filament at their bases and overlapping much like fish-scales. This structure, which is readily seen with a microscope, is perceptible to the touch by its harsh, rough feeling when the fibre is drawn through the fingers from the tip to the root. The number of these scales bears a fairly direct relation to fineness of the fibre. The curliness of wool is due to a spiral structure of the filaments, and although all wool is not curly or wavy, curliness is one of its recognized and important characteristics. There also appears to be a relation between fineness and curliness. Owing to the relation which these three characteristics bear to each other, curliness, or the number of waves to the inch, which can be seen with the naked eye, is one of the factors noted in judging of wool. The waviness and sealiness are utilized in making felt (q.v.) and also in thread-making. A pound of the finest wool will yield nearly 100 miles of thread. In spinning, the filaments interlock by their scales, and the curl of the fibre prevents the threads untwisting and helps to hold them together. These valuable qualities vary greatly in different wools, some being adapted to carding for cloth, and others to combing for worsteds. It is upon minute points of difference that the value of various grades of wool chiefly depends. The lustre also differs greatly and to a certain extent is a breed characteristic, the wool of the Lincoln and the best Leicester sheep being much more lustrous than that of the shorter wools or the fine Merino fleece. The length of staple, which is made a basis of general classification, is largely a constitutional or breed characteristic, the staple being from one to two inches long in the finest Merinos, eight inches or more in the Lincolns, and reaching twelve and even fifteen inches in some combing wools, the length of staple suggesting the grouping of sheep into short-wools, middle-wools, and long-wools. The fine felting wools have a short staple, as a rule, and are used for carding or yarn purposes, while the longer, more lustrous, and less wavy ones are better suited to combing and worsteds.
Another valuable characteristic of wool is its elasticity, which gives it a softness to the touch which is retained in the manufactured goods. Closely related to this is the strength of fibre; a dead or inferior wool will break instead of stretching when strained. Delicate machines have been constructed for testing the strength and elasticity of fibre, for both practical and scientific purposes. Bowman found that wool fibre is fully one-fourth stronger than cotton, the strength being proportional to the diameter. Great variation, however, exists in the strength of fibres from different wools of the same class of sheep.
All wool in its natural state contains fatty or greasy matter called yolk or suint, secreted by the skin and covering the individual hairs. This serves to lubricate the fibres and prevent their matting together, and also protects the fleece from injury. It differs in quantity and exact character with various breeds and is believed to render the wool soft and pliable. The fats and the potash salts which the yolk contains form a sort of natural soap. For manufacturing purposes the yolk, which is partly soluble in water, must be removed so as to increase the felting tendency and the ability of the wool to take dye. White is the most common color of cleaned sheep wool, and is generally preferred for manufacturing; but the black, fawn, cream, and gray shades produced by various breeds are utilized in their natural colors for certain kinds of clothing.
Variation in Properties. The wool from different parts of the same animal differs greatly in length of fibre, fineness, and structure. As a rule, the best is obtained from the shoulders and sides. That from the fore part is irregular and likely to be filled with burrs, while the loin wool is shorter and coarser, that on the hind quarters still more, and that from the under side of the throat and the belly is likely to be short, worn, and dirty. As the wool is finer on the shoulders, it is likewise superior in soundness of fibre, softness, curl, and evenness of length. Purity of blood, good general management, and uniform feeding tend toward greater uniformity of the fibre grown on different parts of the body, whereas a period of insufficient feeding or of ill health leaves a weaker and less healthy fibre at the point represented by it. Such wool is usually noticeably deficient in yolk. The importance of breeding, climate, and feeding is evidenced by the changes which occur in the wool when sheep of a given breed are removed from one region or district to another quite different. Coleman states that wool in certain districts of Yorkshire brings a higher price than that of other localities, the advantage being probably due to favorable conditions of soil and climate. On the other hand, the ability of man to counteract unfavorable conditions of a particular section is testified to by Lastereye (as quoted by Darwin), who cites the preservation of the Spanish Merino sheep in their utmost purity under such varying conditions as are found at the Cape of Good Hope, in the marshes of Holland, and under the rigorous climate of Sweden, and contends that “fine-wool sheep may be kept wherever industrious men and intelligent breeders exist.”
Kinds and Grades of Wool. The wool clipped from lambs, called in England ‘hog wool,’ differs from the wether wool, or subsequent clippings, in the staple being somewhat pointed, softer, and more wavy or curly. Lamb's wool is more valuable than wether's wool, and can be used for purposes to which the later clippings are not suited. Fleece wool, or that clipped from the live animals, is marketed as (1) ‘unwashed’ or ‘in the grease,’ i.e. as shorn from the sheep with the yolk and dirt adhering to it ; (2) ‘washed,’ i.e. washed on the sheep in cold water, which removes a part of the yolk and dirt; and (3) ‘scoured’ or cleaned ready for manufacture. ‘Tub washed’ includes fleece's broken and washed more or less by hand or machinery; ‘unmerchantable’ is applied to wool partially washed on the sheep's back but not sufficiently to be classed as ‘washed.’ By far the larger part of the wool produced in the United States, and especially west of the Mississippi River, is marketed ‘unwashed,’ which is generally preferred by wool-buyers. ‘Skirted’ is a term applied to certain fleeces imported into the United States, from which the head, belly, and breech wool (the inferior parts) have been removed, to avoid the full effect of the tariff. ‘Pulled wool,’ also called ‘skin wool,’ generally an inferior grade, comes from the pelts of sheep which have been slaughtered or have died from disease or exposure. The
