In order to gain insight into the macroscopic behaviour of gas interacting with electric and magnetic fields, while its degree of ionization is changing, the one-dimensional unsteady flow of gas with temperature-dependent conductivity is investigated. A simple continuum model is used for the gas. It is assumed to be compressible and to obey polytropic gas laws and its conductivity is supposed to change discontinuously at a critical temperature. Particular attention is devoted to the various types of transition boundaries which can occur as the conductivity changes, and it is shown that complete flow patterns can be constructed with these as elements. A wide variety of transitions are possible and some of these have remarkable properties. For example, it is shown that discontinuous deionising fronts can exist and are expansive in nature. This contrasts sharply with the situation in conventional gas dynamics and magneto-gasdynamics where only compressive discontinuities can exist.