  Direct measurements of resistivity and caloric equation of state have been
performed for fluid iron at pressures of 2 to 12 GPa in a wide density range.
We found that the isochoric temperature coefficient of resistivity becomes
negative, and this is considered as an indication of the metal-to-nonmetal
transition, when density decreased by a factor of 3 to 4 compared to the normal
solid density. We detected also that isentropes plotted in the pressure -
specific volume plane have well-defined kinks localized on a convex curve with
a maximum at about 5 GPa. Such behavior of isentropes evidences about a first
order phase transition with a critical pressure one order of magnitude higher
than the predicted pressure of the liquid-vapor critical point. Arguments are
presented that the observed phase transition is most likely the liquid-vapor
transition rather than an extra first order transition in the fluid state. We
show that the gaseous nonmetallic phase represents dense plasma in the 1-2-th
state of ionization so that it is a plasma phase transition as well.
