The tensile strength of wool

Abstract

Introduction: It is my purpose in this experiment to attempt to demonstrate the tensile strength of single wool fibers from four of the chief breeds, viz. Cotswold, Shropshire, Southdown, and the Rambouillet. Samples from different parts of the body were also compared. The apparatus used consisted of two jolly balances, a compound microscope with ocular or eye piece, micrometer, small forceps, mechanical stage, and other microscopic equipment. Two jolly balances were used because of the wide variation between the Cotswold and Rambouillet wools, the Cotswold fibers being so strong that a special balance with an extra strong spring or coil was required. The test was begun by first determining the constant of each balance, which was done by making the zero reading and then noting the displacement caused by a weight of one gram. Next a wool fiber was fastened on the hook of the balance by knotting one and half-hitching. The tensile strength was then easily read in grams by simply pulling down on the fiber until it broke, the reading being made just at the moment the fiber parted. No particular length of fiber was used as the weight of a single fiber is so very slight that it was concluded the results would not be influenced. The only opportunity for a variation might be based on the cry that in a greater length the chances for weak points are greater. No objection can be raised on account of this theory, however, because a thread is no stronger than its weakest point. This last statement might also be sited as a reason for testing many fibers and each but one. In connection with obtaining the strength of each fiber the diameter was also taken as it was found that the strength varied directly with the diameter. For the purpose of measuring the diameters, the fibers were fastened on a glass slide by means of balsam and cover slips. In this condition the fibers were held firm and straight, so that with the aid of a micrometer–microscope and mechanical stage the diameter was very easily determined.