- Take a long tube, hold it vertically, and place one plug at the bottom end of the tube.
- Partially fill the tube with the indicator solution.
- Add a few drops of acid to the end of the tube and close it by another plug.
- Turn the tube over. The air bubble in the tube mixes the solution.
- Remote the plug (which now is on top) and add a few drops of base to the end of the tube.
- Close the upper end of the tube and turn the tube over again.
- The rainbow colored solution in the tube is formed.