Sodium Acetate has a melting temperature of 51 C and below this temperature it prefers to be a solid. However, when Sodium Acetate is hydrated and melted it forms a supersaturated solution that will happily exist as a liquid below its melting point. (Cooling the solution in a clean and texture free container is vital to prevent crystals forming and the solution solidifying prematurely). If this supersaturated liquid is then made to crystallise, the solution temperature rises to its melting temperature (around 51 C) immediately and solidifies. This is where the name HOT ICE comes from and Sodium Acetate is used commercially for hand warmers, applying this very same principle.
HOW TO MAKE HOT ICE: Place an amount of Sodium Acetate Trihydrate in a pan (without water) and begin heating slowly (Sodium Acetate Trihydrate does not need to be completely dissolved in water, as it is already hydrated). When you see the Sodium Acetate melting, add a small volume of water, enough to stop the solution forming a crust at the surface (do not add too much water, as the solution will be too dilute and will not solidify). You will now have a hot solution of Sodium Acetate.
In order for the solution to remain a liquid, it needs to be completely free from contaminates that may have entered the solution during preparation (hairs, small bits of food, etc); either let the contaminates sink to the bottom of the pan and spoon off the top into a glass or you could use a coffee filter to filter the solution into a glass. Then, with the solution still hot and filtered into a glass, place in the fridge to cool. Once cool touch the liquid and it should instantly form HOT ICE before you eyes.