Density column

Follow these instructions to build a density column and investigate why the layers don't mix.

• 10 January 2007 | Updated 14 October 2011

• What you need
• What to do
• What's happening

What you need

To do this activity you will need the following items:

• a tall clear jar or PET bottle
• golden syrup or honey
• water
• oil
• screws, paperclips, and any other small objects
• ice cubes
• food colouring
• detergent.

What to do

1. Carefully pour some golden syrup, water, and oil into the container in that order. You might want to add food colouring to the different layers to be able to see them better. What do you see?
2. Drop in the small objects. Do they reach the bottom? Try dropping in the ice-cubes.
3. Add a drop of detergent. What happens?

What’s happening

Diagram of the Density Column experiment

Golden syrup, water, and oil have different densities so they don’t mix. Instead they form three different layers. The denser fluids sink to the bottom while less dense fluids rise to the top. Where other objects sit in the density column depends on how dense the objects are.

Temperature can affect the density of fluids and solids. The strange thing about ice is that it is less dense than water, so it floats in the oil level. However, cold water is denser than warm water. Try adding a few droplets of colouring to half a cup of very hot water (ask an adult to help you) and add it to your density column. Does the colouring mix with all the water or does the hot coloured water form another layer?

Ever wondered why you need detergent for washing up your dishes? Normally, oil and water don’t mix together. When you add soap or detergent it reduces the surface tension of water, allowing it to dissolve the oil. Adding a few drops of detergent won’t be enough to dissolve all the oil in your density column. However, you should be able to see ‘breaks’ in the layers where some of the oil dissolved in the water.

For more hands-on activities, join CSIRO's Double Helix Science Club.