Electrical Conductivity of Dielectrics.

(A. F. Ioffe. Electrical conductivity of quartz. Proceedings of the Petrograd Polytechnic Institute, 1915—I, XXIV).

Ioffe’s work is of great interest for clarifying the mechanism of electrical conductivity in dielectrics. The phenomenon of electric current in quartz, it turns out, is readily explained on the assumption that free ions are present in quartz—probably \(Na_2SiO_3\)—the number of which is determined by the dynamic equilibrium of the processes of dissociation and association. Experiment yields a series of weak currents, since a strong current alters the properties of quartz; the proportionality of the current to the applied potential difference, i.e. Ohm’s law. Ioffe also investigates the occurrence in quartz of an electromotive force of polarization. This force may reach tens, hundreds, and even thousands of volts—which, incidentally, led Warburg to abandon the polarization hypothesis, since the normal electromotive force does not exceed the order of \(2\) Volt. It then turns out that in quartz the polarization is not concentrated in the layer immediately adjacent to the electrodes, but extends inward. In Ioffe’s laboratory a new investigation on the same question has been completed, in which the substance studied was crystals of rock salt. It must be said that now, in connection with the development of the dynamic conception of the structure of the atom and the molecule, a greater detailing of the processes of metallic, dielectric, and electrolytic conduc-

...ness. Here it is pertinent to note that, for electromagnetic waves, the very notion of a dielectric or of a conductor is to a certain degree conditional: everything depends on the frequency of the oscillations. A substance will be a dielectric if, in the expression for the velocity

\[ v=\frac{1}{\sqrt{k\mu}}\cdot \frac{1}{\sqrt{\frac{1}{2}\left[1+\sqrt{1+\left(\frac{4\pi\gamma}{k\omega}\right)^2}\right]}} \]

\(\omega\) (the frequency of the oscillations) is so large that the term \(\left(\frac{4\pi\gamma}{\omega}\right)\) may be neglected.

E. V. Il’in.