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Paint the sky.

Sparks! Colors! Stuff that blows up! Chemistry doesn't get much better than this.

Ever notice how minutes seem to drag on for hours when you're waiting for a fireworks show to begin? Everyone's thinking the same thing: The sky is dark enough, the hot dogs are all eaten ... come on, when are they going to get going?

Then the first rockets streak into the sky ... Ooh! Aah! Yes, it was worth the wait.


What goes on when fireworks go off? To find out, there's no better place to start than the Brookhaven, N.Y., factories of the Grucci family. Dubbed the First Family of Fireworks, the Gruccis have been splashing colors across the sky for 150 years. They are masters of pyrotechnics (fireworks science).

Pyrotechnics is really just chemistry dressed up in flashy clothing. It works because every fireworks shell contains a mixture of powdered chemicals. When the shell detonates, the chemicals react. In other words, the bonds between the atoms that make up the chemicals break and rearrange themselves to form new substances.

In the case of fireworks reactions, that rearranging releases loads of heat energy. But heat, as you know, is hardly sufficient to attract a crowd. For that you need the other kinds of energy released by the reaction: light and sound. These are the key ingredients of a Grucci display.

If you work for the Gruccis, you quickly learn the rules of pyrotechnics. Number one: A spark is your worst enemy. Why? Because a spark is a good way to kick off a chemical reaction.

Chemical reactions don't happen "just like that." It takes a jolt of energy to get things started (that is, to break the original chemical bonds). A spark (or a burning match or a lit fuse) will provide this activation energy.

So you don't slam metal tools together inside the Grucci factory. And you don't rub your wool sweater and then shock the person working next to you. Static electricity is a big no-no.

In fact, before you step inside a Grucci building, you have to touch your finger to a copper plate. Copper conducts electricity easily, so any static electric charge on your body zips harmlessly through the plate to the ground outside.

The Gruccis learned their safety lessons the hard way. Ten years ago an enormous explosion destroyed their factory and killed two family members. Since then, they leave the most dangerous part of fireworks-manufacture--mixing together the chemicals that react so violently--to someone else. They buy the shells containing the chemicals from other fireworks makers.

Then, at a small cluster of fireworks assembly buildings, Grucci workers add lift charges--small explosives that boost the shells high into the air. They also tack on fuses that ignite the fireworks once they're in the sky.


At showtime, cousin Butch Grucci usually does the launching honors, lighting both the lift charge and the fuse with (you guessed it) a spark, from a spark-generating machine. The crowd holds its collective breath. Meanwhile the fuse flame races toward the shell. When it makes contact, that's when the real fun begins. Two chemical reactions take place to produce the burst of color you see in the sky.

First, the burning fuse ignites a charge of black powder (similar to gunpowder) inside the shell. Bang! Chemical bonds shatter and reform, releasing loads of energy--much more energy than contained in the spark that got the whole thing started.

This exothermic (energy-releasing) reaction blows the shell apart: It transforms the mixture of chemical powders into hot gases that expand suddenly, as hot gases do.

There's not really much to look at yet--maybe just a flash. But in an instant, the heat from the first reaction provides the energy jolt needed to start the second. It's colorburst time.

The heat ignites tiny pellets (called stars), which were originally packed around the black powder inside the shell. As the pellets stream outward, propelled by the expanding gases, the chemicals inside react fiercely. The result: streaks of colored light. Ooh! Aah! Another exothermic reaction!

And don't forget the energy released from both reactions in the form of kaboom!--er, sound. It may take a few seconds to reach you because light travels faster than sound.

If all goes well, your eyes and your ears will be smiling--and you'll be far enough away so that you don't feel the heat. For half an hour, you can forget how long it took for the show to start--and how long you'll have to wait for the next one to begin.
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Title Annotation:chemistry of fireworks
Author:Pope, Greg
Publication:Science World
Date:May 7, 1993
Previous Article:Shades of summer.
Next Article:Salt of the season.

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