An investigation of the linear thermal expansion of high purity specimens of polycrystalline has revealed that a ferroelectric phase is stable in this compound between 226° and 236°C on heating. The same phase exists between 226° and 212°C on cooling. The data were all obtained at a constant heating and cooling rate of 1°C/min. The thermal expansion of high purity specimens containing about 200 ppm more calcium than those exhibiting the ferroelectric phase did not indicate the existence of such a phase. Hysteresis loop measurements of the low calcium containing materials showed well defined ferroelectric hysteresis loops with and whereas similar measurements on the more impure material revealed a field induced antiferroelectric → ferroelectric phase transition. The substitution of 0.05 weight per cent of calcium for lead in the purer resulted in the disappearance of the ferroelectric phase.