GB237235A - Improvements in gaseous electric conduction devices - Google Patents

Abstract

237,235. British Thomson-Houston Co., Ltd., (Assignees of Charlton, E. E.). July 17, 1924, '[Convention date]. Vacuum tubes.-Discharge devices operating by the ionization of a gaseous filling contain the oxide of an alkali metal, such as caesium or rubidium, and preferably also a small quantity of an alkaline-earth or other oxidizable metal, the operating voltage being thus reduced by absorption of deleterious gases. After the bulb has been heated to 450‹ C. to remove v a p o u r and evacuated, caesium is introduced, for example, by heating a mixture of caesium chloride and a reducing agent such as calcium in a chamber connected to the bulb, and is oxidized by admitting oxygen and heating to 50‹ C. The excess oxygen is removed and magnesium, calcium or other alkaline earth metal is deposited on the bulb by affixing to an electrode and introducing the device into a high-frequency electromagnetic field, the bulb being finally filled with helium or neon at 5 to 80, and preferably 19, m.m. of mercury. In a modification, a mixture of caesium chloride or other alkali halide with an excess of alkaline-earth metal is introduced, for example, as a pellet. On continued heating, both metals are deposited on the bulb and the alkali metal is then oxidized as before, the alkaline-earth metal being unaffected if the temperature is not raised above 50‹ C. Either method may be applied to the rectifier described in Specification 237,236, and comprising two tungsten wires which are in hard glass tubes and the exposed ends of which form anodes surrounded by interconnected housings forming the cathode; in the first method, the alkaline-earth metal is fixed to the cathode before, vaporization. Either method may be applied to a lamp containing plate electrodes 17, 18 of iron, nickel, molybdenum or aluminium, separated by a sheet 24 of hard glass, fused quartz or other refractory dielectric, one lead 19 being insulated from the plate 18 by mica 25 and connected to the plate 17 by a screw 22; in the second method, a pellet 28 of the reaction mixture is heated by a tungsten spiral between the leads 19, 20 and the spiral 28 is ultimately burned out. The alkali metal may also be introduced into a lamp as a vapour and subsequently oxidized. Reference has been directed by the Comptroller to Specifications 175,254, and 224,544* (as open to inspection under Sect. 91 of the Act).