Where to Buy Saltpeter or Potassium Nitrate

You used to be able to buy potassium nitrate as saltpeter in many garden supply stores. While it is difficult to find saltpeter, you can still purchase potassium nitrate, which is used to make smoke bombs and certain other fireworks.

Stores That Sell Potassium Nitrate

One of the most common sources of pure potassium nitrate is "stump remover." In the United States, you can find it at Lowes or Home Depot, among other places. Look for the Spectracide brand in those stores near the insecticides. Be sure to check the label to make certain potassium nitrate is the first (and preferably only) ingredient.

If you can't find potassium nitrate at a store in your area, you can order it online at Amazon, plus it's a chemical you can make it yourself.

Make Potassium Nitrate

Even if you can't find potassium nitrate, you can make it. All you need is a cold pack that lists potassium nitrate as an ingredient and salt substitute that lists potassium chloride as the only ingredient. It has to be salt substitute and not "lite salt", because the latter also contains sodium chloride. If you use lite salt, you'll end up with a mixture of sodium nitrate and potassium nitrate, which might be useful for your purpose, but isn't the same as pure potassium nitrate and will burn yellow rather than purple.

You need;

• 40 grams ammonium nitrate from the cold pack
• 37 grams potassium chloride from the salt substitute
• 100 milliliters water

1. Dissolve the ammonium nitrate in the water.
2. Filter the solution to remove any undissolved matter. You can use a coffee filter or a paper towel.
3. Add the potassium chloride to the liquid and gently heat the mixture to dissolve the salt. Don't boil it.
4. Filter the solution to remove solids.
5. Chill the liquid on ice or in the freezer. The potassium nitrate will freeze out as crystals, leaving ammonium chloride in solution.
6. Pour off the liquid and let the crystals dry. This is your potassium nitrate. You could also save the ammonium chloride, too. If you want the ammonium chloride, let the water evaporate and recover the solid material.

The reaction exchanges the ions in the compounds:

NH₄NO₃ + KCl → KNO₃ + NH₄Cl

The products can be separated because they have different solubilities. As you chill the mixture, potassium nitrate readily solidifies. Ammonium chloride is more soluble, so it remains in solution. Even though the solution is on ice or in the freezer, it won't freeze because the particles cause freezing point depression of the water. This is why these chemicals can be used to de-ice roads!

Keep in mind, the potassium nitrate you get from the reaction won't be reagent-grade purity. However, it should be pure enough for most chemistry experiments and fireworks projects.