Black Powder: Tang Fire Medicine, Corned Kernels and Gunpowder Soup

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Gunpowder began in ninth century Tang China, where Daoist alchemists seeking an elixir of immortality heated sulfur, realgar and saltpeter with honey. A text of the period warns of burned hands and faces and houses burned to the ground. They called it huoyao, fire medicine, and used it for skin and digestive ailments before soldiers took notice. The mature recipe settled at about 75 percent saltpeter, 15 percent charcoal and 10 percent sulfur, with the saltpeter supplying its own oxygen. Black powder deflagrates at subsonic speed rather than detonating, so it pushes a projectile instead of shattering the barrel.

The 11th century Wujing Zongyao records formulas with only about 50 percent saltpeter, suited to fire arrows and incendiaries, but stronger mixes led to bombs and metal guns such as the Heilongjiang hand cannon of 1288. Mongol armies carried Chinese engineers west, and the Syrian Hasan al-Rammah soon listed 107 recipes, calling saltpeter Chinese snow. Early European serpentine powder separated in wagons, so in the 14th century makers began corning it into grains, up to 300 percent more powerful. Later, Mysore's iron-cased rockets under Hyder Ali and Tipu Sultan inspired William Congreve's rockets, the rockets' red glare of 1812.

• Hasan al-Rammah described an egg which moves itself and burns, an early torpedo design.
• Old words such as the Arabic naft and the Chinese pao make it hard to tell when texts mean gunpowder weapons.
• France's droit de fouille let saltpeter men dig up peasants' stables until Antoine Lavoisier built managed nitrate beds of manure and urine.
• Its gentle push made black powder ideal for quarrying slate and marble without shattering the stone.
• Sailors rubbed gunpowder into needle pricks for tattoos, and surgeon Dominique Jean Larrey seasoned horse meat broth with it.