Norman Wiesman, age 10 of St. Paul, Minn., for his question:
WHAT EXACTLY IS FIRE?
Through the ages, man has used a number of different methods to make fire. In ancient days he twisted sticks in holes in wood until the friction caused flames. Later he learned to strike certain types of rocks together to create sparks that would set fire to dry material. Today he uses matches. Their heads, made of chemicals, ignite when struck on rough surfaces.
Fire is the heat and light that comes from burning substances. Earliest man learned to use fire to keep him warm and to cook his food. A French chemist named Antoine Lavoisier proved in 1777 that burning is actually the result of the rapid union of oxygen with other substances. As a substance burns, he discovered, heat and light are produced.
Burning is also called combustion. When oxygen comes together with other substances at such a slow rate that little heat and no light are given off, we call this process oxidation rather than burning or combustion. Oxidation takes place whenever oxygen unites with other substances either rapidly or slowly.
When oxygen unites with gasoline, the action takes place rapidly and heat and light are given off. This process may be described as either burning, combustion or oxidation. When oxygen unites with iron and causes it to rust, burning or combustion does not take place but oxidation does.
Substances burn in different manners. Wood, oil, magnesium, gas and coal give off heat and a flame while a substance like charcoal gives off heat with only a glow. But all of these substances need oxygen, which may be obtained from the air, in order for them to burn.
Sometimes old paint or oil soaked rags can cause a type of fire called spontaneous combustion. Oxygen from the air may slowly unite with the rags. At first there will not be a fire but as oxidation gradually takes place, enough heat accumulates to set the rags on fire.
Rapid burning can cause explosions like those produced by gunpower or dynamite. Here oxidation takes place so swiftly that great volumes of gas are produced. The gas requires hundreds of times the space that was formerly occupied by the gunpowder before it was oxidized. These gases expand so rapidly that they produce an explosion.
For fire to be produced there must be fuel or a substance that will burn. Then the fuel must be heated to its kindling temperature. Then there must be plenty of oxygen.
Fuels are either solids, liquids or gases. Coal and wood are examples of solids while oils and gasoline are liquid fuels. Natural gas and hydrogen are gaseous fuels.