GB191337A - Improvements in and relating to electric incandescent arc devices - Google Patents

Abstract

191,337. British Thomson - Houston Co., Ltd., (General Electric Co.). June 17, 1922. Arc lamps; arc-lamp electrodes.-In an are lamp having a container in which the electrodes are arranged in a gaseous atmosphere, the arc is prevented from playing between the leading-in wires by associating with the leading-in wire adjacent to the cathode a material having a higher electron emissivity than the rest of the conductor. The electrodes 1, 2 are substantially equal in size and are formed of a refractory metal such as tungsten; they normally operate at bright incandescence. The parts 6, 7, Fig. 1, of the leading-in wires 3, 4, which may also be of tungsten, are bent inwards so that the gap between the electrodes is less than that between the leading-in wires. Beads 14, 15 of thorium, an alloy of thorium, thoriated tungsten, cr other material of high electron emissivity, are arranged at the ends of the straight portions 6, 7 of the leading-in wires, or these portions may be formed of thoriated tungsten wire. A suitable composition is tungsten containing 5 per cent of thoria. The bulb 5 contains argon, nitrogen, or other inert gas and a quantity of mercury 8. A condensing-cham'ber 11 is arranged with a constricted orifice 12 in line with the blast of mercury vapour from the electrodes 1, 2, and serves to determine the vapour pressure about the electrodes. In a modification the leading-in wires project downwardly from the top of the condensing chamber. The arc may be started by a high-potential discharge or, as shown in Fig. 3, by arranging auxiliary conductors 20, 21 below the electrodes so as to dip into mercury 8 which communicates with an auxiliary chamber 23 containing gas at the same pressure as that in the main bulb. The conductors 20, 21 become heated and ionize the gas between the electrodes 1, 2, thereby starting the arc; the resulting increase of vapour pressure in the bulb 5 lowers the level of the mercury 8 and breaks the circuit through the conductors 20, 21. In a modification, contact between the conductors 20, 21 and the mercury is effected by tilting the bulb, the chamber 23 being dispensed with. Auxiliary arcs are formed which lengthen and break on restoring the bulb to the vertical, at the same time ionizing the space between the electrodes 1, 2.