Photo-Electric Properties of Solid and Liquid Mercury: The Effect of Toluene on Liquid Mercury. The Effect of Temperature on Solid and Liquid Mercury

Effect of Toluene on liquid Mercury: An apparatus is described which permits the measurement of the photo-electric emission and threshold for pure mercury contaminated with pure toluene vapor/ It was found that the vapor from small amounts of toluene held at the temperature of liquid air produces no appreciable effect on the photo-electric behavior of pure liquid mercury. When, however, toluene vapor of considerably higher pressures (6mm and 30 mm) is introduced into the photo-cell, the sensitivity immediately increases and the threshold immediately shifts 100A toward the red. This shift in threshold is the same for both of the higher pressures and is independent of the time that the vapor is retained in the photo-cell. A mercury surface which has been contaminated with toluene can be brought back to its normal behavior for pure mercury simply by connecting the photo-cell with the liquid air trap and pumps, and without the necessity of redistilling the mercury. The time of return to normal behavior varies between a few minutes and several days; the time increases both with the pressure of the introduced vapor with the time that the vapor is held in the cell before pumping is begun. The minimum cell voltage required for a saturated photo-current is increased by the introduction of vapor into the cell or by the formation of an adsorbed layer of vapor on the mercury. Effect of Temperature on Solid and Liquid Mercury: Apparatus for measuring the photo-electric sensitivity at different temperatures is described. The range of temperature was -190° to 25°. Monochromatic light was used and both the sensitivity and threshold were determined for various temperatures in this range. The threshold is independent of temperature. At room temperature it is 2735 10A, which is an independent confirmation of the value established earlier by Kazda and by Hales. At temperatures between -190° and -39°, where the mercury is in the solid phase, the threshold is at 2750 25A. The photo-sensitivity of solid mercury is higher than that of liquid mercury, but it does not vary with temperature in the region below -39°. The increased sensitivity, without accompanying shift of threshold toward the red, is attributed to an increase in the optical absorptivity, occuring when the mercury changes from the liquid to the solid phase. No evidence was obtained of a change in the crystal structure of solid mercury in the region of temperature investigated.