What is the Difference Between Ostwald and Ubbelohde Viscometers?

Ostwald and Ubbelohde viscometers are both instruments used to measure the viscosity of a fluid, but they have some key differences:

1. Measurement Method: Ostwald Viscometer, also known as U-tube viscometer, is suitable for lower viscosity liquids, while Ubbelohde Viscometer is recommended for higher viscosity cellulosic polymer solutions.
2. Independence from Concentration: The values obtained using an Ubbelohde Viscometer are independent of the total volume, which is not the case for an Ostwald Viscometer.
3. Third Arm: The Ubbelohde device has a third arm extending from the end of the capillary and open to the atmosphere, ensuring that the pressure head only depends on a fixed height and not on the total volume of the liquid.

Similarities between Ostwald and Ubbelohde Viscometers include:

• Both are U-shaped instruments.
• Both instruments have two glass bulbs.
• Both instruments use capillary tubes.

In summary, while both Ostwald and Ubbelohde viscometers are used to measure viscosity, they differ in their measurement methods, suitability for different viscosity ranges, and independence from concentration. The Ubbelohde Viscometer is specifically designed for higher viscosity solutions and has a third arm that ensures the pressure head depends only on a fixed height.

Comparative Table: Ostwald vs Ubbelohde Viscometers

The main difference between Ostwald and Ubbelohde viscometers lies in their suitability for measuring different ranges of viscosity. Here is a table comparing the two types of viscometers:

Ostwald Viscometer, also known as U-tube viscometer, is suitable for measuring low to moderate viscosity, while Ubbelohde Viscometer is designed for measuring high to very high viscosity. The Ostwald Viscometer consists of a U-tube with two bulbs separated by a capillary tube, where the two bulbs act as reservoirs for the liquid. Ubbelohde Viscometer, on the other hand, is a capillary viscometer that does not have separate reservoirs.