Density Ladder

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This concept is often covered in GCSE science as a thought experiment, but producing a practical equivalent needs thought.


A density ladder is a column of different liquids that are stacked depending on their density.
The most dense is at the bottom, with the least dense floating on top.

Choosing Chemicals

Care should be used when selecting suitable chemicals to make a ladder to ensure that no reactions occur between the different components. Occasionally solid items (e.g. pieces of plastic, wood etc.) are dropped in to see between which layers they will float.
Some ladders have mercury as the densest medium. Care should always be taken when using mercury, both as it is toxic and has the ability to form amalgams. Floating a wedding ring on mercury is not encouraged!.
One inconvenience is that most common chemicals used will mix with one or other of the other layers when stirred. What is desirable is a series of mutually immiscible liquids that are reasonably safe to handle.
A selection of three mutually immiscible has been found to work which are:

  • Diethyl Phthalate,1.12g/cm3 (Risk phrases R36,R37,R38 and R63-may damage unborn babies with prolonged exposure)
  • Water
  • and oil
test-tubes containing 3 liquids

Using a coloured oil (for Boyles' Law apparatus) and adding fluorecein to the water layer for display, gave an interesting effect when shaken
The Dye appears to be preferentially absorbed by the phthalate.

--D.B.Ferguson 15:19, 28 September 2010 (UTC)

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