Gunpowder
2007 Concise Encyclopedia. Related subjects: General Chemistry
Gunpowder, whether black powder or smokeless powder, is a substance that burns very rapidly, releasing gases that act as a propellant in firearms. Both forms of gunpowder are low explosives. 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 was invented in China and is considered one of the Four great inventions of ancient China.
Gunpowder was the first known chemical explosive and propellant. The earliest record of gunpowder, a Chinese book from c. 850 AD called "Classified Essentials of the Mysterious Tao of the True Origin of Things," indicates that gunpowder was a byproduct of Taoist alchemical efforts to develop an elixir of immortality:
Some have heated together sulfur, realgar and saltpeter with honey; smoke and flames result, so that their hands and faces have been burnt, and even the whole house where they were working burned down.
The Chinese first used gunpowder in warfare in 904, as incendiary projectiles called "flying fires." Its use was soon expanded to explosive grenades hurled from catapults. The third step was to use gunpowder as a propellant. Its first such use was recorded in 1132 in experiments with mortars consisting of bamboo tubes. Mortars with metal tubes (made of iron or bronze) first appeared in the wars (1268-1279) between the Mongols and the Song Dynasty.
Gunpowder spread to the Arabs in the 13th century.
There is no direct record of how gunpowder came to be known in Europe. Most scholars believe that the knowledge spread west from China to the Middle East and then Europe, possibly via the Silk Road. Other historians believe that gunpowder was probably discovered independently by different cultures at different times, as James Partington writes in his History of Greek Fire and Gunpowder:
Gunpowder is not, of course, an 'invention' in the modern sense, the product of a single time and place; no individual's name can be attached to it, nor can that of any single nation or region. Fire is one of the primordial forces of nature, and incendiary weapons have had a place in armies' toolkits for almost as long as civilized states have made war.
In Europe, the first written mention of the composition of gunpowder in express terms was in Roger Bacon's "De nullitate magiæ" at Oxford in 1216. In Bacon's "De Secretis Operibus Artis et Naturae" in 1248, he states: "We can, with saltpeter and other substances, compose artificially a fire that can be launched over long distances... By only using a very small quantity of this material much light can be created accompanied by a horrible fracas. It is possible with it to destroy a town or an army ... In order to produce this artificial lightning and thunder it is necessary to take saltpeter, sulfur, and Luru Vopo Vir Can Utriet." The last part is probably some sort of coded anagram for the quantities needed. In the "Opus Maior" he describes firecrackers around 1267: "a child’s toy of sound and fire made in various parts of the world with powder of saltpeter, sulphur and charcoal of hazelwood." The confusion of these two references have led to many widespread misunderstandings about Bacon and Gunpowder.
The process of "corning" black powder was a further important improvement, and was developed in Europe probably during the late 14th century. Corning involves forcing damp powder through a sieve to form it into granules which harden when dry, preventing the component ingredients of gunpowder from separating over time, thus making it far more reliable and consistent. It also allowed for better ignition, as the granules allowed for air pockets in between granules.
Composition
Black powder is a mixture of saltpeter (potassium nitrate or, less frequently, sodium nitrate), charcoal and sulfur with a ratio (by weight) of approximately 15:3:2 respectively. The ratio has changed over the centuries of its use, and can be altered somewhat depending on the purpose of the powder.
Characteristics and use
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 tactical 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 greater surface area, 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.