Water vapor

   Water vapor is the vaporized, or gaseous, form of water. It is invisible. There is water vapor everywhere—in the outside air, inside houses and buildings.
   Water evaporates constantly from oceans, lakes, rivers, and from the grassy portions of the earth.    As water is heated, the molecules move faster and faster until they bounce out into the air, independently of each other.
   Water vapor is also formed when any substance containing hydrogen is burned.
   The hydrogen combines chemically with the oxygen in the air to form water molecules—chemical symbol, H2O (2 atoms of hydrogen, 1 atom of oxygen). Any kind of COMBUSTION—wood, fire, gas flame, burning candle—results in the formation of water vapor. Every gallon of gas burned in an automobile engine produces seven pints of water—which can be seen streaming from the exhaust on a cool day.