Playing with Sodium Acetate, or "Hot Ice"
Channel: Kyle Clements
Date: 2012-01-31

Sodium acetate is often called "hot ice" due to it's reaction to agitation.  Clicking the button inside this hand warmer causes the solution to crystallize, and within seconds what was liquid is now solid.  The reaction is also exothermic; it creates a lot of heat.

It is also indefinitely reusable.  Boiling the packet re-liquefies the material.

Science: It works, Bitches!