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A Ubbelohde type viscometer or suspended-level viscometer is a measuring instrument which uses a capillary based method of measuring viscosity . It is recommended for higher viscosity cellulosic polymer solutions. The advantage of this instrument is that the values obtained are independent of the concentration. The device was invented by the German chemist Leo Ubbelohde (1877-1964).
Additional recommended knowledge
The Ubbelohde viscometer is closely related to the Ostwald viscometer. Both are u-shaped pieces of glassware with a reservoir on the right and a measuring bulb with a capillary on the left. A liquid is introduced and a pressure head forces this liquid from the bulb through the capillary to the reservoir. The time it takes for the liquid to pass through two calibrated marks is a measure for viscosity. The Ubbelohde device has a third arm extending from the end of the capillary and open to the atmosphere. In this way the pressure head only depends on a fixed height and no longer on the total volume of liquid.
The determination of viscosity is based on Poiseuille's law:
The average pressure head is given by:
Usually the viscosity of a liquid is compared to a liquid with an analyte for example a polymer dissolved in it. The relative viscosity is given by:
where ηsp/c is called the viscosity number.
The intrinsic viscosity can be determined experimentally by measuring the viscosity number as function of concentration as the Y-axis intercept.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Ubbelohde_viscometer". A list of authors is available in Wikipedia.|