Smoke bomb ingredient: potassium nitrate (aka saltpeter)

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I learned how to make smoke bombs when I was 12 by reading a recipe in Abbie Hoffman's Steal This Book. The recipe calls for two ingredients: ordinary sugar and potassium nitrate (also known as saltpeter). In those days I was able to buy potassium nitrate from the pharmacy at K-Mart in Boulder, Colorado.

Here's Hoffman's recipe:


Sometimes it becomes strategically correct to confuse the opposition and provide a smoke screen to aid an escape. A real home-made stroke bomb can be made by combining four parts sugar to six parts saltpeter (available at all chemical supply stores). This mixture must then be heated over a very low flame. It will blend into a plastic substance. When this starts to gel, remove from the heat and allow the plastic to cool. Embed a few wooden match heads into the mass while it's still pliable and attach a fuse.

The smoke bomb itself is a non-explosive and non-flame-producing, so no extreme safety requirements are needed. About a pound of the plastic will produce thick enough smoke to fill a city block. Just make sure you know which way the wind is blowing. Weathermen-women!

The problem with this recipe is that the mixture can easily ignite while heating it over a stove burner. My friend and I made a batch when I was 13, and it went off in his kitchen and caused a lot of damage (when it burns it produces a red hot liquid that looks like molten lava). So I do not recommend this recipe. Has anyone tried melting the sugar first, then turning off the burner and pouring the potassium nitrate into the molten sugar? I've also read that you can mix together powdered sugar and potassium nitrate and ignite the powder. Other people have reported success adding melted paraffin to the powdered mixture.

Potassium nitrate is also an ingredient in gunpowder (which also contains charcoal and sulfur). There's an interesting paragraph about potassium nitrate in William Gurstelle's excellent book about acceptable risk-taking, Absinthe & Flamethrowers: Projects and Ruminations on the Art of Living:

In parts of China, gunpowder makers could merely scoop up saltpeter that lay on the ground, the result of fermentation of soil and animal waste in the humid subtropical climate. Europeans living in a dryer, colder environment had to work much harder to get saltpeter. The early European method of obtaining potassium nitrate involved aggregating great heaps of rotting organic matter, especially that which contained high percentages of rotted meat and animal dung. "Petermen" would search out promising places to collect their smelly treasure. Abandoned outhouses and animal pens were especially prized. The petermen picked up and taste-tested handfuls of dirt. When they found a place that tasted right, they'd cart out the soil, boil it in vats, then evaporate the liquid and strain the slurry-like residue. The result was high-purity saltpeter.
The image of a peterman tasting saltpeter brings to mind the widely held belief that militaries add saltpeter to soldier's food as a way to deaden their sex drives. But saltpeter's reputation as an anti-Viagra is false. From Snopes:
There's no proof potassium nitrate (also known as saltpeter) has any effect on libido, plus or minus, so there would be nothing to be gained from such a doctoring of edibles. Yes, saltpeter has long rumored to be an anaphrodisiac, a substance that reduces sexual drive. But it's all rumor and no fact.
If you are interested in experimenting with potassium nitrate, you can buy it from Amazon. 5 lb Potassium Nitrate on Amazon

Photo by M. Kelley. Creative Commons Attribution 2.0 Generic license.