The Dyeing of Cotton Fabrics | Page 2

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 is soluble in boiling water, and the solution has a faint acid reaction. Acids and many metallic salts, such as mercury, chloride and lead acetate, precipitate pectic acid from its solutions. Alkalies combine with it, and these compounds form brown substances, are but sparingly soluble in water, and many of them can be precipitated out by addition of neutral