Once the rust is dissolved, potassium carbonate is slowly added to the solution, turning it a bright green. The rest of the process happens more or less naturally, as crystals begin to form in the ...

The first 'reaction' that we tried for our hand warmer involved dissolving potassium carbonate (K 2 CO 3) in water. Potassium carbonate is one of the chemicals left behind in the ashes of burnt wood.