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Gunpowder, made of a mixture of sulfur, charcoal, and saltpeter (potassium nitrite), owes its explosive force to the fact that 1 mole of solid powder will, when ignited, produce 6 moles of gas. This rapid expansion in the enclosed space of a metal tube could be used to drive a projectile at high speed in a specified direction. Modern gunpowder is simply a refined version of the primitive substance in which the chemical composition has been altered to provide the greatest expansion with the smallest quantity and the least residue. The manufacture of modern powders is standardized enough that gunpowder residue can be analyzed by methods which identify specific components, which can aid the forensic scientist greatly. We will enlarge upon this subject later on.|
The force of a projectile is related to the kinetic energy (KE) imparted to it, given by the formula:
Kinetic Energy = 1/2 MV2 where M=Mass and V=Velocity
Historically, the first way the KE was enhanced was increasing the "caliber" of the weapon. Caliber refers to the diameter of the bore of the barrel, given in decimal fractions of an inch or, in metric systems, in millimeters. Thus, a handgun or rifle could be referred to as .45 cal or .38 cal (called 45 caliber or 38 caliber) or 9mm. The second way modern weapons increase KE is through velocity, as impelled by modern gunpowder, which increases the force tremendously because it increases KE as a square of any increment of improvement in velocity.
Velocities of bullets increased with the use of a "jacket" of a metal such as copper or copper alloys that covered a lead core and allowed the bullet to glide down the barrel more easily than exposed lead. Such bullets are designated as "full metal jacket" (FMJ). Such FMJ bullets are less likely to fragment on impact and are more likely to traverse through a target while imparting less energy. Hence, FMJ bullets impart less tissue damage than non-jacketed or partly jacketed bullets that expand.
Gunpowder, also known since the late 19th century as black powder, is a mixture of sulfur, charcoal, and potassium nitrate. Gunpowder can be made just using potassium nitrate and charcoal (or alternatively without charcoal), but without the sulfur (or coal), the powder is not as strong. It burns rapidly, producing a volume of hot gas made up of carbon dioxide, water, and nitrogen, and a solid residue of potassium sulfide. Because of its burning properties and the amount of heat and gas volume that it generates, gunpowder has been widely used as a propellant in firearms and as a pyrotechnic composition in fireworks. The term gunpowder also refers broadly to any propellant powder. Modern firearms do not use the traditional gunpowder (black powder) described in this article, but instead use smokeless powder. Antique firearms or replicas of antique firearms are often used with black powder substitute.
Gunpowder is classified as a low explosive because of its relatively slow decomposition rate and consequently low brisance. Low explosives deflagrate at subsonic speeds. High explosives detonate, producing a supersonic wave. Ignition of the powder packed behind a bullet must generate enough pressure to force it from the muzzle at high speed, but not enough to rupture the gun barrel. Gunpowder is thus less suitable for shattering rock or fortifications, where high explosives such as TNT are preferred.
Gunpowder was, according to prevailing academic consensus, discovered in the 9th century by Chinese alchemists searching for an elixir of immortality. This discovery led to the invention of fireworks and the earliest gunpowder weapons in China. In the centuries following the Chinese discovery, gunpowder weapons began appearing in the Arab world, Europe, and India. The consensus is that this was spread from China, through the Middle East, and then into Europe, although there remains some dispute over the amount of Chinese influence on later advancements in gunpowder techology.
The term black powder was coined in the late 19th century to distinguish prior gunpowder formulations from the new smokeless powders and semi-smokeless powders. Semi-smokeless powders featured bulk volume properties that approximated black powder in terms of chamber pressure when used in firearms, but had significantly reduced amounts of smoke and combustion products; they ranged in color from brownish tan to yellow to white. Most of the bulk semi-smokeless powders ceased to be manufactured in the 1920s.
Black powder is a granular mixture of
* a nitrate, typically potassium nitrate (KNO3), which supplies oxygen for the reaction;
* charcoal, which provides carbon and other fuel for the reaction, simplified as carbon (C);
* sulfur (S), which, while also serving as a fuel, lowers the temperature required to ignite the mixture, thereby increasing the rate of combustion.
Potassium nitrate is the most important ingredient in terms of both bulk and function because the combustion process releases oxygen from the potassium nitrate, promoting the rapid burning of the other ingredients. To reduce the likelihood of accidental ignition by static electricity, the granules of modern black powder are typically coated with graphite, which prevents the build-up of electrostatic charge.
Charcoal does not consist of pure carbon; rather, it consists of partially pyrolyzed cellulose, in which the wood is not completely decomposed.
The current standard composition for the black powders that are manufactured by pyrotechnicians was adopted as long ago as 1780. Proportions by weight are 75% potassium nitrate (known as saltpeter or saltpetre), 15% softwood charcoal, and 10% sulfur. These ratios have varied over the centuries and by country, and can be altered somewhat depending on the purpose of the powder. For instance, power grades of black powder, unsuitable for use in firearms but adequate for blasting rock in quarrying operations, is called blasting powder rather than gunpowder with standard proportions of 70% nitrate, 14% charcoal, and 16% sulfur; blasting powder may be made with the cheaper sodium nitrate substituted for potassium nitrate and proportions may be as low as 40% nitrate, 30% charcoal, and 30% sulfur. The British Government in 1635 used the raitio 75% Charcoal, 12.5% Saltpetre, 12.5% Sulfur.
 Combustion rate
The burn rate of black powder can be changed by corning. Corning first compresses the fine black powder meal into blocks with a fixed density (1.7 g/cm³). The blocks are then broken up into granules. These granules are then sorted by size to give the various grades of black powder. In the United States, standard grades of black powder run from the coarse Fg grade used in large bore rifles and small cannons, through FFg (medium and smallbore arms such as muskets and fusils), FFFg (smallbore rifles and pistols), and FFFFg (extreme small bore, short pistols and most commonly for priming flintlocks). In the United Kingdom, the gunpowder grains are categorised by mesh size: the BSS sieve mesh size, being the smallest mesh size on which no grains were retained. Recognised grain sizes are Gunpowder G 7, G 20, G 40, and G 90.
A simple, commonly cited, chemical equation for the combustion of black powder is
2 KNO3 + S + 3 C → K2S + N2 + 3 CO2.
A more accurate, but still simplified, equation is
10 KNO3 + 3 S + 8 C → 2 K2CO3 + 3 K2SO4 + 6 CO2 + 5 N2.
The burning of gunpowder does not take place as a single reaction, however, and the byproducts are not easily predicted. One study's results showed that it produced (in order of descending quantities): 55.91% solid products: potassium carbonate, potassium sulfate, potassium sulfide, sulfur, potassium nitrate, potassium thiocyanate, carbon, ammonium carbonate. 42.98% gaseous products: carbon dioxide, nitrogen, carbon monoxide, hydrogen sulfide, hydrogen, methane, 1.11% water.
Black powder made with sodium nitrate tends to be hygroscopic, unlike black powders made from saltpeter. (In this article, "saltpeter"--also spelled "saltpetre"--means potassium nitrate and not any of the other nitrates that are also sometimes called "saltpeter.") Because black powder made with saltpeter is less affected by moisture in the air, it can be stored unsealed for centuries without degradation if it is kept dry. Muzzleloaders have been known to fire after hanging on a wall for decades in a loaded state, provided they remained dry. By contrast, black powder made with sodium nitrate must be sealed from the moisture in the air to remain stable for long periods.
In quarrying, high explosives are generally preferred for shattering rock. However, because of its low brisance, black powder causes fewer fractures and results in more usable stone compared to other explosives, making black powder useful for blasting monumental stone such as granite and marble.
Black powder is well suited for blank rounds, signal flares, burst charges, and rescue-line launches. Black powder is also used in fireworks for lifting shells, in rockets as fuel, and in certain special effects.
Black powder has a low energy density compared to modern "smokeless" powders, and thus to achieve high energy loadings, large amounts of black powder are needed with heavy projectiles. In military applications black powder also produces thick smoke as a byproduct, which may give a soldier's location away to an enemy observer. The smoke may also impair aiming for additional shots.
Combustion converts less than half the mass of black powder to gas. The rest ends up as a thick layer of soot inside the barrel. In addition to being a nuisance, the residue from burnt black powder is hygroscopic and with the addition of moisture absorbed from the air, this residue forms a caustic substance. The soot contains potassium oxide or sodium oxide that turns into potassium hydroxide, or sodium hydroxide, which will corrode wrought iron or steel gun barrels. Black powder arms must be well cleaned both inside and out to remove the residue. The Matchlock musket or pistol (an early gun ignition system), as well as the flintlock would often be unusable in wet weather, due to powder in the pan being exposed and dampened. Because of this unreliability, soldiers carrying muskets, known as musketeers, were armed with additional weapons such as swords or pikes. The bayonet was developed to allow the musket to be used as a spear, thus eliminating the need for the soldier to carry a secondary weapon.
Edge-runner mill in a restored mill, at Eleutherian Mills
For the most powerful black powder meal, a wood charcoal is used. The best wood for the purpose is Pacific willow, but others such as alder or buckthorn can be used. The ingredients are mixed as thoroughly as possible. This is achieved using a ball mill with non-sparking grinding apparatus (e.g., bronze or lead), or similar device. Historically, a marble or limestone edge runner mill, running on a limestone bed was used in Great Britain; however, by the mid 19th century CE this had changed to either an iron shod stone wheel or a cast iron wheel running on an iron bed. The mix is sometimes dampened with alcohol or water during grinding to prevent accidental ignition.
Around the late 14th century CE, European powdermakers began adding damp to the constituents of gunpowder to reduce dust and with it the risk of explosion. The powdermakers would then shape the resulting paste of dampened gunpowder, known as mill cake, into corns, or grains, to dry. Not only did corned powder keep better because of its reduced surface area, gunners also found that it was more powerful and easier to load into guns. Before long, powdermakers standardized the process by forcing mill cake through sieves instead of corning powder by hand.