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Armstrong's mixture is a highly sensitive
primary explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An expl ...
. It is very friction-sensitive. Formulations vary, but one consists of 67%
potassium chlorate Potassium chlorate is a compound containing potassium, chlorine and oxygen, with the molecular formula KClO3. In its pure form, it is a white crystalline substance. After sodium chlorate, it is the second most common chlorate in industrial use. It ...
, 27%
red phosphorus Elemental phosphorus can exist in several allotropes, the most common of which are white and red solids. Solid violet and black allotropes are also known. Gaseous phosphorus exists as diphosphorus and atomic phosphorus. White phosphorus White ...
, 3%
sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
, and 3% calcium carbonate. It is named for
Sir William Armstrong William George Armstrong, 1st Baron Armstrong, (26 November 1810 – 27 December 1900) was an English engineer and industrialist who founded the Armstrong Whitworth manufacturing concern on Tyneside. He was also an eminent scientist, inventor ...
, who invented it sometime prior to 1872 for use in explosive shells.


Toys

Armstrong's mixture can be used as ammunition for toy cap guns. The mixture is suspended in water with some
gum arabic Gum arabic, also known as gum sudani, acacia gum, Arabic gum, gum acacia, acacia, Senegal gum, Indian gum, and by other names, is a natural gum originally consisting of the hardened sap of two species of the '' Acacia'' tree, ''Senegalia sen ...
or similar binder and deposited in drops, each containing a few milligrams of explosive, to dry between layers of paper backing. The dots explode with some smoke when struck. Armstrong's mixture can be used in impact
firecrackers A firecracker (cracker, noise maker, banger) is a small explosive device primarily designed to produce a large amount of noise, especially in the form of a loud bang, usually for celebration or entertainment; any visual effect is incidental to ...
known as ''cap torpedoes'', which explode on impact when the ball (made of clay or
papier-mâché upright=1.3, Mardi Gras papier-mâché masks, Haiti upright=1.3, Papier-mâché Catrinas, traditional figures for day of the dead celebrations in Mexico Papier-mâché (, ; , literally "chewed paper") is a composite material consisting of p ...
) is thrown or launched by
slingshot A slingshot is a small hand-powered projectile weapon. The classic form consists of a Y-shaped frame, with two natural rubber strips or tubes attached to the upper two ends. The other ends of the strips lead back to a pocket that holds the pro ...
. The firecrackers may include gravel with the explosive mixture to ensure detonation.


Military use

With the addition of a grit such as
boron carbide Boron carbide (chemical formula approximately B4C) is an extremely hard boron–carbon ceramic, a covalent material used in tank armor, bulletproof vests, engine sabotage powders, as well as numerous industrial applications. With a Vickers hard ...
(in a modified formulation given as 70% KClO3, 19% red phosphorus, 3% sulfur, 3% chalk, and 5% boron carbide by weight), Armstrong's mixture has been considered for use in
firearm A firearm is any type of gun designed to be readily carried and used by an individual. The term is legally defined further in different countries (see Legal definitions). The first firearms originated in 10th-century China, when bamboo tubes ...
primers. This use as primer for artillery propellants may have been Armstrong's original purpose. Armstrong's mixture has been used in thrown impact-detonated
improvised explosive devices An improvised explosive device (IED) is a bomb constructed and deployed in ways other than in conventional military action. It may be constructed of conventional military explosives, such as an artillery shell, attached to a detonating mechan ...
, made simply by loading it into hollow balls. It also was seen in various patents for matches, novelty fireworks, and signalling devices.


Safety

Armstrong's mixture is both very sensitive and very explosive, a dangerous combination that limits its practical use to toy caps. Such toy caps and fireworks typically contain no more than 10 milligrams each, but gram quantities can cause maiming hand injuries. The mixture is likely to explode if mixed dry and is even dangerous wet. It is recommended that Armstrong's mixture be prepared as a slurry in water and adjusted to a slightly basic pH with an alkaline buffer, such as calcium carbonate, in order to neutralize any acid that may have been generated by oxidized phosphorus on contact with the water, which would cause it to deteriorate while slowly drying. The wet slurry or paste is loaded into the fireworks, then allowed to dry. Simple mixtures of red phosphorus and potassium chlorate can detonate at a wide range of proportions; a 20% phosphorus mixture had 27% of the equivalent power of a like mass of
TNT Trinitrotoluene (), more commonly known as TNT, more specifically 2,4,6-trinitrotoluene, and by its preferred IUPAC name 2-methyl-1,3,5-trinitrobenzene, is a chemical compound with the formula C6H2(NO2)3CH3. TNT is occasionally used as a reagen ...
in a laboratory experiment, and the detonation of the 10% and 20% phosphorus mixtures even in small unconfined samples of 1 gram was described by the authors as "impressive" and "scary". Pyrotechnician John Donner wrote in 1996 that it "is the most hazardous mixture commonly used in small fireworks." Davis Tenney called it "a combination which is the most sensitive, dangerous, and unpredictable of the many with which the pyrotechnist has to deal. Their preparation ought under no conditions to be attempted by an amateur." Toy charges, such as the several-milligram dots used for cap guns, are individually harmless but potentially dangerous in large numbers. On May 14, 1878, such an accident occurred in Paris. A store containing some six to eight million paper caps, totaling about 64 kilograms of explosive mass, caught fire and exploded, killing 14 and injuring 16 more.


References

{{reflist Explosives Pyrotechnic compositions