Density of cellulose fibers. III. Density and refractivity of natural fibers and rayon

A micromethod is described for density determinations of artificial cellulose fibers by the floating method, in carbon tetrachloride in a dry and air‐free atmosphere, permitting an accuracy of one part per thousand. The density is derived from the temperature at which the samples neither sink nor float. This temperature varies, with the kind of fiber, between 45° and 65°C. Measurements of the refractive power were carried out simultaneously. The refractivity calculated according to Gladstone and Dale yields slightly lower figures than those found for model fibers in the preceding communication (Part II). The average difference amounts to seven parts per thousand and is ascribed to a systematic error in the density determinations, due to a slight absorption of carbon tetrachloride by the fibers at elevated temperatures. This explanation is supported by experiments. The density of native ramie, of contracted and reoriented ramie, and of several series of rayon fibers spun with increasing stretch, is given. The conclusion is reached that the density is a measure of the percentage of crystalline substances in the fiber and it is shown that there is a correlation between density and sorptive capacity toward water vapor. The percentage of crystalline matter is estimated to be 55–60% in native ramie and 20–25% in rayon.