Before you attempt this please do it with safety glasses on and be careful, as with any chemicals. You do this at your own risk please take the time to read our disclaimer
Sodium acetate or hot ice is an amazing chemical you can prepare yourself from baking soda and vinegar. You can cool a solution of sodium acetate below its melting point and then cause the liquid to crystallize. The crystallization is an exothermic process, so the resulting ice is hot. Solidification occurs so quickly you can form sculptures as you pour the hot ice.
This would be a great thing to know if you wanted to make your own hand warmers when its cold if SHTF these may even help you do jobs outside you wouldn’t normally be able to do with out heat or extra clothes…