  A sharp phase transition from a crystalline state with the area per molecule
A = (17 +/- 1) Angstrom^2 to a liquid state with A = (23 +/- 1) Angstrom^2 at
the n-hexane - water interface in a Gibbs monolayer of melissic acid has been
revealed in data of X-ray reflectometry with the use of synchrotron radiation.
