IMPROVEMENTS IN THE METHOD OF RECOVERING INDIGO, WHICH METHOD IS ALSO APPLICABLE FOR OTHER PURPOSES
Year: 1878

page_text: LETTERS PATENT to Frank Wirth, of the Firm of Wirth and Company, Patent
Solicitors, at Frankfort-on-the-Main, in the Empire of Germany; for the Inven-
tion of "IMPROVEMENTS IN THE METHOD OF RECOVERING INDIGO, WHICH
METHOD IS ALSO APPLICABLE FOR OTHER PURPOSES." A communication from
Ferdinand Victor Kallab, Chemist, of Wiese, in the Empire of Austria.
PROVISIONAL SPECIFICATION left by the said Frank Wirth at the Office of
the Commissioners of Patents on the 22nd April 1878.
FRANK WIRTH, of the Firm of Wirth and Company, Patent Solicitors, at
Frankfort-on-the-Main, in the Empire of Germany. "IMPROVEMENTS IN THE METHOD
OF RECOVERING INDIGO, WHICH METHOD IS ALSO APPLICABLE FOR OTHER PURPOSES."
[A communication from Ferdinand Victor Kallab, Chemist, of Wiese, in the Empire
of Austria.]
This Invention relates to the recovering of indigo from textile fibres which have
been dyed with indigo blue, and which for any cause cannot further be employed
in their dyed state, whilst the indigo being a very durable colour is unaltered, even
if its vehicle has by wear or for any other cause become valueless.
The Invention relates further to the recovering of the indigo from the washing
water and the fulling lye of woollen fabrics or threads which are dyed with indigo
blue, and which by the washing and fulling process loose a certain part of the
indigo, the latter having been imperfectly fixed to the fibre.
The Invention further relates to the recovering of the fatty matter with which
the said textile matter has been impregnated, this recovering of the fatty matter
being a continuation of the said process of recovering indigo blue.
In carrying the said Invention into practice hydrosulphurous acid is used' with or
without alkaline baths.
I desire it to be understood that although this Invention relates to indigo, and
to the use of hydrosulphurous acid, it is thoroughly different to and independent of

page_text: the well-known process of "Schützenberger & de Lalande," which process has for
its object the dyeing of textile fibre with, indigo blue, and by which the indigo is
the means for obtaining a certain result, whilst the present Invention consists in a
process for recovering the indigo from the dyed fibre, in which process the indigo is
the product to be obtained.,
The hydrosulphurous acid is in this Invention preferably employed as a salt of
sodium.
For recovering the indigo from textile fibres the operation is in some way different,
according to the nature of the fibre to be treated.
For recovering the indigo from woollen fibre the proceeding is as follows, that is
to say-A bath of hydrosulphite of from 1/2 to 2° B. is heated to from 40 to 60° C.,
and as much crystallized soda is added as will make the temperature of the bath
3° B. A bath so prepared I term the "reducing bath." The fibre having pre-
viously been cleaned is steeped in this bath, in which the indigo is reduced and
partially dissolved, so that both the bath and the fibre become yellow. The indigo
being but partially separated from the fibre the latter is quickly pressed out, and
brought into a bath containing from 1 to 2% of carbonate of alkali or of caustic
ammoniac, and which is heated to 60° C. Care is to be taken that by the tran-
sportation of the fibre from one bath to another the fibre is prevented from coming
in contact with the atmospheric air. In this alkaline bath the whole quantity of
indigo is separated from the fibre, when the latter is rinsed in running water, and
utilized in any desired manner. If the fibre has been impregnated with fatty
matter the latter is now contained in the recovering baths, and is by means of caustic
lime precipitated therefrom as an insoluble lime soap.
°
For recovering the indigo from silk fibre a bath of hydrosulphite of from 1/2 to
1° B., to which a small quantity of carbonate of ammonium is added, will suffice.
The "alkaline" bath is dispensed with.
For recovering the indigo from cotton or linen fibre the baths may, if desired, be
more concentrated, and contain a larger quantity of alkali; but, by reason of the indigo
being in cotton or linen fibres more on the surface of the fibre, its separation there-
from is not so difficult, and even hydrosulphite baths to which the alkali is added
for B., and which have the ordinary temperature will suffice. An elevation
of the temperature, however, will expedite the process.
The best results are obtained by a bath of hydrosulphite of from 1/2 to 1° B.,
which by the addition of caustic soda has been brought to 3° B., and the tempera-
ture of which is from 50 to 100° C. The "alkaline bath" may be a weak milk of
lime, warm or cold.
The indigo is by oxidation obtained as indigo blue out of the hydrosulphite bath
saturated with reduced indigo. For this purpose the liquid is brought in contact
with the atmospheric air. The precipitated indigo blue is washed, and then brought
into the consistency of dough, or in the form of powder.
The indigo contained in the alkaline bath becomes deposited on the bottom, and
after the deposition of the indigo the liquid is drawn off, and used anew as an
alkaline bath.
The above-described processes can also be used for the partial separation of the
indigo from textile matter, which has been dyed by indigo blue to a too dark colour:
The same can further be employed for separating the indigo from printed fabrics,
the patterns of which are out of fashion, and which in consequence cannot be sold
in this state, and the processes can also be employed for equalizing textilé matters
which have spots, or are unevenly dyed.
The indigo is recovered out of the washing water and fulling lye of indigo dyed
woollen fabrics in the following manner :-The washing water or fulling lye having
by filtering been freed from the particles of woollen fibre kept in suspension is
treated by a surplus of an acid (muriatic acid), in consequence whereof the fatty
matters contained therein become separated, and rise to the surface of the liquid;
and at the moment of their separation they take the indigo with them. The blue-
grey substance obtained by this means is washed with water for removing the acid;

page_text: and then it is cooked during from half an hour to an hour by adding successfully
as much soda lye of 10%, as is wanted for complete saponification. In this mixture
of solution of soap and indigo successfully as much hydrosulphite of sodium and
caustic soda lye is added as will cause the liquid to become of a yellow colour, when
the soap by means of chloride of sodium is salted out when it appears as a coagulum
on the surface of the liquid. The lower lye is now drawn off, and cleaned by a lye
of sodium and hydrosulphite. The indigo is by oxidation separated from the lower
lye as indigo blue, and is allowed to set on the bottom when the liquid is drawn
off, and the indigo blue after having been washed brought to a doughy consistency
or powdery form.
The regeneration of the bars of hydrosulphite is effected in the following manner;
namely By the above-described process of reduction of indigo blue to reduced
indigo the hydro-sulphurous acid, that is to say, the hydrosulphite of sodium, is by the
addition of oxygen converted into sulphurous acid, that is to say, into bisulphite of
soda. Oxidized indigo recovery baths contain in consequence, after the indigo blue
has been removed, principally sulphite of soda and a surplus of carbonate of soda, or
of caustic soda.
By the preparation of the hydrosulphite of soda the resulting sediment contains
besides oxide of zinc and a surplus (if any) of hydro-oxide of calcium a considerable
quantity of sulphite of calcium. The latter is formed by the addition of milk of line
with the liquid resulting from the action of the zine to bisulphite of soda, because
this liquid contains besides hydrosulphite of soda a double salt, namely, Zn SO, +
Na O, SO,.
The sediment containing sulphite of calcium is treated by the double weight of a
solution of crystallized soda of 10° B. by intermitting stirring when the calcium
sulphite, together with the solution of bicarbonate of soda, is decomposed into
sulphite of soda which dissolves, and into insoluble carbonate of calcium.
The sulphite of soda can in the well-known manner be converted into bisulphite
of soda. This latter can also be obtained by decomposing by muriatic acid a part
of the sediment which contains sulphite of calcium, and by conducting the
developed sulphurous gas into the solutions of sulphite of sodium obtained in both
manners.
The bisulphite of soda is by means of zinc converted into bydrosulphite, which
can be used again for recovering indigo.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Frank Wirth in the Great Seal Patent Office on the 18th October
1878.
FRANK WIRTH, of the Firm of Wirth and Company, Patent Solicitors, at
Frankfort-on-the-Main, in the Empire of Germany. "IMPROVEMENTS IN THE METHOD
OF RECOVERING INDIGO, WHICH METHOD IS ALSO APPLICABLE FOR OTHER PURPOSES."
A communication from Ferdinand Victor Kallab, Chemist, of Weise, in the Empire
of Austria.
This Invention relates to the recovering of indigo from textile fibres which have
been dyed with indigo blue, and which for any cause cannot further be employed
in their dyed state, whilst the indigo being a very durable colour is unaltered, even
if its vehicle has by wear or for any other cause become valueless.
The Invention further relates to the recovering of the indigo from the washing
water and the fulling lye of woollen fabrics or threads which are dyed with indigo
blue, and which by the washing and fulling process lose a certain part of the indigo,
the latter having been imperfectly fixed to the fibre.
The Invention further relates to the recovering of the fatty matter with which
the said textile matters has been impregnated, this recovering of the fatty matter
being a continuation of the said process of recovering the indigo blue.
In carrying the said Invention into practice hydrosulphurous acid is used with or
without alkaline baths.
I desire it to be understood that although this Invention relates to indigo, and
to the use of hydrosulphurous acid, it is thoroughly different to and independent of
the well-known process of "Schützenberger & de Lalande," which process has for
its object the dyeing of textile fibre with indigo blue, and by which the indigo is
the means for obtaining a certain result, whilst the present Invention consists in a
process for recovering the indigo from the dyed fibre, in which process the indigo is
the product to be obtained.
The hydrosulphurous acid is in this Invention preferably employed as a salt of
sodium.
For recovering the indigo from textile fibres the operation is in some way
different, according to the nature of the fibre to be treated.
For recovering the indigo from woollen fibre the proceeding is as follows, that is
to say A bath of hydrosulphite of from 1/2 to 2° Be is heated to from 40 to 60° C.,
and as much crystallized soda is added as will make the temperature of the bath
3° B. A bath so prepared I term the "reducing bath." The fibre having pre-
viously been cleaned is steeped in this bath, in which the indigo is reduced and
partially dissolved, so that both the bath and the fibre become yellow. The indigo
being but partially separated from the fibre the latter is quickly pressed out, and
brought into a bath containing from 1 to 2% of carbonate of alkali or of caustic
ammoniac, and which is heated to 60° C. Care is to be taken that by the trans-
portation of the fibre from one bath to anotherthe, fibre is prevented from coming
in contact with the atmospheric air. In this alkaline bath the whole quantity of
indigo is separated from the fibre when the latter is rinsed in running water, and
utilized in any desired manner. If the fibre has been impregnated with fatty
matter, the latter is now contained in the recovering baths, and is by means of
caustic lime precipitated therefrom as an insoluble lime soap.
For recovering the indigo from silk fibre a bath of hydrosulphite of from 1 to
1° B., to which a small quantity of carbonate of ammonium is added will suffice.
The "alkaline bath" is dispensed with.
For recovering the indigo from cotton or linen fibre the baths may, if desired, be
more concentrated, and contain a large quantity of alkali; but, by reason of the
indigo being in cotton or linen fibres more on the surface of the fibre, its separation
therefrom is not so difficult, and even hydrosulphite baths, to which the alkali is

page_text: added for
B., and which have the ordinary temperature will suffice. An ele-
vation of the temperature, however, will expedite the process.
The best results are obtained by a bath of hydrosulphite of froni 1 to 1° Bº.,
which by the addition of caustic soda has been brought to 3° Bo., and the tempera-
ture of which is 50 to 100° C. The "alkaline bath may be a weak milk of lime,
warm or cold.
The indigo is by oxidation obtained as indigo blue out of the hydrosulphite bath
saturated with reduced indigo. For this purpose the liquid is brought in contact
with the atmospheric air. The precipitated indigo blue is washed, and then brought
into the consistency of dough, or in the form of powder.
The indigo contained in the alkaline bath becomes deposited on the bottom, and
after the deposition of the indigo the liquid is drawn off, and used anew as an
alkaline bath.
The above-described processes can also be used for the partial separation of the
indigo from textile matter, which has been dyed by indigo blue to a too dark colour.
The same can further be employed for separating the indigo from printed fabrics,
the patterns of which are out of fashion, and which in consequence cannot be sold
in this state, and the processes can also be employed for equalizing textile matters
which have spots, or are unevenly dyed.
The indigo is recovered out of the washing water and fulling lye of indigo dyed
woollen fabrics in the following manner:-The washing water or fulling lye having
by filtering been freed from the particles of woollen fibre kept in suspension is
treated by a supply of an acid (muriatic acid), in consequence whereof the fatty
matters contained therein become separated, and rise to the surface of the liquid;
and at the moment of their separation they take the indigo with them. The blue-
grey substance obtained by this means is washed with water for removing the acid,
and then it is cooked during from half an hour to an hour by adding successively
as much soda lye of 10% as is wanted for complete saponification. In this mixture
of solution of soap and indigo successively, as much hydrosulphite of sodium and
caustic soda lye is added as will cause the liquid to become of a yellow colour, when
the soap by means of chloride of sodium is salted out when it appears as a coagulum
on the surface of the liquid. The lower lye is now drawn off, and cleaned by a lye
of sodium and hydrosulphite. The indigo is by oxidation separated from the lower
lye as indigo blue, and is allowed to settle on the bottom when the liquid is drawn
off, and the indigo blue after having been washed brought to a doughy consistency
or powdery form.
The regeneration of the baths of hydrosulphite is effected in the following manner,
namely By the above-described process of reduction of indigo blue to reduced
indigo the hydrosulphurous acid, that is to say, the hydrosulphite of sodium is by
the addition of oxygen converted into sulphurous acid, that is to say, into bisulphite
of soda. Oxidized indigo recovering baths contain in consequence, after the indigo
blue has been removed, principally sulphite of soda and a surplus of carbonate of
soda or of caustic soda.
By the preparation of the hydrosulphite of soda the resulting sediment contains
besides oxide of zinc and a surplus (if any), of the hydro-oxide of calcium a con-
siderable quantity of sulphite of calcium. The latter is formed by the addition of
milk of lime with the liquid resulting from the action of the zinc into bisulphite of
soda, because this liquid contains, besides hydrosulphite of soda, a double salt,
namely, Zn SO, +Na O, SO...
The sediment containing sulphite of calcium is treated by the double weight of a
solution of crystallized soda of 10° Bo. by intermitting stirring when the calcium
sulphite, together with the solution of bicarbonate of soda, is decomposed into
sulphite of soda, which dissolves, and into insoluble carbonate of calcium."
The sulphite of soda can in the well-known manner be converted into bisulphite
of soda. This latter can also be obtained by decomposing by muriatic acid a part
of the sediment which contains sulphite of calcium, and by conducting the

page_text: developed sulphurous gas into the solutions of sulphite of sodium obtained in both
manners.
:
The bisulphite of soda is by means of zinc converted into hydrosulphite, which
can be used again for recovering indigo.
Having thus fully described the said Invention, and the manner of performing
the same, I wish it understood that I claim,-
First. For recovering indigo from textile fibres which have been dyed with
indigo blue the employment. of hydrosulphurous acid or its salts to extract the
said indigo, whilst the fibres remaining intact can again be used for any further
purpose.
Second. Recovering in the manner above set forth indigo from the washing water
and the fulling lye of woollen fabrics or threads which are dyed with indigo blue,
and which by the washing and fulling process lose a certain part of the indigo, the
latter having been imperfectly fixed to the fibre.
Third. The regeneration of the baths of hydrosulphite in the manner above set
forth.
In witness whereof, I, the said Frank Wirth, have hereunto set my hand and
seal, this Fifteenth day of October, in the year of our Lord One thousand
eight hundred and seventy-eight.
FRANK WIRTH. (L.S.)
2