CHAPTER XL

TEXTILE FIBERS OF ANIMAL ORIGIN. WOOL AND SILK

TEXTILES for clothing and for household furnishings can be made from any kind of fiber, natural or artificial, which has sufficient length, strength, and elasticity. The mineral kingdom furnishes some such fibers asbestos, spun gold and silver, and spun glass. On account of their costliness and other defects, however, the mineral fibers find only limited application. Both the vegetable and the animal kingdoms, on the other hand, yield us fibers of very wide utility.

The animal fibers are of two classes, viz. (1) Hair fibers, of which wool is by far the most important; (2) Silk fibers. Both classes are composed of protein substances, but the silks are sulphur-free, while the hair-fibers, being keratins, are rich in sulphur. (See Expt. 112, p. 191.)

Experiment 123.

Materials:
Wool.

Silk.

Burn a little of each kind of fiber in a flame, noting the odor and the shape which the end of the fiber assumes. Heat portions in small, dry test tubes and test the evolved gases for ammonia with red litmus paper, and for hydrogen sulphide gas, H2S, with paper moistened with lead acetate solution. Hydrogen sulphide reacts with lead acetate to give lead sulphide, PbS, which is black.

Make the xanthoproteic test (Expt. 105, p. 186) and Millon's test (Expt. 106, p. 187) on other portions of the wool and silk.

FIG. 44.1

Cotton fibers magnified.

FIG. 45.1

Flax fibers magnified. From Kinne and Cooley's" Shelter and Clothing," From Kinne and Cooley's "Shelter and Clothing," by kind permission.

by kind permission.

Experiment 124.

Materials:

Silk fibers.

Wool.

Human hair.

Cat's hair.
Apparatus:
Microscope and slides.

Examine the fibers, noting points of similarity among the various hair fibers and differences of these from the silk. Observe particularly the scaly surface of the hair fibers. Is there any noticeable difference between wool and the coarser hair fibers in regard to (a) diameter, (b) appearance of the scales?

Wool

A hair fiber comprises' three distinct portions: (1) the medulla, a cellular marrow, which frequently contains the pigment to which the wool owes its color; (2) the fibrous cortical tissue, to which the fiber owes most of its strength and elasticity; (3) the epidermis of horny scales, consisting of flattened cells, overlapping one another like shingles.

The characteristics which distinguish wool from other hair fiber are its fineness, its softness, and the abundance of its scales or serrations. To these scales is due the characteristic "felting" property of wool; that is to say, the tendency of the fibers to mat together, and also the tendency of woolen goods to shrink, the scales catching upon one another and so preventing the fibers returning to their original position.

The length and fineness of wool depend chiefly upon the breed of sheep producing it, but these qualities, as well as the strength and luster, are influenced also by the climate in which the sheep are grown, by the nature of the soil providing the pasture, and by the condition of the animals' health. Ordinarily, the length of the fibers is between 1 and 8 inches and the diameter between and inch. The quality of the wool varies not only in different fleeces, but also in the different parts of the same fleece, the wool of the shoulders and sides excelling in length, strength, and uniformity,

while that from the upper parts of the legs is coarse and that from the head, chest, and lower parts of the legs is likely to be coarse, stiff, and dirty. The uses of the wool depend upon its quality, which in turn depends upon such physical properties as the length, diameter, strength, elasticity, and glossiness of the fibers.

Only the longer and brighter fibers, for instance, are suitable for the manufacture of worsteds. The wool manufacturer grades and sorts his wool and uses the different kinds for the manufacture of different classes of goods.

Raw wool contains a large proportion of impurities. In some merino wools these impurities constitute as much as 70 per cent of the total dry weight of the fleece. The impurities consist of:

(a) Wool grease, a fatty substance, which serves as a protective covering to the fibers.

(b) Suint, that is, dried perspiration, consisting chiefly of potassium soaps.

(c) Vegetable matter, such as burrs, straw, and vegetable fibers from sacks and twine.

(d) Mineral matter, such as clay.

Unwashed wool contains from 4 to 24 per cent of moisture; from 12 to 47 per cent of yolk (grease and suint); from 3 to 24 per cent of dirt; and from 15 to 72 per cent of true wool fiber.

Wool grease, the chief constituent of which is an alcohol, called cholesterol, is the source of a product known as lanolin. Lanolin has remarkable capacity for forming emulsions with water and aqueous solutions, and is readily absorbed by the skin. On this account it is used in many pharmaceutical ointments and cosmetics.

The impurities are removed from the wool by " scouring," that is, washing with soap and an alkali. Only the milder alkalies, such as the carbonates of potassium and sodium, ammonia or borax, may be used, not the caustic alkalies. By this treatment the soaps in the wool are dissolved, the fats are emulsified and removed from the wool fibers, and the earthy matters are thereby loosened and washed out. Much of the vegetable matter, however, remains in the wool and is removed by subsequent treatment. In the worsted pro