GB313729A - Improvements in and relating to metallic vapour electrical discharge devices - Google Patents

Abstract

313,729. Freedman, P. May 25, 1928. Low-pressure metallic-vapour apparatus.-In metallic-vapour arc-discharge devices having vitreous envelopes containing one or more permanent gases, and adapted to act as rectifiers. oscillators, or emitters of visible or ultra-violet radiation, a tubular member of refractory insulating material is provided to enclose the arc discharge, this tube having at least two apertures the lower of which is immersed in the vaporizable metal pool and being arranged to confine the arc discharge within it to vapour arising from the pool and to prevent diffusion of the gas into the arc region and of vapour from the arc region into the gaseous atmosphere outside the tubular member. The glass envelopes of ultra-violet ray emitters may be prevented from deteriorating by providing generators of infra-red radiation within the devices, as described in Specification 313,726. The discharge device shown in Fig. 1 is constructed as described in Specification 313,726, but is provided with an arc-confining tube 13 having a bulbous part 14 to the centre of which the anode 16 is drawn when the arc is struck. In a modification, (Fig. 2, not shown) the arc tube is arranged so that the anode just leaves its upper end when the arc is struck. In the device shown in Fig. 4 the leading-in wires to the several electrodes are sealed into a common stem, as described in Specification 313,727. The cathode consists of a non-inductively wound conical filament 32 located in the upper end of the arc tube 31 and surrounded by a grid 34 to which it is electrically connected, whereby it is protected from ionic bombardment. The grid consists of a cylinder closed at its lower end by a network 35. The device shown in Fig. 5 is constructed as described in Specification 313,726 and is provided with an arc tube 41 made integral through a graded seal 39 with the envelope. An auxiliary starting electrode 47 passes into the tube 41 and an external coil 37 is provided to heat the mercury to start the arc through a preliminary glow discharge as described in Specification 313,292. The arc tube is also shown, (Fig. 6, not shown), in a device having a thermostat for striking the arc, as described in Specification 313,726. Fig. 7 shows a rectifier having a plate anode 49 of molybdenum, nickel, or carbon, outside the arc tube 53 and a tungsten bead cathode 50 inside the tube. The tube is tied to a lead 56 that feeds a heater 59 by which the mercury is vaporized. The heating- resistance is sealed in a gas-filled container 60. A glow discharge precedes the striking of the arc, as described in Specification 313,292. Fig. 8 shows a lamp for visible or ultra-violet ray emission. Similar tungsten beads 71, 72 arranged in the arc tube 68 act as the cathode and anode, and the mercury is vaporized by a filament 74 arranged above it in the tube 68. A constricted bend 66 in the tube 68 prevents the arc from passing from the electrodes to the filament. Fig. 9 shows an A.C. lamp or full-wave rectifier in which two anodes 87, 88 and a filamentary cathode 90 are enclosed in a tube having separate passages 84, 85 for the two arc discharges. Sodiumpotassium or cadmium-gallium alloy or other vaporizable metal may be used in place of mercury.