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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^ for 175 hours. For this condition the and A values are very high. Aging at 1785^ 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. /cm^2deg. ^2, is estimated to be 5. 29 volts.
H. L. Van Velzer (Wed,) studied this question.