The integral latent heats of vaporization of formic acid-water mixtures at 760 mm. Hg. are reported and used to prepare an enthalpy-concentration chart for the system. The data provided a basis for the estimation of the heats of mixing in the vapor phase, and the results indicate that the exothermic heat of mixing may be attributed to the partial dimerization of monomeric formic acid coupled with the association of water and acid molecules.
Vapor-liquid equilibria data for the system are also reported.