The cultivation of sheep for wool consists in keeping the animal in the most healthy condition possible, in careful breeding, and in shelter from the worst rainstorms. Care must be exercised to protect the sheep from parasites, or they must be dipped with preparations which destroy the parasite. The sheep must also be kept as free as possible from burrs and other vegetable matter, which decrease the value of the wool.
Among textile industries, wool is second only to cotton in importance. Before the Industrial Revolution wool was most important, but the ease of preparation of cotton by machinery and the cheapness of production have placed it in the front rank. In the United States wool manufacture, as well as wool culture, is an important industry, but a large amount of raw material, cloth and yarns, is annually imported. The manufacture is largely concentrated in the New England and Middle Atlantic states, especially in Massachusetts, Rhode Island, and Eastern Pennsylvania, although there are many mills in other parts of the country.
Turning to the study of the individual fiber, we find that it has very important physical and chemical properties, which play a large part in determining how it is to be treated in manufacture.
Chemically wool is a protein substance, composed of carbon, hydrogen, oxygen, sulphur, nitrogen, and phosphorus. Nitrogen may be detected by charring wool with caustic potash, when an odor of ammonia is given off. When distilled by itself, hydrogen sulphide may be detected in the fumes.
In raw wool there is a large percentage of foreign substance, dirt, and products secreted by the skin of the animal. The natural oil secreted keeps the fiber in a soft condition, and must not be entirely removed before manufacture. Different compositions are given for raw wools, the impurities varying from fifty to eighty per cent of the weight of the fleece.
Matthews classifies these impurities as follows:1 a. Grease or wool fat.
b. Suint or dried-up perspiration.
c. Dirt, consisting of dust, sand, burrs, etc.
Suint, or yolk, is a secretion from the skin of the sheep; it is soluble in water and contains potash salts of fatty acids. This suint coats the fibers when they are on the back of the animal, and prevents them from felting. It also keeps them soft after shearing.
Strong alkali removes all oil, making the wool harsh, and also destroys the fiber if its action is allowed to proceed far enough. Five per cent caustic soda dissolves wool at boiling temperature in ten minutes. On the other hand, dilute mineral acids have no injurious effect, and the most concentrated acids dissolve wool only when heated.
It is possible to mercerize wool with caustic alkali, and the mercerization is more effective if glycerol is present. The wool becomes strong and more lustrous, both qualities probably being due to the fusion of the scales on the surface of the fibers, which present a more continuous reflecting surface and are not so easily pulled apart Mercerized wool is not used much for commercial purposes. An increased luster may be given to wool by the action of chlorine, a process that is used commercially. Both these changes increase the affinity of the fiber for dyestuffs and also destroy the felting property. Novel effects are produced in cloth by the combination of chlorinated with unchlorinated wool, the two differing in the amount of dye taken up and also in the amount of shrinking and felting.
1 Laboratory Manual of Dyeing and Textile Chemistry, p. 15.
Lime has a deleterious effect on wool, making it harsh and brittle. Therefore, when wool is pulled from the skins of dead animals, as is sometimes the case, lime being put on the back of the skin to loosen the wool, great care must be taken that no lime remains in the wool.
Water at 1300 C. under pressure disorganizes the fiber, and at a higher temperature dissolves it completely.
Wool is bleached with the fumes of sulphur or with hydrogen peroxide. The latter process is, however, too expensive for wide application. The affinity of the animal fibers for dyestuffs is much greater than that of the vegetable fibers. Wool may be dyed in many dyestuffs without the use of an assistant, and the color is quite lasting.
Physically the wool fiber is a complex arrangement of cells. An inner or medullary layer, containing the natural pigment, may or may not be present; in highest bred, pure white wool they are lacking. The cortical layer gives the fiber its strength and also absorbs dyestuffs, while the outside layer of horny scales, generally overlapping each other and projecting out from the surface of the fiber to a greater or less extent, gives it that characteristic peculiar to wool, the property which the fibers have of felting together, so that cloth may be made without spinning or weaving. These serrations produced on the surface of the fiber hook into each other, especially when the fiber is warm and moist and the scales open more; then when dry again they hold fast together. To this property the shrinking of wool is also due.
The difference between hair and wool is largely in this layer of horny scales. On hair they are much less marked, and often do not project at all at the edges. The internal structure of the two varies so in different varieties of each that it is hard to make a distinction; in fact, some wools are so similar to hairs that it is difficult to distinguish between the two.
Between hair and wool are a number of fibers varying in the number of scales and the amount of projection. Among these are alpaca, llama, camel, and others already mentioned. The distinction is sometimes made that hair is straight and wool is curly, or that hair is stiffer than wool; but here again the difference is sometimes greater between the extremes of wool or the extremes of hairs than between a given wool and a given hair.
The microscopic structure of the wool fiber serves to distinguish it from all other textile fibers, as well as to distinguish the different kinds of wool from each other.
The amount of luster which wool has also depends on the scales. If the edges of the scales are rough and uneven, the fiber as a whole will not be as smooth and lustrous as a fiber in which the scales are more regular and reflect the light evenly. The fiber from the Angora goat, which has less prominent scales, has greater luster than the wool from most sheep, but there is also great variation in different breeds of sheep.
In certain classes of sheep, or on fleeces which have had very hard wear, fibers often lack part of this surface layer of cells, are irregular in size or even may be bent at an angle, lack strength, and are therefore not as valuable as the perfect fibers. They lack luster usually, cause trouble in manufacture, and do not always take dye, and so make a streak in the finished cloth. These fibers are called kemps.
In tensile strength and elasticity wool fibers vary greatly. The structure of the fiber makes it elastic and also gives it strength. The kinky nature of the wool also makes it elastic. In its hygroscopic property, or power to absorb water, wool stands first among fibers, being able to absorb within itself as much as fifty per cent of water without appearing wet, although the average amount of moisture absorbed is twelve to fourteen per cent. In European and English markets sixteen to nineteen per cent of water is usually allowed in wool. This percentage varies with the form of the wool, whether loose, combed, yarns, etc. The price is regulated according to the percentage of water. So important is this percentage of water to the buyer that there are conditioning houses whose business it is to determine the amount of water in samples of wool.