Piezo-Electric and Allied Phenomena in Rochelle Salt

Electric Hysteresis in Rochelle Salt.—On the doublet theory of dielectric action, the dielectric displacement $D$, electric intensity $E$, and the polarization $P$ are analogous to $B$, $H$, and $I$ in the case of magnetism. Rochelle salt shows an electric hysteresis in $P$ analogous to the magnetic hysteresis in the case of iron. The loops obtained are displaced from the origin by an amount which gives a measure of the permanent polarization in the natural state. The moment per unit volume in the natural state is of the order of 50 e.s.u./${\mathrm{cm}.\mathrm{}}^2$ under ordinary conditions, this being about 13.3 × ${10}^{-21\mathrm{}}$ e.s.u./${\mathrm{cm}.\mathrm{}}^2$ per molecule.