Rainbow columns
Ingredients
- Water
- Salt
- Food colouring
WHAT TO DO
Take 2 large spoonfuls of salt and dissolve them in 100ml of water.
Add a few drops of green food colouring.
Then you take another large spoonful of salt and dissolve it in 100ml of water.
After, add a few drops of yellow food colouring, (If you don’t have yellow, use any other colour.)
Add a small spoonful of salt and dissolve it in 100ml of water.
Add a few drops of blue food colouring.
Add some red food colouring to 100ml of water, without adding any salt.
Gently add a bit of the green water to a test tube.
Add a bit of the yellow water very gently.
Repeat this two more times with the blue and red water.
If it mixes together, start again and keep on trying until 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 water.
The green water has the most salt in it, so it is the most dense. It remains at the bottom of the test tube.
The red water has the least salt in it, so it is the least dense. It remains at the top of the test tube.
Written for younger readers
Rainbow columns, in simpler words
This version comes from Wikijunior, a set of books written for children aged 8 to 11. It is shorter and uses plainer language than the article above.
From Wikijunior: Big Book of Fun Science Experiments
Water
Salt
Food colouring
Take 2 large spoonfuls of salt and dissolve them in 100ml of water.
Add a few drops of green food colouring.
Then you take another large spoonful of salt and dissolve it in 100ml of water.
After, add a few drops of yellow food colouring, (If you don’t have yellow, use any other colour.)
Add a small spoonful of salt and dissolve it in 100ml of water.
Add a few drops of blue food colouring.
Add some red food colouring to 100ml of water, without adding any salt.
Gently add a bit of the green water to a test tube.
Add a bit of the yellow water very gently.
Repeat this two more times with the blue and red water.
If it mixes together, start again and keep on trying until you get a rainbow.
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 water.
The green water has the most salt in it, so it is the most dense. It remains at the bottom of the test tube.
The red water has the least salt in it, so it is the least dense. It remains at the top of the test tube.
Where this page comes from
The article above is adapted from “Rainbow columns” on Simple English Wikipedia, by its contributors. We removed reference markers, navigation boxes and tables, expanded measurement templates into readable numbers, and kept the prose otherwise intact. The simpler version is adapted from Wikijunior on Wikibooks.
Both sources are published under CC BY-SA 4.0, so this page is published under the same licence. You may share and adapt it, including commercially, as long as you credit the original and keep the same licence.
Worksheets, answer keys and printable layouts elsewhere on K5Print are our own work and are not covered by this licence.