Do not use a copper pot.
You cannot use baking powder, which contains other chemicals that interfere with the process.
This measurement assumes you’re using 5% acetic acid, which is a common concentration for commercial vinegar. This doesn’t need to be a precise measurement, though.
If it does get very brown and cloudy, add a bit more vinegar and boil again. The sodium acetate starts out as “sodium acetate trihydrate,” meaning it contains water. Once all the water around it is gone, those water molecules start to evaporate and the sodium acetate becomes “sodium acetate anhydrous,” meaning “without water. "
It’s a good idea to add 1 or 2 tablespoons (15–30 mL) of vinegar. The vinegar will help keep the solution in its aqueous state, instead of forming that crust again.
If the liquid freezes during this stage, there might be a solid piece of crystal in it, or some other impurity. Add more vinegar, return to the stovetop, and try again. This is a difficult process, so it’s rare that you’ll get it on your first try.
If this does not happen, there is a problem with your solution. Add more vinegar and boil again — or try the more reliable store-bought method below.
Sodium acetate is also sold as “sodium acetate anhydrous,” and some vendors do not specify which form they mean. The instructions below cover both forms.
If the sodium acetate does not melt, you’ve bought sodium acetate anhydrous. To turn it into sodium acetate trihydrate, add hot water while it’s still in the boiling water bath. It will take about 2 mL water for every 3 grams of sodium acetate to fully dissolve the substance. Don’t use all of your sodium acetate. You’ll need a little for later.
Other impurities can trigger the freezing if they happen to be the right shape. This means you can sometimes trigger it by touching it with a toothpick or your finger, but solid sodium acetate is the only reliable way.
