All known methods for chemically purifying woolen stuffs from vegetable
fibers depend on the action of acids or substances of acid reaction.
The excessive temperature, hitherto unavoidable in the operation, acts
injuriously on the woolen fibers, especially during the formation of
hydrochloric acid, with which process especially the development of an
injuriously high temperature has been hitherto unavoidable. The best
method of absorbing the heat developed is in the evaporation of the
moisture naturally present in the wool. The patentees find agitation of
the fabric and the use of an exhauster during the process of material
assistance. The operation maybe successfully performed in two
ways--either by acting on the fabric at the ordinary pressure with
constant agitation, or by saturation without agitation in a vacuum. For
the first method the patentees employ a wooden cylinder with an aperture
at one end for inserting and removing the cloth, and having apertures
all round to allow free access of air. This cylinder rests on a hollow
axle, closed at one end and perforated with holes, through which the
acid gas is passed. By the rotation of the cylinder the gas is drawn
through the material and the latter exposed to the atmosphere, whereby
it gives up a quantity of aqueous vapor. An average temperature of 30°
Cent. is best suited to the operation, and it can be regulated according
to the supply of gas by opening or shutting a three-way cock between the
gas generator and the revolving cylinder. This process is assisted by
the use of an exhauster of the usual construction. When fully saturated,
the fabric is allowed to remain until the vegetable fibers are
sufficiently friable. The treatment _in vacuo_ is as follows:
The hydrochloric acid gas passes into a vessel of suitable material
provided with a perforated false bottom. From under this false bottom
a pipe connects with a second similar vessel connected itself with a
vacuum pump having a let-off pipe. As soon as the maximum vacuum is
attained, the gas is turned on through a three-way cock at a pressure of
40 mm. mercury. The gas fills the first vessel and saturates the cloth.
The warmth set free (about 500 calories per kilo, gas) is taken up
by the combined water in the wool, as, owing to the low pressure, a
quantity of vapor is formed sufficient to take up the heat. This vapor
streams through the second vessel at a temperature of 35° Cent.,
penetrates the material, and passes out through the pump. After
saturating the contents of the first vessel the gas passes into the
second. AS soon as this is one-quarter or one-third saturated the first
vessel is taken out and replaced by a third, which receives the overplus
from No. 2 in like manner, and so on. This plan of working prevents gas
passing through and damaging the pump. Instead of working under reduced
pressure, the desired low temperature can be maintained by passing
alternately with the gas currents of air which absorb heat in
evaporating the moisture of the material. The cloth, after saturation by
these processes, is left from six to twelve hours in the vessels, after
which it is freely exposed to the air until the vegetable particles
are friable. As soon as this occurs, the fabrics are washed. It is
advantageous to add to the wash water powdered carbonate of baryta,
strontia, magnesia, or preferably lime, and subsequently to rinse in
pure water. Phosphate of lime containing carbonate may also be employed
for neutralizing the acid, and the residue recovered and separated from
the organic residues mixed with it.--"_H. J.," Journal of the Society of
Chemical Industry._
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APPLICATION OF ELECTRICITY TO THE BLEACHING OF VEGETABLE TEXTILE
MATERIALS.
It is a recognized fact that chemical bodies in a nascent state are
characterized by peculiarly energetic affinities, and the results of
numerous experiments permit us to affirm that animal and vegetable
fibers are rapidly bleached when they are placed in contact with oxides
and chlorides which, when submitted to electrolysis, permit oxygen and
chlorine to disengage themselves in the nascent state.
The coloring matter that impregnates the majority of vegetable textile
substances, such as cotton, flax, and hemp, to cite only those most
generally known, is in fact completely destroyed only by the combined
action of oxygen and chlorine, which always act in the same manner,
whether the fibers be in a raw or woven state.
In the application of electrolysis to the bleaching of textile
materials, it is only necessary to have the electrodes of any
sufficiently powerful generator of electricity end in a vessel
containing in aqueous solution such decolorizing agents as the
hypochlorites in general, and chlorides, bromides, and iodides that are
capable of disengaging chlorine, and iodine or an iodide in a nascent
state. These gases perform the role of oxidizing or decolorizing agents.
The fibers that are immersed in the solution during the passage of the
electric current must necessarily remain therein for a greater or less
length of time, according to the nature of the material to be bleached,
and must, after this first operation, be washed, rinsed, and dried.
The use of an electric current for decomposing the metallic chlorides
and disengaging their elements is not new, and there have been specially
utilized for this purpose, up to the present time, the alkaline
hypochlorites that are obtained by well known processes.
In the latter case the metal is brought to the state of oxide in
presence of the water that is necessary for the reaction. But the
results obtained in practicing this method are deceiving, as far as
bleaching is concerned, and it is evidently more rational and economical
to endeavor to compound the hypochlorite directly by borrowing all its
elements from the metallic chloride itself, and from the water by means
of which such transformation is to be effected. This is a reversal of
the problem, and, _à propos_ thereof, we would call the attention of
the reader to an apparatus invented by Messrs. Naudin & Schneider for
effecting such synthesis in a simple and practical manner.
If a solution of chloride of sodium or kitchen salt, NaCl, be submitted
to electrolysis in a hermetically closed vessel containing the material
to be bleached, a formation of hypochlorite of soda is produced in the
following way:
2NaCl + 2 H_{2}O = NaCl + NaO, ClO + 4H.
In operating in this manner we shall have the advantage that results
from the nascent body through the electrical double decomposition of the
chloride of sodium and water, which puts the chlorine, the metal, the
hydrogen, and the oxygen simultaneously in presence. The chlorine and
oxygen will combine their action to decolorize the textile material.
While starting from this idea, it will nevertheless be preferable to
adopt Naudin & Schneider's arrangement.
The apparatus consists of a hermetically closed electrolyzer, A,
into the lower part of which enters the electrodes, E and F, of any
electrical machine whatever. The receptacle, A, is provided with a
safety-tube, T, that issues from its upper part and communicates with
a reservoir, B. A second tube, D, forms a communication between the
electrolyzer and the vessel, C. The liquid contained in this latter is
sucked up by a pump, P, and forced to the lower part of the vessel, A,
by means of the tubes, G and H.
The apparatus operates as follows:
The closed vessel, C, in which the material to be bleached is put, is
filled, as is also the electrolyzer, with a solution of chloride of
sodium. This solution is then submitted to the action of an electric
current, when, as a consequence of the chemical decomposition of
the chloride and the water, the elements in a nascent state form
hypochlorite of soda. When the partial or total conversion of the liquid
has been effected (this being ascertained by chlorometric tests), the
pump, P, is set rapidly in operation, and, as a consequence, draws up
the chloride of sodium from the bottom of the vessel, C, to the lower
part of the electrolyzer, A. The hypochlorite that has formed passes
through the tube, D (as a natural consequence of the elevation of the
level of the liquid in A brought about by the entrance of a new supply
of chloride), and distributes itself throughout the vessel, C, where it
acts upon the textile material.
[Illustration: APPARATUS FOR BLEACHING TEXTILE FIBERS BY ELECTRICITY.]
The safety-tube, T, which is attached to the electrolyzer, permits
of the escape of the hydrogen which is produced during the chemical
reaction, and fixes, through an alkaline solution contained in the
reservoir, B, the chloride whose escape might discommode the operator.
As may be conceived, the slow transfer of the saline solution from
the receptacle, C, to the electrolyzer, and its rapid conversion into
decolorizing chloride, as well as its prompt application upon the
materials to be bleached, presents important advantages.
While, in the present state of the industries that make use of bleaching
chlorides, the chloride of sodium is converted into hydrochloric acid,
which, in order to disengage chlorine, must in its turn react upon
binoxide of manganese, we shall be able, with this new method, to
utilize the chloride of sodium, which is derived from ordinary salt
works, and extract from it the constituent elements of the hypochlorite
by a simple displacement of molecules produced under the influence of an
electric current.
Another and very serious advantage of electric bleaching is that of
having constantly at hand a fresh solution of hypochlorite possessing a
uniform decolorizing power, which may be regulated by the always known
intensity of the current.
We must remark that the hypochlorites require a certain length of time
to permit the chlorine to become disengaged, and that, besides, all
chlorides, bromides, and iodides that are isomorphous are capable of
undergoing an analogous chemical transformation and of being employed
for the same purpose. This is especially the case with the chlorides
of potassium or barium, the bromides of strontium or calcium, and the
iodides of aluminum or magnesium. On another hand, as sea water contains
different chlorides, it results that it might serve directly as a raw
material for bleaching textile fibers. Then, when the solution of
chloride of sodium has been deprived of its chlorine by electrolysis,
there remains a solution of caustic soda which may be utilized for
scouring fibers.--_H. Danzer, in Le Génie Civil_.
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