Energy Content of Mercury Arc Lines and the Photoelectric Effect for Mercury

Abstract

A.- Energy Content of ultra-violet lines of the quartz Mercury Arc. By means of a vacuum thermocouple it is possible to use a Leeds and Northrup high sensitivity galvanometer for these measurements directly. The sensitivity of the couple is increased from 6 to 15 fold by operation in a vacuum. Stabilization of the operation of the arc enables one to get accurate and reproducible results for long periods of time. The deviation from average between 3000A and 2400A does not exceed 2.2%. Limitations due to absorption by quartz and air and also to the increasing amount of stray light below 2400A causes the deviation to increase up to 10% at 2225A. B. - Long Wave-Length Limit of a clean surface of liquid mercury. Apparatus is designed to permit continual distillation and intermittent overflow of the mercury in the same circuit. Rate of change of surface can be varied. For a wide range of rapidly changing surfaces the long wave length limit is found to be constant and independent of the presence of gases in the photochamber. The long wave-length limit of Mercury is fixed at 2735A and is an intrinsic property of the metal. The maximum deviation, from average, of the photocurrents is 2.8% down to 2300A for successive measurements. C. - Influence of Dry Air, Oxygen and Hydrogen on the Long Wave-length limit and photocurrent. When the surface is slowed up or allowed to become stationary gases affect it. Hydrogen very quickly raises the limit to a new value and increases the photocurrents considerably. Oxygen very slowly lowers the limit and decreases the photocurrents. The behavior of air is attributed to the hydrogen and oxygen it contains. It is concluded that pure metals do have a definite photo-effect and that the effect is modified by the presence of gases either occluded or in the neighborhood of the metal and that gaseous conditions may be stable enough to give reproducible effects which vary depending on the elements entering into the combination. D. - Discussion. A brief summary of previous methods used in photoelectric work and recent theoretical explanations are given. The simultaneous measurement of photocurrents and presentation of clean surface is a distinct advantage. A list of references is put at the end.