Several of you have written in asking for help with your homemade hot ice or sodium acetate. Here are the answers to the most common hot ice questions as well as advice for how to fix the usual problems making hot ice.
What is hot ice?
Hot ice is a common name for sodium acetate trihydrate.
How do I make hot ice?
In the lab, you could make hot ice from sodium bicarbonate and weak acetic acid (1 L 6% acetic acid, 84 grams sodium bicarbonate) or from acetic acid and sodium hydroxide (dangerous! 60 ml water, 60 ml glacial acetic acid, 40 g sodium hydroxide). The mixture is boiled down and prepared the same as the homemade version.
You can also buy sodium acetate (or sodium acetate anhydrous) and sodium acetate trihydrate. Sodium acetate trihydrate can be melted and used as-is. Convert sodium acetate anhydrous to sodium acetate trihydrate by dissolving it in water and cooking it down to remove the excess water.
Can I substitute baking powder for the baking soda?
No. Baking powder contains other chemicals which would act as impurities in this procedure and prevent the hot ice from working.
Can I use another type of vinegar?
No. There are impurities in other types of vinegar which would prevent the hot ice from crystallizing. You could use dilute acetic acid instead of vinegar.
I can't get the hot ice to solidify. What can I do?
You don't have to start from scratch! Take your failed hot ice solution (won't solidify or else is mushy) and add some vinegar to it. Heat the hot ice solution until the crystal skin forms, immediately remove it from heat, cool it at least down to room temperature, and initiate crystallization by adding a small quantity of the crystals that formed on the side of your pan (sodium acetate anhydrous). Another way to initiate crystallization is to add a small amount of baking soda, but if you do that you will contaminate your hot ice with sodium bicarbonate. It's still a handy way to cause crystallization if you don't have any sodium acetate crystals handy, plus you can remedy the contamination by adding a small volume of vinegar afterward.
Can I Re-Use the Hot Ice?
Yes, you can re-use hot ice. You can melt it on the stove to use it again or you can microwave the hot ice.
Can I eat hot ice?
Technically you can, but I wouldn't recommend it. It is not toxic, but it is not edible.
You show glass and metal containers. Can I use plastic?
Yes, you can. I used metal and glass because I melted the hot ice on the stove. You could melt the hot ice in a microwave using a plastic container.
Are containers used to make hot ice safe to use for food?
Yes. Wash the containers and they will be perfectly safe to use for food.
My hot ice is yellow or brown. How do I get clear/white hot ice?
Yellow or brown hot ice works... it just doesn't look that much like ice. The discoloration has two causes. One is overheating your hot ice solution. You can prevent this type of discoloration by lowering the temperature when you heated the hot ice to remove the excess water. The other cause of discoloration is the presence of impurities. Improving the quality of your baking soda (sodium bicarbonate) and acetic acid (from the vinegar) will help prevent discoloration. I made my hot ice using the least expensive baking soda and vinegar I could buy and managed to get white hot ice, but only after I lowered my heating temperature, so it's possible to get decent purity with kitchen ingredients.