Electrical properties of ´natural´ films developed on platinum contacts

Insulating films grow on surfaces of platinum-group metals in environments which are ´ordinary´ in the sense that they are not artificially polluted. Such films can interfere with the closure of electrical contacts which are left open and unattended for months or years. They need not do so, however, as they can readily be removed. They can also be detached in intact portions for experimental purposes. Their precise composition is not yet known, but some of their properties have been determined. A film grown on platinum appears to have a permittivity of several hundred, and exhibits a loss which depends on frequency and temperature: at room temperature, this loss has a maximum at about 600c/s.