33—a Gravimetric Technique for Determining the Mean Fibre Diameter of Wool

A method is presented for determining the diameter of wool gravimetrically by using fibre snippets instead of full-length fibres. A quantity of the snippets is weighed and then counted with an electronic particle-size analyser (a Coulter Counter). The average length of snippets is obtained by measuring the length of a small random sample. The product of the average snippet length and the number of snippets present in the weighed sample provides an estimate of the total length of the weighed snippets. Hence their mass per unit length can be calculated, and, if the fibre density is known, the r.m.s. diameter can also be determined. For continuous-filament nylon, the method gives excellent agreement with diameter values obtained by a conventional gravimetric technique. For combed wool, the snippet gravimetric diameter is always less than the projection-microscope diameter, corrected to r.m.s. Some of this difference is attributed to reentries in the wool-fibre surface.