Properties of Rochelle Salt

Measurements of the dielectric, pyroelectric, optical and electro-optical properties of Rochelle salt, and a theory correlating all observations are given. The theory is based on the assumptions that all properties depend on the inner field $F=E+fP$, and that the Curie point changes with temperature. The theory explains the observed variation of the susceptibility with temperature and field strength, the anomalies of the quadratic electro-optical effect, the pyroelectric effect, the hysteresis loop, the abnormal temperature variation of the birefringence and the change of these properties if the piezoelectric deformations are prevented. It is shown that the electro-optical effect is a Kerr effect. A longitudinal Kerr effect is discovered. A small crystal represents a single Weiss region, but large crystals show a Barkhausen effect.