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Gunpowder, whether black powder or smokeless powder, is a substance that burns very rapidly, releasing gases that act as a propellant in firearms. Gunpowder is a low explosive. As it burns, a subsonic deflagration wave is produced rather than the supersonic detonation wave which high explosives produce. As a result, pressures generated inside a gun are sufficient to propel a bullet, but not sufficient to destroy the barrel. At the same time, this makes gunpowder less suitable for shattering rock or fortifications, applications where high explosives are preferred.
History and origins
Gunpowder is considered one of the Four Great Inventions of the Chinese, though in fact it is not known whether it was first invented in China.
The first type of gunpowder was black powder. Neither its inventors nor exact date of creation is known. Historians of various cultures have postulated that it was invented between the seventh or ninth centuries by either the Chinese or the Arabs. It is also possible that black powder was invented independently by more than one culture at around the same time.
The Arabs are generally credited with being the first to purify gunpowder to contain almost no sodium nitrate (only potassium nitrate) and to have a high enough quality to use effectively as a combat explosive. By the 15th century they had invented both a rocket and torpedo, both spear-tipped. The spear would lodge into a boat or other large surface and then the explosives would detonate as the propellant burned out.
Composition, characteristics and use
Black powder is a mixture of saltpeter (potassium nitrate or, less frequently, sodium nitrate), sulphur and charcoal with a ratio (by weight) of approximately 15:3:2 respectively. The ratio has altered over the centuries of its use, and can be altered somewhat depending on the purpose of the powder. Unlike smokeless propellants, it acts more like an explosive since its burn rate is not affected by pressure, but it is a very poor explosive because it has a very slow decomposition rate and therefore a very low brisance. This same property that makes it a poor explosive makes it useful as a propellant — the lack of brisance keeps the black powder from shattering the barrel, and directs the energy to propelling the bullet. Historically, potassium nitrate was extracted from manure by a process superficially similar to composting. Nitre beds took about a year to produce crystallized potassium nitrate.
The main disadvantages of black powder are a relatively low energy density (compared to modern smokeless powders) and the extremely large quantities of soot left behind. During the combustion process, less than half of black powder is converted to gas. The rest ends up as a thick layer of soot inside the barrel and a dense cloud of white smoke. In addition to being a nuisance, the residue in the barrel is hydrophilic and an anhydrous caustic substance. When moisture from the air is absorbed, the potassium oxide or sodium oxide turn into hydroxides, which will corrode wrought iron or steel gun barrels. Black powder arms must be well cleaned inside and out after firing to remove the residue. The thick smoke of black powder is also a disadvantage, as it can quickly become so opaque as to impair aiming.
The size of the granules of powder and the confinement determine the burn rate of black powder. Finer grains result in a closer mix of the ingredients, which results in a faster burn. Tight confinement in the barrel causes a column of black powder to explode, which is the desired result. Not seating the bullet firmly against the powder column can result in a harmonic shockwave, which can create a dangerous over-pressure condition and damage the gun barrel. One of the advantages of black powder is that precise loading of the charge is not as vital as with smokeless powder firearms and is carried out using volumetric measures rather than precise weight. However, overloading causing damage to a gun and its shooter is still possible. The lack of pressure sensitivity means that the mass of the bullet makes little or no difference to the amount of powder used. A full charge of black powder seated by just a small wad of paper, with no bullet, will still burn just as quickly as if it had a full weight bullet in front of it. This makes black powder well suited for blank rounds, signal flares, and rescue line launches.
See also
External links and references
- Gun and Gunpowder
- The Origins of Gunpowder
- Cannons and Gunpowder
- History of Science and Technology in Islam
- Ulrich Bretschler's Gunpowder Chemistry page
- A letter on gunpowder chemistry and sodium vs. potassium nitrate
- James Riddick Partington (1998). A History of Greek Fire and Gunpowder. The Johns Hopkins University Press. ISBN 0801859549.