Gunpowder, also named black powder, is a mixture of sulfur, charcoal, and potassium nitrate. It burns rapidly, producing volumes of hot solids and gases which can be 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. The gases produced by burning gunpowder generate enough pressure to propel a bullet, but not enough to destroy a gun barrel. This makes gunpowder less suitable for shattering rock or fortifications, where high explosives such as TNT are preferred.
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 AD 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 AD, European powdermakers began adding liquid to the constituents of gunpowder to reduce dust and with it the risk of explosion. The powdermakers would then shape the resulting paste of moistened gunpowder, known as mill cake, into “corns”, or granules, 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.
During the 18th century gunpowder factories became increasingly dependent on mechanical energy.
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