The Coulter Counter, an electronic particle-sizing instrument, can appraise the average fineness and fineness distribution in wool tops with precision equivalent to that of the standard microscopic method. A time saving of 1/2 to 3/4 is realized over the microscopic method, with avoidance of subjective errors inherent in the latter. Oper ating conditions are described, along with methods of sampling, preparing a nonswelling but conductive solvent system, calibrating and checking the instrument, and minimizing error. Examples of results are presented with comparative microscopic data.

A comparison of yarn irregularity is made between the Pacific Evenness Tester and the cut-and-weigh technique through use of length-variance analysis. It is shown that the Pacific Tester adequately measures short-term unevenness in a worsted yarn. Results for medium-term unevenness are only moderately different from those of the cut-and-weigh method. Long-term unevenness is best measured by the simple cut-and-weigh method used in normal practice.

Dear Sir :While measuring the fineness of Alpaca fiber with the Coulter Counter [4] we noted discrepancies which required explanation. Several methods of measurement have now been compared to resolve these differences. Because Alpaca fiber is generally medullated (that is, it is often hollow) and ellipsoidal in cross section, the apparent or eflective diameter can vary according to the method of measurement.The standard micrdprojection method [la], ASTM D 2130, is liable to error due to fiber ellipticity (as discussed in Appendix A2 [la] ) but is not concerned with medullation as it is a method for measuring diameter per se. The Coulter Counter indirectly gives an average diameter calculated from the cross sectional area, assumed to be circular. Deviation from circularity, accordingly, may produce differences from the microscopic method. Differences would also result when diameters are calculated from measurements based on linear density, as found with the vibroscope or by cutting and weighing [lb]. With respect to medullation, the Coulter tnethod might conceivably &dquo;see through&dquo; a hollow fiber section, sensing only solid material. According to Berg [2]. this is unlikely. Methods based on the linear density measure only solid material.Besides the methods already mentioned, major and . minor axes of cross sections were measured on photographs of known enlargement. To convert these measurements to area, a shape factor was calculated from planimeter readings on 200 sections; the factor 0.80 was obtained. If the sections were truly elliptical, the calm culated factor would be ir/4 T 0.78.The fiber sample tested was of Haucayo Alpaca obtained from W. von Bergen and