With a Bang: The Science of Fireworks

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You've probably set off a firework or two in your time, but do you know how fireworks work? This Fourth of July, we'll burn our way through a few common examples of every stripe, flash, and boom. You've seen the lights. Now know the science.

By John Wenz

", credit: "", sourceid: null, sourcename: "", sourceurl: null, sourcelogo: "", thumbsrc: "/cm/popularmechanics/images/H6/fireworks-science-01-0713-smn.jpg", src: "/cm/popularmechanics/images/DM/fireworks-science-01-0713-lgn.jpg", srcwidth: 600, srcheight: 450 }, { id: "slide2", url: "with-a-bang-the-science-of-fireworks-2", slidetype: "image", title: "Sparklers", description: "Sparklers are a familiar sight on Independence Day. Essentially, they\'re made from iron filings and aluminum powder stuck to a metal rod, with a starchy water solution that acts as a glue. Once the sparkler is lit, the metals rapidly oxidize with the help of an oxidizing agent, barium nitrate, which is how they give off sparks. The sparkler burns out when it reaches the end of its fuel.", credit: "", sourceid: null, sourcename: "", sourceurl: null, sourcelogo: "", thumbsrc: "/cm/popularmechanics/images/Ld/fireworks-science-02-0713-smn.jpg", src: "/cm/popularmechanics/images/iN/fireworks-science-02-0713-lgn.jpg", srcwidth: 600, srcheight: 450 }, { id: "slide3", url: "with-a-bang-the-science-of-fireworks-3", slidetype: "image", title: "Firecrackers", description: "We know there\'s a fuse and some gunpowder involved with firecrackers, but what\'s happening at the chemical level?\n

\nEach little tube is packed with black powder, which is 75 percent potassium nitrate, 15 percent charcoal and 10 percent sulfur. When the fuse is lit, it sets off a chain reaction: The fuse ignites the charcoal, the charcoal reacts with the sulfur, and the sulfur reacts with the potassium nitrate. Or, to be more specific: The charcoal causes the sulfur to oxidize, which causes the potassium nitrate to oxidize, which creates a little tube of burning oxygen in a closed space. As the gases fill the tube, they run out of room. That\'s when the whole thing goes \"bang.\"", credit: "", sourceid: null, sourcename: "", sourceurl: null, sourcelogo: "", thumbsrc: "/cm/popularmechanics/images/AO/fireworks-science-03-0713-smn.jpg", src: "/cm/popularmechanics/images/56/fireworks-science-03-0713-lgn.jpg", srcwidth: 600, srcheight: 450 }, { id: "slide4", url: "with-a-bang-the-science-of-fireworks-4", slidetype: "image", title: "Ground Spinners", description: "Inside a ground spinner there\'s a tapered tube with clay on either end, and a series of propellants inside to give the firework a variety of colors (we\'ll get to that later.) When the fuse is lit, it ignites the first of the propellants. The gas from the reactions escapes out the small hole where the fuse once went into the firework, which propels the firework along its center axis. The tube spins because it\'s off-balance?the weight not being evenly distributed throughout?causing it to jump around.", credit: "", sourceid: null, sourcename: "", sourceurl: null, sourcelogo: "", thumbsrc: "/cm/popularmechanics/images/AH/fireworks-science-04-0713-smn.jpg", src: "/cm/popularmechanics/images/Bc/fireworks-science-04-0713-lgn.jpg", srcwidth: 600, srcheight: 450 }, { id: "slide5", url: "with-a-bang-the-science-of-fireworks-5", slidetype: "image", title: "Artillery Shell Fireworks", description: "These are the real crowd-pleasers: those balls that are placed into a mortar tube and shot into the air, creating a dazzling sight with a delayed effect. \n

\nThe artillery shells are filled with gunpowder in two tiers. When the fuse burns down to the bottom, it lights a bit of gunpowder called the (lift charge)?the charge that shoots the shell into the air. \n

\nWhile the shell flies through the air, a time fuse is burning. This burns slowly up into the upper chamber of the shell until it reaches the second supply of gunpowder, called the (burst charge.) This burst charge ignites a series of small projectiles called (stars.) The shell is packed with these stars, which create the colorful arrangements seen in the sky.", credit: "", sourceid: null, sourcename: "", sourceurl: null, sourcelogo: "", thumbsrc: "/cm/popularmechanics/images/j5/fireworks-science-05-0713-smn.jpg", src: "/cm/popularmechanics/images/LO/fireworks-science-05-0713-lgn.jpg", srcwidth: 450, srcheight: 600 }, { id: "slide6", url: "with-a-bang-the-science-of-fireworks-6", slidetype: "image", title: "So What Gives Them Color?", description: "If fireworks were strictly gunpowder, there\'d be no excitement, really. They\'d all just be balls of fire in the air. Salts and other metal compounds allow a firework to detonate in burst of bright blue or rich red.\n

\nTo make red, fireworks contain strontium salts and/or lithium salts, with the strontium producing a brighter red reaction. Calcium salts make orange, while sodium salts (as in table salt) explode in yellow. Green comes from the compound barium chloride, blue from copper chloride. Silver or white colors are made of aluminum or magnesium.\n

\nIf you want purple, you\'ve got to work a little harder: Combine strontium salts for red and copper chloride for blue to create a purple explosion.", credit: "Ken Reid/Getty Images", sourceid: null, sourcename: "", sourceurl: null, sourcelogo: "", thumbsrc: "/cm/popularmechanics/images/MC/fireworks-science-06-0713-smn.jpg", src: "/cm/popularmechanics/images/SJ/fireworks-science-06-0713-lgn.jpg", srcwidth: 600, srcheight: 450 } ] };

Snap 'n' Pops

These little balls of paper so harmless they're legal year-round. But what's going on under there?

Silver fulminate is an incredibly reactive explosive. The slightest impact or heat sets it off. Because of that instability, it's rarely used as a commercial explosive compound. You don't want to set off a stick of dynamite by bumping it the wrong way.

There is one use for it, though. You'll find about 80 micrograms of it in every snap 'n' pop, along with a bunch of tiny bits of gravel. The gravel gives the silver fulminate the friction it needs to ignite.

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