Butane and propane << BYOO tayn and PROH payn >> are colorless, flammable gases. They are found in natural gas, light crude oil, and gases that are formed when heavy oil is cracked (broken down chemically) to produce gasoline.
Both butane and propane liquefy readily under pressure at ordinary temperatures. Mixtures of liquefied butane and propane are called LPG (liquefied petroleum gas). These mixtures, which are usually composed primarily of propane, are used as fuel in industry, trucks, and homes in isolated areas. Butanes are also added to gasoline in order to increase its volatility (evaporation rate) in cold climates. Isobutane, a form of butane, is used to make high-octane gasolines. Propane is an important source of ethylene, a colorless, flammable gas.
Propane boils at –43.7 °F (–42.1 °C). Normal butane boils at 31.1 °F (–0.5 °C), and isobutane boils at 10.9 °F (–11.7 °C).
