Elemental phosphorus has several allotropes. Among them, white phosphorus or yellow phosphorus is a colorless or pale yellow transparent crystalline solid. Density 1.82 g/cm3. Melting point 44.1°C, boiling point 280°C, ignition point 40°C. Phosphorescence is emitted in the dark. There is odor. Poisonous. White phosphorus is almost insoluble in water and easily soluble in carbon disulfide solvent. Heating under high pressure will turn black phosphorus with a density of 2.70 g/cm3, slightly metallic. The ionization energy is 10.486 eV. Generally insoluble in common solvents. White phosphorus can be converted to red phosphorus by placing it in air at 250°C for several hours or by exposure to light. Red phosphorus is a red-brown powder, non-toxic, having a density of 2.34 g/cm3, a melting point of 59°C (at 43 atm, a melting point of 590°C, a sublimation temperature of 416°C), a boiling point of 200°C and an ignition point of 240°C. Insoluble in water. In nature, phosphorus exists in the form of phosphate and is an important element of life. Exist in cells, proteins, bones and teeth. In phosphorus-containing compounds, phosphorus atoms are bonded to other atoms or groups via oxygen atoms.