Studies of Cataphoresis and Electrophoresis—Some New Effects

Abstract

A study is made of the rate of transport of Hg in a uniform positive column in a mixture of a rare gas and Hg vapor. In one case, the phenomenon of retrograde cataphoresis is encountered, that of Xe+Hg at currents above 1 A, in which the Hg is carried to the anode end of the tube. In all other cases, the Hg is transported to the cathode end. A pulsating discharge is described in which the color changes from the red of Ne to the blue-white of Hg and back again within a period of 1–2 sec. The boundary between the two colors travels along as a wave motion. This phenomenon is related to the properties of the tube walls and the nature of the ions striking them. When an ac discharge is passed through a cataphoretic mixture, the trace gas of lower ionizing potential is urged from the ends toward the center of the tube, e.g., Hg in Ar, Ne and Kr, but from the center to the ends in He+Hg. With a trace of Ar in He, the Ar is urged toward the center of the lamp. With Xe+Hg, the Hg may go either to the center or to the ends, depending upon conditions. The phenomenon is believed to be due to traveling striations which start out from the anode and progress only part way toward the cathode. Such a striated discharge pumps Hg faster than a steady discharge in the case of Ar, Kr, and Ne, but apparently slower in the case of He. Attempts to demonstrate electrophoretic effects in a straight sealed-off tube failed. However, the positive pressure effects are quite striking in a tube with an external return path.