IMPROVEMENTS IN PRODUCING SULPHO COLOURING MATTERS BY ELECTROLYSIS
Year: 1884

page_text: I EMIL CAPITAINE of 89 Chancery Lane in the County of Middlesex, Civil
engineer, do hereby declare the nature of the said invention for IMPROVEMENTS IN
PRODUCING SULPHO COLOURING MATTERS BY ELECTROLYSIS to be as follows:-
My invention is based on the following observations :
If two plates of platina which constitute the two poles of an electric generator
are immersed in a solution of sulphide of hydrogen of Paramidodimethylaniline in
diluted sulphuric acid an active development of hydrogen is to be observed on the
cathode (negative pole) while the fluid around the anode (positive pole) is getting
blue.
This blueing ceases however in a short time and the platina plate of the positive
pole becomes covered with a grey coating. If the platina-plate is cleaned by
means of a small brush or otherwise of this grey coating the blueing begins again
ceasing however after a short time. If this cleaning of the platina plate by the
brush is continued so that the platina is kept bright, then in a little while under
continuous evolution of hydrogen at the negative pole the whole of the sulphide of
hydrogen disappears from the fluid and the fluid commences to take a blue colour.
The fluid now contains chiefly methylen white in solution.
Upon continuing the electrolysis the fluid continues up to a certain point to
become a darker blue colour, at which point the deepening of the colour ceases.
Instead of sulphide of hydrogen, sulphocyanic acid (rhodanwasserstoff) persul-
phide of hydrogen, or sulfocarbonic acid may be employed, in fact, any combinations
which upon electrolysis in acidulated solution, eliminate sulphur at the positive
pole.
Treated in the same manner all the paramido derivates of primary, secondary
and tertiary aromatic amines give from violet to greenish blue colours. Those from
paramidophenylamine, etcetera, are insoluble in water.
The production of sulphurous colouring matters by electrolysis under the before-
mentioned conditions is not confined to the amido derivatives of aromatic amines

page_text: but may include the leuco combinations (Leuko-verbindungen) of the bodies which
belong to the dimethylaniline green group, as also the hydrazo-dimethylaniline,
etcetera.
I will now describe the practical application of my invention:
In a wooden coop preferably coated over with varnish is fitted an insulated
rotary wooden shaft which is provided with three wooden wings which serve for
stirring the fluid; on the same shaft are mounted two other wings one above the
other in the same direction, which at the sides standing towards each other are
furnished with bristles or hair.
Further two horizontal copper plates coated with platina are placed in the
wooden coop opposite each other, reaching with their upper ends nearly to the axle
and arranged in such a manner that by the rotation of the axle the two brushes
are to pass every part of the two sides of the plates and remove in this way
continually the film or residue covering the platina.
Those plates form the electrodes of an electro dynamic machine.
If a dynamo-machine is used with changing currents then of course each plate
serves alternately as anode and cathode.
The wooden coop is filled by a solution of one part amidodimethylaniline in
40 parts water and 4 prts sulphuric acid of 66° Bé. Then a solution of sulphide
of sodium is gradualy infused into the fluid in such a manner that while the
stirring apparatus and the dynamomachine are in action the fluid becomes
thoroughly saturated by the sulphide of sodium without material escape of sulphide
of hydrogen.
From time to time the fluid is tested then the further supply of the solution of
sulphide of sodium is ceased, and, without interruption of the electric current an
energetic current of air is passed through the fluid.
Now the blueing of the fluid begins and as soon as the growing of intensity of
the blue colouring ceases the electric current is interrupted as well as the entrance
of air.
The pure colouring matter is then extracted from the solution in the known and
usual manner. Instead of platinised copperplates any other electrode may be used,
for instance such as of silver, lead, carbon etc.
In a solution of hydrochloric acid the methylenwhite or methylenblue which is
originated becomes destroyed to the greater part by the formation of chlorine or
chloric acids.
The electrolysis may be adapted in different modifications with regard to the
concentration of the solution or the construction of the apparatus without inter-
ference with the nature of our method of producing sulphurous colours by the
electrolytical proceeding.
For instance it may be executed in the following manner: A suitable vessel A
(the fluids of which communicate with the fluids of a vessel B by means of a
siphon or connecting-tube or a porous cell or a parchment membrané etc. in such
a manner that they are in electric communication) contains a solution of diamine
(diamin) and the anode while the other vessel B contains diluted sulphuric acid or
a solution of nitrosodimethylanilin and the cathode.
During the time that in the vessel A methylenblue is originated a partial reduc-
tion of Nitrosodimethylanilin takes place in the vessel B.
Instead of continuing with the electrolysis until methylenblue is originated, it
may then of course be interrupted and the methylen white which has been formed
may be reduced by oxydation to methylenblue but the reduction of methylenwhite
to methylenblue by oxydation is more expensive than by means of the electrolysis.
128

page_text: "
I EMIL CAPITAINE, of 89 Chancery Lane, in the county of Middlesex, Civil
Engineer, do hereby declare the nature of this invention for "IMPROVEMENTS IN
PRODUCING SULPHO COLOURING MATTERS BY ELECTROLYSIS and in what manner
the same is to be performed, as communicated to me from abroad by Ewer and Pick,
of Berlin, Prussia, to be particularly described and ascertained in and by the
following statement :-
Our invention is based on the following observations:
If two plates of platinum, constituting the poles of an electric circuit, be
immersed in a solution of paramido-dimethyl-aniline in dilute sulphuric acid and
which contains sulphide of hydrogen, a rapid evolution of hydrogen takes place on
the negative pole, while the liquid around the positive pole assumes a blue colour.
But this colour soon vanishes again, and the platinum plate of the positive pole
becomes covered with a grey film. If this film is removed by means of a brush or
otherwise, the blue colour will be formed anew, but soon disappear again. If,
however, the platinum plate be maintained bright by constant brushing, the
sulphide of hydrogen will, in a short time, have become decomposed under con-
tinuous evolution of hydrogen at the negative pole, and the blue colour which then
sets in does not disappear again. When the liquid thus commences to become blue,
it mainly contains the leuco-compound of methylene-blue, i.e. methylene-white,
which has been formed by the electrolytic process from the paramido-dimethyl-
aniline and the sulphide of hydrogen. By continued application of the current,
after the sulphide of hydrogen has been wholly decomposed into sulphur and
hydrogen, the said methylene-white is converted into methylene-blue. As the
process progresses the colour of the liquid gradually becomes deeper, and when no
further increase of intensity takes place, the operation is finished.
Instead of sulphide of hydrogen, all other sulphurous compounds may be
employed, which, when subjected in acid solution to the electric current, separate
out sulphur on the positive pole, as for instance persulphide of hydrogen and sulfo-
carbonic acid.
This treatment may be applied to any of the paramido-derivatives of primary,
secondary and tertiary aromatic amines, and also to the hydrazo-compounds of the
latter class of amines. The colours thus obtained from the different substances
vary from violet to greenish blue. Those produced from paramido-diphenyl-amine
and from the homologues thereof, are insoluble in water.
Instead of the sulphuric acid herein before mentioned, hydrochloric acid may be
used; but in this case protochloride of iron has to be added for absorbing and
thereby rendering innocuous the chlorine, and the chloric and perchloric acids
originating from the hydrochloric acid, and which would otherwise decompose the
methylene-white as well as the methylene-blue.
On the annexed sheet of drawings Figs 1 and 2 represent, respectively in vertical
sectional view and in plan, an apparatus for carrying out the process. Fig. 3 shows
a modification thereof.. f is a wooden vat preferably coated with varnish and

page_text: adapted to contain the substances to be treated. Within the same there is an
insulated wooden shaft l, having the arms i for stirring the liquid, and the arms m
arranged in pairs one above the other, and provided on their opposite faces with
bristles so as to form brushes for cleaning the electrodes. The latter consist in the
platinized copper plates n and o. These are fixed to the vat f, and extend from
the walls thereof nearly to the shaft L, and they are placed in horizontal position
at such a height, as that, when the shaft / rotates, the brushes on the arms m will
sweep off from both surfaces of the same all deposits that may form thereon. The
said plates are connected by the conductors o¹ and n¹ to the two poles of a dynamo-
machine. The currents produced by this machine may be of uniform or of alter-
nating direction. The vat is closed by a cover g through which passes a pipe h for
the introduction of the liquid materials. k is a pipe for conducting away the gases
evolved during the process, and c a pipe for introducing air.
Supposing the substance to be decomposed be paramido-dimethyl-aniline, and
that, for producing the requisite sulphide of hydrogen, sulphide of sodium be
employed, the process is carried out by means of the described apparatus in the
following manner. A solution of one part of the said substance in fourty parts of
water and four parts of sulphuric acid of 66° Beaumé having been run into the
vat, and the stirring-apparatus as well as the dynamo-machine being in motion, the
sulphide of sodium dissolved in water is added slowly and in such quantity that
the liquid will become and remain as much as possible saturated with the sulphide
of hydrogen generated, but that no considerable quantity of the latter will escape.
From time to time the liquid is tested, and if it is found that it contains, besides
the leuco-compound of methylene-blue, i.e. methylene-white, but very little
paramido-dimethyl-aniline, the supply of sulphide of sodium is stopped. The
residual sulphide of hydrogen, which is now no more required, may be eliminated
by electric decomposition, but I prefer to remove the same by passing a strong
The liquid
current of air through the liquid by means of the aforesaid pipe c.
will then, under the continued action of the electric current, soon commence to
become blue. When the intensity of the colour does not increase any more, the
electric current and the introduction of air are stopped.
From the solution thus obtained the colouring substance, or methylene-blue, is
precipitated in known manner by chloride of zinc and chloride of sodium.
Instead of the platinized plates of copper, electrodes made of other suitable
substances, such as silver, lead or carbon may be used.
The described electrolytic process may be carried out with various modifications
respecting the apparatus employed, or the details of the mode of operation, without
departing from the nature of the invention.
The apparatus shown by Fig. 3 consists of a receptacle divided into two cham-
bers a and b by means of a wall made of materials through which a contact of the
liquids with each other can take place, such as unglazed earthenware, wood or
parchment-paper. In the drawing the wall is supposed to be made of earthenware
plates fitted into the wooden frameworks 8. Both chambers are provided with
a stirring and brushing apparatus alike to the one described; but in either chamber
there is one electrode only.
This apparatus is designed not only for obtaining methylene-blue, but also for
producing from nitroso-dimethyl-aniline the paramido-dimethyl-aniline required for
generating the former. The procedure for this purpose is as follows. The
chamber a is filled with a solution of paramido-dimethyl-aniline, and the chamber b
with a solution of nitroso-dimethyl-aniline, both solutions being prepared with
diluted sulphuric acid. Into the chamber a an aqueous solution of sulphide of
sodium is then allowed to flow, while the stirring-apparatus and the dynamo-
machine are put in action, the current from the latter being so directed that the
plate o of the chamber a will be the positive electrode and the plate n of the
chamber b the negative electrode. Under these conditions methylene-blue will be
formed in the chamber a, while the nitroso-dimethyl-aniline contained in b, is
converted into paramido-dimethyl-aniline. Thereupon chamber a is filled with

page_text: solution of nitroso-dimethyl-aniline, and the process repeated with inverted electric
current, so that n is now the positive, and o the negative electrode. The paramido-
dimethyl-aniline produced during the first process then serves for the formation of
methylene-blue, while the new portion of nitroso-dimethyl-aniline in a is again
converted into paramido-dimethyl-aniline, to serve in a third operation, and so on.
Instead of using porous plates and the like for allowing the liquids in the two
chambers to come in contact with each other without mixing, a communication
may be established between the chambers by a bent pipe, such as the pipe p, shown
in dotted lines in Fig. 3. Through this pipe the electric current will pass from
one liquid to the other without that any appreciable amount of mixing of the
liquids takes place.
Having thus particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, as communicated to
me by my correspondents, I declare that what I claim is
The process of producing sulphurous colours and their leuco-compounds from
paramido-derivatives of primary, secondary and tertiary aromatic amines and from
the hydrazo-compounds of the latter, by electric decomposition in acidulated
solution, in the presence of such sulphurous substances as, under the action of the
electric current, separate out sulphur on the positive pole, substantially as herein-
before described.