Improvements in the Manufacture of Cyanides.
Year: 1894

page_text: Date of Application, 10th May, 1894
Complete Specification Left, 9th Feb., 1895-Accepted, 4th May, 1895
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Cyanides.
We, HORACE WOODWARD CROWTHER, of The Beeches, West Bromwich,
EDMUND CHARLES ROSSITER, of Smethwick near Birmingham, both Chemists,
and GEORGE STACEY ALBRIGHT, of The Elms, Edgbaston, Birmingham,
Gentleman, do hereby declare the nature of this invention to be as follows:-
We have found that if ferrocyanide of potassium be fused with metallic zinc,
the zinc displaces the iron from combination in accordance with the following
equation―
K. FeCy. + Zn = 4 KCy+ ZnCy2 + Fe.
While however the whole of the iron is separated we do not obtain the
corresponding quantity of cyanide of zinc, inasmuch as a portion of the cyanogen
is decomposed during the reaction. The quantity of cyanogen so decomposed
depends upon the temperature employed, the intimacy with which the materials are
mixed and other such circumstances; but we have obtained in practice cyanide of
zinc amounting to as much as from 80 to 91% of the theoretical yield.
In the above reaction ferrocyanide of sodium may be substituted for ferrocyanide
of potassium, when cyanides of sodium and zinc are obtained.
From the cyanides of potassium and zinc or of sodium and zinc so or otherwise
prepared, a cyanide of the alkali may be obtained by fusing with carbonate or
sulphide of the alkali sufficient to throw down the zinc as oxide or sulphide
respectively. Before doing this, we may if we please pour off the fused cyanides
from the iron but this is not necessary.
If carbonate of the alkali be added, oxide of zinc is formed and is allowed to
settle in the fused cyanide after which the latter is poured off from the solid
residue. If sulphide of the alkali be used, sulphide of zinc is formed, and may
be similarly separated from the fused cyanide, or the cyanide and the sulphide of
zine may be poured off together from the iron (if present), and separated by
solution of the cyanide in water and filtration. The solution of cyanide is then
evaporated in vacuo and the product dried and fused.
We have also found that alkaline cyanides containing small quantities of sulphide
may be easily freed from the sulphide by fusing them with cyanide of zinc or with
the cyanides of zinc and potassium or of zinc and sodium prepared as above
or otherwise, whereby cyanide of the alkali and sulphide of zinc are formed.
Alkaline cyanides prepared by the process described by D. J. Playfair,
English Patent, 7764, 19th May 1890, usually contain small but varying amounts
of one or more of the following impurities viz.: cyanide of zinc, sulphide, carbonate
and sulphocyanide of the alkali.
By suitable combination of the reactions described above an alkaline cyanide
containing such impurities can be freed from them in one operation.
We proceed as follows, if the alkaline cyanide contain more sulphide and
carbonate than is equivalent to the cyanide of zinc present, we fuse it with
sufficient cyanide of zinc or the cyanides of zinc and potassium or of zinc and
sodium prepared as aforesaid or otherwise whereby the excess of such sulphide
and carbonate of the alkali is converted into cyanide of the alkali and sulphide
and oxide of z'nc are thrown down; at the same time if any sulphocyanide be
present, (since by fusion of alkaline sulphocyanides with metallic zinc or lead the

page_text: corresponding cyanides and sulphide of zinc or lead are formed), we add sufficient
metallic zinc or lead to decompose such sulphocyanide.
If however the alkaline cyanide contain more cyanide of zinc than is equivalent
to the sulphide and carbonate of the alkali present we fuse it with a sufficient
quantity of sulphide or carbonate of the alkali with a like result. In this case also
if any sulphocyanide be present it is decomposed by adding sufficient metallic zinc
or lead.
In either case the precipitate is allowed to settle in the fused mass which it does
easily and completely and allows a clear white cyanide to be decanted off con-
taining, if the operation has been conducted properly, no sulphide carbonate or
sulphocyanide and no zinc or mere traces thereof.
HORACE W. CROWTHER.
EDMUND C. ROSSITER.
GEO. S. ALBRIGHT.
We, HORACE WOODWARD CROWTHER, of The Beeches, West Bromwich,
EDMUND CHARLES ROSSITER, of Smethwick near Birmingham, both Chemists,
and GEORGE STACEY ALBRIGHT, of The Elms, Edgbaston, Birmingham,
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 :-
Our invention relates firstly to the production of cyanides from ferrocyanide of
potassium and of sodium.
We have found that if ferrocyanide of potassium be fused with metallic zinc,
the zinc displaces the iron from combination in accordance with the following
equation
K. FеCy. + Zn
=
4 KCy+ZnCy₂ + Fe.
To carry this operation out in practice we proceed as follows:-The ferrocyanide
of potassium previously powdered and dehydrated by well known means as by
drying on a heated plate is gradually introduced into a fusion pot containing an
excess of fused metallic zinc and the contents are stirred and heated until the
whole is completely melted; in a short time the reaction is complete. The
apparatus we employ is a cast iron pot capable of containing some hundredweights
of charge and preferably lipped and fitted with an agitator consisting of a vertical
axis with arms upon it. The axis is carried by a cross bar and it is suitably driven.
The pot is also provided with trunnions and it has a cover made in two parts;
in the cover there is a suitable opening for the introduction of the dehydrated
ferrocyanide. The whole apparatus is so arranged that after the operation is
complete the agitator can be withdrawn and the pot placed on a trunnion stand.
The contents are allowed to settle and the fused and clear supernatant product,
consisting of cyanide of potassium and zinc, is poured off into dishes and allowed
to cool.
Ferrocyanide of sodium may be substituted for ferrocyanide, of potassium in the
above reaction.
Our invention also relates to the treatment of the mixed cyanides of potassium or
of sodium and zinc to transform the cyanide of zinc into the cyanide of the alkali.
Now we have discovered that although in solution cyanide of zinc does not
efficiently react upon the alkaline sulphides or carbonates a complete reaction is
obtained when the salts are fused together.

page_text: In carrying out the operation on mixed cyani les prepared as above described, it
is not necessary to separate the fused cyanides of zinc and potassium or zinc and
sodium from the iron and excess of zinc obtained in the first operation, but after
the first reaction is complete the carbonate or sulphide of the alkali is added at
once. If it be carbonate of soda which we employ we add 106 parts thereof for
every 65 parts of zinc contained in the cyanide mixture.
If sodium sulphide be used 78 parts thereof will be required for every 65 parts
of zinc, these being the equivalent proportions.
In this way cyanide of the alkali is obtained in one operation. If carbonate of
the alkali has been used oxide of zinc is formed, it is allowed to settle in the fused
cyanide after which the latter is poured off from the solid residue. If sulphide of
the alkali has been used sulphide of zinc is formed and may be similarly separated
from the fused cyanide. Or the cyanide and the sulphide of zinc may be poured
off together leaving the iron if this has not previously been separated. The cyanide
is then dissolved in water and the solution is filtered; then it is evaporated in vicuo
and the product dried and fused. The cyanides so obtained are of higher strength
than cyanides obtained by the direct fusion of ferrocyanide with carbonate of the
alkali.
The residues containing iron which are obtained in the above operations are
lixiviated with water to dissolve out the cyanide and this is converted into ferro-
cyanide by boiling with sulphide or oxide of iron with the addition when necessary
of alkali, as is well understood.
Our invention also relates to the purification of cyanides of the alkalies.
Cyanides of the alkalies however prepared containing sulphides may be freed
from the sulphide by fusing them with cyanide of zinc, or with the cyanides of
zine and potassium or of zinc and sodium, whereby cyanide of the alkali and
sulphide of zinc are formed.
Alkaline cyanides prepared by the process described by D. J. Playfair's
Patent 7764, 19th May 1890, usually contain small but varying amounts of one or
more of the following impurities viz. :-cyanide of zinc, sulphide, carbonate and
sulphocyanide of the alkali.
By suitable combination of the reactions mentioned above an alkaline cyanide
containing such impurities can be freed from them in one operation.
We prefer to conduct the operation in the following manner :-In a suitable
vessel we fuse the bulk of cyanide of the alkali which we desire to purify.
We have in the vessel a smaller quantity of metallic zinc in order to convert
into cyanide any sulpho-cyanide which may be present.
The fusion being complete and the mass well stirred, we test it for sulphur by
dissolving a sample in water and adding solution of acetate or nitrate of lead which
gives a black or dark precipitate if (as is usually the case) sulphur be present.
We then add cyanide of zinc or a mixed potassium or sodium cyanide and zinc
We draw
cyanide gradually and carefully keeping the mass thoroughly stirred.
When this
test samples from time to time until sulphur can no longer be detected.
is the case we dissolve a sample in water and test with barium chloride for carbonic
acid. If any be found we continue the additions of cyanide of zinc until it
disappears. If sufficient care be taken this can be done without leaving more than
a trace of cyanide of zinc in the fused mass, but failing this or if (as will rarely
occur) an excess of cyanide of zinc was originally present as an impurity in the
mass, we carefully add sulphide or carbonate of the alkali until its presence is
just apparent in the test. Afterwards by a minute addition of cyanide of zinc the
excess of sulphide or carbonate is removed. The fused mass is afterwards left at
rest for the insoluble zinc compounds to deposit and the pure and clear white
cyanide of the alkali is poured off.
In place of working in the manner described it is of course possible to analyse
the impure cyanide of the alkali to adjust the impurities above named in accordance
with the indications of this analysis and then to fuse the mass. The method of
working which we have described is however more convenient.

page_text: Having now particularly described and ascertained the nature of our said inven-
tion and in what mauner the same is to be performed we declare that what
we claim is —
1. The treatment as herein described of ferrocyanide of potassium or ferro-
cyanide of sodium by fusion with metallic zinc obtaining thereby mixed cyanides of
the alkali and of zinc.
2. The treatment of mixed cyanides containing an alkaliue cyanide and cyanide
of zinc by fusion therewith of alkaline carbonate or sulphide whereby the zinc is
displaced yielding a comparatively pure alkaline cyanide."
3. The purification of alkaline cyanides by the fusion therewith of cyanide of
zine or of the cyanides of zinc and potassium or of the cyanides of zinc and sodium
in due proportion to react with such sulphide or carbonate as the impure alkaline
cyanide may contain.
4. The purification of alkaline cyanides by the fusion therewith of alkaline
carbonate or sulphide in due proportion to react with any zinc the impure alkaline
cyanide may contain.
Dated this Fifth day of February 1895
HORACE WOODWARD CROWTHER.
EDMUND CHARLES ROSSITER.
GEO. S. ALBRIGHT.