The Margules Method of Measuring Viscosities Modified to Give Absolute Values

Abstract

Measurement of absolute viscosities. A method for determining absolute viscosities in a Margules rotating cylinder type viscometer, without the aid of calibrating liquids of known viscosities, is described. This method involves the determination of true viscosity by extrapolating apparent viscosities for several lengths of inside cylinder to that viscosity corresponding to infinite length. By this method the viscosity of the commercial castor oil used is found to be 9.99 poises at 20\ifmmode^\circ\else\textdegree\fi{}C, and 4.61 poises at 30\ifmmode^\circ\else\textdegree\fi{}C, as compared with 9.86 and 4.51 poises quoted in the Smithsonian Tables for pure oil at corresponding temperatures.End corrections. The additional length to be applied to the measured length to correct for finite dimensions is computed for several inside cylinders or spindles. When the radius of the outer containing cylinder is 3.2 cm, and the ends of the spindle are 1.5 cm from the upper and lower boundaries of the liquid, the corrections for spindle radii of 0.556 cm and 0.477 cm are found to be 0.62 cm and 0.52 cm respectively as long as the length of the spindle is 5 cm or greater. Accordingly, the end correction is apparently proportional to the 1.18 power of spindle radius.Constancy of calibrating factor. Comparisons are also made between relative viscosities measured by this method and those for the same liquids measured by capillary flow. Results indicate that within experimental error these relative values are the same by both methods, for viscosities between 5 and 3500 poises, showing that the calibrating factor of the concentric cylinder system is constant over this range of viscosities.