Experiments on the propagation of ion acoustic solitons that propagate in a positive ion-negative ion plasma are described. The solitons are launched from a solid metal disk to which a small negative step voltage [DELTA-phi almost-equal-to - 2(T(e)/e) V] is applied. The mechanism for the excitation of the soliton, the identification of the fast and the slow modes in such a plasma, and the observation of a transient sheat are presented.