In week 6 Joe did an experiment on hot ice. Hot ice is a liquid,and when you touch it, it crystalizes.
In the poster it says how to make sodium acetate. Instructions:

1. Sodium acetate is a powder and you add water and boil it.
2. After about 2 minutes of it boiling you pour it in a container and store it in the fridge or freezer.
   
3. After about 5 minutes in the fridge it will be cold put a bit of sodium acetate on your finger and dip it in the mixture and take it out and watch it freeze.
4. You can reuse it by simply boiling it up and repeating the process.

Sodium acetate is also found in heat packs that is what makes the heat pack freeze and go warm when you click the metal, the mixture reacts and heats up the heat spreads and the rest of the liquid freezes over. By Joe