On every Diwali, known as the festival of lights, our family has a big discussion on the kind of lighting we should have. And after talking about candles or electric bulbs we invariably choose the _diya_s or earthen lamps for their beautiful flames. But last year, we reached the kumhara or potter’s roadside shop a bit too late. The lamps had been sold out and the potter had a big smile on his face. So we decided to light candles.
On Diwali eve we lit up the house with candles, putting one small candle between two large ones, to create a pattern. Horror of horrors, when we looked at them some time later, they had become much smaller. My five-year-old cousin thought it was magic. “Where did the wax disappear?” he asked. I smiled and remembered my uncle Prosanto, who had solved this mystery for me when I was a child.
When wax disguises itself
“When you wear a disguise, people cannot recognise you. Similarly when candle burns, the wax simply changes into something else.” That’s how my uncle had explained it.
That process of burning is called combustion. Combustion is a chemical change which takes place in the presence of oxygen. During combustion one form of matter is changed into another. The burning of wood or coal is also combustion.
The candle story
If you take a close look at the candle you will find that it has a thread running though its centre – this is called the wick. The moment we light the wick the wax starts melting because of the heat. The molten wax rises up through the wick to meet the flame. The molten wax further heats on reaching close to the flame and evaporates to form a gas. The gaseous wax then starts burning, producing heat and light.
What is wax made of?
The wax of the candle is actually formed of carbon and hydrogen and so is called a hydrocarbon. Most fuels including petrol and coal are hydrocarbons. During the process of burning the carbon combines with the oxygen of the air and forms carbon dioxide. Hydrogen in turn combines with oxygen to form water vapour. In these two reactions wax is consumed and the size of the candle keeps reducing.
So now you know what to tell someone who wants to know where the wax disappeared on burning.