GB204057A - Improvements in and relating to electric discharge devices - Google Patents

Abstract

204,057. British Thomson - Houston Co., Ltd., (Assignees of Charlton, E. E.). Sept. 13, 1922, [Convention date]. Void [Published under Sect. 91 of the Act]. Low-pressure metallic-vapour apparatus.- The vapour of an alkali metal such as caesium or rubidium is introduced into a discharge tube for use as a lamp; rectifier, or lightning-arrester, the starting voltage being lowered thereby. The gas filling consists of neon at pressures varying from 2 mm. to 3 cm. of mercury, or of krypton, or of mixtures of neon, helium, and argon. It is stated that such a lamp containing neon at a pressure of 2.7 cm. starts at 76 volts continuous and 60 volts alternating. The lamp shown in Fig. 1 comprises two electrodes 2, 3 of iron, nickel, molybdenum, aluminium, or other material having a neglible vapour pressure at the operating temperature, separated by a sheet 4 of glass. Conductors 8, 9 are connected by screws with the electrodes, the conductor 8 being insulated from the electrode 2 by mica 12. Anchors 13 connected with and insulated from the electrodes are held loosely in projections 15 on the tube. A distillation bulb 18, Fig. 5, having two or more purification bulbs 19, 20, is attached to the tube, and the tube and bulb are baked out at 450‹ C., and exhausted, care being taken to remove, water vapour, for instance, by means of a liquid air trap. When the apparatus has cooled to air temperature a mixture of calcium turnings with an excess of caesium chloride is admitted into the bulb 18, which is then sealed and heated with the tube while on the pump to 250‹ to remove water vapour. Heat is applied to the bulb 18 to distil caesium successively into the bulbs 19, 20 and into the tube, which is then sealed off. The connection 23 to the pump is closed and gas admitted through a tube 22. In another form of lamp the electrodes consist of closely adjacent helices. In the rectifier shown in Fig. 2, the cathode 28, which has a surface at least 300 times as great as that of the anode 29, is mounted on an insulating stem 32, the anode consisting of tungsten, iron, nickel or carbon. In another rectifying tube the anode consists of tungsten wire surrounded, except for an exposed tip, by a jacket of hard glass, and the cathode consists of a cylinder of light metal such as an alloy of magnesium and aluminium, for instance, magnalium. A lighting-arrester having a breakdown voltage of 50 volts has aluminium electrodes with convex sparking surfaces of magnesium.