Abstract
The variation of the photoelectric sensitivity of a molybdenum surface during prolonged heat treatment has been studied over a period of 300 hours of intense heating. Thin ribbons of molybdenum were heated to a temperature of 1325°C in a high vacuum and the photocurrents produced by the light from a quartz mercury arc were measured with a quadrant electrometer. The photoelectric sensitivity was found to increase as the heating progressed, finally reaching a limiting value. The increase in sensitivity was accompanied by a shift in the wave-length limit from approximately 2600 A. U. to approximately 3800 A. U.