The Dyeing of Cotton Fabrics | Page 2

when brought into contact with
various chemical substances--acids, alkalies, salts, etc. These reactions
have a very important bearing on the operations of bleaching and
dyeing of cotton fabrics.
A few words on vegetable textile fibres in general may be of interest.
Fibres are met with in connection with plants in three ways.
First, as cuticle or ciliary fibres or hairs; these are of no practical use,
being much too short for preparing textile fabrics from, but they play
an important part in the physiology of the plant.
Second, as seed hairs; that is fibres that are attached to the seeds of
many plants, such, for instance, as the common thistle and dandelion;
the cotton fibre belongs to this group of seed hairs, while there are
others, kapok, etc., that have been tried from time to time in spinning
and weaving, but without much success. These seed hairs vary much in
length, from 1/4 inch to 1-1/2 inches or even 2 inches; each fibre
consists of a single unit. Whether it is serviceable as a textile fibre
depends upon its structure, which differs in different plants, and also
upon the quantity available.
The third class of fibre, which is by far the most numerous, consists of
those found lying between the bark or outer cuticle and the true woody
tissues of the plant. This portion is known as the bast, and hence these
fibres are known as "bast fibres". They are noticeable on account of the

great length of the fibres, in some cases upwards of 6 feet, which can
be obtained; but it should be pointed out that these long fibres are not
the unit fibres, but are really bundles of the ultimate fibres aggregated
together to form one long fibre, as found in and obtained from the plant.
Thus the ultimate fibres of jute are really very short--from 1/10 to 1/8
of an inch in length; those of flax are somewhat longer. Jute, flax,
China grass and hemp are common fibres which are derived from the
bast of the plants.
There is an important point of difference between seed fibres and bast
fibres, that is in the degree of purity. While the seed fibres are fairly
free from impurities--cotton rarely containing more than 5 per
cent.--the bast fibres contain a large proportion of impurity, from 25 to
30 per cent. as they are first obtained from the plant, and this large
quantity has much influence on the extent and character of the
treatments to which they are subjected.
As regards the structure of the fibres, it will be sufficient to say that
while seed hairs are cylindrical and tubular and have thin walls, bast
fibres are more or less polygonal in form and are not essentially tubular,
having thick walls and small central canals.
=The Cotton Fibre.=--The seed hairs of the cotton plant are separated
from the seeds by the process of ginning, and they then pass into
commerce as raw cotton. In this condition the fibre is found to consist
of the actual fibrous substance itself, containing, however, about 8 per
cent. of hygroscopic or natural moisture, and 5 per cent. of impurities
of various kinds, which vary in amount and in kind in various
descriptions of cotton. In the process of manufacture into cotton cloths,
and as the material passes through the operations of bleaching, dyeing
or printing, the impurities are eliminated.
=Impurities of the Cotton Fibre.=--Dr. E. Schunck made an
investigation many years ago into the character of the impurities, and
found them to consist of the following substances:--
=Cotton Wax.=--This substance bears a close resemblance to carnauba
wax. It is lighter than water, has a waxy lustre, is somewhat translucent,

is easily powdered, and melts below the boiling point of water. It is
insoluble in water, but dissolves in alcohol and in ether. When boiled
with weak caustic soda it melts but is not dissolved by the alkali; it can,
however, be dissolved by boiling with alcoholic caustic potash. This
wax is found fairly uniformly distributed over the surface of the cotton
fibre, and it is due to this fact that raw cotton is wetted by water only
with difficulty.
=Fatty Acids.=--A solid, fatty acid, melting at 55° C. is also present in
cotton. Probably stearic acid is the main constituent of this fatty acid.
=Colouring Matter.=--Two brown colouring matters, both containing
nitrogen, can be obtained from raw cotton. One of these is readily
soluble in alcohol, the other only sparingly so. The presence in
relatively large quantities of these bodies accounts for the brown colour
of Egyptian and some other dark-coloured varieties of cotton.
=Pectic Acid.=--This is the chief impurity found in raw cotton. It can
be obtained in the form of an amorphous substance of a light yellow
colour, not unlike gum in appearance. It