Rolling-sphere viscometer for structured liquids

In the apparatus described, since the sphere is very small compared with the cylindrical tube containing the sample, fresh channels can be found for quite large numbers of tests. In this way measurements are made on hitherto unsheared material, and this is important in studying thixotropic or otherwise structured systems. The instrument may be used even when inertia effects are considerable since, over a wide range of experimental conditions, a very simple correction of the Oseen type is found to apply. Relative viscosities of glycerine-water mixtures and of fat-free milks determined in the sphere viscometer agree adequately with those from an Ostwald or other capillary viscometer; but the structure of renneted milk, even before rigidity sets in, is damaged by the drastic shearing and, for such systems, the rolling-sphere viscometer gives a more reliable picture of viscosity changes.