The effects of the addition of A1203 on the large stable two liquid field in the SiO2-TiO2-CaO-MgO-FeO system were experimentally determined. The increase of A1203 content in the starting composition results in the decrease of critical temperature, phase separation and liquidus temperature of the two liquid field iantil it is rendered completely metastable. The shrinkage of the two liquid field indicates that A1203 is acting in the role of a network former and homogenizes the structure of the two melts. In this alkali-free system AI + 3 utilizes the divalent cations, Ca + 2 and Mg + 2, for local charge balance with a preference for Ca +2 over Mg +2. Thus, A104 tetrahedra combine with SiO4 tetrahedra to form an aluminosilicate framework which polymerizes the SiO2-poor melt and makes it structurally more similar to the SiO2-rich melt. However, Ca +2 and Mg +2 are not as efficient in a charge balancing capacity as the monovalent K § and Na § cations. The lack of alkalis in this system limits the stability of A10~ tetrahedra in the highly polymerized SiO2-rich melt and results in the preference of AlzO3 for the SiO2-poor melt. The partitioning systematics of Ti are virtually identical to those of A1. It is concluded that Ti occurs in tetrahedral coordination as a network forming species in both the high -and low -SiO immiscible melts.