  The work is presented, leading to the universal contact molecular mechanism
of phase transitions and other reactions in solid state. The two components of
the mechanism - nucleation and interface propagation - are investigated in
detail and their role in the kinetics is specified. They were shown to be
peculiar: nucleation is "pre-coded", rather than resulted from a successful
fluctuation, and the interface propagates by molecular filling of thin layers
in the transverse direction. The structure of the nucleation sites is
determined. The inherent instability and irreproducibility of the kinetics in
question is revealed. A linear kinetics, as opposed to the bulk kinetics, is
introduced and shown to be in accord with the contact mechanism. Ferromagnetic
phase transition and magnetization are added to the list of solid-state
reactions; neither occurs without structural rearrangement.
