The Thermionic Constants for Platinum

The thermionic constants for platinum in the form of cylindrical filaments were investigated. The slope of the supersaturation curves was taken as a criterion of filament condition. It was found that a very stable state, probably not indicative of a pure surface was obtained which withstood aging at 1650^∘{}K for 175 hours. For this condition the φ and A values are very high. Aging at 1785^∘{}K produced a new surface for which the supersaturation slopes were correct, and for which the constants were assumed to be approaching correct values. If A is taken to be 60 amp./cm²·{}deg.², φ is estimated to be 5.29 volts.