Year: 1896

page_text: Date of Application, 20th Feb., 1896
Complete Specification Left, 13th Nov., 1896-Accepted, 19th
ec., 1896
This reaction is, according to this invention, utilized in the manufacture of ferro-
cyanides from sulphocyanides as follows:-
To a solution of any sulphocyanide (calcium sulphocyanide for example) we add
a soluble iron salt, preferably one which does not give a precipitate with the base
of the sulphocyanide employed; for instance ferrous, or ferric, chloride, or a
mixture of these. The object of adding an iron salt to the solution of sulpho-
cyanide is to form a solution of ferrous, or ferric, sulphocyanide.
The solution of sulphocyanide of iron thus prepared, or a solution of sulpho-
cyanide of iron, obtained in any other manner, we treat in an autoclave at an
elevated temperature and under pressure with an excess of metallic iron. We
agitate the contents of the autoclave continually and when the whole, or nearly
the whole, of the sulphocyanogen has disappeared from the solution (which may
be ascertained by withdrawing and testing a sample from time to time) we
discharge the contents of the autoclave and separate the precipitate from the
solution by decantation or by filtration. If necessary we wash the precipitate, and
then we boil it with a solution of caustic soda, or caustic potash, by which means
we obtain solutions of either sodium, or potassium, ferrocyanide, as the case may
be. From these solutions the ferrocyanides may be obtained by concentration and
crystallisation.
The insoluble residue left after the treatment with caustic alkalies, consists of a
mixture of sulphide of iron, oxides of iron, and some metallic iron. We utilise
part of this residue for the production of the soluble iron salt needed in the first
operation. We dissolve the residue in a suitable acid such as hydrochloric acid,
or sulphuric acid. This operation must be carried out in a closed vessel, provided
with exit pipes which convey the sulphuretted hydrogen, evolved during the

page_text: solution, to absorbers, or to any other apparatus or place in which the sulphuretted
hydrogen may be utilised.
Deted this 20th day of February 1896.
JOHNSONS & WILLCOX,
47 Lincoln's Inn Fields, London, W.C., Agents.
This reaction is, according to this invention, utilized in the manufacture of
ferrocyanides from sulphocyanides as follows:-
To a solution of any soluble sulphocyanide (calcium sulphocyanide for example)
we add a soluble iron salt, preferably one which does not give a precipitate with
the base of the sulphocyanide employed; for instance ferrous, or ferric, chloride,
or a mixture of these. The object of adding an iron salt to the solution of soluble
sulphocyanide is to form a solution of ferrous, or ferric, sulphocyanide.
The solution of sulphocyanide of iron thus prepared, or a solution of sulpho-
cyanide of iron obtained in any other manner, we treat in an autoclave at an
elevated temperature and under pressure with an excess of metallic iron. We
agitate the contents of the autoclave continually and when the whole, or nearly
the whole of the sulphocyanogen has disappeared from the solution (which may be
ascertained by withdrawing and testing a sample from time to time) we discharge
the contents of the autoclave and separate the precipitate from the solution by
decantation or by filtration. If necessary we wash the precipitate and then we
boil it with a solution of caustic soda, or caustic potash, by which means we obtain
solutions of either sodium, or potassium, ferrocyanide, as the case may be.. From
these solutions the ferrocyanides may be obtained by concentration and crystalli-
sation.
The insoluble residue left after the treatment with caustic alkalies, consists of a
mixture of sulphide of iron, oxides of irou, and some metallic iron. We utilise
part of this residue for the production of the soluble iron salt needed in the first
operation. We dissolve the residue in a suitable acid such as hydrochloric acid,
or sulphuric acid.

page_text: This operation must be carried out in a closed vessel, provided with exit pipes
which convey the sulphuretted hydrogen, evolved during the solution, to absorbers,
or to any other apparatus or place in which the sulphuretted hydrogen may be
utilised.
In carrying out our invention we find it best to employ a solution of calcium
sulpho-cyanide containing about fifteen pounds of the dry salt in one cubic foot of
the solution. To this solution we add for each equivalent of calcium sulpho-
cyanide contained therein at least one equivalent, but preferably one and one-half
equivalents, of ferrous coloride, in the form of a strong solution prepared as
hereinafter described.
The mixed solution should not contain less than five pounds, but may with
advantage contain more than five, preferably, ten, pounds of calcium sulpho-
cyanide per cubic foot. It is not advisable to use more concentrated solutions
owing to the mass becoming too thick towarls the end of the next operation.
This mixed solution may be considered as containing ferrous sulphocyanide,
calcium chloride, and ferrous chloride.
We next treat this solution in an autoclave at an elevated temperature and
pressure with metallic iron; we employ from about one and one half to twice the
theoretical anantity of metallic iron as indicated by the equation:
The iron should be in a finely divided condition. We prefer to use iron obtained
by reducing iron oxide without fusion by a reducing gas such as carbon monoxide.
When using ordinary iron borings we employ a much larger excess amounting to
at least six times the theoretical quantity. In this case any iron not acted upon
is allowed to remain in the autoclave and is used again in subsequent operations,
fresh iron being added to compensate for that which has taken part in the
reaction.
The autoclave is fitted with a pressure gauge, a safety valve, a mechanical
agitator, and is steam jacketted, so that the contents may be heated to the
necessary temperature. It must also be provided with suitable openings, capable
of being hermetically closed for charging and discharging the contents.
We heat the contents which should not occupy more than two thirds of the
cubical capacity of the autoclave, to boiling and expel the air by means of the
steam evolved. We then close the autoclave and continue to heat until a pressure
of from fifty to sixty pounds per square inch is indicated and a temperature of
from 270° to 280° Fahrenheit is reached. The contents are continually agitated
which may be done by any suitable mechanical means. Any gas evolved during
the reaction escapes through the safety valve which is loaded to correspond
to the desired pressure. According to the more or less finely divided condition of
the iron and the efficiency of the agitation the operation may last from five to twelve
hours.
When the reaction is completed, or nearly so, we discharge the mass still hot.
By settling, or by filtration, and washing we free the precipitate from the calcium
chloride solution.
The precipitate consisting of ferrous sulphide and cyanide of iron may now be
treated with an alkali for the purpose of obtaining the ferrocyanide of the alkali
in solution.
If soda be the alkali used we employ a solution of from about 20° to 40°
Twaddel, and boil the precipitate with it until the whole of the cyanogen has
passed into solution. The solution is then filtered and the ferrocyanide separated
in the solid form by concentration and crystallisation.
The precipitate, consisting of ferrous sulphide, ferrous and ferric hydrates,
is washed (the washings being used for dissolving fresh quantities of caustio
soda) and is then used for the preparation of ferrous chloride solution.
If the alkali employed be caustic potash we find it more advantageous to

page_text: dissolve out first the ferrous sulphide from the mixture of cyanide and sulphide of
iron by means of hydrochloric acid. If the precipitate from the autoclave be
treated with the alkali directly, a considerable amount.of the alkali combines
with the ferrous sulphide, and cannot be removed by washing. In the case of the
cheaper alkali soda this is not of much importance, but in the case of the more
expensive potash this loss adds considerably to the cost of production.
We therefore treat the precipitate first with hydrochloric acid, which we add in
quantity sufficient to dissolve most of the sulphide of iron. This operation must
be carried out in a closed vessel and the sulphuretted hydrogen should be conveyed
to suitable absorbing apparatus or otherwise disposed of.
The precipitate now consists essentially of a cyanide of iron and we add it to a
solution of caustic potash, preferably hot, and agitate until the cyanogen has passed
into solution as ferrocyanide of potassium.
The filtered solution is then concentrated and the ferrocyanide obtained in the
solid state by crystallisation.
Whether we treat the precipitate obtained in the autoclave first with alkali and
afterwards with acid, or first with acid, and afterwards with the alkali, in either
case the resulting solution of ferrous chloride must be obtained sufficiently
concentrated to be used again in the first part of the -process. It is therefore
necessary to free the precipitate as far as possible from water by filter pressing it
or by means of a vacuum filter, and to use for dissolving it a strong solution of
hydrochloric acid.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed we declare that what
we claim is :-
1. In the manufacture of ferrocyanides from sulphocyanides treating a solution
of a sulphocyanide of iron with metallic iron at an elevated temperature and under
pressure substantially as and for the purposes herein before described.
2. In the manufacture of ferrocyanides from sulphocyanides mixing a solution of
a soluble sulphocyanide with a solution of a salt of iron and treating the mixed
solution with metallic iron at an elevated temperature and under pressure substan-
tially as and for the purposes herein before described.
3. The treatment of the cyanide of iron, obtained by the processes according to
either of the preceding claims with an alkaline solution, substantially as and for the
purposes hereinbefore described.
4. The treatment of the sulphide of iron obtained by the processes according to
either of the preceding claims with an acid, substantially as and for the purposes
hereinbefore described.
5. The manufacture of ferrocyanides from sulphocyanides by adding to a solution
of a soluble sulphocyanide a soluble iron salt and then treating the mixture at an
elevated temperature and under pressure with metallic iron and separating the
precipitate and boiling it with a solution of caustic alkali for the obtainment of
ferrocyanides as hereinbefore described.
Dated this 13th day of November 1896.
JOHNSONS & WILLCOX,
47 Lincoln's Inn Fields, London, W.C., Agents.