Wikijunior:Big Book of Fun Science Experiments/Rainbow columns

INGREDIENTS

• water
• salt
• food colouring

WHAT TO DO

• Take 2 large spoonfuls of salt and dissolve them in 100mls of water.

• Add a few drops of green food colouring.
• Then you take another large spoonful of salt and dissolve it in 100mls of water.

• Then add a few drops of yellow food colouring (if you don't have yellow use any other colour).
• Then add a small spoonful of salt and dissolve it in 100mls of water.

• add some red food colouring to that.

• add a bit of food colouring to a test tube.
• then add another colour of food coloring very very gently.
  
• add different types of food colouring 2 more times very gently.
• if it mixes together start again and keep on trying till you get a rainbow.

Principle

The principle of this experiment is density. Density is the ratio between volume and mass. When different substances of different densities are added to a container, one frequently floats on top of the other because it has lower density. The perfect example of this is oil on top of gasoline.