Diethyl Ether, CH3CH2OCH2CH3, is an extremely flammable organic solvent, and also one of the first anesthetics to be discovered. It boils at 34.6°C, just under average human body temperature, so ether evaporates very easily. Its vapor is more dense than air, so ether fumes tend to sink in the atmosphere. The combination of ether's high volatility, flammability, and vapor density can easily result in a fire is ether is used in a room in which open flames are present.
In the following demonstration, a pile of cotton balls is placed at one end of a metal trough, with a lit candle at the other end. A small amount of diethyl ether is then poured onto the cotton balls. Some of the ether evaporates, and the vapor drifts down to the candle. The candle ignites the ether fumes, and the entire trail of ether vapor leading back to the cotton balls is lit, and the cotton balls themselves catch on fire. If the cotton balls are placed in a metal scoop, they can be simply lifted out, and dumped into a sink where the fire can be extinguished by smothering it with wet rags.
This video consists of three film clips, each taken
from a different angle.
!!! Hazards !!!
Ether, as can be seen here, is extremely flammable — if you look at this stuff the wrong way, it'll catch on fire. (Okay, that's a little bit of an exaggeration.) NEVER use water to put out an ether fire; the burning ether will simply float on top of water, causing the fire to be spread over a larger area. Ether fires should be smothered with a damp cloth, sand, or some other appropriate smothering agent. Ether fumes are also an anesthetic; prolonged exposure can cause drowsiness.
Ether is a great solvent for many types of reactions in organic chemistry, but its flammability does pose some safety hazards. It is a standing rule in all organic chemistry labs (intact ones, that is), that open flames are not allowed when ether is being used.
Martha Windholz (ed.), The Merck Index, 10th ed. Rahway: Merck & Co., Inc., 1983.