US2202199A - Discharge device - Google Patents

Description

y 28, 4 E. GERMER 2,202,199

DI S CHARGE DEVI CE Original Filed Dec. 5, 1930 Zhweutor Patented May 28, 1940 UNITED STATES PATENT orrlcr.

DISCHARGE DEVICE Edmund Germer, Berlin-Wannsee, Germany, assignor to General Electric Company, a corporation of New York 24 Claims.

This invention relates to vapor electric discharge devices and more particularly to such devices of the type having electrodes at opposite ends of a sealed envelope between which an electrical discharge occurs. The invention relates also to a method of operation of vapor electric discharge devices.

Prior to my invention vapor electric devices have in general been of three types. In the first place, there have been liquid electrode lamps, such as the well known Cooper-Hewitt lamps used for illumination purposes and the well known Kuch mercury are for therapeutic and industrial uses where ultra-violet radiation is required.

by the heat developed at the arcing point on the surf-ace of the metal. Such devices are subject to many disadvantages which are well known in the art, among which may be mentioned that they must be operated on direct current or, if

- only alternating current is available, one must use a rectifier circuit, e. g., a middle tapped transformer, with the mercury functioning only as cathode on both half cycles. Anotherdisadvantage is that it is not practicable to maintain the arc on such liquid electrodes with small current loading, e. g., less than about 1.5 amps. With lesser currents the arcing point on the surface of the liquid electrode cools so rapidly that the arcing point cannot be adequately heated and the discharge can function only as a cold electrode discharge and only at high voltage. Another disadvantage, especially if one wishes to use a glass instead of a quartz envelope, is that the are often tends to strike the contact line between the mercury electrode and the wall of the envelope and this, particularly if its occurs while the vapor pressure in the envelope is relatively high, may result in cracking and failure of the device.

In the second place, there has been known and in common use, a type of lamp in which a positive column or are discharge occurs between fixed, i. e., permanently spaced electrodes mounted within a sealed envelope. The most satisfactory of such lamps are described in a series of copending applications of Hans J. Spanner alone, jointly with others and jointly with myself respectively. It is a disadvantage of even the best of these previously known devices, however, that the voltage required for starting must be several times as high as the ordinary operating voltage and/or that the current loading which may be applied to the lamp is substantially limited.

A third type of arcing device known prior to In both of these devices the arc burns on a pool of mercury and the metal is evaporated my invention utilized closely spaced electrodes of refractory metal in which the major energy conversion was at the surface of the electrode rather than in the discharge path between the electrodes and the light output consequently came primarily from the incandescent electrodes rather than from the are.

It is one object of the present invention to combine in a single lamp advantages of these several older types, which advantages had heretofore been considered incompatible, and to avoid objections, which in the older types had been necessarily coincident with their advantages.

Another object of the invention is to provide an electrical discharge device adapted to operate normally at a voltage between the electrodes which is substantially above that existing in the moments following starting of the discharge and advantageously above that normally attained in the older fixed electrode discharge devices of the same electrode spacing.

Another object of the invention is to produce lampsand radiation devices of high efficiency.

Another object of the invention is to provide a simple rugged lamp capable of practical and commercial application wherever illumination or. ultra-violet radiation is required.

According to the present invention, I have so controlled the environment-of a discharge between spaced electrodes that the density of the atmosphere in which the discharge occurs'is so far increased by the operation of the discharge that the voltage drop therein rises substantially above that which exists when the initial atmosphere is first ionized and even to a voltage which is nearer to the break-down voltage at which a discharge first starts than to the reduced voltage at which the initial discharge operates. In this way I have achieved that during normal operation a relatively small voltage is consumed in the ballasting impedance, which is necessary with discharge devices of this'type, and that during operation the voltage may be increased to whatever value gives the highest over-all emciency for the device and its auxiliary circuit equipment.

This progress I have achieved according to my invention, first by the utilization of specially activated solid electrodes, e. g., of the type described in the copending applications of Hans J. Spanner, Serial No. 387,986, filed August 23, 1929, and Serial No. 130,872, filed March 15, 1937, or in the patent of Hans J. Spanner and Oskar ,Gadamer No. 2,073,885, dated March 16, 1937, which are capable of quickly establishing an arc discharge and of operating with any current loading which may be required to produce the al gaseous materials into the atmosphere of the desired increase in density of the gaseous atmosphere of the arc, whether such current be a fraction of an ampere, e. g., amp. or many amperes, e. g., 10 amps. or more, and with sufiiciently low disintegration or evaporation of the electrode material that the device may have a useful life of many hundreds or even thousands of hours. By s01id" electrodes I distinguish from liquid or pool electrodes and without reference to compactness or apparent density.) Secondly. the discharge space between the electrodes enclosed by an envelope or confining means approximately fitted to the discharge path and designed to restrict heat dissipation from the discharge to such an extent that equilibrium between the heat generated in the discharge and on the electrode anfi heat dissipated from the envelope can occur only at temperatures suflicient to maintain the desired increased density in the arc path. Thirdly, there is provided in the envelope a vaporizable material, i. e., a material such, for example, as mercury, which is adapted upon heating by the discharge to release additiondischarge and thereby to increase its density and consequently the voltage of the are. This material is in amount suflicient to increase the voltage to the desired extent, e. g., up to or more of the supply line voltage or maximum voltage available for operation of the lamp from whatever source is used. And finally, my invention includes the providing of an energizing circuit adapted to give suflicient energy loading to the discharge so that the temperatures in the lamp are at least as high as are necessary for the desired increase in density of the discharge atmos phere.

When such a tube is started the discharge first occurs in the relatively low pressure gaseous atmosphere and at the outset will ordinarily occur as a glow discharge which, due to the nature of the electrodes, is quickly converted into an arc discharge. The energy conversion in the are quickly results in a heating of the tube with consequent vaporization of the vaporizable materials supplied therein. The vaporization of this material increases the density of the gaseous atmosphere and, because of the shape and the dimensions of the tube approximately fitted to the discharge path, this increased density occurs in the discharge path, with the result that it crowds the discharge closer andcloser into a central constricted luminous cord. As this process progresses the arc consumes an ever increasing portion of the total available voltage, e. g., up to or more of this total available voltage as compared with only about in low pressure tubes. When this desired voltage is attained the condition will be maintained by an equilibrium between the energy conversion. resulting from the loading of the arc and the: energy dissipation from the envelope in which the arc occurs.

In the accompanying drawing and the following description I have shown and described a preferred embodiment of my invention and various modifications thereof. It is to be understood that these are not intended to be exhaustive or limiting of the invention, but on the contrary are chosen and set forth for the purpose of illustrating the invention and instructing others in the principles thereof and in the best manner of embodying and using the same in practice so that others may be enabled to modify and adapt the invention and to embody it in numerous forms, each as may be best suited to the cumstances of a particular use.

Parts of Fig. 2 which correspond to parts of Fig. 1 are designated by having the same character number, with the additional reference a.

In the drawing:

Fig. 1 is a longitudinal section of a substantially straight radiating tube;

Fig. 2 is a longitudinal section of a U-shaped radiating tube.

Referring first to Fig. 1, the device there shown comprises a sealed tube I having at opposite ends electrode chambers 2 and 3, through the ends of which are sealed the electrode inlead and support wires 4 and 5. These electrode chambers 2 and 3 are tilted up and are separated from the arc tube proper by the constrictions l3l4 whereby convection currents occur within the electrode chambers which are advantageous both because they tend to limit any deposit of sputtered or evaporated electrode material to the upper part of the electrode chamber behind the electrode and because they assist in heating the portion of the electrode chamber behind the electrode and thus in assuring that the desired high vapor pressure will be attained within the envelope I.

The electrode body proper as indicated at 6 consists of three or four thick turns of electrode material, which may consist of conductors of small section for example, of metal gauze, mesh or twisted wires or ribbons of nickel or other refractory metal. The electrode body is not in the form of a filament but in the form of a more compact unit and with a porous absorbent structure'into which an activating material may be filled. This filling and/or coating of activating material is an important feature of the electrode used in this embodiment of my invention.

The activating mass which is sucked or filled into the porous cathode electrode body proper is deposited onto said body byrepeatedly dipping, brushing or pressing it in a suitable solution or paste and with the application of heat. Such paste may consist firstly of highly emissive substances such as barium oxide, and/or other electro-positive compounds, and secondly, of materials which are diflicult to dissociate and thus preserve their insulating character during the life. of the tube, are immune or highly resistant to ionic disintegration; zirconium oxide is such a material. The emissive substance is further activated, advantageously by application of high frequency heating, until the barium oxide is mostly reduced and the remaining mass is saturated with free barium and/or complex compounds formed of barium. Further activation may be effected by the initial operation of a discharge between the electrodes, e. g., as described and claimed in the copending applications of Hans J. Spanner alone and with others referred to above.

The electrode body 6 is mounted upon the inlead and support wires 4 and 5 respectively, advantageously by a short-circuiting loop I of heavy wire, which in its turn is mounted on a frame 8 carried by the inlead wire 4. The ring or loop 1 provides, with the electrode body 6, a short circuited loop in which high frequency currents can beinduced, e. g., by applying a high frequency coil around the electrode chambers 2 or 3 respectively. The eddy currents induced in the ring 1 pass through the electrode body proper 6 and cause a heating of the fine wires or ribbons, of which it is composed, to a temperature at which the electrode is effectively degassed-and the coating material thereon is effectively activated.

Instead of the ring I there may be used a slotted disc ll as shown at the right hand end of Fig. 1; and to the edge of this disc is suitably secured the'electrode body proper 6. High frequency currents can be induced in the disc "I in the same manner as in the ring I, and due to the slotting of the disc at the part where the electrode 6 is inserted, e. g., as shown in Fig. 1, such induced currents will pass through the electrode body proper 6 as already described in the case of the ring 1. Likewise, instead of using the frame 8 the electrode support wire 5 may be welded directly to the ring or disc, e. g., as shown at the right hand end of Fig. 1. It will be found, however, that the extended connection provided by the frame 8 and the ring I is advantageous in maintaining the desired high temperature in the electrode chambers-behind the electrodes so that the desired high pressure is maintained and undesired condensation is avoided. By suitably determining the thickness of the ring I or disc Ill and the frame 8, if used, these parts will serve to conduct away from the electrode body 6 any superfluous anodic heat and to utilize this heat as already stated for maintaining the desired high temperature in the electrode chambers. This is more particularly described and claimed in the Patent No. 2,047,390, dated July 14, 1936, granted to Hans J. Spanner.

In the example-shown in Fig. l a depression I2 is provided in the lower wall of the arc tube.

proper in order to hold the necessary quantity of mercury or other vaporizable material. This depression is advantageously situated near the middle of the length of the tube where the vaporizable material is exposed to the heat of the are for rapid vaporization.

In order to obtain the necessary increase in pressure and density of the atmosphere in which the arc occurs, it is important that the dimen-' sions of the tube and the electrode be properly proportioned with respect to the energy loading of the tube. As already stated above, this proportioning should be such that thermal equilibrium is established at or above the temperatures at which the desired pressure is attained. Incorrect proportions, if such as to result in excessive cooling, may prevent the desired high pressure. Otherwise, the excessive energy input, which would be necessary to supply the heat lost by cooling, might give too great a radiant output and might even destroy the electrodes by overloading; or, if the tube is too small, it may get too hot with the watt loading required for the desired radiant output or even with a loading suflicient to establish and maintain the arcing point'on the electrode. There is, however, a considerable latitude within which satisfactory lamps can be successfully made and operated.

It is important in the dimensioning of the tube that it should be closely fitted to the discharge path so that the vaporization will result not only in an increase in pressure, but in an actual increase in density of the gaseous atmosphere within the luminous are. In general, the closer the wall of the tube is fitted to the arc path the more effective the vaporization will be in increasing the voltage drop in the arc, but, of course, the spacing should be sufficient to avoid fusion or destruction of the tube wall by the arc. As one specific example of my invention a practical and economical lamp may be made with the distance between the two electrodes amounting-to 150 mm., the arc t'ube I having an internal diameter of 20 mm., the electrode chambers 2 and 3 having an inside diameter of about 28 mm. This tube may be made of quartz or of glass. Where ultra-violet rays are desired, quartz is to be preferred. If a glass envelope is employed, it should be one which is permeable to ultra-violet rays. Quartz is also of advantage because, being more refractory to high temperatures, it permits design of the tube for operation at higher temperature and, therefore, at higher pressures and for the same reason permits the use of smaller tubes more closely fitted to the discharge.

The electrodes'may consist of 20 nickel wires twisted together, each of 0.35 mm. diameter, and

the twisted composite wire wound to a spiral of e. g, 5 turns with an outer diameter of about 8 mm. The space between adjacent windings of this spiral is less than 1 mm. The support 1 is of nickel wire 3 mm. in diameter, flattened, e. g., by hammering, to a thickness of about 1 -2 mm.

The starting of a discharge between the spaced electrodes, of course, requires a gaseous atmosphere, i. e., a fixed gas or vapor or both. If it is desired to obtain a discharge in the cold lamp without the necessity of heating to vaporize the mercury or other vaporizable material, an atmosphere should be provided which will remain gaseous in the cold state and thereby provide a conductive path for the initial discharge. This, in my preferred example, I achieve by filling the tube with an inert or rare gas such as neon, or especially argon, at a suitable pressure which depends upon the voltage available and the dimensions of the tube. For the given dimensions and for operation on ordinary supply line potentials, e. g., of the order of 220 volts, and in the preferred example described above, I have provided argon at a pressure of 1.5 to 3 mm. mercury column, or neon at a pressure of 4 to 9 mm.

- mercury column. These pressures aresuitable particularly for a tube of dimensions of about 20 mm. diameter and 250 mm. in length and a supply line voltage of the order of 220 volts.

With this lamp as just described the arc starts to burn at 6 amps. The voltage drop in the tube is then about volts. The increase in the current load of the tube when this initial arc is formed will increase the initial pressure, owing-to the presence of the easily vaporizable mercury in the tube, to such as extent that this metal vapor takes over the current conduction and light emission within a few seconds. After about 3 minutes the mercury is so ,far evaporated that a high pressure are is formed and the lamp burns stably at a voltage drop in the tube of about 120 volts and at a current of about 3.2 amperes. The remaining voltage is, of course, consumed in the ballasting device which is used with this as with all arcing devices.

It will be understood, of course, that when operating from an ordinary constant voltage supply line the energy consumption in the tube depends on the amount of series impedance serving as ballast for the arc, and that this may be adapted with respect to the dimensions of the tube and the heat losses by radiation and conduction from the tube so that the heat generation in the arc path and at the electrode results in a vapor pressure far exceeding the pressure ranges common in the older activated cathode tube and which, as already described, consumes an increasing portion of the total voltage applied. c. g., up to more than of this voltage.

The electrodes as described are capable of starting in the cold condition and without preheating. Upon the application of a voltage to the tube a glow discharge arises particularly from pointson the electrode where there is suitable or higher'frce barium concentration. These points form the initial visibly glowing points. Because of the heat concentrating materials surrounding these points, they are rapidly transformed into arcing points from which an arc starts and replaces the initial glow discharge and operates with a cathode drop of only a few volts.

When the tube is operated on alternating current, the electrodes 6 each operate. alternately as anode and cathode. If direct current is used only one of the electrodes needs to be of the activated type described. However, it is an important advantage of the lamp as shown, with two such electrodes, that it may be used satisfactorily in all cases. It is especially important in the case of such 'a lamp used on direct current that the electrode support, e. g., the ring I or disc I and frame 8, if used,'and electrode support wires 4 and 5 be of dimensions correctly determined to conduct away and dissipate any superfiuous anodic heat generated at the end of the tube which serves as anode.

An additional expedient which will assist in the starting of the are directly from the applied voltage is the provision of a conductive layer or layers on the outside of the tube wall, e. g., in the form of strips or streaks I I or cuffs extended into close proximity of the cathode. In the case of direct current it is only necessary to bring the anode. through the external conductive strip. electrically into the vicinity of the cathode. In the case of alternating current operation, such a conductive layer may be connected to either electrode and extended into the neighborhood of the other. In the preferred example I have made a uniform conductive streak from one .electrode to the other and interrupted it near one electrode by a narrow gap, as clearly shown in Fig, 1. This is a most efiicient arrangement. The conductive layer extends over as large a part of the surface of the tube as is practicable. It may consist of a metallic layer, which reflects generated light to a good degree; and, to the extent that it reflects heat also, it will hasten the evap oration of the mercury and consequently the attainment of high pressure operation and likewise will assist in reaching the desired high temperature of thermal equilibrium at which the desired pressure and voltage drop are attained.

Upon the application of voltage for the starting of the lamp this conductive layer serves as a capacity electrode to facilitate the first feeble glow discharge and subsequently assists in transforming the glow into an arc. This action is more fully described and claimed in the copending application of Hans J. Spanner, Serial No. 130,872, filed April 15, 1937.

The voltage drop of the initial arc discharge depends primarily on the spacing of the electrodes and, with the lamp and dimensions as described, is initially of the order to 5 0 volts for an electrode spacing of 20 to '70 cm. It will be understood, however, from what has already been said, that the final voltage drop which the lamp maintains after equilibrium has been attained depends principally upon the density of vapor in the discharge path after the initial vaporization. This in turn depends firstly upon the amount of vaporizable material supplied to the envelope and secondly upon the design and heat dissipating capacity of the envelope and the energy loading supplied thereto.

In the example shown in Fig. 1, the mercury is supplied in the quantity necessary to produce the desired increase in pressure and voltage, and if the tube should be overheated the vaporization would continue beyond the point at which the desired voltage consumption is reached and may even result in the voltage consumption increasing so far that the energizing circuit is no longer able to supply sufficient current to maintain the are at the increased voltage consumption; and the arc would, therefore, be extinguished. This can be taken advantage of by supplying an excess of mercury and decreasing the series resistance with the result that during the warming-up period the tube is overloaded and consequently overheated so that, even after the energy consumption of the tube begins to decrease because o the drop in current with increasing voltage consumption, the mercury may continue to vaporize until the current drops below the minimum necessary to maintain a stable arc. Thus .is brought about an automatic interruption of the arc with repeated and successive intervals of operation and cooling respectively.

This may be advantageous especially for signalling and display purposes.

For ordinary illumination, of course, the circuit will be ballasted to avoid such over-shooting of the vaporization. With the greater series resistance the heating and vaporization occur more slowly; and, as the energy loading begins to decrease, the equilibrium may be approached and maintained without carrying the vaporization so far as to make the are unstable. A series resistance which consumes during normal operation approximately one-third of the line voltage (e. g., from a 220 volt line) has been found satisfactory with a tube as described in Fig, 2, but with stable operating conditions the series resistance may be substantially less, and the greater the current the less voltage need be consumed in the series resistance.

Such over-shooting is also prevented if only the necessary amount of vaporizable material is supplied to the envelope, as described in connection with Fig. 1.

It is an important advantage of the combination, as shown and described herein, including the electrodes having fine conductive portions such as wires, ribons, or other members providing projections, etc., or heat insulating materials surrounding narrow arcing points so that these projections or points are readily heated toareing temperatures, and hence an arc may be maintained thereon with even a fraction of an ampere current loading. Thus it is possible to construct lamps of given wattage for operation at a much higher pressure and, therefore, higher voltage without danger of the are becoming unstable or being extinguished by cooling of the arcing point. Likewise even if vaporization should over-shoot to a considerable extent, the reduced current may be sufiicient to maintain the arc on these special electrodes provided that the ballast is sufiicient to avoid unstable operation which results when the increasing voltage brings the operation onto a negative slope portion of the over-all characteristic of the lamp and its ballast.

If the heating up is slow and the current and voltage can be held steady and the surrounding atmospheric conditions can also be maintained substantially constant the thermal equilibrium temperature can be determined and maintained close to the maximum voltage at which the arc will operate stably in the circuit and regardless of the amount of mercury or other vaporizable material 'present in the lamp. Where these factors are subject to wide fluctuation, however, one or more of the other expedients discussed above may be necessary to stable operation.

When the above described tube is put in operation the vaporizable metal is soon evaporated and takes over the current conduction and light emission, and at the same time constricts the arc column until, instead of filling the entire tube, as in the first moment after starting, the luminous cord is contracted away from and is much narrower in diameter than the tube, e. g., less than half.

In the ordinary gas filled incandescent cathode tube the useful operating voltage on the tube is low as compared with the ignition voltage. According to my preferred embodiment, however, the tube dimensions on the one hand and the series resistance or other ballast on the other hand are chosen so that the current load, determining the heat development, is so large that the metal vapor pressure will be considerably, even remarkably, over atmospheric pressure. Thus, for example, with 220 to 260 volts applied to the tube and the voltage drop in the first moments of starting decreasing to 20 to 40 volts, the voltage will, according to my invention, increase again and reach at least 130 to 150 volts; preferably not more than of the total voltage applied is consumed in the series resistance.

Furthermore, the efficiency, e. g., the light and ultra-violet radiating economy of watts consumed in the arc will be, at medium pressures, twice that of the low pressure tube, and even three to four times as high with a vapor pressure about 1 atmosphere; that is to say, it is shown that with increasing pressures an increasing efliciency' of the device will be obtained.

It is an advantage of these lamps as just described that they may be operated at any desired pressure and at any given pressure they burn reliably at amp. as well as at 10 amps. or more. When the lamp has an electrode spacing of 20 cm. and operates at 130 volts with a current of /2 ampere the loading is just under 10 watts per cm. When the lamp has an electrode spacing of 20 cm. and operates at 150 volts with a current of 10 amperes the loading amounts to '75 watts per cm. For the smaller types of lamps, e. g., up to 1.5 amps. current input, it is advisable to insulate at least a part of the tube against heat transmission. This may be done, for example, by covering at least a part of the electrode container with heat insulating material 20, such as asbestos, or by insulating the back of the whole tube against heat loss.

Fig. 2 shows another advantageous arrangement. This is a U or Vshaped lamp which is operated in vertical position, as shown in the figure, with the electrode chambers 2a and 3a uppermost. The vaporizable metal, advantageously mercury, is placed at the lowest point of the lamp, preferably in a depression I20, of the tube proper and there it is heated by the discharge which causes the vapors to rise from it into the other parts of the tube.

In the example illustrated in Fig. 2, an excess of mercury is provided and the electrodes 6a are partially shielded from thewalls of the electrode chambers (2a and 3a) by special cylinders l5 and I6 provided inside. of the electrode chambers. These cylinders may be fused to the upper or to the main part of the chambers or to the inlead.

and electrode support wires or they may be fastened in any other suitable manner. This results in the upper portion of the electrode chamber behind the cylinders l5 and "5 being at a condensing temperature, whereby a reflux condensation can occur, with small drops of mercury forming behind the shields l5 and I6 and rolling down, as soon as they are formed, along the lower and consequently the cooler side of the tube la to the depression lZa where they are again evaporated by heat of the arc. Thus, a continual stream of mercury vapor is blown from the reservoir l2 into the direction of the electrode 6a and the electrode chambers 2a and 3a respectively.

In this way any materials such as nickel or barium sputtered or vaporized from the cathode are hindered from migrating into the arc tube proper; but instead they are repulsed and blown back into the electrode chambers where they are condensed upon the walls behind the electrodes where they do not substantially interferewith light emission from the tube. Whereas the normally solid materials vaporized or sputtered from the electrodes condense upon the first surfaces with which they come in contact, either the inside of the cylinders E5 or it or; the upper end of the electrode chambers, the mercury does not condense upon these relatively hot surfaces but only upon the cooler surfaces between the cylinders l5, l6 and the walls of the electrode chambers. The mercury, of course, runs back toward the bottom of the tube in little globules, whereas the electrode materials remain upon these surfaces behind the electrodes. By reason of the fact that the mercury and the electrode materials condense at different places the mercury will not wash out the deposited nickel, barium, etc., whereby the mercury would be spoiled and the tubes blackened. On the contrary, the mercury which condenses and runs back into the arc tube is clean. and pure.

This action is improved by the constricted portions l3, l4; and, as shown, there may be successive constrictions, e. g., at the edges of the cylinders l5, it as well as in the tube itself. This feature is more particularly described and claimed in my copending application, Serial No. 60,774, filed January 25, 1936.

Although I have described particularly the operation of these shields l5 and I6 when mercury is continually condensed during normal operation, they may be important also where any excess of vaporizable material remains unvaporized in the bottom of the tube. In such case the condensation occurs only during the warming-up period;

but it is most important at this time firstly because the electrodes may be overloaded and, therefore, most likely to evaporate material therefrom during this period so that the. control of dark deposits by the increased convection is most important at this time; and secondly because the relatively cool condensing area tends to avoid the production of excessive pressures by overheating of the tube with residual vaporization after the desired pressure has been reached.

Obviously, the shape of the U or V mentioned is not the only one possible, on the contrary there are various forms in which a mercury vapor stream will rise from the evaporating mercury and be directed against and over the electrodes into the end of the electrode chamber and the condensed mercury allowed to run back to the tube proper.

The devices embodying my invention may, as already stated, be made of glass, quartz, or any other suitable material. The inlead and electrode support wire may be sealed into the container in any usual way. I have also made satisfactory tubes by the use of a metal cone fitted and ground into a socket provided in the body of the container and made vacuum tight by mercury. Such seals have been used prior to my invention in the well known quartz burners of the Quartz-lampenfabric at Hanau, Germany. Another way of making a pressure tight seal, especially with quartz which is very diihcult to handle, is shown in Fig. 2 of the drawings. In this case the lead wire 9 is fused to a thick walled quartz tube I! which in turn is fused to the container at the upper part of the main quartz tubing. At the outer end there may advantageously be provided a cup I8 into which may be filled the vacuum sealing material, such as sealing wax and the like.

It is one advantage of my invention that the voltage increase which results from vaporization allows the use of smaller currents and, therefore, smaller inleads with given wattage. This, of course, reduces the strain between glass or quartz and the inlead to which it is fused, and permits seals which would fail with thicker inleads.

The lamps as described above may be used for lighting purposes as well as for ultra-violet radiation purposes. Where they are intended for ultra-violet radiation use advantageously they are filled with mercury; whereas, for light other metals may be used, especially such as thallium, gallium, alkaline metals, etc.

The lamps may be operated at low as well as advantageously at high pressures.

Another advantage of the lamps as shown is that all parts of the tube are strongly and directly heated by the discharge, except for the shields l5l6 in the case of Fig. 2, which intercept radiant heat directed toward the walls of the electrode chambers, and that the supply of mercury is held at the bottom of the tube where it is-cooled by convection currents passing over the tube. Thus it results that the vapor filling in the tube is unsaturated (except in the condensing zone behind the shields |5--l6 of Fig. 2), as a result of which it is able to stand considerable variations of external atmospheric conditions or fluctuations of energy loading without serious effect on its operation, even though excess .liquid mercury may remain in the tube.

Moreoversince, as already pointed out above, the coolest area after that of the mercury pool, if such pool remains, is behind the electrodes; and, inasmuch as this area. tends to collect any solid metals sputtered or vaporized from the electrode it will be coatedv with a deposit which absorbs and reflects radiation and thus raises the temperature of these electrode chambers. Even behind the shields I5 and IS the condensing area is so small that it is easily kept at the desired temperature by the heatboth sensible heat and latent heat of vaporization conveyed thereto by the vapors which circulate thereto.

From the above it will be understood that my invention eliminates the necessity for the various complications and disadvantages which have been essential with the older types of tubes. Only one lead-in wire is required at each end of the tube. No auxiliary heating circuits for the electrodes are required. No tilting or other special starting devices are required. The lamps may be operated in series either with a resistance, as for example an incandescent resistance used to supplement radiation from the arc, as well as with other types of impedance, e. g., choke coils, flux leakage transformers, etc., and may be operated from A. C. or D. C. lines at ordinary commercial supply line voltages; and with all these advantages the lamp operates with higher efliciency and with a radiation spectrum which is desirable both for ultra-violet and for illumination purposes.

This application is a continuation of copending application Serial Number 500,346, filed December 5, 1930.

What I claim is:

1. An arc discharge device comprising an energizing circuit including a source of current and means for limiting the current loading, and a discharge tube which comprises a sealed envelope, fixed electrodes positioned at opposite ends thereof at least one of which is a solid activated arcing electrode, and filling material adapted to provide a gaseous atmosphere for starting an electrical discharge at a potential available from said energizing circuit and a vaporizable material in amount adapted by its vaporization to increase the voltage drop of the discharge tube to at least of the total voltage which the energizing circuit is adapted; to apply for operation of the arc, and the energizing circuit being adapted to supply to the discharge an energy loading suflicient to vaporize said vaporizable material to an extent equivalent to at least of said voltage but less than the maximum voltage consumption at which the arc will operate stably.

2. A radiant electrical discharge device which comprises fixed electrodes spaced apart a distance greater than twice the diameter of the confining means hereinafter mentioned at least one of which is a. solid activated arcing electrode, and adapted to carry without destruction a current loading sufiicient to maintain increased vaporization as hereinafter specified, means for confining the atmosphere of the discharge and for limiting the heat dissipation therefrom, the heat dissipating surface of which is limited so that, at the temperature required to maintain said increased vaporization, the dissipated energy in still air at room temperature does not exceed that attainable by current loading within the capacity of the electrodes to carry without substantial destruction, a filling in the confining means adapted to provide an ionizable atmosphere at relativelylow pressure for starting, and including also vaporizable material the vapor of which is adapted to carry the discharge which is in amount suiiicient when vaporized to increase the operating voltage drop of the discharge to at least double that of the lowest voltage reached after starting, and an energizing circuit connected to the electrodes adapted to supply the discharge with electrical energy sufficient to maintain said vaporization.

3. A radiant arc discharge device comprising an energizing circuit, including a source of current and means for limiting the current loading, and a discharge tube comprising a sealed envelope permeable to at least a part of the radi-' ation from the discharge, fixed electrodes positioned therein at opposite ends of the envelope at least one of said electrodes being an activated arc electrode, and a filling in said envelope comprising a starting atmosphere adapted to carry an initial discharge at a voltage of the order of A to V./mm. between the electrodes and a vaporizable metal in amount adapted by its evaporation to increase the voltage drop of the discharge tube to more than V./mm. between the electrodes, the energizing circuit being adapted to give sufiicient loading to the discharge to maintain said evaporation of the vaporizable metal.

4. A radiant electrical discharge device which comprises fixed electrodes spaced a distance greater than the diameter of the envelope adapted to carry the discharge current, at least one of said electrodes being a solid activated arc electrode provided with means for concentrating the discharge at narrow arcing points thereon and with masses of activation material closely associated with said arcing points but protected from direct action of the arc, an envelope permeable to radiation from the discharge enclosing the electrodes and approximately fitted to the discharge space between them, a filling in said envelope comprising a starting gas adapted to give an initial difi'use discharge substantially filling the envelope and a vaporizable material the vapor of which is adapted to carry the luminous discharge and in amount adapted when vaporized to give in said envelope a characteristic high pressure arc discharge with a brilliant cord constricted away from the envelope wall and a concentrated incandescent arcing point on the electrode, and an energizing circuit connected to the electrodes and adapted to supply a current loading for the discharge sufiicient to effect the vaporization necessary to establish said high pressure arc.

5. A high pressure vapor discharge device comprising an envelope permeable to radiation from the discharge, a vaporizable filling therein adapted to give a characteristic high pressure discharge with constricted luminous cord with a concentrated incandescent arcing point on the electrode, spaced electrodes therein at least one of which is a self-heating activated arc electrode adapted to carry without destruction an arc sufficient to produce and maintain by vaporization of said filling material a vapor pressure which gives the characteristic high pressure are each of said electrodes being short-circuited inside of the envelope for high frequency heating and whereby to provide a plurality of thermally and electrically conducting paths from the arcing point and a single lead-in wire for each of said electrodes, whereby the heat loss through the electrode connections is minimized.

6. A high pressure vapor discharge device as defined in claim 4 in which the envelope is of glass.

'7. A radiant electrical discharge device as defined in claim 2 in which the connections to the electrodes are sealed into the confining means by outwardly directed seals with the inner wall meeting the tube approximately at the end of the space within said confining means whereby condensation pockets remote from the electrodes are avoided.

8. A high pressure vapor discharge device as defined in claim 4 which further comprises thermal insulating means over at least those parts of the envelope on which condensation would be most likely to occur whereby to reduce fluctuation in the operation of the lamp due to uneven condensation or re-evaporation.

9. A high pressure vapor discharge device as defined in claim 4 which further includes reflecting means associated with the envelope in a limited area thereof and adapted to reflect back into the envelope heat and light radiated therefrom and thereby to reduce any tendency to condensation of the vapor filling during operation.

10. A radiant electrical discharge device as defined in claim 4 which further comprises an auxiliary electrode closer to said activated electrode than is the opposite principal electrode, whereby to hasten restarting of the lamp when it is energized before its vapor is fully condensed and to prevent accumulation of charges and thereby hasten the warming-up period after the lamp is started.

11. An intermittent illuminating device which comprises an energizing circuit and a discharge tube connected thereto, said tube comprising electrodes, an envelope enclosing the discharge space between and around the electrodes, a filling comprising vaporizable material adapted to carry the luminous discharge between the electrodes and with increasing vapor pressure during operation to increase the voltage drop across said electrodes and in amount in excess of that equivalent to the maximum voltage at which an operating current is available from said circuit, and the heat dissipating capacity of the envelope being limited to less than the heat generation of said discharge under the energy loading provided by said circuit whereby such an excess of vapor pressure will be generated in the envelope as to extinguish the discharge until substantial condensation of said filling and consequent reduction of vapor pressure has occurred.

12. The method of operating an arc discharge in a gaseous atmosphere between fixed electrodes, at least one of which is an activated cathode, which comprises starting a discharge by imposing on the electrodes a potential suflicient to ionize the gas and establish the discharge, ballasting the discharge to absorb a substantial part of the applied potential when the voltage consumption of the discharge path is reduced by ionization, and increasing the voltage consumption of the discharge by raising the pressure of the gaseous atmosphere until said voltage consumption is increased to at least double the voltage consumption of the discharge in the first moment after starting the arc.

13. The combination of a source of current, a high pressure electrical discharge device having electrodes spaced apart therein at least one of which is a solid activated arcing electrode. a sealed envelope enclosing the electrodes and approximately fitted to the discharge path between them, and a filling in said envelope adapted to provide a gaseous atmosphere for starting a discharge and including a vaporizable material adapted by vaporization after starting of the discharge to raise the operating voltage of the discharge device to at least double that of the lowest voltage after starting, and means for supplying current from said source to the device which is adapted to ballast the discharge in said device, in which the heat dissipating capacity of the discharge device, the amount of vaporizable material therein and the current capacity of said current source and said current supplying means are adapted to raise the voltage consumption at least to said doubled value and the wattage consumption of the discharge device by said vaporization to at least about 10 watts per cm. of the distance between electrodes at said operating voltage.

14. The combination of a source of current. a

high pressure electrical discharge device having electrodes spaced apart therein at least one of which is a solid activated arcing electrode, a sealed envelope enclosing the electrodes and approximately fitted to the discharge path between them, and a filling in said envelope adapted to provide a gaseous atmosphere for starting a discharge and including a vaporizable material adapted by vaporization after starting of the discharge to raise the operating voltage of the discharge device to at least double that of the lowest voltage after starting, and means for supplying current from said source to the device which is adapted to ballast the discharge in said device, in which the heat dissipating capacity of the discharge device, the amount of vaporizable material therein and the current capacity of said current source and said current supplying means are adapted to raise the voltage consumption at least to said doubled value and the wattage consumption of the discharge device by said vaporization to at least about 75 watts per cm. of the distance between the electrodes at said operating voltage.

15. An electric lamp which comprises fixed electrodes spaced apart a distance greater than twice the diameter of the confining means hereinafter mentioned and at least one of which is a solid activated arcing electrode, and adapted to carry without destruction a current loading sufficient to maintain increased vaporization as hereinafter specified, means for confining the atmosphere of the discharge and for limiting the heat dissipation therefrom, the heat dissipating surface of which is limited so that, at the temperature required to maintain said increased pressure, the dissipated energy in still air at room temperature does not exceed that attainable by current loading within the capacity of the electrodes to carry without substantial destruction, a filling in the confining means adapted to provide an ionizable atmosphere at relatively low pressure for starting, and including also mercury in amount sufficient when vaporized to increase the operating voltage drop of the discharge to at least double that of the lowest voltage reached after starting, and an energizing circuit connected to the electrodes adapted to supply the discharge with electrical energy sumcient to'maintain said vaporization.

16. An electric lamp comprising an energizing circuit, including a source of current and means for limiting the current loading, and a discharge tube comprising a sealed envelope permeable to at least a part of the radiation from the discharge, fixed electrodes positioned therein at opposite ends of the envelope at least one of said electrodes being an activated arc electrode, and a filling in said envelope comprising a starting atmosphere adapted to carry an initial discharge at a voltage of the order of A5 to & v./mm. between the electrodes and mercury in amount adapted by its evaporation to increase the voltage drop of the discharge tube to more than A; v./mm. between the electrodes, the energizing circuit being adapted to give sufiicient loading to the discharge to maintain said evaporation of the mercury.

17. An electric lamp comprising the combination of an energizing circuit, including a source of current and means for limiting the current loading, and a discharge tube comprising a sealed tubular envelope capable of transmitting at least a part of the radiation from the discharge, fixed electrodes positioned therein at opposite ends of the envelope, at least one of said electrodes being an activated arc electrode, said envelope also containing a starting atmosphere of rare gas at a pressure of a few millimeters of mercury, and a quantity of mercury adapted by its evaporation to result in a voltage drop between said electrodes exceeding 2.5 volts per centimeter, the energizing source being adapted to give sufficient loading to the discharge to maintain the pressure of mercury vapor sufficiently high to result in such voltage drop.

18. An electric lamp which comprises fixed electrodes spaced apart a distance greater than twice the diameter of the confining tube, which is hereinafter specified, and at least one of which is an activated thermionic electrode adapted to carry without destruction a current loading suflicient to maintain increased vaporization as hereinafter specified, a tubular container for confining the atmosphere of the discharge and for limiting the heat dissipation therefrom, the heat dissipation surface of said container being limited to such extent that, at the temperature required to maintain said increased pressure, the dissipated energy in still air at room temperature does not exceed that energy attainable by current loading which the electrodes are adapted to carry without substantial destruction, a rare gas at relatively low pressure in said container whereby starting is facilitated, a quantity of mercury in said envelope in amount sufiicient when vaporized to produce a vapor pressure of at least about one atmosphere, and an energizing circuit connected to said electrodes, said circuit including means for supplying the discharge with electrical energy sufiicient to maintain said vaporization.

19. An electric lamp which comprises fixed electrodes spaced apart a distance greater than twice the diameter of the confining container, which is hereinafter specified, andat least one of which is a solid activated arcing electrode adapted to carry without destruction a current loading sufficient to maintain increased vaporization as hereinafter specified, a tubular container for confining the atmosphere of the discharge, means for reducing heat dissipation from said container, the heat dissipation of said container being limited to such extent that, at the temperature required to maintain said increased pressure,

the dissipated energy in still air at room temperature does not exceed that energy attainable by current loading which the electrodes are adapted to carry without substantial destruction,

a rare gas at relatively low pressure in said concluding a source of current and means for limiting the current loading and a discharge tube which comprises a sealed, elongated envelope, fixed electrodes positioned at opposite ends thereof, at least one of which is a solid, activated electrode consisting of closely compacted conductors of small section, a gaseous filling at relatively low pressure for starting an electrical discharge at a potential available from said energizing circuit, and a quantity of mercury in amount adapted by its vaporization to increase the voltage drop of the discharge tube to at least two-thirds of the total voltage which the energizing circuit is adapted to apply -for'operation of the arc, and the energizing circuit being adapted to supply to the discharge an energy loading sufficient to vaporize said vaporizable material to an extent equivalent to at least twothirds of said voltage but less than the maximum voltage consumption at which the arc will opcrate stably.

21. An electric lamp which comprises fixed electrodes spaced apart a distance greater than twice the diameter of the confining means hereinafter mentioned, at least one of said electrodes being a solid arcing electrode having an absorbent structure filled with activating material and comprising closely compacted conductors of small section providing projections, said electrodes being adapted to carry without destruction a current loading sufiicient to maintain increased vaporization as hereinafter specified, means for confining the atmosphere of the discharge and for limiting the heat dissipation therefrom, the heat dissipating capacity of said lamp being so lim-' cuit connected to the electrodes adapted to supply the discharge with electrical energy suflioient to maintain said vaporization.

22. A radiant electrical discharge device which comprises fixed electrodes spaced apart a distance greater than twicethe diameter of the confining means hereinafter mentioned at. least one of which is a solid activated arcing electrode of compact form and provided with projections, and adapted to carry without destruction a current loading sufficient to maintain increased vaporization as hereinafter specified, means for confining the atmosphere of the discharge and for limiting the heat dissipation therefrom, the heat dissipating surface of which is limited so that, at the temperature required to maintain said increasedpressure, the dissipated energy in' still air at room temperature does not exceed that attainable by current loading within the capacity of the electrodes to carry without substantial destruction, a filling in the confining means adapted to provide an ionizable atmosphere at relatively low pressure for starting, and including also vaporizable material the vapor of which is adapted to carry the discharge which is in amount sufllcient when vaporized to increase the operating voltage drop of the discharge to at least double that of the lowest voltage reached after starting, and an energizing circuit connected to the electrodes adapted to supply the discharge with electrical energy suflicient to maintain said vaporization.

23. A radiant arc discharge device comprising an envelope permeable to radiation from the discharge, fixed solid electrodes spaced apart in said envelope and at least one of which is an activated electrode consisting at least in part of an activation material, a gaseous filling in said envelope comprising a. starting gas adapted to give an initial discharge on imposition of a potential on the electrodes suflicient to ionize said gas and a vaporizable metal adapted to give an arc discharge when vaporized by the heat of the initial discharge and sufficient in amount to raise the pressure of the atmosphere within the envelope until the voltage consumption of the discharge is increased to at least double the voltage consumption of the discharge in the first moment after starting the arc, and an energizing circuit and a ballast in circuit with the discharge device to absorb a substantial part of the imposed potential when the voltage consumption of the discharge path is reduced by ionization of the gaseous atmosphere.

24. A radiant arc discharge device comprising an envelope permeable to radiation from the discharge, fixed solid electrodes spaced apart in said envelope, and at least one of which is an activated electrode consisting at least in part of an activation material, a gaseous filling in said envelope comprising a starting gas adapted to give an initial discharge on imposition of a potential on the electrodes sufficient to ionize said gas and mercury to give an arc discharge when vaporized by the heat of the initial discharge and sufilcient in amount to raise the pressure of the atmosphere within the envelope until the voltage consumption of the discharge is increased to at least double the voltage consumption of the discharge in the first moment after starting the arc, and an ener gizing circuit and a ballast in circuit with the discharge device to absorb a substantial part 01. the imposed potential when the voltage consumption of the discharge path is reduced by ionization of the gaseous atmosphere.

EDMUND GERBER.

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