What is black powder made of? The chemistry in Dr Stone
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To stand up to Tsukasa, Senku decides to make a firearm. He points out that Japan is a volcanic archipelago, and therefore rich in sulfur, and launches the production of powder, presenting it as the first great weapon of the kingdom of science.
The subject in depth
Black powder relies on a redox reaction [Wikipedia] . Saltpeter (potassium nitrate, KNO₃) plays the role of oxidizer: when heated, it releases oxygen. That oxygen is immediately consumed by a fuel, charcoal (essentially carbon). Sulfur is the third player: it ignites at a lower temperature than charcoal and acts as a primer, speeding up the ignition of the whole mixture.
A simplified equation for the combustion reads: 2 KNO₃ + S + 3 C → K₂S + N₂ + 3 CO₂. The essential point lies in the ratio between solid and gas. A few grams of solid powder produce, in a fraction of a second, hundreds of times their volume in hot gases (nitrogen, carbon dioxide). It is this sudden expansion that propels a bullet or bursts a charge.
Black powder deflagrates; it does not detonate: its combustion front advances at a few hundred meters per second, well below the speed of sound in the material, unlike modern high explosives (nitroglycerin, TNT), which detonate at several kilometers per second. Grain size matters too: a powder that is finely ground and then recompacted into grains burns more evenly than a loose dust, a major innovation of medieval pyrotechnics.
Going further
Sources
- Black powder (French Wikipedia)
- Saltpeter (French Wikipedia)
- Robert P. Multhauf, The Origins of Chemistry (1966)
- Lewis Dartnell, The Knowledge: How to Rebuild Our World from Scratch (2014)
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