On the Conductivity of Glass at Various Temperatures.

R. Ambron. Über die elektrische Leitfähigkeit von Natron-Kalk-Silicatgläsern (Ann. d. Phys. 58, p. 139, 1919).

The author investigated 13 varieties of pure glass made from melts, \(SiO_2\), with \(Na_2O\) and \(CaO\) of different composition, manufactured for this purpose by the firm “Schott und Gen. in Jena.” To study the conductivity of these varieties of glass, rods 1.5 and 1 cm in diameter and 1 and 3 cm high were made. To supply the current and to distribute it uniformly, the ends of these rods were platinized by heating. Measurement of the conductivity was carried out with direct current by means of a galvanometer and a commutator, which made it possible to change the direction of the current supplied to the glass up to 200 times per second; this avoided the influence of polarization, and the accuracy of the measurement was then not less than 0.2%. Heating of the rods was carried out from \(60^\circ\) to \(500^\circ C.\) in baths of liquids boiling at different temperatures; and, in order to avoid cracking of the glass rods, they were first coated with a thin layer of insulator and then wrapped with a silver foil for uniform distribution of temperature.

As a result of the experiments it turned out that the dependence of conductivity on the temperature \(\vartheta\) is expressed by the formula

\[ L = L_\infty e^{-\frac{B}{\vartheta}}. \]

Here \(L_\infty\) is the conductivity of the rod at \(\vartheta = \infty\), and \(B\) is a constant. \(L_\infty\) and \(B\) depend on the sort of glass, i.e. on the concentration of \(Na_2O\) and \(CaO\) atoms in the glass solution. Namely, \(L_\infty = M + p n + q c\), where \(n\) is the concentration of \(Na_2O\) atoms, and \(c\) the concentration of \(CaO\) atoms, and \(M\), \(p\), \(q\) are constants. \(B = \alpha n c + \beta n + \gamma c + \delta\), where \(n\) and \(c\) have their former meanings, and \(\alpha\), \(\beta\), \(\gamma\), \(\delta\) are constants. The values of the constants \(\alpha\), \(\beta\), \(\gamma\), \(\delta\) show that not all the atoms of \(Na_2O\) and \(CaO\) contained in the glass can dissociate, but that, of the total number of atoms in \(Na_2O\) and \(CaO\), those contained in the glass—about 11% (in relation to the whole number of atoms of the glass)—do not dissociate, being apparently bound with the atoms of \(SiO_2\); and only what is in excess of this dissociates and increases the conductivity of the glass. For the undissociated part, the atoms of \(CaO\) and the atoms of \(Na_2O\) are completely equivalent, i.e., the mentioned 11% may include either \(CaO\), or \(Na_2O\), or both together.

N. Shchodro.