Noun
red phosphorus (uncountable)
(chemistry) A stable allotrope of phosphorus; used in the manufacture of safety matches, pesticides etc.
In general, the rate of evaporation (m) of a substance in a high vacuum is related to the pressure (p) of the saturated vapor by the equation m=\sqrt{\frac{M}{2\pi RT}}p. Red phosphorus and some other substances probably form exceptions to this rule. Irving Langmuir