A New Correction in Viscometry by the Capillary-Tube Method

The hydrostatic head correction as ordinarily made in viscosity measurements may be in error. This is made evident when one determines this correction at widely different pressures or with liquids of widely differing fluidities. It is concluded that this error is due to differences in the value of the coefficient m of the kinetic energy correction in different directions of flow. Such differences are due to departure of the capillary tube from a true cylinder which may have arisen in the manufacture of the capillary or of the viscometer. These differences in the value of m are so considerable that not only should the value of m for each viscometer be determined but a separate value should be determined for each direction of the flow through the capillary. Fortunately, this measurement is simple.