  The liquid-gas phase transition is analyzed from the topologic properties of
the event distribution in the obervables space. A multi-canonical formalism
allows to directly relate the standard phase transition with neutral particles
to the case where the non saturating Coulomb interaction is present, and to
interpret the effect of Coulomb as a deformation of the probability
distributions and a rotation of the order parameter. This formalism is applied
to a statistical multifragmentation model and consequences for the nuclear
multifragmentation phase transitions are drawn.
