Procedure:

1. Fill the Tygon tubing with a solution of Universal Indicator in water.
2. Into one open end of the Tygon tubing a weak acid (such as vinegar) is added by a pipette and into the other end a weak base (such as a baking soda solution) is added by a pipette.
3. The Tygon tubing can be gently shaken so that the materials slowly mix. This will lead to interesting color changes but will eventually even out in color.
4. Allow for discussion.

This can be repeated many times with out change materials. As the tube fills a little can be siphoned off and discarded.

----Contributed by Frank Salter, Mark Twain Section