Dry-Bulb? Wet-Bulb? What's the Difference?

Although the acts of melting ice and boiling water are mundane occurrences, the underlying physics are not so simple. The illustration shows what happens to the temperature of water as heat is added (Btu per pound on the horizontal axis). The graph shows plateaus at 32ºF and 212ºF. Why does the temperature hold steady, even as heat is being added, right at water’s melting and boiling points?

The temperature holds steady because it takes so much energy to accomplish the phase changes. Only when the last molecule of water has changed phase does the temperature of the material rise. All the energy it takes to accomplish phase changes is hidden.