Children can't wait to write with these incredible pens. Heat from your fingers causes the colored liquid inside the pen's chamber to "boil", creating oodles of bubbles and fun.  A great learning tool that is both innovative and value priced!  See thermodynamics in action when you hold the bottom glass bubble and the liquid inside “magically” rises to the top glass bubble! The heat generated from your fingers causes the liquid to “boil” and rise to the top bubble. Once you let go of the bottom bubble, gravity causes the liquid to return to the bottom bubble. Includes a stand for holding pen upright.  Perfect for school or the office, and a conversation starter.  Colors vary:   Blue, Red, Purple or Green. Note - NOT A TOY!  Boiler chamber is made of glass and should be handled with care! Approximately 5 3/4" long.  Ages 7+