IMPROVEMENTS IN THE MANUFACTURE OF PRUSSIAN BLUE
Year: 1856

page_text: LETTERS PATENT to Bonnet Frédéric Brunel, of Hampstead Road, in
the County of Middlesex, Chemist, for the Invention of "IMPROVEMENTS
IN THE MANUFACTURE OF PRUSSIAN BLUE."
Sealed the 26th September 1856, and dated the 27th March 1856.
PROVISIONAL SPECIFICATION left by the said Bonnet Frédéric Brunel
at the Office of the Commissioners of Patents, with his Petition, on the
27th March 1856.
I, BONNET FRÉDÉRIC BRUNEL, of Hampstead Road, in the County of
Middlesex, Chemist, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN THE MANUFACTURE OF PRUSSIAN BLUE," to be as follows:-
My Invention consists in adding to the ingredients usually employed in
the manufacture of prussian blue, chromic acid and oxalic acid, in mixing
the whole together in a precipitating vessel, and in the application thereto of
a current of electricity. I dissolve in water in separate vessels, so constructed
as to allow of heat being applied thereto, yellow ferrocyanide of potassium,
protosulphate of iron, and sulphate of alumina, salts now used in the manu-
facture of prussian blue, and when at the desired degree of concentration I
pour them into a precipitating vat together with chromic acid and oxalic acid,
and excite their action by an electric current from the two poles of a battery
led into the vat, for a period depending upon the quantity operated upon. On
cutting off the electric current, the matters are allowed to precipitate for from
10 to 12 hours, the supernatant liquor is drawn off, and the precipitate with-
drawn from the vat. This precipitate is prussian blue in a more or less thick
paste, which is allowed to drain, then pressed and dried.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Bonnet Frédéric Brunel in the Great Seal Patent Office
on the 26th September 1856.
TO ALL TO WHOM THESE PRESENTS SHALL COME I, BONNET
FREDERIC BRUNEL, of Hampstead Road, in the County of Middlesex, Chemist,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-seventh day of March, in the year of our Lord
One thousand eight hundred and fifty-six, in the nineteenth year of Her reign,
did, for Herself, Iler heirs and successors, give and grant unto me, the said
Bonnet Frederic Brunel, Her special licence that I, the said Bonnet Frederic
Brunel, my executors, administrators, and assigns, or such others as I, the said
Bounet Frederic Brunel, my executors, administrators, and assigns, should at
any time agree with, and no others, froin time to time and at all times there-
after 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 OF PRUSSIAN BLUE,' upon the condition (amongst others)
that 1, the said Bonnet Frederic Brunel, 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 inime-
liately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Bonnet Frederic Brunel, 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 Invention consists in adding to the ingredients usually employed in the
manufacture of prussian blue, chromic acid and oxalic acid, in mixing the
whole together in a precipitating vessel, and in the application thereto of a
current of electricity.
I dissolve in water in separate vessels (so constructed as to allow of heat
being applied thereto) yellow ferrocyanide of potassium, protosulphate of
iron, and sulphate of alumina (salts now used in the manufacture of prussian
blue,) and when at the desired degree of concentration I pour them into a
precipitating vat together with chromic acid and oxalic acid, and excite their

page_text: action by an electric current from the two poles of a battery led into the vat,
for a period depending upon the quantity operated upon. On cutting off the
electric current, the matters are allowed to precipitate for from 10 to 12
hours (more or less), the supernatant liquor is drawn off, and the precipitate
withdrawn from the vat. This precipitate is prussian blue in a more or less
thick paste, which is allowed to drain, then pressed and dried.
Instead of placing in the precipitating vessel chromic acid previously prepared,
or in a state of acld, I sometimes place in the vessel bichromate of potassa,
which becoming decomposed in the course of the operation, chromic acid is
formed therefrom; or in other words, this acid is formed in the precipitating
vat itself, and answers precisely the same object as chromic acid previously
prepared would have done.
My Invention may be carried into effect in the following manner :—1
employ ferrocyanide of potassium, known as the yellow prussiate of potash
of commerce, protosulphate of iron (green copperas of commerce), sulphate
of alumina (alum), oxalic acid, and chromic acid; or I improve the product
by adding hydrochlorate of peroxide of manganese, in which case 1 adopt the
following proportions (though I do not confine myself thereto) :-
20 parts ferrocyanide of potassium,
30
30
23
"
3
"
3
"
14
גי
protosulphate of iron,
sulphate of alumina,
oxalic acid,
chromic acid, and add
hydrochlorate of peroxide of manganese; making
100
Or 20 parts ferrocyanide of potassium,
30
50
3
1
"
39
"
protosulphate of iron,
sulphate of alumina,
oxalic acid,
chronic acid

page_text: The foregoing proportions are not based on the weight or volume of the
substances in a solid state, but on the degrees of density of the matters in
liquid and of the solutions. To arrive at these proportions, I prepare a solution
of each salt in a separate vessel, and ascertain their respective densities by
means of Beaumé's arcometer; I then calculate their relative proportions,
whereby I determine the quantity of each solution I shall require. Thus, for
example, if the degrees indicated correspond precisely to the proportions given
above, and the vessels holding the solutions be filled equally, then the whole
of each solution would be required. (The peroxide of manganese should be
digested in hydrochloric acid;) or the proportions required of each solution
may be ascertained by calculating the degrees of concentration and taking as
a base the proportions I have just mentioned.
"But I occasionally vary the foregoing proportions; as for example, for
different shades of blue I increase the quantity of sulphate of alumina from
30 parts up to, say, 100 parts or more; again, when the protosulphate
of iron happens to be a subsalt, the quantity of hydrochlorate of manganese
should be increased to, say, 20 parts, to make up for the deficiency of acid;
but when a supersalt, the quantity may be diminished to 8 parts. I prefer to
use filtered or potable water for the purposes of my Invention. Having thus
jrepared the solutions in separate vessels, and ascertained the quantities I shall
require of cach, I first introduce into a precipitating vat the proper propor-
tions of the ferrocyanide of potassium, protosulphate of iron, and sulphate of
alumina, and stir them well together to facilitate their combination and
chemical action; I then lead the two poles of a powerful battery into the
precipitating vat, and pass electric currents through the solutions all the time
they are being poured in; after the whole is in, I stir the mixture for about
a quarter of an hour, (more or less,) and add (in their respective proportions)
first the oxalic acid, then the hydrochlorate of manganese, and lastly the
chromic acid or bichromate of potassa, keeping up the electric currents the
whole time and stirring at intervals. About ten minutes. after adding the
bichromate of potassa the electric current is cut off.
The matters are then left to precipitate or deposit for 10 to 12 hours,
and the supernatant liquid drawn off. The sediment deposited is prussian
blue, which should be left to drain for about forty-eight hours on cloth or other
porous material, next subjected to pressure, and then dried in a drying
chamber or otherwise. If preferred, however, the pressing may be dispensed
with. The quantity and intensity of the electric currents are regulated
according to the quantity and dégree of concentration of the liquid matters

page_text: under treatment; the higher the degree of concentration the more energetic
should the current be.
The currents of electricity used in my process exert a vigorous action on
the saline molecules, which they separate or tear into the most minute particles
conceivable, and carry them through the excipient liquid, wherein some are
attracted to the positive and others to the negative pole, throwing them into
continuous contact, which facilitates the chemical action of the matters upon
each other. The currents of electricity also decompose the water in the pre-
cipitating vat, and resolve it into its constituent gases, hydrogen and oxygen.
A portion of the oxygen passes to the iron and increases its oxidation, while
the hydrogen is liberated and allowed to escape.
The electric currents, morcover, decompose the hydrochloric acid into its
constituents, hydrogen and chlorine. When I employ bichromate of potassa,
the currents of electricity, aided by the sulphuric acid, (and also by the hydro-
chloric acid, when hydrochlorate of peroxide of manganese is used,) decompose
the bichromate of potassa, and the sulphuric and hydrochloric acids combining
with the potassa and oxide of the bichromate, liberate the chromic acid in the
course of the operation, in which it answers the same purpose as chromic acid
would have done if previously placed in the vat in a state of acid, as before
stated. I thus obtain a cheap chromic acid. When the chromic acid passes
on to the iron, bydrocyanic acid is produced.
The electric currents also decompose the hydrochloric acid into its con-
stituents hydrogen and chlorine, and thus chlorine may be obtained from the
mixture. To the employment of chromic acid, the process is indebted for the
rapidity with which the blue color is obtained when protosulphate of iron is used,
the oxide of which is in the first stage of oxidation of which that salt is sus-
ceptible. I employ oxalic acid for the purpose of dissolving the heterogeneous
and extraneous matters with which the protosulphate of iron of commerce is
commonly combined, as during crystallization iron is collected in a state of
oxide, or in a state of sulphuret when the sulphate is made from ferruginous
pyrites. By means of my Invention, not only are time and labor saved in the
process of manufacturing prussian blue, but a stronger and better, as well as
cheaper color is produced.
And having now described the nature of the said Invention, and in what
manner the same may be performed, I declare that I claim,-
First, the employment in the manufacture of prussian blue of oxalic acid
and chromic acid in addition to the ingredients hitherto usually employed,
and the passing of currents of electricity into and among the same.

page_text: And, second, the manufacture of prussian blue in the manner heroin-before
particularly described.
In witness whereof, I, the said Bonnet Frederic Brunel, have hereunto
set my hand and seal, this Twenty-sixth day of September, One thousand
cight hundred and fifty-six.
BRUNEL. (L.S.)