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A long held tradition for first projects in pyrotechnics

Introduction

def Gunpowder Black powder is a granular mixture of

   * a nitrate, typically potassium nitrate (KNO3), which supplies oxygen for the reaction;
   * charcoal, which provides carbon and other fuel for the reaction, simplified as carbon (C);
   * sulfur (S), which, while also a fuel, lowers the temperature of ignition and increases the speed of combustion.

Recipe

It is 75% potassium nitrate, 15% softwood charcoal, and 10% sulfur.

It is often made with the cheaper sodium nitrate substituted for potassium nitrate in proportions of 60% nitrate, 20% charcoal and 20% sulfur.

A simple, commonly cited, chemical equation for the combustion of black powder is

   2 KNO3 + S + 3 C → K2S + N2 + 3 CO2.

A more accurate, but still simplified, equation is

   10 KNO3 + 3 S + 8 C → 2 K2CO3 + 3 K2SO4 + 6 CO2 + 5 N2.

The burning of gunpowder does not take place as a single reaction, however, and the byproducts are not easily predicted. One study's results showed that it produced (in order of descending quantities): 55.91% solid products: potassium carbonate, potassium sulfate, potassium sulfide, sulfur, potassium nitrate, potassium thiocyanate, carbon, ammonium carbonate. 42.98% gaseous products: carbon dioxide, nitrogen, carbon monoxide, hydrogen sulfide, hydrogen, methane, 1.11% water.

Acquiring the materials

A very useful website for finding chemicals for any experiment is The Household Products Database

Potassium Nitrate (KNO3)

This chemical used to be widely available as a fertilizer. Now the best way to purchase fairly pure quantities is as stump remover. This source is usually around 98% pure, the other 2% being an anti-caking agent.

Stump removers confirmed as KNO3 sources:

  • Gordon's stump remover
  • Hi-Yield brand stump remover

Sulfur

This chemical is often sold as a soil acidifier and fungicide. These sources tend to be only about 50% sulfur. Given the low melting point of sulfur (115.21 °C, 239.38 °F) it may be possible to purify it by heating it and either relying on density to cause the sulfur to float to the top (the other ingredients are often more dense) and pouring it off. Depending on the particle size of the ingredients, heating it on a screen and alowing the sulfur to drip through could be another option.

Charcoal

Although it may seem like one of the easier ingredients to find and buy, it is a better idea to just make your own. Charcoal that is sold for barbecues contains a clay binder to make it into the nice briquette shape.

Making charcoal is very easy and allows you complete control of ingredients. All that is required is a fireproof container with a small hole in it to vent the gas produced(CAUTION: this gas is very flamable). The container is filled with your wood of choise and then heated until no more gas is produced. Let it cool and open the container. Instructions for large scale production

Status:

    * Completed

Conclusions:

    * must grind up oxidizer very finely, recommend blender or mortar and pestle
    * coarser mixtures are cool to watch
    * leaves too much sludge to be pleasant to clean up