Patent GB-248796-A (GB)
Title: Improvements in and connected with mercury vapour lamps
IPC: H01J13/00
Filed: 1924-09-11
Abstract: 248,796. Nisbet, J. Sept. 11, 1924. Low-pressure metallic-vapour apparatus; arc lamps.-A mercury-vapour lamp for projecting pictures by means of transparencies, or of opaque objects by reflection on to a screen or for emitting remedial rays is of parabolic, concave, spiral, tubular, or square shape silvered on the back or provided with a separate metallic reflector, and is provided at each end with tubular or channel section annular electrodes dipping into mercury or an annular electrode surrounding a tubular electrode without touching each other so that a current may be passed through the mercury to volatilize it. The lamp shown in Fig. 1 comprises inner and outer shells B, A of quartz glass &c. held concentric by slightly tapered distancepieces or gaskets C which seal the space X between the shells A, B so as to be gas-tight, and are held in place by screwed metal caps J engaging screw-threads on the outer shell A or on an outer perforated or other casing K. The inner faces of the gaskets C are protected by mica and tungstened copper discs E<3>, E<4>, Fig. 16. The outer shell A is enlarged at each end to form a circular pocket D containing mercury. Into each of these pockets is inserted an electrode ring E o! flat, channel, or tubular section. The mercury pocket consists of rings of mercury at the neck and mouth of the lamp with the two platinum or tungsten tubular electrodes and/or annular electrodes of channel section at opposite sides dipping into the mercury, and thus when the current is switched on completing a circuit to vaporize the mercury. Platinum, tungsten, copper, or other electrodes may also be provided at the lip of the wide end and also at the neck of the lamp body, so that when the lamp is tilted the mercury flows in a continuous stream from the electrodes at the higher end to those at the lower end, completing the circuit and causing complete vaporization. The lamp is provided with hollow trunnions G provided with stopcocks H for exhausting or charging the space X with mercury or gases, and a small bare ribbon coil may be provided round the necks of the trunnions for preliminary heating. An initial or auxiliary electric heating and illuminating or tinting lamp M is adjustably supported at the small end of the lamp by its stem M<1> so as to protect the inner shell B and condenser V from fracture by sudden heat when the current is turned on. Air cooling spaces are provided through the narrow neck of the shell B, the warm air escaping round the edges of the condenser V, which is itself cooled by circulating liquid therethrough by thermo-siphon action. Instead of closing the space X with gaskets C, the shells A, B may be sealed together at each end. In alternative forms, the lamp may be a double-walled cylinder or cone or a single-walled tube with mercury and electrodes at each end. Four such straight tubes may be arranged around a lens to illuminate a opaque object for projection. Alternatively a long single-walled tube may be formed into a spiral surrounding the lens. The tubular electrode shown in Figs. 15 and 16 consists of two semicircular tubas E<10>, E<11> connected at their bottom ends by a T-piece E<5>. An elbow E<6> is secured to the other end of the tube E" and to a tube E' projecting through an asbestos gasket C' and a tungstened-copper disc E' and mica washer E<3> provided on its inner face. A stopcock is provided in the tube E<7> and is connected to an elbow-piece E<8>. A tube E<9> is connected to the T-piece E‹ and extends through the disc E<4>, washer E<3>, and gasket C<1>, and is furnished with a stop-cock G<3>. Terminal nuts are provided on both tubes E<7>, E<9>. The tube E<10> is formed, at its upper open end which faces the disc E<4>, with a valve seat V<1> and valve V<3> having a screwed stem V<2> and milled head V<5> so as to control the mercury and vapour issuing, when the electrode is connected to the electric supply source, from the tube E<10> and impinging on the tungstened-copper gaskets E<4>. Mercury outside the tubular electrode also is vaporized. The stopcocks are used for charging the electrode with mercury, liquids, chemicals, or gases, or for use when exhausting the electrode. For this purpose a detachable tube G', Fig. 14, may be screwed into the vertical limb of the elbow F<8>. This tube is provided with two stop-cocks, a screwed metal cap G<2>, and a filler mouth G<4>. The doublewalled mercury-vapour lamp shown in Fig. 1 may be hinged to the gate W or side of a camera projector or may be pivoted on an adjustable stand with gimbals for supporting the lamp by its terminals on the bottom of the lantern bodv to facilitate threading the film, or the lamp or lamps may be attached to adjustable stands in a lantern body. The outer space Z' between the metallic reflector and the outer quartz glass shell may be used for circulating a cooling-fluid or air current or part mercury and vapour and gas. The mercury vapour space X and the space Z' may be a vacuum or a plenum filled with gases, or open to atmospheric pressure. To improve the colour of the light, cadmium &c. may be added to the mercury. Zirconia, silica, or other metallic oxides may be added to prevent the mercury from adhering to the walls or electrodes. Carbon dioxide or other gas may be added to counteract any residual air or oxygen.