In The Rainbow Tube: Chemical Demonstration—ChemTopic™ Lab Activity, saturated sodium carbonate solution is added to a test tube containing a dilute solution of hydrochloric acid and universal indicator. A rainbow column of colors develops as the dense sodium carbonate solution sinks to the bottom and carbonate ions gradually diffuse upward and neutralize acid solution. Available as part of the Acids and Bases—ChemTopic™ Labs digital collection. Click the Price link for digital collection pricing.