Improvements in the Manufacture of Ferrocyanides of Potassium and Sodium from their Sulphocyanides, and Apparatus relating thereto.
Year: 1894

page_text: Date of Application, 26th Apr., 1894
Complete Specification Left, 21st Feb.. 1895-Accepted, 24th May, 1895
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Ferrocyanides of Potassium
and Sodium from their Sulphocyanides, and Apparatus relating
thereto.
We, HORACE WOODWARD CROWTHER, of The Beeches, West Bromwich,
EDMUND CHARLES ROSSITER, of Smethwick, both in the County of Stafford,
JOHN JAMES Hood, of 1 Fenchurch Avenue, in the City of London, all
Chemists, and GEORGE STACEY ALBRIGHT, of The Elms, Elgbaston,
Birmingham, in the County of Warwick, Gentleman, do hereby declare the nature
of this invention to be as follows:-
It is well known that sulphocyanides of the alkalies may be converted into their
ferrocyanides by heating with metallic iron and subsequently lixiviating the
product with water. It is very important as has been pointed out before that the
sulphocyanides should be quite free from water, and also that the iron used should
be clean and free from oxide.
Our improvements consist in a method of drying the sulphocyanide, in a method
of preparing from ordinary turnings or borings, a very suitable iron for mixing
with the sulphocyanide, and in the mechanical stirring of the mixture during
the heating of the same.
The last portions of water are obstinately retained by the sulphocyanide and
cannot easily be expelled by heat alone and we find that the easiest and best
method of thoroughly freeing the sulphocyanide from water is to blow through
the melted salt an inert gas, such as nitrogen, or carbonic acid (lime-kiln gases)
which latter we prefer to use, as it is cheap and easily obtainable. We heat the
melted sulphocyanide during the passage of the gas to about 500° F. and the
presence of the inert gas during the operation of drying protects the surface of
the fused salt from oxidation.
Our method of preparing the iron free from oxide is to treat such iron with any
soluble sulphide whereby all oxide of iron is converted into sulphide. It is then
well drained and at once put into the vessel containing the just melted but
undried sulphocyanide. The two are dried together by the method mentioned
above. If iron borings or turnings are obtainable free from appreciable
quantities of rust or oxide we prefer simply to dry the iron at a gentle heat,
and to add it to the previously dried sulphocyanide.
We dry the sulphocyanide or mixture of sulphocyanide and iron, in the vessel in
which the reaction is to take place. The vessel we find very suitable is a deep
cylindrical iron pot, with a moveable cover fitted with an agitator carrying strong
paddles, which agitator is so arranged that it can be expeditiously removed from
the pot. The mechanical power to turn the agitator is conveyed in such a manner,
that the pot containing the product, together with the agitator may be easily
removed from the furnace.
After the mixture of sulphocyanide and iron is dried we commence stirring, and
raise the temperature until the reaction commences, when the fire is drawn, but the

page_text: agitation must be continued for some time in order that a complete reaction may
take place.
Deted thie 25th day of A with 1904
HORACE W. CROWTHER.
EDMUND C. ROSSITER.
JOHN JAMES HOOD.
GEO. S. ALBRIGHT.
Improvements in the Manufacture of Ferrocyanides of Potassium
and Sodium from their Sulphocyanides, and Apparatus relating
thereto.
We, HORACE WOODWARD CROWTHER, of The Beeches, West Bromwich,
EDMUND CHARLES ROSSITER, of Smethwick, both in the County of Stafford,
JOHN JAMES HOOD of 1 Fenchurch Avenue in the City of London all
Chemists, and GEORGE STACEY ALBRIGHT of The Elms, Edgbaston,
Birmingham in the County of Warwick, Gentleman, do-hereby declare the nature
of this invention, and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement :-
It is well known that sulphocyanides of the alkalies may be converted into their
ferrocyanides by heating with metallic iron and subsequently lixiviating the
product with water. It is very important as has been pointed out before that the
sulphocyanide should be quite free from water and also that the iron used should
be clear and free from oxide.
Partly owing to these conditions being difficult to satisfy and partly owing to
unsatisfactory apparatus having been employed the reaction has not been brought
into general use for manufacturing purposes.
The
The sulphocyanide of potassium is difficult to dry by heat alone, as the last
portions of the water are obstinately retained; we find the best method of drying
is to force through the mass melted by heat an inert gas such as nitrogen, or
carbonic acid gas or lime kiln gases which latter we prefer to use as they are easily
obtainable. The lime kiln gases should contain as little oxygen as possible.
temperature of the sulphocyanide of potassium is gradually raised until about 450°
to 500° F. is reached. The inert gas besides driving out the water, protects the
sulpbocyanide from oxidation or firing, as the temperature rises. As the melting
point of the damp crystals and the fusion point of the dry sulphocyanide of
potassium are very near together no mechanical agitation is necessary.
In the case of sulphocyanide of sodium which crystallises with 2 molecules of
water, the salt first melts in its water of crystallisation and as this is driven off the
anhydrous salt settles on the bottom of the pot, and thus renders further drying
difficult, we prefer to dry this salt with the aid of mechanical agitation which will
be described more fully below, whereby at first a dry anhydrous sulphocyanide of
sodium as a loose powder is obtained, which when the temperature is raised fuses.
To prevent firing or oxidation of the sulphocyanide we pass into the pot lime-kiln
gases but in this case the gases need not necessarily pass through (and we prefer
them only to pass over) the sulphocyanide.
Our method of preparing iron free from oxide is to treat such iron with a soluble
sulphide the mother liquors after the separation of the ferrocyanide of potassium
or ferro-cyanide of sodium obtained in the manufacture of ferrocyanide by this
method are well suited for the purpose. After such treatment the iron is washed
with water to remove any soluble sulphide well drained, and then as speedily as
possible without further drying put into the just melted mass of sulphocyanide of

page_text: appreciable amount of water has been driven off.
The sulphocyanide and the iron are then dried together as described above. If
iron borings are obtainable free from any appreciable quantities of rust or oxide, we
simply dry the iron at a gentle heat and add it to the fused sulphocyanide of
potassium or sodium after the drying operation has been completed.
The apparatus we prefer to employ is shewn by the drawings annexed.
Figure 1 is a plan partly in section.
Figure 2 is a vertical section through line E F.
Figure 3 is a front elevation.
Figure 1 shows a convenient arrangement of four furnaces, viz., two furnaces
with no mechanical apparatus overhead for stirring which may be used for drying
the potassium sulphocyanide, and two furnaces with the overhead mechanical
apparatus for agitation required for the fusion together of the dried sulphocyanide
and iron. The drying and decomposing furnaces are alike. The furnaces are
cylindrical lined with firebrick, and built in the manner shewn in the drawings the
top of each is covered with an iron plate having a hole in the centre somewhat
larger than the outside diameter of the pot near the top are a number of lateral
openings which connect to the flue c and thence to the chimney. The heated
gases from the fire underneath the pot pass up all round the pot, whereby it is
heated uniformly. Dampers are provided to regulate the draught.
The mechanical arrangements for agitating the mixture of sulphocyanide and
iron are d a main shaft driven by an engine which by means of the pulleys and
belts as shewn communicates its motion to bevelled wheels e¹ and and thence to
the vertical shaft f, which is so arranged as to be exactly over the centre of the
pot when the pot is in position in the furnace. The shaft is so arranged at its
lower end, that it may be coupled with the removable piece 9 and then to the
stirrer or agitator in the pot beneath. The removal of this piece y allows of the
introduction or withdrawal of the pot from the furnace. The stirrer h consists of
an axis, square at its lower part and having strong iron arms or paddles bolted on
as shewn. The stirrer is supported in the pot by the collar on the agitator
axis resting upon the cross bar i which is supported some little distance above the
top of the pot by the pillars p p tastened on the top flange of the pot the top
cross bar i serving to keep the shaft vertical, and to add rigidity to the stirring
apparatus. The cross bars are so fixed on the pillars that they are removeable
with the agitator.
The pot we prefer to use is cylindrical, the top flange besides serving for
supporting the pillars for carrying the cross bars mentioned above, also serves for
fastening the cover on to the pot, it has also a lower flange to support the pot
in the furnace at a proper height above the fire, this flange is of sufficient
width so that it rests firmly on the iron plate covering the top of the furnace
as mentioned above. The pot is also furnished with lugs k. k to receive hooks
attached to crane chains to enable the pot either to be removed from the
drying furnace to the decomposing furnace, or from this to a place to cool.. An
overhead travelling crane not shewn in the drawings is convenient for the purpose.
The pot is also furnished with a moveable cover made in two halves and nearly
air tight it is fastened on to the pot by means of bolts, with a joint of asbestos
packing between it and the pot. A small sight hole is provided in the lid which is
closed by a plug when not in use.
The drying of the sulphocyanide and the fusion of the sulphocyanide with iron
are done in the same pot, but in the case of sulphocyanide of potassium, the first
operation of drying takes place in the drying furnace, and the decomposition in the..
decon posing furnace.
We proceed to perform the operations as follows; in the case of sulphocyanide..
of potassium, a known quantity of. the sulphocyanide is put into the pot which,
when melted will occupy about one third the capacity of the pot. The pot is then "
put into the drying furnace, and the sulphocyanide is just melted by the fire
1..

page_text: underneath; then the iron (if found necessary to treat in the manner above
described) is added and the two are dried together by further heating, whilst inert
gases (lime kiln gases) are passed through by means of a pipe baving a ring at the
bottom perforated with a. number of small holes. This pipe is connected by means
of a stout india rubber tube or pipe, to a main supplying the inert gas, (lime kilo
gases) under pressure and free from water. When the temperature reaches 450°
to 500° F. and the fused sulphocyanide is free from water the gas pipe is
removed and the pot transferred to the decomposing furnace, the agitator is
introduced and connected by means of the piece g. to the vertical shaft the lids
having been fastened on, the pot is fired, the materials being continually stirred.
When the reaction has taken place the mass inside becomes red-hot, and is then
only stirred with difficulty. The connecting piece is then disconnected from the
agitator and shaft and the pot (together with agitator) is taken from the furnace to
a place to cool.
If the iron is practically free from oxide, and therefore requiring no treatment as
described the sulphocyanide is dried by itself, and the iron previously dried is
added after the pot has been removed to the fusion or decomposing furnace, the
agitator running at the same time. The subsequent procedure is as described
above.
In the case of sulphocyanide of sodium the pot with the agitator fitted and
containing a charge of sulphocyanide of sodium is at once put into the decomposing
furnace, and the sulphocyanide melted in its water of crystallisation and the treated
iron added (if found necessary to treat the iron). The charge is dried by heat and
continuous stirring until a greater part of the water has been removed, then a stream
of inert gas (lime kiln gases) is passed into the pot to prevent oxidation of the iron
and sulphocyanide. The heat is then raised with continual stirring and passage of
limekiln gases over the surface until the mass is fused, the lid is then fastened on.
The subsequent procedure is then exactly the same as described in the case of the
potash salt.
If it is not necessary to treat the iron as above described, the sulphocyanide is
first dried and fused in the manner described the dried iron being added after the
sulphocyanide is in a state of fusion.
To facilitate the removal of the charge from the pots, it is as well to pull up the
agitator so that the top paddle touches underneath the cover, this breaks up
the mass in the pot and enables it when cold to be easily removed.
We use 65 parts or thereabouts of iron to every 97 parts sulphocyanide of
potassium or 81 parts sulphocyanide of sodium. The iron we prefer to use is fine
turnings or borings.
When the pots have become cold the lids and agitators are removed, and the
mass transferred as speedily as possible to a vat, a suitable quantity of water being
added, the vat is boiled by live steam, until the mass is disintegrated and the whole
of the cyanide converted into ferrocyanide. The steam is then stopped, the
sulphide of iron allowed to settle, and the clear liquor is removed by decantation
and evaporated to a suitable strength for crystallisation. We prefer to boil down
to such a strength that only a very small quantity of prussiate remains in the
mother liquor. The sulphide of iron left in the vat is filtered and washed free or
nearly free from ferrocyanide. The weak liquors are used again for dissolving
fresh charges.
The crude prussiate is then freed from as much mother liquor as possible, and
then by recrystallisation as is well understood made into pure or nearly pure
ferrocyanide of potassium or sodium of commerce.
The mother liquors left from the first crystallisation of the ferrocyanide, consisting
chiefly of sulphide of potassium or sodium, with any undecomposed sulphocyanide
are converted into carbonates by the action of carbonic acid. The method
described in Patent No. 1495 (Chance, A. M. and J. T.) is well suited for the
purpose. The carbonates so formed together with the sulphocyanide left in solution
are then again used for precipitating fresh quantities of sulphocyanide of calcium.

page_text: Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed we declare that what we
claim is
1. The method of drying the sulphocyanide and the use therein of inert gas (as
lime kiln gas) substantially as described.
2. The preparation of the iron used in the manufacture of ferrocyanide of
potassium or sodium from their sulphocyanides, by treatment with an alkaline
sulphide, or sulphide of alkaline earth, substantially as described.
3. Bringing together the thus treated iron and the sulphocyanide previous to
drying, and drying the mixture in the presence of inert gas, substantially as
described.
4. The apparatus substantially as described for the manufacture of ferrocyanide
of potassium or sodium so arranged that the reaction takes place in an air tight or
nearly air tight pot, with mechanical agitation; that the pot together with the
agitator can be taken from the furnace to cool and that the agitator can be removed
from the pot for the purpose of withdrawing the charge.
Dated this 20th day of February 1895.
HORACE W. CROWTHER.
EDMUND CHARLES ROSSITER.
JOHN JAMES HOOD.
GEO. S. ALBRIGHT.
HORACE W. CROWTHER.
EDMUND CHARLES ROSSITER.
JOHN JAMES HOOD.
GEO. S. ALBRIGHT.