Electric ...
Ben Franklin



Wonder how the weatherman is able to tell you if it's hot or cold outside? Chances are he or she uses an instrument called a thermometer. It is a special instrument that is able to measure heat in the air. To be your own weatherperson you're going to need a thermometer. So let's make one.


You'll need these materials to make the thermometer:

  • tap water
  • rubbing alcohol (don't drink this)
  • a clear, narrow-necked plastic bottle
  • food coloring
  • clear plastic straw
  • modeling clay


  1. Pour equal parts of tap water and rubbing alcohol into the bottle, filling it about 1/8 of the way up.
  2. Add a few drops of food coloring to the mixture and stir or swirl the bottle to mix.
  3. Place the straw in the bottle but don't let it touch the bottom of the bottle.
  4. Seal the neck of the bottle with modeling clay so that the straw stands upright. Hold your hands on the bottle, and watch what happens to the liquid inside the straw.

How it Works

The alcohol in the mixture heats up when you place your hands around the bottle. Once the alcohol has heated up, it starts to expand (get bigger) and has nowhere else to go but up inside the straw. If you had held the bottle long enough, the mixture may have come out the very top of the straw. That would mean that the alcohol has expanded more than the bottle and straw can handle, thus causing the overflow.


Fun with Franklin is a great opportunity to learn and have fun, but if you are conducting an experiment you should be careful. Although the experiments on Fun with Franklin are relatively safe, you should make sure to do the following:

  • Follow all directions carefully and work in a clean, safe area.
  • Tell your parents/teachers you are conducting an experiment and ask if they want to help.
  • If you have questions or problems, feel free to ask an adult for help.
  • Don't do any experiment that you feel is too complex.