Strength and elongation measurements were made on single cotton fibers and on yarns which had been subjected to various temperatures from 110° to 162°C and various moisture conditions from 3% R.H. up to saturation for periods of heating from 2 to 128 hrs. Moisture contents and degrees of polymerization were also determined, the latter being used to calculate cellulose chain rupture. The simultaneous reduction in strength and elongation at break indicates that heat degradation weakens fibers by creating or intensifying weak points along the fiber. An equation similar to that derived by Sippel, relating fiber strength loss to time of heating and percentage of cellulose links broken, is discussed. Yarn strength, although not as readily affected by heat degradation as fiber strength, follows a similar pattern.

Yarns manufactured from samples of the same six cotton varieties discussed in the previous paper were partially acetylated to an acetyl content of approximately 24% while held under tension. Certain physical properties of the component fibers, fiber bundles, and yarns were then measured. The changes in most properties were found to be associated with differences in the cottons and the acetyl contents. The averages for breaking loads and tenacities of the fibers were decreased while their linear densities and secant moduli were increased. Breaking loads, linear densities, and secant moduli of the yarns were increased. Elongation of the yarns at break was decreased, while tenacity remained essentially unchanged. The changes were greater for some cottons than for others; whether the changes were advantageous or disadvantageous would depend somewhat upon the use to which acetylated cotton is to be put.

Yarns from six cottons selected for their widely different inherent fiber characteristics were mercerized (1) under sufficient tension to maintain their original length, and (2) while permitted to contract freely. Fibers were removed from the yarns and were sub jected to certain physical measurements. Moisture regain, cellulose density, linear den sity, breaking load, and elongation at break were measured on either or both fibers and yarns. Samples of the different cottons were found to differ in their response to the treatment. Those samples with a low value in a property generally displayed the greatest per cent change in that property. Large differences in the properties of the fibers and yarns were associated with the condition of mercerization whether at constant length or slack. Mercerization tended to equalize differences between the properties of fibers in a sample as well as between those of different samples.

The relation of the cross-sectional shape of the raw fiber to the changes that occur upon mercerization without tension was studied for a number of cotton varieties representing a wide range of maturities.Perimeters and diameters of fiber cross sections were measured by the use of an especially designed instrument. Areas also were measured.It was found that the percent increase in area and the percent decrease in perimeter caused by loose mercerization are dependent upon the cross-sectional shape of the original raw fibers. Flat fibers shrank more in perimeter and increased more in area than did round fibers. This was partly explained as being due to a change toward circularity. THIS PAPER reports data, obtained during an investigation of the fundamental swelling properties of cotton, which show that the cross-sectional shape of the raw cotton fiber is related to the changes that occur in mercerization without tension.The undried fibers from a fresh, undried boll of cotton, which are tubular in form, consist of a thin primary wall surrounding a secondary wall, the thickness of which depends upon the maturity of the fiber. The central opening, or lumen, ranges from very small for thick-walled (mature) fibers to a large proportion of the whole cross-sectional area for thinwalled (immature) fibers [5]. As the fiber dries, the lumen collapses. This gives the fiber cross section various shapes, ranging from almost circular for mature fibers to flat for immature fibers.It has long been known that treatment of the raw cotton fiber in strong swelling agents, as in the mercerization process, causes the fiber to swell toward a circular cross-sectional shape by the thickening of the secondary wall. It has been shown that the primary wall tends to limit the swelling, and that the resulting pressure closes the lumen [7,15] . This restricting action was attributed to the alignment of the fibrils of the primary wall, which are nearly perpendicular to the axis of the fiber [4]. The primary wall, however, may be ruptured by very strong swelling agents [9]. The relation of cross-sectional shape to swelling in water was studied by Skau [14] and Moore [ 12] . Skau predicted that, although thin-walled fibers might reach their maximum swelling in water, thick-walled fibers might be prevented from doing so by the constricting action of the primary wall and might develop a real swelling pressure. Observations by Moore et al. [12] indicate that the shape of the fiber cross sections is changed little with swelling in water. This led to the belief that the secondary wall offered considerable resistance to deformation by swelling.Calvert and Summers [6] showed that upon washing out the mercerizing agent and drying, the fiber shrank in diameter, but retained the more or less circular cross-sectional shape assumed in the mercerizing solution. There was a decrease in both crosssectional area and perimeter from the swollen stage; but, compared to the raw fiber, the area of the cross section was larger and the perimeter was smaller.Marsh [11] ] ...