Viscosity measurement of a liquid

The viscosity of two liquids can be compared by making use of an Ostwald Viscometer which consists of two bulbs, one attached with a capillary tube and U-tube below the capillary tube while other bulb is attached to the other arm of U-tube at a level lower than the other bulb. The liquids of known densities are allowed to flow through the capillary maintaining the same differences of levels in the limbs and the time equation which governs the flow lead to the relation:

where and are viscosity coefficients of the liquid and water, respectively and d₁ and d₂ are the densities of liquid and water, respectively. Knowing the value of viscosity of one liquid, one can calculate the viscosity of other liquid.

The procedure for measurement of viscosity is as follows. The viscometer is fixed vertically on the stand and 10 mL or 20mL of water is pipetted into the lower bulb. The volume of water (10 mL or 20 mL) is chosen so that the liquid can be conveniently sucked into the upper bulb leaving some in the lower bulb. It is sucked up into the other bulb to a point about the mark above the bulb. Now it is released and stop clock is started when the meniscus crosses the mark. The clock is stopped when the mark below the bulb is passed. The time is recorded at the moment. The same procedure is repeated twice or thrice and their average is used in calculations.

Similarly, the experiment is repeated with the given liquid. Using the specific gravity bottle, one can determine the specific gravity of the liquid and then calculate the viscosity. The viscosity of water at room temperature is used from the tables.