The viscosities of liquids can be compared by observing their rates of flow through a glass tube.
A simple device called a Redwood viscometer can be adapted easily for the laboratory.
Comparing viscosities using a viscometer
A viscometer is shown in Figure 1.
Using the apparatus in Figure 1, fill the funnel with liquid to a level just above the upper mark.
- Open the clip to allow the liquid to flow through the tube into the beaker.
- Start timing when the level passes the upper mark and stop as it passes the lower one.
- Repeat for various samples, and then list your samples in order of increasing viscosity.
For runny liquids, like water or sugar solutions of a low concentration, a capillary tube with a diameter of 1 mm should be used so that very short times (and large percentage uncertainties) are avoided. For viscous liquids, like syrup and honey, tubes with bores of 5 mm or wider can be used.
A sample Result of viscometer experiment to compare viscosities of liquids
The results of such an experiment may be presented as done in Table 1.
|Sugar solution concentration(%)||0||10||20||30||40|
Conclusion: If the conditions are kept the same throughout, the time taken for the same volume of the solutions to pass through the tube will be proportional to the viscosity of the sugar solution.