*This experiment was first published in Double Helix magazine.
Double Helix is the official science club of CSIRO Education.

Thermometers usually contain mercury or alcohol. But we decided to use another, more readily available, liquid. Yes... water!

Remember to ask your parents before beginning this experiment, because you don't want to get into hot water. Ha, ha, ha!

WHAT YOU NEED
- A small glass bottle
- Some moulding clay
- A clear drinking straw
- Cold water
- Food colouring to put in the water (optional)

WHAT YOU DO
1. Fill your bottle to the brim with ice-cold water and add some food colouring.

2. Make sure your bottle is standing on a flat surface.
Now put your straw into the bottle. Some of the water might go up the straw or over the edge of the bottle. That's okay, but try not to loose too much water.

3. Form an air-tight lid for the bottle out of the moulding clay.

<< Here's one that monkey man prepared earlier.

4. Now your simple bulb thermometer is ready to test. Place the bottle in your kitchen sink. Half fill the sink with hot water.

<< Careful you don't scald yourself with the hot water monkey man!

5. Wait a few seconds and you will see the coloured water move up the straw.

<< It's just a couple of centimetres above the lid.

WHAT'S GOING ON?
Simple bulb thermometers, like the one you've just created, work on the principle that the liquid takes up more room when it's hot.

The temperature of the liquid in your home made thermometer increased when it was surrounded by the hot water in the sink.

As it was warmed, the volume of the water increased. That's why you saw it creep slowly up the straw. It was displaced because it had nowhere else to go!

HOT LINKS

º How A Galileo Thermometer Works

º How to read a max/min thermometer