A study of phase equilibria in the condensed system SiO2–ZnO by the quenching method shows the existence of (a) only one compound, Zn2SiO4, the mclting point of which is 1512°C; (b) a region of two immiscible liquid phases in equilibrium with cristobalite at 1695°C, extending from 2 to 35 mol. per cent ZnO; (c) a euiectic between tridymite and Zn2SiO4 at 1432°C and 49.1 mol. per cent ZnO; (d) a eutectic between ZnO and Zn2SiO4 at 1507°C and 77.5 mol. per ceut ZnO. The mclting point of Zno is found to be 1975°± 25°C.An irdium vessel is described which can be used in an induction furnace to obtain constant temperatures up to 2300°C in an oxidizing atmosphere.