Phosphorus is found in three main forms: white, red, and black. (There are also numerous allotropes of each of these forms.)
In this demonstration, a small chunk of white phosphorus has been left exposed to air for about 15 minutes (which is not shown); the white phosphorus then spontaneously ignites, producing a brilliant yellow-orange flame, and a dense cloud of choking vapor:
Video Clip: REAL, 8.94 MB
In order to make the demonstration start faster, the phosphorus may also be ignited with a match.
A variation on this procedures, which I've sometimes heard referred to as the "Barking Dogs" demonstration, involved making a solution of white phosphorus in carbon disulfide, and allowing it to spontaneously ignite when poured onto a piece of filter paper on top of a large graduated cylinder. (See Shakhashiri below.) When the white phosphorus ignites, the filter paper catches fire, lighting the carbon disulfide in the cylinder, and producing a sharp, "bark-like" sound. If I can ever get this to work right, I'll film it.
!!! Hazards !!!
White phosphorus is extremely toxic; the approximate fatal dose is about 50 to 100 mg. Even in very small quantities, it produces severe gastrointestinal irritation, diarrhea, and liver damage. It also causes burns when it comes in contact with skin. Chronic exposure to white phosphorus causes bony necrosis (especially of the jaw, a condition called "phossy-jaw") and anemia.
White phosphorus should be handled with gloves! This procedure must be performed in a fume hood!
Spontaneous Combustion of White Phosphorus: Bassam Z. Shakhashiri, Chemical Demonstrations: A Handbook for Teachers of Chemistry, Volume 1. Madison: The University of Wisconsin Press, 1983, p. 74-76.
F. Albert Cotton and Geoffrey Wilkinson, Advanced Inorganic Chemistry, 5th ed. New York: John Wiley & Sons, 1988, p. 386-387.
John Emsley, The Elements, 3rd ed. Oxford, Clarendon Press, 1998, p. 152-153.
David L. Heiserman, Exploring Chemical Elements and their Compounds. New York: TAB Books, 1992, p. 63-64.
Martha Windholz (ed.), The Merck Index, 10th ed. Rahway: Merck & Co., Inc., 1983.