GB191505741A - Improvements in and relating to Devices for the Discharge of Electricity through a Vacuum, Gases or Vapours. - Google Patents

Abstract

5741. British Thomson-Houston Co., [General Electric Co.]. April 16. Arc lamps; vacuum tubes.-The ends and other cool parts of an incandescent cathode are protected from electric erosion, supposed to be due to ionic bombardment, by a conductive shield between them and the anode. The shield may be spaced apart from the cathode but in electric connexion with its support. Tungsten, molybdenum, and iron are suitable materials for such shields, which may have the form of tubes, close coils 14, 15, Figs. 1 and 3, or open coils 16, Fig. 4. In a rectifier, the cathode 4, Figs. 1 and 3, may be a heated coiled filament of tungsten, protected as described. Tungsten helices 8, 9, advantageously supported at both ends, may also be employed as anodes. The envelope, of the form shown, may be of lowexpansion or other glass, or silica; when silica is used, stems of low-expansion glass may be joined to it by graded seals. Nitrogen, argon, neon, or other inert gas at a pressure of 10-760 mm. of mercury fills the envelope; or a globule of mercury is introduced, in which case the vapour pressure may be as low as 1 mm. Mixtures of gases may also be used. In an arc lamp, refractory-metal electrodes 21, 22, Fig. 4, are attached to long leading-in wires by narrow stems 26 both protected by open coils or tubes, unless direct current is to be used, in which case only the cathode stem need be protected. The bulb is filled with inert gas, such as nitrogen, argon, or mercury vapour, at a working pressure of about 1 atmosphere. High electric pressure is used for starting.