Did you know that another name for fireworks is pyrotechnics? And these days we can have amazing displays – including setting them to music! Do you remember the fantastic displays at the opening of the Olympic games and other celebrations such as the Golden Jubilee? Science has a hand in this. Let’s see how: -
Fireworks date back to ancient China but most of the effects you'll see in a typical display have been invented in this century. For example, coloured flames. Different chemical elements burn to give different coloured flames. Before the 19th century, only yellows and oranges could be produced with steel and charcoal. In the 19th century chlorates were developed and gave reds and greens. Good blues and purples were not developed until this century. Let’s hear it for chemistry! What would we do without it? Now every time we need a new colour in our fireworks we can rely on scientists to find a way to make it.
But what about the smell? What is that strange smell that lingers after fireworks? Well, that is due to one of the ingredients, sulphur. Sulphur is notorious for causing bad smells. Have you ever smelt rotten eggs? Yes that’s due to sulphur too – a gas called hydrogen sulphide. Phewee! Was that you?
Don’t forget the bangs! Firecrackers have been around for hundreds of years. They consist of black powder (also known as gun powder) in a tight paper tube with a fuse to light the powder. The black powder contains charcoal, sulphur and potassium nitrate. Sometimes aluminium is used instead of, or as well as, charcoal to brighten the explosion.
It is very common for fireworks such as Roman Candles, Silver Showers etc. to contain aluminium, iron, steel, zinc or magnesium dust in order to create bright, shimmering sparks. The metal flakes heat up until they are incandescent and shine brightly or, at a high enough temperature, actually burn. A variety of chemicals can be added to create colours.
Sparklers are made by mixing ingredients such as black powder with a binder like sugar or starch. Mixed with water, these chemicals form a slurry that can be coated on a wire (by dipping). Once it dries, you have a sparkler. When you light it, the sparkler burns from one end to the other. The types and amounts of chemicals are chosen so that the sparkler burns slowly rather than exploding like a firecracker.
A rocket is normally formed as a shell that consists of four parts:
- Container - Usually pasted paper and string formed into a cylinder
- Stars - Spheres, cubes or cylinders of a sparkler-like composition
- Bursting charge - Firecracker-like charge at the centre of the shell
- Fuse - Provides a time delay so the shell explodes at the right altitude
Simple shells consist of a paper tube filled with stars and black powder. Stars come in all shapes and sizes, but you can imagine a simple star as something like sparkler compound formed into a ball the size of a pea. The stars are poured into the tube and then surrounded by black powder. When the fuse burns into the shell, it ignites the bursting charge, causing the shell to explode. The explosion ignites the outside of the stars, which begin to burn with bright showers of sparks. Since the explosion throws the stars in all directions, you get the huge sphere of sparkling light that is so familiar at fireworks displays.
And if you are ‘burning’ to know more, then check out fireworks on the How Stuff Works website http://people.howstuffworks.com/fireworks.htm
Or for more details on the different sorts of fireworks try http://about-fireworks.net/hardware.html
