Paragraph 50. Of the animal fibers, wool is by far the most plentiful and the most important. Wool is the hair of a certain class of animals, of which the sheep is most common. There are a great many kinds and varieties of wool which vary principally in the length and fineness of their fibers, however, they are all very similar in their general characteristics. Wool fiber, if carefully examined with a magnifying glass, will reveal a surface covered with scales somewhat similar to the shingles on a roof or the scales of a fish. It is the presence of these scales, which cling to each other, that makes it possible to use the short wool fibers in spinning and weaving valuable fabrics.

Woolen fibers are very elastic but do not present as great strength as cotton or linen. The soft, loosely twisted and loosely woven fibers produce the woolens or the kinds of cloth which have considerable nap or pile. These woolen fibers are sometimes combed until they lie almost straight and parallel; they are then twisted into a rather hard glossy thread of regular, even size. Such treatment of wool produces the fine worsteds, so well known in clothing, particularly in men's suits.

Wool absorbs and retains coloring matter very readily, it does not fade or lose its color when exposed to sunlight and other conditions to which clothing must be subjected. This is one property which makes wool very valuable for fine clothing.

There are a great many kinds of cloth made from wool. On account of its many excellent properties it is used in a greater variety of ways than any other textile. The most characteristic and peculiar quality of woolen fiber is its tendency to "felt." That is, the woolen fibers may be brought so close together that their scales seem to mesh and form a continuous fabric without weaving. There is no other textile fiber which has this property. Wool is very sensitive to alkalies; this explains why in laundering all-wool garments they should not be treated with strong soap or other caustic alkalies.

Wool is very frequently adulterated with cheaper fibers, especially cotton. While the introduction of a certain amount of cotton in a woolen fabric may give it added strength, yet such material will, for the most part, be inferior and should be less expensive than all-wool material. It requires a great deal of training and practice to be able to determine the presence of cotton in so-called "wool cloth." A great many different tests have been devised but they belong to technical lines of work. There are, however, a few simple tests which are easily made and are therefore pretty generally known. The burning test is quite common; woolen material burns very slowly and leaves a distinct ash, usually curled or rounded in a bead-like end. The burning of wool is accompanied by a very disagreeable odor somewhat resembling that of burning feathers. This odor is due to the presence of the animal oil found in the woolen fibers.

By picking a small sample of cloth to pieces and examining the different threads, the presence of cotton can usually be detected. (This can often be done on underside and exposed seams). Sometimes by setting fire to a piece of mixed goods, the cotton, which burns rapidly, can be readily burned out, while the woolen portion, which burns more slowly, is left. While it is not always convenient to make these tests, by careful practice one can become sufficiently acquainted with the general appearance of various woolen materials to identify them with a reasonable degree of certainty.

The following are the most common kinds of wool fabrics.