Solid phosphorus cannot be melted by heating in a container because it sublimes before it reaches its melting point. Sublimation is the process by which a solid directly changes into a gas without passing through the liquid phase. The sublimation point of phosphorus is 44.1 °C, while its melting point is 44.2 °C. This means that when phosphorus is heated in a container, it will sublimate directly into a gas before it has a chance to melt.