air may be passed through
the same tower along with the other gases containing sulphuretted
hydrogen, so that the protosalt is re-oxidised in the same proportion as
the persalt becomes reduced by the sulphuretted hydrogen.
Having thus declared and ascertained the nature of my said Inven-
tion, and the manner in which it is to be performed, I would observe
in conclusion that what I consider novel and original, and therefore
claim as constituting the Invention secured to me by the said herein-
before in part recited Letters Patent are, the methods and processes
herein-before mentioned, substantially as and for the purposes described
and set forth, or any mere modifications thereof.
In witness whereof, I, the said Carl Friedrich Claus, have here-
unto set my hand and seal, this Twenty-seventh day of August,
in the year of our Lord One thousand eight hundred and sixty-
nine.
CARL FRIEDRICH CLAUS. (L.S.).