The Dyeing of Woollen Fabrics | Page 2

one of the most important textile fibres used in the manufacture of woven fabrics of all kinds. It belongs to the group of animal fibres of which three kinds are met with in nature, and used in the manufacture of textile fibres; two of these are derived from quadruped animals, such as the sheep, goat, etc., while the third class comprises the products of certain insects, e.g., silk.
The skin of all animals is covered with more or less of a fibrous coat, which serves as a sort of protecting coat from the weather to the skin underneath. Two different kinds of fibres are found on animals; one is a stiff kind of fibre varying in length very much and called hairy fibres, these sometimes grow to a great length. The other class of animal fibres are the woolly fibres, short, elastic and soft; they are the most esteemed for the manufacture of textile fabrics, it is only when the hairy fibres are long that they are serviceable for this particular purpose. There is a slight difference in the structure of the two kinds of fibre, woolly fibres having a more scaly structure than hairy fibres; the latter also differ in being more cylindrical in form.
#Wool.#--By far the most important of the animal fibres is wool, the fibre of the domestic sheep. Other animals, the llama or alpaca, the Angora and Cashmere goats also yield fibres of a similar character, which are imported under the name of wools. There are many (p. 002) varieties of wools Which are yielded by the various breeds of sheep, but they may be roughly divided into two kinds, according to the length of "staple," as it is called. In the long-stapled wools the fibres average from 7-1/2 to 9-1/2 inches in length, while the short-stapled wools vary from 1 to 2 inches long. The diameter varies very considerably from 0.00033 to 0.0018 of an inch.
[Illustration: Fig. 1.--Wool Fibre under the Microscope.]
Two varieties of thread are spun from wool, one is known as "worsted," the other as "woollen" yarns; from these yarns two kinds of cloths are woven, distinguished as worsted and woollen cloths; the former are in general not subjected to any milling or felting process, while the latter invariably are.
#Physical Properties.#--When seen under the microscope the wool fibres show a rod-like structure covered with broad scales, the edges of which project from the body of the fibre, and all point in one direction.
Fig. 1 shows typical wool fibres as viewed under the microscope; the sketch shows very well the scales.
The shape of the scales varies in different breeds of wool. The (p. 003) outer scales enclose inner medullary cells, which often contain pigment matter. A transversed section of the wool fibre shows the presence of a large number of cells. Sometimes wool fibres are occasionally met with which have a peculiar white horny appearance; these do not felt or dye well. They are known as "kempy" fibres. See figure 2. The microscope shows that they are largely devoid of structure, and are formed of very horny, impenetrable tissue, which is difficult to treat in the milling or dyeing process.
[Illustration: Fig. 2.--Kempy Wool Fibres.]
The curly or twisted character of the fibre is caused by the unequal contraction of the outer scales, and depends in a great measure upon the hygroscopic nature of the wool. It may be entirely removed for the time by wetting the wool in hot water, then drying it in a stretched condition, or the curl may be artificially induced by unequal drying, a fact which is turned to practical account in the curling of feathers and of hair.
The amount of curl in different varieties of wool is very variable, being as a rule greatest in the finer qualities, and diminishing as the fibre becomes coarser. The diameter of the wool fibre varies (p. 004) from 1/2000 to 1/5000 of an inch, and the number of curls from about 30 per cent. In fine wool as little as 1 or 2 per cent. in the thicker fibres.
Elasticity and strength are properties which, in common with silk, wool possesses in a greater degree than the vegetable fibres. When submitted to strain the wool fibre exhibits a remarkable strength, and when the breaking point is reached the fracture always takes place at the juncture of two rings of the outer scales, the embedded edges of the lower layer being pulled out of their seat. The scales themselves are never broken.
[Illustration: Fig. 3.--Wool Fibre showing Medullary Centre.]
When first formed the cells are more or less of a spherical shape, and contain a nucleus surrounded by the ultimate photoplasmic substance. Those cells which constitute the core or central portion of the fibre retain to some extent this original globular form and pulpy condition. Surrounding this central