A technical article on the factors that determine the tensile strength, elasticity and elongation of textile yarns. It covers the effects of twist, fiber elastic limit, the number of fibers in a yarn cross-section, uneven (thick and thin) places, and fiber quality. It gives formulas and tables for the expected strength of cotton yarns by count and twist, and for linen yarns. It also gives elongation percentages for cotton, strength figures for wool, silk and other fibers, and silk grading standards. It closes with the effect of moisture and test-room conditions and is marked to be continued.