Patent GB-313726-A (GB)
Title: Improvements in and relating to metallic vapour lamps for producing ultra violet radiation
IPC: H01J61/58
Filed: 1928-05-22
Abstract: 313,726. Freedman, P. May 22, 1928. Low - pressure metallic - vapour apparatus.-A metallic-vapour lamp for ultra-violet radiation has two or more electrodes, of which at least one is of vaporizable material, and an envelope of glass transparent to the radiation and containing one or more permanent gases transparent to the radiation and which serve to protect the glass envelope from the hot metal vapour in the region of the discharge. The gas filling may consist of argon, helium, or hydrogen or mixtures thereof. The glass of the envelope may be transparent to both the longer and shorter ultra-violet rays or to the longer only, and may be one of those known under the registered Trade Marks " Uviol " and " Vita." To protect the glass from the deteriorating effect of the ultra-violet radiation a small amount of infra-red radiation may be generated in the lamp by means of hot electrodes or hot ballast resistances. The lamp shown in Fig. 1 is started by its anode 13 being lifted from the mercury pool by means of an electromagnet 22 acting upon a core 15 consisting of an evacuated glass envelope packed with iron powder, the anode and the core being carried by a spring 18 consisting of a doubly-spiralled molybdenum wire. This spring and a spring 24 act in opposite directions as buffers against a constriction 23 in the neck of the container. The cathode hot spot is located by a silica funnel 25 tied by wires to a cruciform glass support 28 carried by a leading-in wire. In a modification (Fig. 2, not shown), the spring 18 is mounted in a frame between the magnet core and the anode. In the lamp shown in Fig. 3, the anode 13 is lifted for starting by a thermostat coil 36 adapted to be heated by a ballast resistance 39 within it. The leads of both electrodes are brought through one seal, as described in Specification 313,727. In the lamp shown in Fig. 4, the anode is fixed and the arc is struck by a discharge between an auxiliary electrode 44 and the mercury cathode. The electrode 44 is a pointed tungsten wire or a rod composed of tungsten mixed with thoria. When the arc is struck, a high resistance 45 causes it automatically to short-circuit the auxiliary discharge path. In the lamp shown in Fig. 6, the arc strikes directly between an incandescent filament cathode 55 and a mercury anode. The cathode may consist wholly of a filament surrounded by a helical grid 60 to which it is electrically connected, the grid protecting it from positive-ion bombardment. The cathode shown consists partly of a conicallywound filament so protected and partly of a straight filament upon which is threaded a tube 59 of tungsten mixed with a refractory oxide. The arc strikes at the first part of the cathode and transfers to the tubular part when the auxiliary heating-current is switched off. In the lamp shown in Fig. 8, two mercury anodes 67 are used and the cathode 68 is protected by a grid consisting of a cylinder 69 closed at its lower end by a wire network. Fig. 9, (not shown), shows the ballast resistances arranged in the mercury-anode lamps.