IMPROVEMENTS IN BLEACHING ANIMAL FIRER
Year: 1876

page_text: LETTERS PATENT to Frank Wirth, of the Firm of Wirth and Company, Patent
Agency, of Frankfort-on-the-Maine, in the Empire of Germany, for the
Invention of "IMPROVEMENTS IN BLEACHING ANIMAL FIRER." A communi-
cation from Ferdinand Victor Kallab, Chemist, residing at Wiese, in the Empire
of Austria.
Sealed the 6th April 1877, and dated the 9th October 1876.
PROVISIONAL SPECIFICATION left by the said Frank Wirth at the Office of
the Commissioners of Patents on the 9th October 1876.
FRANK WIRTH, of the Firm of Wirth and Company, Patent Agency, of Frankfort-
on-the-Maine, in the Empire of Germany. "IMPROVEMENTS IN BLEACHING ANIMAL
FIBER."
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This Invention has for its objects improvements in the method of bleaching
animal fibre, such as wool, woollen thread, woollen fabrics, waste wool, silk thread,
silk fabrics, waste silk. The material to be bleached is first thoroughly cleansed
from all impurities by being scoured, and the gum removed by boiling and other
processes as ordinarily used and practised. A wooden vessel is then taken which
be securely closed by a cover, and in it is placed a solution of 1° 4° Beaumé
of freshly prepared bi-hydrosulphite of sodium in pure water. To this solution is
added acetic acid of 50° in the proportion of 5 to 20 cubic centimetres (305 to 1.22
cubic inches) to every litre (176 pints) of the solution, the proportion varying
according to the quantity of the hydrosulphite in the latter. The whole is then
thoroughly stirred and the material to be bleached, having been previously wetted,
is immersed in it.
The strength or concentration of the bleaching bath prepared as described depends
upon the more or less yellow colour of the material to be treated, but it does not
exceed the limits already given. The vessel containing the solution is tightly closed,
care being taken that the material to be bleached is always covered by the liquid.
After the material has been treated, as described, for a time varying from 24 to 48
hours, it is thoroughly bleached and is removed from the vessel. It is then washed
first in a weak solution (one-quarter to one-half per cent.) of crystallized soda at
ordinary temperature, and then in running water until thoroughly clean. It is
finally dried in the open air or in a drying chamber heated to 30° to 35° centigrade.
[Price 4d.]

page_text: If the material heated as described is not sufficiently white, the process is
reapeated.
It is desirable (especially if silk is the material to be treated) that the process
should be performed in a succession of baths of decreasing density.
The improved process, as above described, is based upon the property of hydro-
sulphurous acid of entering with the animal fibre into chemical combination, which
is separated from the fibre during the bleaching process.
The improved method of bleaching, as described, is novel, easily worked, and not
expensive; it produces, especially in wool, a whiteness which (by the transparency
of the fibre) attains thoroughly the result desired without affecting the softness,
elasticity, and other useful qualities of the fibre.
It is also preferable to the processes heretofore ordinarily adopted and used, as
regards its effect upon the health of the workmen employed.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Frank Wirth in the Great Seal Patent Office on the 9th April 1877.
FRANK WIRTH, of the Firm of Wirth and Company, Patent Agency, of Frankfort-
on-the-Maine, in the Empire of Germany. "IMPROVEMENTS IN BLEACHING ANIMAL
FIBRE." A communication from Ferdinand Victor Kallab, Chemist, residing at
Wiese, in the Empire of Austria.
This Invention has for its objects improvements in the method of bleaching
animal fibre, such as wool, woollen thread, woollen fabrics, waste wool, silk thread,
silk fabrics, waste silk, in a more economical and effective manner than by the
methods heretofore ordinarily used and practised.
The Invention consists in the use for the said purpose of hydrosulphurous acid in
the form of an acid salt, namely, bi-hydrosulphite of sodium (bi-hydrosulphurous
sodium) in combination with the addition of very small quantities of indigo blue
permanently fixed for the purpose (which I call " azurage") described in the
following Specification.
In order to bleach animal fibres sulphurous acid has heretofore been commonly
used, either in the form of gas or as a solution of the said sulphurous acid gas in
water; and in the latter case sulphurous or bi-sulphurous natrium (soda) has often
been employed, to a solution of which in water muriatic acid or sulphuric acid is
added in order to set free the sulphurous acid.
As by the bleaching process described the animal fibres are rendered colourless,
and in consequence of their transparency have even a somewhat yellow appearance,
I add and incorporate with the fibre a violet colour (the complementary colour to
yellow) in order to obtain a wholly white appearance of the fibre. This incor-
poration of the complementary colour I term "azurage," as already described, and it
may be imparted to the fibre either before the bleaching (in the case of
sulphuration) or after the bleaching, by means of blue or violet dyeing matters or
by means of mechanically fixed dyes (such, for instance, as ultramarine); but this
dyeing process is not an absolutely permanent one, as it is unable to resist the
action of the atmosphere or alkaline washing baths.
Before proceeding to a more complete description of the Invention and of the
manner in which it is to be performed, I will point out the differences which exist
between it and other methods hitherto used and practised.
Hydrosulphurous acid is distinguished from sulphurous acid principally by the
fact that the former cannot exist in a free state, since if it is set free from its
compounds by the addition of a strong mineral oxide (such as muriatic or sulphuric
acid) it is decomposed into sulphurous acid and sulphur, in the same manner as is
the case with hyposulphites; moreover bydrosulphurous acid is distinctly different
from hyposulphurous acid (which gives only neutral salts), as only the former
reduces indigo blue to indigo white.

page_text: In order to put this Invention in operation, the bi-hydrosulphurous sodium to be
employed for the bleaching process is preferably made as short a time as possible
before it is required to be used. It is made by adding to a concentrated solution of
bi-sulphite of sodium metallic zinc. These two substances are allowed to act upon
one another for about an hour in a closed vessel, the liquid being occasionally
agitated. The mixture is then allowed to settle and the clear liquid is drawn off,
the latter containing as well as acid hydrosulphite of sodium a small quantity of
dissolved zinc.
The bleaching process is as follows:-The fibre to be bleached is first cleaned
from fatty, starchy, and gummy matters and other impurities by boiling or other
suitable means, as ordinarily used, and it is then placed whilst thoroughly wet in a
bath of clear cold water to which has previously been added a small quantity of
finely ground indigo, preferably of a kind which gives a lustrous red-blue. The
fibre is quickly drawn through this bath in order that it may become regularly
coated with indigo, and it is then removed to the bleaching bath. The bleaching
bath is prepared by placing a sufficient quantity of clear water at ordinary temper-
ature in a wooden vessel which can readily be tightly closed. To the water is
added sufficient bi-hydrosulphite of sodium to give the solution a strength of 1-4°
Beaumé. From 5 to 20 cubic centimetres (305 to 1.22 cubic inches) (according to
the quantity of the hydrosulphite to be used) of acetic acid of 50° thoroughly free
from strong mineral acids are to be added, and the whole is then well stirred and
the fibro immersed. During the bleaching process which now takes place the vessel
must be closed in order to exclude atmospheric air. The effect of the bleaching
bath begins to appear at once, but the time required to complete it varies with the
fibre treated, so that in many cases it may be advisable to leave the fibre immersed
for twelve to twenty-four hours or more.
In order to ascertain whether the bleaching process is completed, a small quantity
of the fibre is taken out, rinsed in water, and exposed to the air, when it should
show a colour wholly white. The fibre is then removed from the vessel, drained,
and exposed to the air (and if concentrated bleaching baths have been employedit
should be treated with a solution of 1/2 to 1 per cent. of crystallized soda). It is
then well rinsed in flowing water, and finally dried in a centrifugal drying machine
or in the open air, or in a hot-air chamber at 30° to 35° C.
If the fibre treated in the method described has not a sufficiently white colour, it
is again treated in the bleaching bath, the preliminary blueing process, however,
being dispensed with.
The quantity of indigo to be used in the process above described is 1/2 to 1
gramme (0175 oz. to 035 oz.) to 100 litres of water (176 pints); the exact pro-
portion should be found by trial, a cup of white porcelain being filled with the
blueing bath which should then shew a weak blue colour.
During the bleaching process the indigo, which at first is fixed only mechanically,
is reduced to indigo-white, which being dissolved is instantly permanently fixed.
By subsequent exposure to the air this indigo-white is again changed to indigo-blue,
and the blueing or "azurage" of the fibre is consequently most permanent.
The strength of the bleaching baths must be less for bleaching silk than for
bleaching wool, and is made dependent upon the more or less yellow colour of the
fibre to be bleached, its strength never however exceeding the above-named limits.
Should the resulting white have a greenish appearance, which may be the case if
the fibre has been very yellow, the latter should be passed through cold water, to
which sufficient muriatic or sulphuric acid has been added to give an acid taste.
The bleaching bath used as above described may be used for a second bleaching
process in the following way:-It is first tested to ascertain whether hydrosulphite
of sodium is still contained in it; this can be done by adding muriatic acid to a
small quantity of the solution, which after some minutes becomes milky if it still
contains hydrosulphite. If no hydrosulphite of sodium is still contained in it,
about one-tenth part of the previously used acid hydrosulphite is added, and a fresh
quantity of fibre (which has previously been blued in the way already described) is

page_text: placed in the bath and is allowed to remain there until the hydrosulphite is proved
to have been converted into sulphite (in which case muriatic acid added to a small
quantity of the liquid disengages only sulphurous acid without eliminating sulphur).
The fibre is then removed and muriatic acid is added to the bath until the
penetrating smell of sulphurous acid is percepible, when the half bleached fibre is
returned to the bath and allowed to remain until the bleaching process is complete,
when the fibre is treated and finished in the way already described.
In some cases the bath may be used still more concentrated than that first
described, that is to say, of a strength of 5-6° Beaumé, when the acetic acid need
not be added. The acid bath containing only sulphite may be converted again into
one containing hydrosulphite by adding to it muriatic acid until the smell of
sulphurous acid is perceptible, when zinc (three-fourths of the quantity previously
employed) is added. The resulting hydrosulphite is employed in the way first
described by adding acetic acid.
A bath used in the way described for the second time may also be used in a
similar manner for a third time, and so on.
If a wool fibre of a very yellow colour is to be bleached, the process may be
modified by using instead of the acid hydrosulphite the neutral one, which is
obtained by adding to the solution of the acid salt milk of lime in such quantity
that the clear liquid (removed from the resulting sediment) bleaches blue litmus
paper and turns turmeric paper a weak brown. By this neutral hydrosulphite a
corresponding strong blueing bath (1-4° Beaumé) is made without any addition,
and the fibre to be bleached is placed in it without previous treatment with indigo.
The bleaching process being complete the fibro is rinsed in cold water and is then
treated with a very weak solution of acetic acid and again washed. The bleaching
bath must be as neutral as possible.
Although the novel process of bleaching by means of hydrosulphite, as herein
described, is applicable to all animal fibres, it is especially applicable to bleaching
wool.
Having now described my Invention, and the manner in which it is to be
performed, I claim,-
1st. The use of hydrosulphurous acid in the form of a salt in the place of
sulphurous acid, substantially as and for the purpose set forth.
2nd. The method of blueing or "azurage" by means of indigo-blue, substantially
as and for the purpose set forth.
3rd. The method of employing the used bleaching bath for a second or third
bleaching process or more, substantially as set forth.
In witness whereof, I, the said Frank Wirth, have hereunto set my hand and
seal, this Thirty-first day of March, in the year of our Lord One thousand
eight hundred and seventy-seven.
Tn
תחזק
FRANK WIRTH. (L.S.)