  In this paper we study a 3-dimensional filtration of real gases described by
Redlich-Kwong equations of state. Thermodynamical states are considered as
Legendrian (Lagrangian) submanifolds in contact (symplectic) space. Connection
between singularities of their projection on the space of intensive variables
and phase transitions is shown. Explicit formulae for the Dirichlet boundary
problem are given and the distribution of phases in space is shown.
