I'm confused regarding the phase diagrams of binary systems. Let's suppose we mix 2 liquids, A and B at a given pressure P that won't change during the whole experiment. I raise the temperature until I observe that some of the mix of liquids vaporizes. What boggles me is that it seems I can actually raise the temperature and there's still liquid remaining (less and less if I raise the temperature more and more), until when I raise the temperature enough and it vaporizes entirely. But as far I as thought previously, you could not raise the temperature without the liquid passing entirely to gas if you saw it started to vaporize. I mean, for a pure substance it seems that at a given pressure there's a single temperature at wich there's a phase transition. Now for a mix of substance, there is no more a single temperature for which there's a phase transition. Is this correct? If it's correct, is the latent heat meaningless for mix of substances?