The Chemistry of Gunpowder

Gunpowder, or black powder is a very important factor in chemistry. Although gunpowder can explode, it is primarily used as a propellant. Invented by the Chinese in the 9th century, gunpowder was mainly composed of sulfur, charcoal, and potassium nitrate. When the ingredients were ground together, the end result was a powder that called serpentine. The ingredients usually required remixing prior to each use, which made gunpowder especially dangerous.

Black powder consists of a fuel (charcoal and sometimes sugar) and an oxidizer (potassium nitrate), and sulfur, to create a stable reaction. The carbon from the charcoal combined with the oxygen forms carbon dioxide and energy. The reaction would be slow, like a wood fire, without help from the oxidizing agent. Carbon in a fire must draw oxygen from the air which is where the potassium nitrate comes in. Potassium nitrate, or saltpeter, provides extra oxygen. Potassium nitrate, sulfur, and carbon react together to form nitrogen and carbon dioxide gases and potassium sulfide. The expanding gases, nitrogen and carbon dioxide, are propelled to create a lasting effect.

The recipe for black powder was first recorded by an English philosopher by the name of Roger Bacon in 1242. The original formula, consisting of 7 parts saltpeter, 5 parts hazelwood (charcoal or carbon), and 5 parts sulphur, has been modified in its proportions to serve various uses, but the main ingredients have remained the same. The perfecting of gunpowder was a long ongoing process. Eventually scientists realized that the powder was simply a mixture, and not a new compound.

Gunpowder is classified as a low explosive because of its slow decomposition rate and very low rate of explosion. Low explosives produce a subsonic combusion rather than the supersonic detonation wave produced by the rate in which the substance explodes, or high explosives. The gases produced by burning gunpowder generate enough pressure to propel a bullet, but not enough to destroy the barrel of a firearm. This makes gunpowder less suitable for shattering rock or fortifications, where high explosives such as TNT are preferred.

Gunpowder requires two parts: a fuel and an oxidant. Just about anything that burns can act as a fuel: charcoal, alcohol, fuel oil, sugar, and even metal powders like aluminum and zinc. There are fewer oxidants to choose from. Some of the most popular are saltpeter and ammonium nitrate, both made from nitric acid. Originally, saltpeter was used as the primary oxidant because it was the most commonly known oxidant. A downside about saltpeter is that when it is used as an oxidant, the explosive is burns very slowly. This means that the combustion takes place lazily at a thousanth of a second.