The Mossbauer effect in 67Fe and 161~~ have been used to study the behavior of ice containing equal concentrations of trapped Fe2+ and Eu3+ ions. The ice-phase transition which occurs with each ion separately does not take place in the mixed system. Instead, the recoil-free fractions of both ions exhibit a sharp decrease with temperature, indicative of a pseudo-melting point at -65OC. Mtissbauer studies in this laboratory [l-S] of Fez+, Fe3+, and Eu3+ ions in ice matrices have been interpreted within the framework of the following model. Aquated ions trapped in ice, by quenching of aqueous solutions in liquid nitrogen, induce the formation of a low temperature ice phase which transforms frreversfily to a stable high temperature phase at --80°C. The characteristics of the Mtissbauer spectra of Fe2+ in the high temperature ice phase were shown to be consistent with a structure in which the hexaquometal ion is bound in a more-or-less normal hexagonal ice lattice [l]. The low temperature phase was suggestive of cubic ice (Ic), but the data do not exclude other possibilities. The transition from the low to the high temperature form was accompanied by a substantial time period. during which no Mtissbauer resonance signal was detectable. In the case of Fe2+, the quadrupole splitting was found to be very different in the two ice phases [l], whereas with Fe3+ and Fu3+, which do not exhibit a large quadrupole inte?action, the disappearance and reappearence of the MiSssbauer effect itself was taken as signifying the occurrence of the ice phase transition. The rates of transition are dependent on concentratibn and temperature of the sample and much longer time periods were required for Eu3+ doped ice, compared to samples containing Feaf or Fe3+ ions [2]. The question of whether the induction of "cubic" ice and its subsequent transformation * This work has been supported by the U.S. Atomic Energy Commission. _-** Now at