A compensated moving cylinder viscometer

Abstract

Based on the principle of Lawaczeck's falling cylinder viscometer, a new viscometer has been designed, in which the only measurement to be made is the time taken by the cylinder to move a definite distance, without the necessity of either observing the movement of the cylinder or measuring the densities of the cylinder and of the liquid. The instrument consists of two exactly similar light solid cylinders or cylindrical bulbs moving in similar vertical tubes of slightly larger diameters containing the liquid at the same temperature. The ends of each cylinder are made conical to ensure its coaxial movement in the tube and the cylinders are attached to the ends of a Nylon fibre which passes over a light frictionless pulley. Attached to the same fibre at suitable heights above the cylinders are two similar light weight carriers on either of which riders of equal mass may be placed. When a certain number of riders are placed on one side, the cylinder on that side moves down while the other cylinder moves up with uniform speed, the pulley turning round once in a time T which is directly proportional to the viscosity of the liquid. This result may be used to compare the viscosities η1 and η2 of two liquids using the same number of riders and noting the times T1 and T2 respectively for a complete rotation of the pulley. η1/η2 = T1/T2. The instrument is capable of high accuracy and has the special feature that a knowledge of the density of the liquid is not needed in the calculation of the result.