Page "Viscometer" Paragraph 4

These devices also are known as glass capillary viscometers or Ostwald viscometers, named after Wilhelm Ostwald.

Another version is the Ubbelohde viscometer, which consists of a U-shaped glass tube held vertically in a controlled temperature bath.

In one arm of the U is a vertical section of precise narrow bore ( the capillary ).

Above this is a bulb, with it is another bulb lower down on the other arm.

In use, liquid is drawn into the upper bulb by suction, then allowed to flow down through the capillary into the lower bulb.

Two marks ( one above and one below the upper bulb ) indicate a known volume.

The time taken for the level of the liquid to pass between these marks is proportional to the kinematic viscosity.

Most commercial units are provided with a conversion factor, or can be calibrated by a fluid of known properties.