(Chemical symbol: P) A highly reactive, toxic, non-metallic element used in steel, glass, and pyrotechnics.
In the free state phosphorus has three allotropic forms; yellow, red and black. However, it is almost always found in combination with other elements such as minerals or metal ores. Atomic number, 15; atomic weight, 3 1.02; specific gravity, 12.16; and melting point, 44.2oC (111.6oF).
Phosphorus is usually found in steel and cast iron as an impurity. It is therefore the practice of steel makers to reduce the phosphorus level to 0.05%, or lower if possible. Higher amounts cause embrittlement and loss of toughness; however, small amounts of phosphorus in low-carbon steel produce a slight increase in strength and corrosion resistance.