# Question #156b5

White phosphorus consists of discrete ${P}_{4}$ molecules......
${P}_{4}$ can be obtained as waxy yellow sticks under water (these days it is a bit hard to source). It is steam volatile, and you can steam distil it to give pure white phosphorus (there is not much difference in reactivity between the yellow and white forms). Out of the water, ${P}_{4}$ is a pyrophore, and will (fairly slowly) ignite when exposed to air according to the following equation:
${P}_{4} \left(s\right) + 5 {O}_{2} \left(g\right) \rightarrow {P}_{4} {O}_{10} \left(s\right) + \Delta$