An Electrometer Method for Measuring Dielectric Constants of Liquids

Differential idiostatic electrometer for the measurement of dielectric constants of liquids.—The suspended system includes two cylindrical quadrants $C_1$ and $C_2$ suspended so as partly to overlap two fixed cylindrical plates $A$ and $B$ coaxical with $C_1$ and $C_2$ and so placed and connected that the torque due to the condenser $A{C}_1$ is opposite to that due to the condenser $B{C}_2$. To determine the dielectric constant of a liquid, one of the condensers is immersed in it and the other immersed in a liquid or gas of known constant, and the differences of potentials $V_A-V_1$ and $V_2-V_B$ for zero deflection are read by the potentiometer method. The dielectric constants are then proportional to $\frac{{(V_A-V_1)}^2}{{(V_2-V_B)}^2}=\frac{{R_1}^2}{{R_2}^2}$. This method gave for the dielectric constant for distilled water at 25°C with 60 cycle e.m.f. the value 78.07.