The Dyeing of Cotton Fabrics | Page 7

caustic potash. Like the
last-mentioned nitrates it is soluble in a mixture of alcohol and ether, in
acetic ether, and in absolute alcohol. The solution of the pyroxyline
nitrates in ether and alcohol is known as collodion, and is used in
photography and in medical and surgical work.
One of the most interesting applications of the cellulose nitrates is in
the production of artificial silk. Several processes, the differences
between which are partly chemical and partly mechanical, have been
patented for the production of artificial silk, those of Lehner and of
Chardonnet being of most importance. They all depend upon the fact
that when a solution of cellulose nitrate is forced through a fine
aperture or tube, the solvent evaporates almost immediately, leaving a
gelatinous thread of the cellulose nitrate which is very tough and elastic,
and possesses a brilliant lustre. Chardonnet dissolves the cellulose
nitrate in a mixture of alcohol and ether, and the solution is forced
through fine capillary tubes into hot water, when the solvents
immediately evaporate, leaving the cellulose nitrate in the form of very
fine fibre, which by suitable machinery is drawn away as fast as it is
formed. Lehner's process is very similar to that of Chardonnet. Lehner
uses a solution of cellulose nitrate in ether and alcohol, and adds a
small quantity of sulphuric acid; by the adoption of the latter ingredient
he is able to use a stronger solution of cellulose nitrate, 10 to 15 per
cent., than would otherwise be possible, and thereby obtains a stronger

thread which resists the process of drawing much better than is the case
when only a weak solution in alcohol and ether is employed. By
subsequent treatment the fibre can be denitrated and so rendered less
inflammable.
The denitrated fibres thus prepared very closely resemble silk in their
lustre; they are not quite so soft and supple, nor are they in any way so
strong as ordinary silk fibre of the same diameter.
Artificial silk can be dyed in the same manner as ordinary silk.
ACTION OF OXIDISING AGENTS ON CELLULOSE OR COTTON
Cellulose resists fairly well the action of weak oxidising agents; still
too prolonged an action of weak oxidising agents has some influence
upon the cotton fibre, and it may be worth while to point out the action
of some bodies having an oxidising effect.
Nitric acid of about 1.15 specific gravity has little action in the cold,
and only slowly on it when heated. The action is one of oxidation, the
cellulose being transformed into a substance known as oxycellulose.
This oxycellulose is white and flocculent. It tends to form gelatinous
hydrates with water, and has a composition corresponding to the
formula C{6}H{10}O{6}. It is soluble in a mixture of nitric and
sulphuric acids, and on diluting this solution with water a tri-nitrate
precipitates out. A weak solution of soda dissolves this oxycellulose
with a yellow colour, while strong sulphuric acid forms a pink
colouration. It is important to note that nitric acid of the strength given
does not convert all the cellulose into oxycellulose, but there are
formed also carbonic and oxalic acids. When cotton is passed into
strong solutions of bleaching powder and of alkaline hypochlorites and
then dried, it is found to be tendered very considerably. This effect of
bleaching powder was first observed some thirteen years ago by
George Witz, who ascribed the tendering of the cotton to the formation
of an oxycellulose. Although the composition of this particular
oxycellulose so formed has not yet been ascertained, there is reason to
think that it differs somewhat from the oxycellulose formed by the
action of the weak nitric acid. A notable property of the oxycellulose

now under consideration is its affinity for the basic coal-tar dyes, which
it will absorb directly. The oxycellulose is soluble in alkaline solutions.
In the ordinary bleaching process there is considerable risk of the
formation of oxycellulose by the employment of the bleaching
solutions of too great a strength, or in allowing the goods to lie too long
before the final washing off. The presence of any oxycellulose in
bleached cotton may be readily determined by immersing it in a weak
solution of Methylene blue, when, if there be any oxycellulose present,
the fibre will take up some of the dye-stuff.
Permanganate of potash is a very powerful oxidising agent. On
cellulose neutral solutions have but little action, either in the cold or
when heated. They may, therefore, be used for the bleaching of cotton
or other cellulose fibres.
Alkaline solutions of permanganate convert the cellulose into
oxycellulose, which resembles the oxycellulose obtained by the action
of the nitric acid.
Chromic acid, when used in the form of a solution, has but little action
on cellulose. In the presence of mineral acids, and used warm or