SCIENCE FOR YOUTH The chemistry of fire By Hiya Islam


Fire or the ‘red flower’ as The Jungle Book calls it has been around since the primitive age. Discovered by chance (or not!) and powered by oxygen, it is the reason to prosper as well as suffer. As man evolved with time, he learned how to make it, control it and destroy it. He devised ways to create fire for his advantage and below are listed a few culprits guilty of arson.

Starting with tiny red-headed dudes, the match-boxes are considered to be one of the easiest and safest ways to use fire. Match heads are packed with potassium chlorate, sulfur and powdered glass using glue that also serves the purpose of fuel. The striking surface on the match box is known to have red phosphorus, sand and powdered glass. When rubbed against each other, the friction between powdered glasses creates heat. This heat is just enough to turn red phosphorus into its white form, a highly volatile substance. And hence ignition, which breaks down potassium chlorate, releases oxygen. This released oxygen, is also useful in a sense that it does not rely on the environment for oxygen, reacts with sulfur and keeps the flame going. The wooden stick is coated with a compound; ammonium phosphate which prevents smoke after the flame dies.

Next up, we have, a black powder, the gunpowder, a major component of fireworks. It consists of charcoal and sulfur which act as fuel. Potassium nitrate or saltpeter is present too and provides oxygen for combustion. Somewhat like potassium chlorate in matchsticks. Mixing these components does not simply produce the powder. It requires proper grinding and at times, moisture. There is a specific ratio of chemicals and altering this will affect burning time and burning behavior.

But, what about dynamite? Dynamite is nothing but sawdust or cellulose drenched in nitroglycerin. The dense, yellow liquid is poisonous and unstable and an absorbent material makes it safe to handle. When the wick of a dynamite stick is set on fire, it leads to a small explosion that explodes the blasting cap which in turn triggers a much bigger explosion by nitroglycerin.

And now comes the very well-acquainted, the Molotov cocktail. This is a very simple explosive consisting of a fragile container usually a glass bottle. Its ingredients include a mixture of flammable liquids like, turpentine, diesel, alcohol, jet fuel and so on. It may also contain shards of glasses, metal blades or pins. Detergents, cement rubber, polystyrene foam are added to improve stickiness so that it sticks to the target. Such exquisite variety of ingredients, no wonder why it’s called a cocktail. And of course a wick which is made using cotton, wool or rags. Once lit, the cocktail is thrown. It breaks upon impact and the fuel and flame come into contact and cause an explosion.

And the list goes on, all sharing a common ability to destruct and injure.

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