Gunpowder,alsocalledblackpowder,isanexplosivemixtureofsulfur,charcoalandpotassiumnitrate,KNO3(alsoknownassaltpetre/saltpeter)thatburnsrapidly,producingvolumesofhotsolidsandgaseswhichcanbeusedasapropellantinfirearmsandasapyrotechniccompositioninfireworks.Thetermgunpowderisalsooftenusedmorebroadlytodescribeanypropellantpowderusedinfirearms.Modernfirearmsdonotusethetraditionalgunpowder(blackpowder)describedinthisarticle,butinsteadusesmokelesspowder.Inthisarticle,thetermsgunpowderandblackpowderareusedinterchangeably. 　　Gunpowderisclassifiedasalowexplosivebecauseofitsslowdecompositionrateandconsequentlylowbrisance.Lowexplosivesproduceasubsonicdeflagrationwaveratherthanthesupersonicdetonationwaveproducedbybrisants,orhighexplosives.Thegasesproducedbyburninggunpowdergenerateenoughpressuretopropelabullet,butnotenoughtodestroythebarrelofafirearm.Thismakesgunpowderlesssuitableforshatteringrockorfortifications,wherehighexplosivessuchasTNTarepreferred. 　　Theterm"blackpowder"wascoinedinthelate19thcenturytodistinguishpriorgunpowderformulationsfromthenewsmokelesspowdersandsemi-smokelesspowders.(Semi-smokelesspowdersfeaturedbulkvolumepropertiesthatapproximatedblackpowderintermsofchamberpressurewhenusedinfirearms,buthadsignificantlyreducedamountsofsmokeandcombustionproducts;theyrangedincolorfrombrownishtantoyellowtowhite.Mostofthebulksemi-smokelesspowdersceasedtobemanufacturedinthe1920s.)[1][2][3] 　　Blackpowderisagranularmixtureof 　　anitrate—typicallypotassiumnitrate(KNO3)—whichsuppliesoxygenforthereaction; 　　charcoal,whichprovidesfuelforthereactionintheformofcarbon(C); 　　sulfur(S),which,whilealsoafuel,lowersthetemperatureofignitionandincreasesthespeedofcombustion. 　　Potassiumnitrateisthemostimportantingredientintermsofbothbulkandfunctionbecausethecombustionprocessreleasesoxygenfromthepotassiumnitrate,promotingtherapidburningoftheotheringredients.[4]Toreducethelikelihoodofaccidentalignitionbystaticelectricity,thegranulesofmodernblackpowderaretypicallycoatedwithgraphite,whichpreventsthebuild-upofelectrostaticcharge. 　　Thecurrentstandardcompositionforblackpowdermanufacturedbypyrotechnicianswasadoptedaslongagoas1780.Itis75%potassiumnitrate,15%softwoodcharcoal,and10%sulfur.[5]Theseratioshavevariedoverthecenturiesandbycountry,andcanbealteredsomewhatdependingonthepurposeofthepowder.Forinstance,coarsergradesofblackpowder,unsuitableforuseinfirearmsbutadequateforblastingrockinquarryingoperations,iscalledblastingpowderratherthangunpowder;itisoftenmadewiththecheapersodiumnitratesubstitutedforpotassiumnitrateinproportionsof60%nitrate,20%charcoaland20%sulfur.[citationneeded] 　　Theburnrateofblackpowdercanbechangedbycorning.Corningfirstcompressesthefineblackpowdermealintoblockswithafixeddensity(1.7g/cm³).Theblocksarethenbrokenupintogranules.Thesegranulesarethensortedbysizetogivethevariousgradesofblackpowder.IntheUnitedStates,standardgradesofblackpowderrunfromthecoarseFggradeusedinlargeboreriflesandsmallcann