Screaming into the sky, exploding with a resounding report, and bursting forth in a dazzle of brilliant colours which glow for only a few spectacular moments - this is the life of a firework.
Fireworks are an integral part of many celebrations such as Canada Day or the Fourth of July but they also signal a home run at a Blue Jays game, great athletes at the Pan Am Games, and highlight the night sky in Vancouver during the summer.
For me, my childhood memories of fireworks are deeply connected to Hallowe'en.
Hallowe'en was a night dedicated to trick-or-treating - to candy or costumes. However, once we were all back home, we engaged in the annual ritual of setting off a box of fireworks. When I say "we," it was my dad's responsibility. Almost every house on the block would engage in the same ritual with each dad leading the way. Hallowe'en always ended with the night sky lit by Roman candles and burning sparklers.
Truly, fireworks are spectacular displays of chemistry in action, combined with a smattering of physics.
Looking up at a dazzling display set against a starry backdrop, most people probably think of the artistry and not chemistry or chemical compounds that make the show. But these displays are both fuelled and fired by chemical compounds.
Gunpowder, which provided the source of fuel for the launch of fireworks, was discovered by the Chinese during the seventh century. The exact date of discovery isn't actually known but there are accounts of the use of gunpowder dating back to around this time.
Gunpowder was most originally likely intended as an elixir to be consumed with tea for the promotion of longevity. Its more explosive properties were probably discovered by accident when the elixir came into contact with open flames.
When confined and burnt, gunpowder explodes. The rapid combustion and outward rush of gases - which is all that an explosion really is - can be utilized to blow an object apart. This detonation is used in the "charge" of a firework to spread fiery pellets across the sky. The "charge" is the payload that provides the fireworks.
However, by restricting the rate of combustion of gunpowder and directing the exit of the gases produced through a nozzle, the explosion and resulting gases can also be controlled and used to develop the thrust necessary to propel rockets or fireworks into the nighttime sky.
The original fireworks, developed by the Chinese, appear to have been these rocket types which burnt gunpowder as fuel to provide lift and contained an explosive charge in the nose to produce the spectacular effects.
Most likely, the use of fireworks originated with war. Exploding balls of light over the heads of an enemy would surely intimidate an invader. The Chinese successfully built gunpowder-powered rocket arrows which could travel further than a bow shot.
However, there are accounts of fireworks displays for various emperors dating back to the Tang Dynasty.
More sophisticated, modern fireworks use more sophisticated chemical mixtures to both propel and light them up. They also tend to use a mortar system in which the explosive charge is loaded into a barrel and shot into the air, in the same way that a cannon works.
A burning fuse attached to the charge determines when the explosion will occur and thus, how high the charge is when it generates its spectacular visual effects. This method is safer in that the explosive and propellant are separated from one another.
But, like all fireworks, a tremendous amount of respect is necessary and safety precautions must be observed.
The actual colours produced in fireworks result from the different types of chemical compounds burnt. The explosion of the charge might result in the ignition of strontium nitrate to produce brilliant reds or copper acetoarsenate to produce Paris Green (which is actually blue). The colours are a result of atomic excitation and line spectra emissions but a full explanation of that will have to wait for another column.
Of course, fireworks are much more complicated than just a mixture of gunpowder and colouring compounds. They contain stabilizers to prevent premature explosion and compounds to make the explosion smooth; casings to hold the charges and plugs to separate the various stages that make for the more spectacular multiple displays. The peony, the palm, and the chrysanthemum are examples of some of the myriad shapes fireworks can form. Needless to say, preparing fireworks is something that should be left to the professionals.
But certainly, when I was a child, Hallowe'en was not just about trick-or-treat. It was always marked by the presence of fireworks soaring into the sky throughout my neighbourhood and trying to run around the entire block before my sparkler ran out.
