Here's why:
* Fixed air is an old term for carbon dioxide. It was discovered by Joseph Priestley in the 18th century.
* Candles are typically made of wax, which is composed of hydrocarbons (compounds of carbon and hydrogen).
* When a candle burns, it reacts with oxygen from the air. This reaction releases heat, light, and carbon dioxide.
So, the combustion of a candle produces carbon dioxide, which was historically known as "fixed air."
