US2056628A - Self starting gaseous electric discharge device - Google Patents

Description

@sin 6, T193@ J. A 5T Lows SELF STARTING GASEOUS ELECTRIC DISCHARGE DEVICE Filed NOV. 22, 1933 INVENTOR l jap@ :3 lima-a2, B

Patented Oct. 6, 1936 UNITED STATES PATENT OFFICE SELF STARTING GASEOUS ELECTRIC DISCHARGE DEVICE Application November 22, 1933, Serial No. 699.264

14 Claims. (Cl 176-122) The present invention relates to gaseous electric discharge devices in general, and in particular to metallic vapor devices.

A particular object of the invention is to provide a high efilciency light source. Another object of the invention is to provide a metallic vapor arc which is exceptionally stable in operation. Another object of my invention is to provide a metallic vapor arc device which will operate at a relatively high pressure. Another object of my invention is to provide a metallic vapor discharge device whose electrical characteristics will remain constant throughout an appreciable range of vapor temperature. Another object of my invention is to provide a gaseous discharge device which will start without the use of high voltage or auxiliary apparatus. A further object of my invention is to provide an electrode for a gaseous discharge device which is simple in construction and which will have a long useful life. Still other objects and advantages of my invention will appear from the following detailed specification, or from an inspection of the accompanying drawing.

'I'he invention consists in the new and novel structure and combination of elements which is hereinafter set forth and claimed.

As heretofore operated metallic vapor discharge devices have always had an excess of metal present, this excess metal ordinarily comprising a pool in the coolest part of the discharge device. When so operated these devices have had the inherent fault that any change in the temperature of this pool, whether due to changes in the ambient temperature or to changes in the electrical input, has caused a disproportionately large change in the vapor density within the discharge device. This change in vapor density in turn causes a great change in the voltage required to maintain the discharge. Thus in a mercury vapor arc device even 40 a slight drop in the temperature of the pool so decreases the voltage of the arc that the luminous efficiency of the device is greatly impaired, while a slight increase in temperature may make it impossible for the discharge to operate at the available voltage. As a result it has not been practicable heretofore either to build a vapor discharge device which would operate with given electrical characteristics regardless of normal variations in ambient temperature, or. to operate one of these devices with the maximum vapor density consistent with continuous operation on a given line potential, despite the fact that the highest efciency is attainable only with this higher vapor density. It has recently been pro- 55. posed, however, to overcome these diillcultles by so limiting the available metal that it will all be vaporized when the discharge device is in operation. When such a device is normally operated at a temperature above that at which the metal is all evaporated it is obvious that the vapor will be superheated, but that the density thereof will not vary with temperature in this superheated range.- I'hus the voltage drop in these devices is no longer responsive to temperature changes within this superheated vapor range. The production of such a device has involved many difilculties, however. especially where it is desired that the device should operate at a high pressure, asin a mercury vapor arc. For example, for a mercury vapor arc to operate with a vapor density corresponding to that of mercury at atmospheric pressure it is necessary that the coolest part of the envelope be maintained at a minimum temperature of 357 C., and in order to insure that a possible decrease in ambient temperature will not result in a reduction in this density it is usually desirable to normally maintain an even higher temperature at this point. In the usual discharge device, as heretofore constructed,l wherein there is a great variation in temperature between the diierent parts of the envelope, this would mean that the hottest portion ofthe envelope would be at a temperature far above the softening and gas evolving point of any of the available glasses, so that the extremely expensive fused silica would have to be employed. I have discovered that by making several radical changes in the lamp conn struction the entire envelope may be made to operate at a much more uniform temperature, with the result that any of the harder glasses, such as pyrex, nonex, or the like, may be ernployed for the first time for the envelope et a lamp operating with a minimum temperature at the coolest point which is well above 357 C. One of these changes which I have found to be necessary is the relocation of the electrodes at a point extremely close to the ends of the envelope. which are made hemispherical, so that the zone baci: of the electrodes, which is the coolest part of the envelope, may be heated by the electrodes. With this new construction, which is contrary to the usual practice, l have found that it is essential that the metallic connection between the electrode and the inlead thereto should be relatively long with respect to the actual distance therebetween, in order to avoid excessive heat conduction thereto, both in the manufacture and in the operation of the device. The lower end ofvthis en velope likewise tends to run at a somewhat lower Cil temperature than the upper end thereof, due to convection currents within the mercury vapor and in the air outside, but I have discovered that this can be overcome by coating the lower end of the envelope with an opaque substance which will conserve the radiant heat from the adjacent electrode. I have likewise found that where glass is used it is desirable to enclose the lamp envelope within an outer casing, which diminishes the unequal cooling effect of drafts, and which likewise diminishes the heat conduction therefrom, so that the desired operating temperature may be attained with a lesser expenditure of electrical energy. This outer casing is preferably lled with a gas, such as nitrogen, at a pressure sufiicient to prevent the production of a glow, discharge between the lead wires to the lamp.

Due to the extremely high vapor density at which my novel lamp operates the\discharge is so constricted that it tends to tear to pieces any of the oxide coated cathodes heretofore proposed. I have found, however, that a hot, thermionic, cathode of novel design completely eliminates this difficulty and produces results not heretofore attainable. This new cathode of my invention is so formed as to have an extremely small heat radiating surface in proportion to the electron emitting surface, a relatively low thermal capacity, and poor heat conduction from one part thereof to another. I have discovered that a cathode having all of these novel characteristics can be conveniently produced by folding or rolling a piece of metal gauze into a compact mass, although any other metallic body having a similar maze of internal passages may also be used. Exceptionally good results have been obtained using a cylindrical electrode of tightly rolled metal gauze having a small central opening. The total surface of such an electrode may be easily made of the order of ten times the exterior, heat radiating, surface thereof, with the result that the heat loss from such an electrode per unit of active surface is extremely low. Hence little heat is needed to keep my novel electrode at an elevated temperature. The thermal capacity of this novel electrode is likewise extremely low, as is also the heat conductivity thereof, due to the cellular structure. Both of these factors contribute materially to the rapid heating up of a cathode spot at starting which is necessary to the long life of a cathode of this type, particularly in a lamp which must be frequently started, since the greatest damage is always done to such a cathode during those starting intervals when the necessary electrons are obtained therefrom by the extremely destructive ionic bombardment thereof rather than by the desired thermionic emission. These intervals are greatly shortened by my novel structure. In the preferred embodiment the entire gauze surface is coated with a good thermionic emitter, such as an alkaline earth oxide, and I have found that my novel structure affords unique advantages when thus coated. For example, I have found that my electrode, due to its novel construction, is singularly immune to the flaking off of this active coating, which has heretofore been a serious obstacle to long cathode life. Furthermore, the very extensive interior surfaces of my novel cathode, in addition to contributing a considerable amount of electron'emission, likewise serve as a vast storehouse of the coating material, and I have found that there is a constant replacement by distillation from this storehouse of any material which may be sputtered off the exterior surface, which thus remains activated throughout the long life of the cathode. In this connection it is also to be noted that with my novel structure an unusually large proportion of the particles which may be sputtered of! are intercepted by other parts of the cathode, and are thus available for further use, instead of being lost to the walls of the envelope. I have likewise found that the best results are to be attained when my novel cathode has an open bore of the order of 2 mm. in diameter. This open bore greatly facilitates the coating of the interior portion of the electrode, and likewise makes it possible to easily raise the temperature of the electrode by induction sufficiently to thoroughly degas it and to break down the alkaline compounds used in the coatings. In addition to this, however, this open bore tends to attract the discharge at certain gas pressures, and thus to provide the beneficial effects of a cavity. The many points provided on the end of the electrode by the cut wires of the gauze have likewise been found to be of advantage, the discharge invariably centering upon one of these points which runs so much hotter than the remainder of the electrode, due to the limited heat conduction, that when nickel is employed for this gauze the point soon` melts down into a little nodule on which the discharge continues to center. As a result of all of these effects I have found that my new electrode has an unusually long useful life, even under the conditions existing in my novel high vapor density mercury arc lamp with its constricted arc discharge, although its use is obviously not limited to this particular type of discharge device, or to any particular gas or vapor.

In any of these devices it is, of course, desirable that the discharge should start on the same potential as that on which it will eciently operate. I have discovered that if a band or wire of conducting material is placed around a critical part of the arc tube and connected to one of the electrodes the breakdown potential of the device is so much reduced that this is now commercially practicablefor the first time.

While I have only mentioned mercury hereinbefore, this being the most commonly used metal vapor, it is obvious that other metals, such as sodium, potassium, cadmium, thallium, and the like may also be used. For example, in a sodium lamp the efficiency has been found to be a maximum at a particular vapor density. My novel structure provides a means for constantly operating such a lamp at this desired density regardless of external conditions. Where vapor lamps of any type'are combined with incandescent lamps for color correction or the like my novel structure is of particular advantage, for it eliminates the heretofore paramount problem of so ventilating the light unit as to maintain a predetermined temperature in the vapor device at all times.

For the purpose of illustrating my invention I have shownv a preferred embodiment thereof in the accompanying drawing, in which Fig. 1 is a perspective View of a mercury vapor lamp.

Fig. 2 is a sectional elevation of the arc tube employed in this lamp,

Fig. 3 is an elevational view, in part section, of a modification of the lamp of Fig. 1

Fig. 4 is a perspective view of the electrode material before it is rolled up, and

Fig. 5l is an end view of an electrode, greatly enlarged.

As shown in this drawing, with particular reference to Figs. 1 and 2, a preferred form of my mercury vapor arc lamp has a sealed tubular envelope I of any suitable vitreous material, such as glass. This envelope may be either transparent or translucent, as desired. For a 400 watt lamp this envelope is conveniently made two inches in diameter and eleven inches long. A pair of inleads 2 and 3 extend through a re-entrant pinch seal at one end of said envelope, said inleads being connected to the tip and sleeve, respectively, of a conventional mogul base 4. A supportwire 5 is likewise fused into said pinch symmetrically with the inlead 3. Said inlead 3 and support wire 5 are each bent outwardly and carry at their outer ends the wires 6 and l, respectively, which are of tungsten or any other material having the necessary rigidity. Said wires 6 and l extend parallel to the axis of the envelope l to a point near the opposite end thereof. Said wires 6 and l pass through two spaced metal -rings 8 and 9 which are suitably affixed thereto, as by welding or the like. A sealed tubular envelope lil of suitable heat resisting vitreous material, such as pyrex, nonex, fused silica or the like, has hemispherical ends which rest in said rings, whereby it is supported in a nxed position Within the envelope l. For a 400 watt lamp this envelope is about 7 inches long and 13% inches in diameter. The walls of this envelope are preferably of the order of a millimeter thick, so that it has little heat capacity and thus warms up quickly, without danger of strains. The ring ii has a mica ring ll affixed thereto which snugly nts the inside of the envelope i, whereby lateral support is provided for the free ends of the wires 6 and i. Said envelope lil has an inlead i2, which is conveniently made of tungsten, sealed into each end thereof, each of said inleads terminating just inside of said envelope. A wire i3 of tungsten, molybdenum, or other metal of suicient rigidity, a 25 mil molybdenum wire being entirely satisfactory, is attached to the inner end of each of said inleads l2, each wire i3 being formed into a transverse loop of appreciable diameter and supporting at its free end an electrode iii, these electrodes being about 6 inches apart in a 490 watt lamp. The upper inlead l2 is joined .to the inlead 2 by a flexible lead i8 which is conveniently formed of stranded soft nickel wire, while the lower inlead l2 is similarly connected by a soft stranded wire i9 to the support wire 6. Several turns of wire l5 are closely wrapped about the envelope ll@ at a point about a third of the way from the upper electrode l l toward the lower electrode, this wire being electrically connected to the wire t, and thus to said lower electrode.

` The bottom of said envelope lil about said electrode has a heat intercepting gold lm l5 thereon, which may conveniently beapplied in the form oi a lacquer.

rii'he inner envelope itl has a filling of a rare gas, such as argon at a pressure of the order of 5 mm. of mercury, which constitutes the ionizable medium when the lamp is first started. An accurately measured quantity of the vaporizable metal, such as mercury, sodium, thallium, cadmium, or the like, is likewise sealed within this envelope. The amount of this metal is so chosen that it will all be evaporated when the coolest part of the envelope is at a desired temperature. In a mercury vapor lamp it has been found that a vapor density corresponding to a temperature of the order of 360 C. is especially desirable for many purposes, hence the mercury is preferably so limited as to be completely vaporized when the coolest part of the envelope is at this temperature.

If convenient the'outer envelope l would be evacuated in order to minimize the heat conduction from the inner envelope l0, but in practice it is found to be impracticable to entirely degas the various metal parts therein, with the result that residual gas evolves during operation of the lamp and supports an undesired glow discharge between the inleads 2 and 3. Accordingly, I prefer to ll the envelope l with a gas, such as nitrogen, at a pressure which issuiiicient to prevent the production of a glow discharge between these inleads. 'I'hus in a 220 volt lamp I vpreferably use nitrogen at a pressure of approximately half an atmosphere.

The electrodes I4 are especially designed to minimize the sputtering thereof, both during starting and during operation. As particularly shown in Rigs. 4 and 5 these electrodes are preferably formed of metal gauze which is rolled up to form a cylindrical electrode having an open bore. AThis electrode can be made of nickel, tungsten, molybdenum or the like, but in practice I have obtained extremely good results and long life using a gauze of seven mil nickel wire having 60 wires per inch parallel to the axis of the elec-` trode and 40 in the other direction. In some cases, however, even better results are obtained with a composite gauze having the wires which are parallel to the axis of the electrode made of tungsten, molybdenum, or other refractory metal, and the other wires formed of nickel, since this. combines the easy activation of nickel with the more refractory property of the tungsten, the arc centering on the ends of the latter. The gauze strips from which these electrodes aire formed are approximately :Mg inch wide and aggregate 51/2 inches in length, the several pieces being welded together as shown in Fig. 4 to provide a simple means for attaching the inlead and for holding the end turn, as is clearly shown in the drawing. With this construction there are obviously more than 325 small points provided by the ends of the Various wires on which the discharge can center. The electrode likewise has an electron emitting surface of approximately 2.6 sq. inches, although its effective heat radiatingsurface is only of the order of .3 sq. inch. After the electrode has been assembled as shownin Fig. 4 and attached to its inlead l2 it is carefully cleaned, as by hydrogen rng, and then dipped in a water suspension of a mixture of barium carbonate and strontium carbonate, 15 grams of each of these in c. c. of water having been found to produce the desired result. The porous or cellular nature of the electrode permits this' suspension to penetrate every part thereof, this penetration being obviously assisted by the capillary action of the pores or cells. The central opening in the electrode likewise greatly facilitates this penetration. After the electrodes have been suitably dried they are sealed into the envelope ill in an obvious manner. Since electrodes so coated do not undergo any chemical change in air they may be stored as long as desired without any special precautions, such as have necessarily been observed with the electrodes of the prior art.

The envelope lil is then exhausted and thoroughly baked to drive out any occluded gas, after which the electrodes lt are heated by induction to a temperature suflicient to break down the carbonates to the oxide, the evolved gas being evacuated as produced. The loops I3 restrict heat ow from the electrodes l during this heating, of course, and thus both protect the seals, and make it easier to produce the necessary electrode temperature. After this operation is complete a carefully measured quantity of mercury, 150 mg. in the case which has been described, is lintroduced within the envelope i0, together with a rare gas, argon at a pressure of the order of 5 mm. of mercury being preferred. The envelope I is then sealed off, after which it is placed in the envelope I in the manner which has been shown and described.

My novel device, when constructed as described, will start when an alternating current potential of 150 volts is applied thereto. This relatively low breakdown potential is the result of several factors. In the rst place the wireG, due to its proximity to the envelope I0, is eifective to some extent to reduceA the potential necessary to start the discharge, due to the fact that it is connected to one of the electrodes I4. The presence of the encompassing wire I5, however, greatly increases this effect if this wire is located at a critical point which is approximately two-thirds of the distance from the electrode Il to which it is connected toward the other electrode, although this wire I will be cf value if located anywhere between a quarter and a half of the way toward the electrode to which it is connected. A single turn of said wire I5 at the exact critical point would be suiiicient to produce the major part of this reduction in breakdown voltage, but by providing several turns thereof the effect is slightly enhanced, and at the same time the exact position of the edges thereof becomes less critical, so that the device may be more readily produced by mass production methods. The numerous points on the electrodes I4 are likewise believed to concentrate the static field, since they facilitate the necessary ionization of the gas, with a consequent further reduction in the breakdown potential of the device. The active coating on these electrodes likewise enhances this result.

At the instant of starting the entire emission from the cathode is produced, of course, by ionic bombardment thereof, due to the fact that it is cold. Since this type of emission is extremely destructive of an electrode it is obvious ffthat it is essential that the'heating period of the electrode, during which the thermionic emission thereof is increasing until it is adequate to suppot the discharge, should be as short as possible. I have found that this result is attained "by my novel electrode, for there is obviously but little heat conduction from the wire tip on which 4 the hot spot concentrates at starting, and this itip likewise has but little thermal capacity, with the observed result that this spot almost instantly reaches the requisite temperature to support the discharge by thermionic emission. Likewise, due to this same low heat conduction the remainder of the electrode remains relatively cool, so that there is little tendency for the discharge to shift from this hot wire tip to another one, which ould then have to go through a brief period of ionic bombardment, although it is apparent that the entire surface of the electrode, internal as well as external, contributes to the electron strontium coatings, the interior of the electrode serving as a vast storehouse of this active material. As a result my `novel electrodes -have been operated for thousands of hours, even under extremely unfavorable conditions, without losing any of their desirable characteristics.

Like all gaseous discharge devices my novel lamp has a negativevolt ampere characteristic. Hence as indicated in Fig. l myflamp is ordinarily operated in seriesiwith a\ suitable inductance on 220 volts A. C. This inductance causes the lamp current to lag behind the line voltage and thus continues the light on one half cycle until a favorable moment for the initiation of a reverse discharge on the next half cycle. As a result the usual flicker observable with alternating current discharge lamps is virtually eliminated, due to the unusually short dark interval. For best results the iron of the'finductance should not be saturated by the maximum current drawn, a reactor having an air gap being preferred, since a saturable reactor tends both to peak the current, causing a noticeable flicker, and to so limit the current at the beginning of the cycle as to render the arc unstable.

When the arc is rst started it is, of course, virtually a pure argon discharge, but as the temperature rises the mercury vapor density increases, and the arc becomes virtually a pure mercury vapor discharge. This vapor density continues to increase with the temperature, with a. corresponding change in the arc voltage, until the mercury is completely vaporized. A further increase in temperature will then merely superheat this vapor and the electrical characteristics thereafter are those of a fixed gas. I prefer to operate my device with a considerable amount of superheat, since then a decrease in ambient temperature or line voltage will not change either the vapor density or the arc voltage. Thus my novel device will operate with an arc voltage of the order of 160 volts with a current of 2.8 amperes, regardless of reasonable variations in ambient temperature. 'I'his makes my novel lamp especially suitable for street and other outdoor lighting, where the extreme variations in temperature have made it impracticable to operate a mercury vapor arc heretofore. It likewise is of advantage where my novel lamp is combined in a single fixture with incandescent lamps, for the heat of the incandescent lamps will have virtually no effect upon the operation of the vapor arc. When operated under the above conditions my novel lamp has a. total output of approximately 14,000 lumens, this being about 35 lumens per watt.

By making the lamp smaller in diameter and operating with the same arc current andl voltage the outer envelope may be eliminated, but in this case it is usually necessary to make the envelope of fused silica, fused iluorite, or one of the harder glasses, intermediate between pyrex and fused silica, in order to withstand the higher temperatures which must be developed to insure freedom from mercury condensation due to drafts or the like. The ultraviolet emission of such a lamp is often desirable, however, and hence such a construction, using fused silica, iluorite, or the like, is preferred in some cases. Such a lamp, of course, retains all the advantages of self-starting and stable and high efciency operation which have been heretofore described. A construction which has been found to give good results .in this type of lamp is shown in Fig. 3. In this lamp, which is designed to operate with the same arc voltage and current as the lamp of Fig. 1, the lamp envelope 2| is made of fused silica tubing having an inside diameter of approximately of an inch. The electrodes I4, which are approximately 6 inches apart, are supported by the in-l leads |2 close to each end of said envelope, being attached thereto through transverse loops i3, as in Fig. 1. Said inleads are each sealed into said envelope 2| through an external graded seal 22. An asbestos tube 23 is placed about each of said seals in order to maintain the temperature thereof, and in addition a heater 24 is preferably Acoiled thereabout. Said heater conveniently comprises about 10 or 12 turns of #21 nichrome wire, or enough of any other resistance wire to give approximately 1 ohm resistance. One end of said heater 24 is connected to the adjacent inlead l2, while the other end thereof is connected to a combined terminal and guard 25 which is attached to the end of said envelope 2| in a well known manner. An annular baille 26 is fused to the wall of said envelope 2| at a point slightly above the lower electrode i4, said baille having an opening of .approximately ofv an inch therethrough. A wire 2l is wound about the arc tube 2| for about an inch at a point approximately a third of the distance from one electrode it, said wire being connected to the terminal 25 which is the more remote therefrom. Said envelope 2i is filled with argon at a pressure of the order of mm. of mercury and contains a quantity of mercury,- about 35 mg., which will all be vaporized at the same temperature as that in the lamp of Fig. l.

The lamp of Fig. 3 will start and operate, in series with a stabilizing inductance, on 220 volts A. C. with substantially the same characteristics as the lamp of Fig. l, the baille 26 causing but little change in either the starting or operating potential. The absence of the outer envelope is, of course, compensated for by the smaller heat radiating surface, this lamp operating at a temperature considerably in excess of that of Fig. l

.p in order to insure continuous operation in the superheated range despite drafts and the like. The asbestos tube 23 and the series heater 2d vcause each graded seal 22 to be maintained at the requisite temperature to prevent mercury con densation therein, despite the distance thereof from the discharge, while the baille 2t breaks up the convection currents and thus causes a greater proportion of heat to be retained about the lower electrode lil, so that it will operate at substantially the same temperature as the upper electrode id. ln addition said shield 2B reduces the blackening of the arc tube by particles sputtered from the lower electrode. This lamp has been found to be an extremely eihcient ultraviolet generator, and is useful for various therapeutic and photo-chemical purposes.

While I have described my invention by reference to specific embodiments thereof, it is to be understood that various changes, substitutions, or omissions, within the scope of the appended claims, may be made therein without departing from the spirit of my invention.

I claim as my invention:

l. An electric gaseous discharge device comprising a sealed tubular envelope of vitreous material, an electrode sealed into each end thereof, a vaporizable material within said envelope in an amount which is less than that necessary to saturate the space within said envelope at the normal operating temperature of said device, a heat trap adjacent the lower end only of said envelope to reduce the heat losses therefrom to overcome the unequal cooling effect of convection currents on opposite ends of said device, and electrical connections for supplying suillcient energy to said device to raise it to said temperature.

2. An electric gaseous discharge device-comprising a sealed tubular envelope of vitreous material, an electrode sealed into each end thereof, a vaporizable material within said envelope in an amount which is less than that necessary to saturate the space within said envelope at the normal operating temperature of said device, an

annular baffle within said envelope close to the lower electrode to increase the amount of heat retained at the lower end of said envelope, and electrical connections for supplying sufiicient energy to said device to raise it to said temperature.-

3. An electric gaseous discharge device comprising a sealed tubular envelope of` vitreous material, an inlead sealed into each end thereof, an electrode consisting of a plurality of contiguous layers of metal gauze almost in contact with each end of said envelope, said gauze being coated throughout with an alkaline oxide, a connection between each inlead and the adjacent electrode which is longer than the distance therebetween whereby heat conduction to said inleads is minirnized, a vaporizable material within said envelope and a conducting band having at least one complete turn about said envelope at a point which is substantially a third of the way from one electrode toward the other, said band being electrically connected to the latter electrode.

4. An electric gaseous discharge device comprising a sealed tubular envelope of vitreous material, an inlead sealed into each end thereof, an

electrode almost in contact with each end of said envelope, said electrode being coated with an alkaline oxide', a connection between each inlead and the adjacent electrode which is longer than the distance therebetween whereby heat conduction to said inleads is minimized, a vaporizable material within said envelope, a conducting band having at least one complete turn about said envelope at a point which is substantially a third of the way from one electrode toward the other, said band being electrically connected to the latter electrode, and a heat intercepting coating on one end only of said envelope about the inlead.

5. An electric gaseous discharge device comprising a sealed tubular envelope of vitreous inaterial, an inlead sealed into each end thereof, an electrode almost in contact with each end of said envelope, said electrode being coated with an alkaline oxide, a connection between each inlead and the adjacent electrode which is longer than .the distance therebetween whereby heat conduction to said inleads is minimized, a vaporizable material within said envelope, a conducting band having at least one complete turn about said envelope at a point which is substantially a third of the way from one electrode toward the other, said band being electrically connected to the latter electrode, and an electrical resistance heater about the inlead seals to prevent vapor condensation therein.

6. A gaseous electric discharge device comprising a tubular sealed envelope, a gaseous atmosphere therein, electrodes sealed into said envelope at opposite ends thereof, and an electrically conductive band having at least one complete turn about said envelope at a point substantially one third of the distance `from one electrode toward another, said band being electrically connected with the more remote of said electrodes.

A'1. An electric gaseous discharge device comprising a tubular sealed envelope, a gaseous atmosphere therein, electrodes sealed into said en, velope at opposite yends thereof, an electrical conductor extending along the surface of said envelope from a point adjacent to one of said electrodes to a point two,.thirds of the distance toward the other of said electrodes, said conductor being connected to the first of said electrodes. the free end of said conductor terminating in a conductive band which encompasses said envelope.

8. In a gaseous discharge device, a cathode consisting of a metal body having a maze of internal passages whereby the total surface of said body is several fold the exterior heat radiating surface thereof, the entire surface of said body including that of the internal passages being coated with a substance having a high thermionic emission which is thin enough to not close said passages.

9. In a gaseous discharge device, a cathode consisting of a body of metal gauze having a plurality of contiguous layers of said gauze, the total surface of said gauze being at least several fold the exterior heat radiating surface of said body, the wires forming said gauze being coated throughout said body with a substance having a high thermionic emission which does not vclose the interstices within said body.

10. In a gaseous discharge device, a cathode consisting of a body of metal gauze having a plurality of contiguous layers of said gauze, the wires forming said gauze being coated throughout said body with an alkaline earth oxide, the cut ends of said wires being exposed on at least one surfaceof said body.

11; In a gaseous discharge device, a cathode consisting of a roll of metal lgauze having a plurality of contiguous turns and an open bore of the order of two millimeters in diameter, the wires forming said gauze being coated throughout said roll with an alkaline earth oxide, the cut ends of said wires being exposed at the end of said roll.

12. In a gaseous discharge device. a cathode j,consisting of metal gauze, a portion of the wires of said gauze consisting of nickel while the remainder of said wires consists of a more refractory metal. said wires being coated with a substance having a high thermionic emission. v

13. In a gaseous discharge device. a cathod consisting of a body of metal gauze having a plurality `of contiguous layers of said gauze, part of the `wires forming said gauze consisting of nickel while the remainder consists of a more refractory metal, the cut ends of the latter wires being exposed on at least one surface of said body, said wires being coated throughout with an alkaline earth oxide. l l

14. In a gaseous discharge, device, a cathode consisting of a roll of metal gauze having a plun rality of contiguous turns, the wires of said gauze which extend around the axis of said roll consisting of nickel while the wires parallel to said axis consist of a more refractory metal, the cut ends of the latter wires being exposed at one end of said roll, all of said wires being coated throughout said roll with a substance having a high thermionic emission.

JAMES a s'r. mors.

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