News | Published:

A Simple Viscometer

    Subjects

    Abstract

    PARTICULARS of a remarkably simple viscometer devised by Mr. A. G. M. Michell, of Melbourne, are given in Engineering for April 16. The instrument is intended for workshop use, and gives rapid determinations of viscosity in absolute measure without requiring extraordinary care or skill. It consists of a cup fitted with a handle and a ball of the same curvature as the cup. Contact of these surfaces is prevented by three symmetrically disposed projections in the cup, raised a mil or two above §its surface. The cup is held by its handle, and a few drops of the oil to be tested are placed in it. The ball is then placed in the cup and pressed firmly into it for five or ten seconds; This drives some of the oil out,^ which collects in a channel; enough oil must be provided in the first instance to ensure that the channel is filled. The instrument is then inverted, and the time taken for the ball to drop clear noted. This time in seconds divided by the constant of the instrument is equal to the absolute viscosity of the oil. The action depends upon the rate at which the oil-film between the cup and the ball thickens under the force of gravity exerted by the ball. This flow of oil is resisted by its viscosity, and the time taken for the ball to fall clear is accordingly directly proportional to the viscosity.' The above method is sufficiently accurate for workshop use. To obtain accurate results, the ball is placed at the bottom of a vessel containing a considerable quantity of the liquid. The cup is then lowered over the ball, taking care to exclude air. After pressing the two together as before, they are lifted until the ball clears the bottom of the vessel, and the time it takes to drop clear is noted as before. Mr. W. Ramsay, of Messrs. Cammell and Laird, has made as many as 120 most concordant readings in two hours, and the results plotted quite regularly. With liquids of very low viscosity, the ball is suspended from the arm of a balance. By adjusting the weights, the force tending to separate the ball from the cup can be diminished to, say, one-twentieth of the normal. This increases twenty fold the time needed to effect the separation. The manufacture in this country has been undertaken by Messrs. Michell Bearings, Ltd., 3 Central Buildings, London, S.W.I.

    Rights and permissions

    To obtain permission to re-use content from this article visit RightsLink.

    About this article

    Comments

    By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.