US2007919A - Electrical discharge device - Google Patents

Description

July 9, 1935. c. H. BRAsELToN ELECTRICAL DISCHARGE DEVICE 5 sheets-shed 1 Filed June 3, 1930 INVENTOR Filed June 3, 1950 5 She@CS-Sheet` 2 INVENTOR @MWL July 9, 1935. Q BRASLTON 2,007,919

ELECTRICAL DISCHARGE DEVICE Filed June 3, 1930 5 Sheets-Sheet 3 IN VENTOR Patented July 9, V1935 PATENT OFFICE ELECTRICAL DISCHARGE DEVICE Chester H. lraselton,v New York, N. Y., assignor v to Sirian Lamp Company, Newark, N. J., a corporation of Delaware Application-June '1930, serial No. 459,048

19 claims'.

This invention' relates to'a method and apparatus for the production of conducting paths for electric currentssadjacent but external to the surface of a1 dense body, and to the means and the method forcontrolling the paths for utilization in various arts such as the art of electrical illumination.

One of the objects of the invention is to provide a method and a. d evice for converting electrical energy into radiant energy throughout the entir range of the ether spectrum.

Another object of my invention is to provide an electrical conducting path adjacent a'conducting element serving as an auxiliary or shunt path for the current flowing in said element.

Another object of the invention is to provide a means for causing gas or vapor adjacent a conducting element to serve as an auxiliary conductor for the current which would normally ilow in said conducting element.

' Another object of the invention is to provide a means for causing gas or vapor adjacent an electron emitting element to serve as an auxiliary conductor in the same general direction as the axis of the element.

Still another object of the invention is to maintain an ionic discharge adjacent a heated conductor so that it forms an auxiliary and shunt path for the potential applied to the conductor.

Another object of the invention is to obtain an ionic discharge and kmaintain and control the potential gradient along the path of the discharge by the voltage drop in a heated conductor adjacent to the discharge.

A further object of the invention is to maintain a diiused or non-localized ionic discharge in contact with a heated conductor -by the potential difference between various parts of the conductor.

Still another object of the invention is. to maintain a highly conductive gaseous discharge adjacent to an ionizing element by virtue of -the electron emission from said element and the poten,- tial gradient along said element.

Another object of the invention is to obtain ionic discharge of high energydensity distributed over an ionizing surface.l

A still further objectl of the invention is the efficient production of radiant energy obtained simultaneously from an ionized gas discharge, a glow caused by bombardment of a refractory material, and the thermal eiects of current ow through a conductor, al1 caused by the current flowing through said conductor. Other objects of the invention and objects relatingfto various uses for the phenomena involved will be apparent as the description of the invention proceeds.l

Several embodiments of the invention applying particularly to illuminating devices are illustrated in the accompanying drawings in which:

Fig. V1 is a side elevation of an electric lamp having a double electron emission element;

Fig. 2 is a side elevation of a modified form of the lamp shown in Fig. 1,;

Fig. 3 is a side elevation of still another modi- 10 cation of the lamp;

Fig. 4 is an enlarged perspective view of still another modification of the lamp;

Fig. 5 is another perspective view of a modified form of the lamp;

Figs. 6 and 7 are side elevations of a lamp showing a single element;

Fig. 8 is a side elevation of a lamp with the yelements connected in parallel;

Fig. 9 is a perspective view of a modified form 20 n of the lamp shown in Fig. 8;

Figs. 10, 11, 12, and 13 are enlarged longitudinal sections of one end of diierent embodiments of electron emitting elements;

Fig. 14 is an enlarged view of another ment of an electron emitting element;

Figs. 15, 16, and 17 are enlarged views, the latter two being in section, of several diierent methods of attaching the electron emitting elements to the supports;

Fig. 18 is a longitudinal sectional view of another embodiment of an electron emitting element;

Fig. 19 is a side elevation of still another embodiment of an electron emitting element;

Fig. 20 is a side elevation partly in section of a portion of another embodiment of the lamp;

Fig. 21 is a plan view of the parts of the lamp shownin Fig. 20;

Fig. 22 is a perspective view of a portion of still 40 another embodiment of the lamp; and

Figs. 23 and 24 are perspective views of the active portions of other embodiments of the lamp.

I have discovered that if an electron emitting surface has a potential applied across it and is heated to an electron emitting temperature that a conductive path will be formed adjacent to the surface but outside of it. One way to make effective use of this conductive path is to provide a gas in contact therewith. -The crosssection of the conductive path and its proximity to the emitting surface when a gas is used appears to be dependent upon the gas used and the pressure thereof, as well as the resistance of the conducting base and the potential used across embodi- 25 it. Thus a conducting element coated with electron emitting material and heated by the p sage of a current at a suitable potential and 1n the presence of an ionizable gas at a suitable pressure may be made to maintain an ionic discharge adjacent the emitting surface which has the characteristic of being uniformly. distributed over the surface and apparently follows the electrical field maintained between oppositely charged parts of the element and differs from the ionic discharges of the prior art by being spread out or diffused over a large area and by being independent of the consumption of an electrode material for its maintenance and of ygap-separated electrodes. 'Ijhe gas discharges heretofore used have, in general, been between two or more electrodes maintained at an adequate potential difference, while in making use of the principles discovered by me the discharge may be made to follow the potential gradient produced by the conduction of a current through an electrically resistant and thermally refractive ionizing element. The relation between the potential impressed across the element and the pressure of the gas used is important in preventing the discharge, if desired, from occurring in any other Adirection except along or parallel to the axis of the ionizing element.

For purposes of illumination any desired spectral characteristics may be imparted to the emitting surface by proper choice of gases or vapors and operating pressures. The material chosen as the ionizing agent should be one that will withstand high temperature operation and preferably have selective radiation characteristics, so that if used for illumination purposes the heat energy imparted to it by conduction, radiation, or ionic bombardment will be effectively translated into visible radiation. When this principle is specifically applied to a lamp for general illumination purposes the ionizing element may consist of a coiled refractory filament of tungsten, for instance, coated with a. mixture of calcium and barium oxides or calcium oxide alone, or other oxides may be used depending on the particular characteristics desired. For such a lamp a mixture of argon and neon might be used at a pressure of about two hundred millimeters.

In the construction of a lamp to operate on this principle it is desirable that the emitting oxides beas pure as possible, such as being free from binding elements or inactive materials, and that the gases be as free from impurities as possible./ This is accomplished by the proper exhaustion of the container and elements at suitable temperatures to discharge all occluded gases e or vapors at low pressure prior to the introduction of the inert gas. For uses where the radiation must extend into the invisible part of the spectrum, as in ultra-violet radiations, metallic vapors such as the vapors of mercury, caesium, or rubidium may be used, especially the first mentioned. In general the most preferable gases are those which are inert and monatomic such as neon, argon, krypton, xenon, and helium, and which may be designated as the gases of the argon group. These gases have low ionization potential and chemical inertness. Where exceptionally low ionization potentials are desired metal vapors such as those of rubidium or caesium may be mixed with the inert gases.

The operation of an illuminating device built upon my discovery may utilize a combination of sor'ne or all of effects, such as the formation of a diffused and uniformly distributed ionic discharge maintained by the electron bombardment of a gas from an electron emitting compound intimately contacting with a refractory base, with the drop of potential along the refractory base serving as the Aelectron accelerating potential, the heating of the refractory base by electron bombardmentfrom itself and from the gas, and

lthe heating of the refractory base by the current passing through it. The ionic discharge occurring at the surface of the oxide coatedelement appears to ionize the gas immediately surrounding it so as to make it an auxiliary conductor and because the discharge extends along the ionizing element and is uniformly distributed as an intense sheath around it, localized eflectsv are avoided with resultant elimination of spot vaporization or decomposition of discharge terminals.

It is preferable to activate the electron emitting compounds if, for example, an oxide of the alkaline earth type is used, in order to obtain eilicient thermionic emission.

I have found that in most cases for practical consideration that the drop of potential along the filament or ionizer element should be greater than the breakdown potential of the gas or vapor atmosphere, and that the electron emission temperature necessary for ionization of the gas should be suillciently low so that increased temperature due to the ionic current discharge will not destroy or materially injure the ionizing material or melt or vaporize or detrimentally injure the base metal.

Referring now more specifically to the drawings a lamp is shown in Fig. 1 having a transparent envelope I0 provided with a press II for sealing in the leading-in conductors I2 and I3. 'I'he conductor I2 may extend a short distance into the envelope I0 where it may form a support for one end of a coiled filament I 4 which is coated with a suitable electron emitting material I5. A sec-' ond filament Ila provided with an electron emitting coating I5a. may be supported at one end by the leading-in conductor I3 and may extend substantially parallel to the filament Il. A connector I6 may be attached to the other ends of the filaments and may be sealed in a glass bead Il which may be supported by a central support Il sealed in the press I l. As will be hereinafter described the filament may be either straight or in the form of a coil which is perhaps preferred in order to get a sufficient resistance into a given length and it may be composed of tungsten, molybdenum, tantalum, nickel, or nichrome or other suitable material. The electron emitting material may be mixtures of calcium and barium oxides or calcium oxide alone or other oxides or any other of the well known electron emitting oxides, such as the alkaline earth oxides, may be used depending on the particular characteristics desired. Thus where exceptionally high visible radiation effects are not specifically required the emitting material may be composed of mixtures operable at lower temperatures, such, for example, as a mixture of the oxides of strontium and barium. However, the emissivity of the electron emitting material should be comparable to that of the alkaline earth metal oxides such as barium oxide, strontium oxide and calcium oxide and in excess of that .from such oxides as thorium oxide in order to obtain the effects and results of the invention.

The envelope I0 may be filled with an inert gas I9 such as a mixture of neon and argon at/a pressure of about two hundred millimeters. :Other gases or lmixtures of gases may also be used dependingI on the effectdesired.

In Fig. 2 is shown a constructionsimilar to Fig. 1 except that the supporting rod |8a is welded to the connector I6 at the top and is not brought through the press but is merely sealed therein acting solely as a support for the electron emitting elements and forming during the manufacturing process a convenient electrode for activating the electron emitting surfaces. As in this process it may be found desirable to put an additional potential on the support for activating purposes the construction shown in Fig. 1 may be preferred.. In that construction the center support IB is insulated from the filaments and passes down through the press and in the manufacture of the lamp may be connected to a source of potential, as is the anode of a thermionic amplifying tube during the activating of the cathode.

' A lamp such as is shown in Fig. 2 was made in the following manner: A pair of tungsten filaments wound 'into helices of about 11/2 inches long and .012 of an inch in diameter with approximately 230 turns to the inch were coated With-a material made by mixing about 40 grains of barium carbonate, 40 grains of calcium carbonate and 8 grains of barium nitrate with a binder of suiiicient nitro-cellulose dissolved in amyl acetate tohold the coating on the wire. This coating .was about .003 of an inch thick. These laments, connected in series, had an initial resistance of 150 ohms. After the filaments were mounted onta press and the press sealed in the envelope I0, in a, well known manner and with the filaments spaced vabout 11A; inches apart and substantially parallel to each other, the bulb was connected to an exhaust pump, care being taken that all the manifolds were glass so that there was a. gas-tight connection ,between the /bulb and the pump and that the oil in the Apump was as pure as possible. With the pump operating an oven was placed over the bulb and the'bulb thoroughly baked in the usual manner of treating-lamp bulbs, to free it from water vapo'r orother gases. A low voltage was then connected to the filament leads and the temperature of the coated fllaments was slowly raised by increasing the voltage until they reached a red heat so asto sinter on the coating and make it adhere as closely as possible to the filament wire. During this time all occluded gases were discharged and a high vacuum condition of about .5 micron was maintained. When the current was applied to the filaments a slight blue haze or glowappeared in the bulb,

discharging between the opposite ends of the ionizing laments or the supporting leads, and this glow gradually disappeared as all the gases or vapors were discharged from the bulb. A slight amount of neon gas was then admitted to the bulb and the bulb was evacuated again to the high vacuum of about .5 microns to make sure that all of the occluded gases were removed. When this point was reached a small amount of neon gas at a pressure of about two millimeters was allowed to enter the bulb and a potential of about 30 volts was applied to the filaments and raised until the entire bulb was filled with a reddishcolored discharge which in major quantities was between the coating on each of the filaments and the center supporting rod |8a, Fig.'2. 'Ihe in tensity of the` current applied to the filaments was increased until every portion of the oxide f coating on each of the filaments appeared to have a discharge between it and the support rod or other parts of the filaments. -In this manner the electron emitting oxide on each of the filaments was activated to allow them to discharge more evenly and at lower temperatures. Care was taken during this step to raise the temperature of the filaments materially higher than their normal operating temperature so as to completely remove occluded gases. l

When the oxide\coatings on the filaments had been completely uniformly activated the bulb was again exhausted to around .5 microns and thereafter filled with neon gas at about ten millimeters pressure and then argon gas was added to raise the pressure to about two hundred millimeters. When the filaments were raised to an electron emitting temperature by alternating current at this increased pressure the ionic discharge had an intense bluish-white color and appeared to be uniformly distributed or diffused over the electron emitting oxides Vin the manner illustrated by the dotted lines in Fig. 2. This discharge produced in itself considerable light but the light so produced was augmented by the incandescence of the calcium oxide used on the emitting surface which was apparently caused by ionic bombardment and also because of its inherent selective radiation. The bulb was then sealed off and the lamp completed. When operated on either alternating or direct current at about 60 volts the discharge surrounded the elements as indicated and producedA a steady bluishwhite light.

In Figs. 1 and 2 two electron emitting elements in series have been shown but it may be desirable to provide additional elements and hence the construction of Fig. 3 wherein four electron emitting elements 20, 2|, 22, and 23 are connected in series. A central supportrod 24 may be provided sealed in the press 25 and this rod may extend vertically within the bulb and be provided at its upper end with a glass bead 26 into which may be sealed a pair of oppositely extended support wires 21 and 28. The upper ends of the two filaments 20 and 2| may be connected by means of a connector 29 which is supported by the Wire ,21 while the other two elements l22 and 23 may be connected at their upper-ends by a connector 30 which is supported by the wire 28. The lower ends of the center elements 2| and 22 may be connected together by a connector 3| which is welded to the center support rod 24. The lower ends of the outer elements 20 and 23 may be connected respectively to support wires 32 and 33 which are sealed in the press and form the leading-in wires for the lamp. As thus constructed current flows through the leading-in wire 32,

the element 20, the connector 29, the element 2|, the connector 3|, the element 22, the connector 30, the element 23, and the other leading-in wire 33. The center support rod 24 aids in the activating process as .does also the elements themselves, as each one may form an activating electrode for one or more of the others.

In Fig. 4 another modification of the lamp is shown with four electron emitting elements 34, 35, 36 and 31 equally spaced from the axis of the lamp.A In this construction the center support rod 38 is insulated completely from the filament circuit and extends out at the bottom of the press 39 so that it may be used as an additional electrode during the activating process. A glass bead 40 at the top of the rod 38 may support two oppositely extended wires 4| and 42 for supporting the upper ends of the elements. The elements 34 and 35 are connected at their upper ends by a connector 43 supported upon the hook 4| and the elements 36 and 31 may have their upper ends connected by a connector 44 supportprovided upon the upright 38 just below the lower ends of the elements and a connector 43, bent at an angle, may have its center sealed in the bead and its ends welded to the lower ends of the elements 35 and 31. When the leadingin wires 41 and 48 are connected to a source of electricity, current will flow throughthe leadingin wire 41, the element 34, the connector 43, the element 35, the angular connector 46, the element 31, the connector 44, the element 38, and the leading-in wire 48.

Fig. 5 shows a modified form of the construction of Fig. 4. Here four elements 43, 58, 5|, and 52 are shown connected in series. A center support 53 extends upward to a point about even with the lower ends of the elements and forms a support for a U-shaped'supporting member 54 having uprights 55 and 53 positioned parallel 'to and between the elements 43 and 58 and 5| and 52. A glass bead 51 may be provided at the upper end of the upright 55 anda similar glass bead 53 may b'e provided at the top of the upright 55 for'supporting respectively without making electrical contact therewith connectors 53 and 38 which connect the upper ends of the elements 43 and 38, and 5| and 52 respectively. A connector 3| may be welded to the lower ends of the elements 58 and 52 and a support rod 52 may be sealed in the press and bent' outwardly and upwardly to a point adjacent the connector 5| to which it may be welded. Leading-in wires 33 and 84 may be connected respectively to the lower ends of the elements 43 and 5| and when the lamp is connected in a circuit the current flows through7 the elements in series similar to the manner described in connection with the two previous constructions.

While two or more elements have been shown in the figures already described it may be desirable to have a. single element. Thus in Fig. 6 a single element 65 is shown attached at its lower end to a leading-in wire 66 and at its upper endr to a second leading-in wire 61 which extends outwardly from the top of the element and is bent downwardly at right angles, vhaving a portion 38 parallel to the element which forms a convenient electrode for activating purposes. The lower end of the wire 61, of course, passes through the press as shown.

It may be found desirable to activate the element without the use 'of a cooperating electrode, portions of the element itself acting as the activating electrodes. This may be done with the construction shownwm Fig. r[..where the element 83 has its lower end attached to a leading-in wire 18 and its upper end attached to the other leading-in wire 1|, the downwardly extending portion 12 oi' which is spaced far enough from the element so as not to materially aiiect it during the activation thereof. v

Fig. 8 shows a construction in which two elements 13 and 14 are mounted in parallel. Two leading-in wires 15 and 15 are connected to the lower ends respectively of the elements 13 and 14 and may be joined together after passing through the press 11.

A third leading-in wire 18 is sealed in the press and extends upwardly between the elements and supports at its upper end a connector 13 to which it is attached and which is in turn attached to the upper ends of the elements 13 and 14. As in some of the constructions previously described. the center support, which in this case is one of the leading-in wires, aids in the activating process.

In Fig. 9 a modiiication of the construction of Fig. 8 is shown wherein two sets of parallel elements 88, 8|, 82, and 83 are spaced about a central axis similar to the spacing shown in Figs. 4 and 5. The elements 88 and 8| are connected together at their upper ends by a connector 84, while the elements 82 and 83 are connected by means of the connector 85. The lower ends of the elements 88 and 82 may be connected by the connector 83 and the lower ends of the elements 8| and 83 may be connected by the connector 81. The two connectors 86 and 81 may then be welded respectively to two leading-in wires 88 and 83 which are sealed in the press 38 and form the support for the lower ends of all of the elements. A central support wire '3| is sealed in the press and extends upwardly in the center of the lamp, .terminating at a point slightly above the elements. A vglass head 32 may be sealed at the upperend of the support 3| and two sup- 32 for suppo ng respectively the two connectors 84 and 85 andthusthe upper ends of all the elements. Currentpassing through the leading-in wire 88 divides and passes through both the elements 88 and 82, both the connectors 84 and 85, both the elements 8| and '83, and passes out through the leading-in wire 83. The central support may have a potential connected to it for activating purposes but is intended to be used for supporting purposes only when the lamp is ln use.

In Fig. l0 a longitudinal sectional view of an enlargedend of one of the elements is shown. This element consists of a coil of resistancewire 35, the end 33 being bent outwardly along the axis of the element where-it may be welded or otherwise attached to the support wire 31. The outside of the coil may be coated with an electron emitting material 38 which may be applied to the wire similarly to the manner in which such material is applied to the cathodes of thermionic amplifying tubes. Preferably the material should not extend too far inside the coil.

In Fig. 11 another embodiment of the element is shown in which the wire 33 is coated with electron emitting material |88 either before or after winding into the coil, each coil of the wire being individually coated.

Fig. .l2 shows a construction in which a sleeve |8| of electron emitting material is made with an internal diameter just suflicient to slip a coil |82 inside of it. v

Fig. 13 shows a construction in which the coil |83 of resistance wire is coated with electron emitting material on the outermost sides of each turn as at |84. y

While the coiled filament is deemed preferable for practical purposes, a single straight filament |85, Fig. 14, with a suitable coating |85a of electron emitting material may be used if desired, but ofcourse a much longer filament is necessary in order to e'qual the resistance of a coiled ilament. Y

Fig. 15 shows a method of attaching the element to a relatively large support. As illustrated, the end |85 of the element |81 is merely laid against the end of the support |88 and weldedk thereto. The large support forms a terminal for the end of the discharge and appears to prevent the extra current which flows through the ionized gas from passing through the end oi the vport wires 33 and 34,may be sealed in the bead f illament, thereby preventing any tendency for overheating at this point.

Figs. 16 andV 17 show two alternative methods for accomplishing this same purpose. A cupshaped memberv |09 in Fig. 16'is provided with a hole through which the end I |I of the element ||2 passes. Both the member |09 and the end of the element may be welded to the support wire ||3. In Fig. 17 a solid cup-shaped member ||4 attached directly to the support wire ||5 may have the end ||6 of the element ||1 welded upon the inner central face thereof.

In some instances it may be desiredfvto coat the wire with electron emitting material only in spots, as shown in Fig. 18, where a wire coil 8 is coated lat spaced intervals, as at ||9, |20, and |2I. This construction appears to depend on the ionization of the gas adjacent the coated portions of the element to carry the discharge past the uncoated portions.

Fig. 19 shows a coil of wire I I2 which is coated only at each end, as' at |23 and-|24. With such an element the ionization of gas at each end of the element produced by the electron emitting material must be suiiicient to maintain the discharge along it.

In all the gures so far described the elements have been shown as parallel to the axis of the bulb but in many instances it may be desirable or even preferable to mount the elements transverse to the axis of the bulb, in whichcase a construction similar to that shown in Figs. 20 and 21 may be used. 'I'he press |25 in this instance is provided with an upstanding glass support rod or tube |26 with an enlarged portion |21 at the upper end thereof. A plurality of support wires |28 are sealed in the enlarged portion |21 and may extend outwardly and slightly upwardly to support an electron emitting element |29 which may be formed of a coil of wire coated with electron emitting material similar to the elements already described, but in this case bent in the formof a circle, as indicated in Fig. 21. The en ds of the element are separated far enough apart to prevent any discharge between the ends and are attached to two leading-in wires |30 and v|3| which extend downwardly through the press '|25. Adjacent to the element |29 I preferably provide a member suitable to act as an electrode for activating. 'I'his member may be in the form of a-ring |32 which may be spaced inside of the -.jelement |29 and may be made of a wire one end |33 of'which may be bent inwardly and downwardly extending .through thelod |2 6 and through the press |25 so that it may be given a potential during the step of activating.

Parallel elements may also be used placed transverse to the axis of the bulb, as indicated in Fig. 22, where the elements |34 and |35 have one end eachattached to'the leading-in wires |36 and |31. The other ends of the elements may be. attached to a connector |38 which may be substantially U-shaped with the center part extending downwardly below the plane of the elements. A glass bead |39 may be sealed onto the center of the connector |30 and a third support rod |40 may be sealed in the bead with its end I4| extending parallel with the elements |34 and |35, to a point about even with the ends of the elements. The elements of this construction light up similarly to those already described land the rod |4| may be used when theelectron emitting material is activated. s

As heretofore explained, with a suitable pressure and voltage'the discharge of the lamp follows the electron emitting elements as shown by the dottedlines in Figs. '1, 2, and 3. If the voltage is increased, however, it begins to bridge the gap between the elements, starting adjacent the connector to which the ends of two of the elements may be attached, and spreading-until it appears to cover the entire space between the elements. It may be desired to operate the device in this manner, and lif so, it is necessary to make any support which comes between the elements out of heat resisting material to avoid melting or other deterioration. In Fig. 22, however, the rod |4I, being below theplane of the elements, is outside of the discharge when such a discharge occurs, and may thus be protected from the intense heat. l

Verticalelements such as are used in Figs. 1 and 2 may also be made to operate in this man-` ner with discharge between the elements by supporting them with an oiisetfsupport, as indicated in Fig. 23. -In this gure the. elements|42 and |43 have their upper ends supported by a -connector |44 which isin turn supported upon a wire sealed in a bead |45 mounted at the end of a support rod |46 which is spaced somewhat in back of the elements as shown.

In some instances it may be desired to stop the normal flow of current in .the coiled wire when the discharge has been formed and this may be done by any suitable means, as by the construcmay be sealed upon' the support rod I 52 and forms a support for the lower end of the wire |54 whose upper end forms the terminal |49, the wire being sealed therein'. A bimetallic arm 55 is at` tached to the wire |54 and has a contact I 56 ywhich is adapted to normally touch the contact |51 mounted on the support rod |52 but to move away from it when the arm |55 bends under the influence of heat. In this embodiment of the lamp, .when the current is turned on it flows up the rod I5 through the contacts |51 and |50, through the bimetallic arm- 55, the wire |54, the terminal |49, and element |41 to the terminal |48. The discharge as already described immediately starts around the wire, passing through the 'ring |50, but as soon as the temperature in the lamp has reached a predetermined point the thermostat arm |55 opens the contacts |56 and |51 and breaks the circuit through the element. The heat generated by the discharge is suiiicient to maintain it and the current willthereafter iiow between the-terminal |48 and portions of the element and the ring |50. If desired, another -ri-ng may be provided at the other end of the `highest potential ends of the filaments. This limiting 'of potential is dependent upon the gas pressure, the nature of the gas, and the charac.-

teristics of the ionizing element, such as the material used, temperature, and the geometry of the parts.

The pressure of the gas in the bulb is not critical but may be given such a value that it will prevent the ionic discharge from occurring between the filament elements themselves or between the filament elements and a support rod, or, in other words, where the lamp is designed to operate in that manner the pressure should be such as toconne the ionic discharge along the length of the ionizer element.

If increased glow effect is desired in the lamp, materials having highly selective radiation charactristics, such as thorium oxide with one percent of cerium oxide, may be added to the ionizing agent. When it is desired to have the discharge occur at lower potentials, metal vapors such as caesium vapor may be added. Caesium may be introduced into the lamp by providing a smallimetal'- container, such as I have shown at |58 in Fig. 1, with magnesium metal and caesium chloride in it. 'I'his container is inductively heated till the reactive temperature is reached,

at which time the caesium is distilled and condenses on the walls of the bulb. The same method may be used with rubidium or mercury. When the lamp is used the heat from the filament is conducted by the gas to the walls of the bulb and revaporizes the caesium or other vapor condensed thereon. When radiations of other wave lengths are desired, such as ultra-violet radiation, mercury vapor may be used either with or without the gas discharge. When heat is necessary to increase the eil'ect of the metal vapors a low pressure of helium, such as about five millimeters, may be of great advantage because oi' its high conductivity.

While I have specifically described my discovery in connection with illumination devices this unique form of discharge may be used for other devices wherein the conducting path adjacent the electron emitting element is used as a means of control or as a conductive element in a circuit using either direct or alternating current. 'I'he invention is not therefore intended to be limited to what has been specifically shown and described except as such limitations occur in the appended claims.

What I claim is:

1. In an electric lamp a resistance element, a coating of electron emitting material on said .resistance element, a terminal for one end of said resistance element, an electrode adjacent the electron emitting material and symmetrically positioned with respect thereto but out of contact therewith, a leading-in wire connected -to said electrode and to said terminal, and means to break the circuit between said terminal and said leading-in wire when the temperature of said lamp has been raised to -a predetermined degree.

2. An electric lamp comprising a closely wound coil o! tungsten wire, a coating of a mixture of the oxides of barium and strontium on the surface of said coil, and an ionizable gas consisting of approximately 10 mm. of neon gas and 190 mm. of argon gas surrounding said coil,

3. An electric lamp comprising a transparent envelope, a pair of tungsten laments within said envelope each formed of a closely wound helix about one and one-half inches long and .012

. of an inch in diameter with approximately 230 turns to the inch and having a coating of .a mixthickness of approximately .003 of an inch, the total resistance of the two filaments in series being about ohms, means to electrically connect said filaments in series and support said filaments spaced about one and ,one-eighth inches apart and substantially parallel to each other, and a mixture of argon and neon gases at a pressure of substantially 200 mm. of mercury surrounding said iilaments.

4. In an electrical discharge device an envelope, a conductor constituting the sole source of the discharge within said envelope, a gaseous iiuid within said envelope surrounding said conductor, and means to render said fluid conductive in the immediate vicinity only of said conductor when said conductor is heated and a potential is applied to the ends thereof, said means consisting of a coating of an electron emitting substance having an emissivity in excess of that from thorium oxide.

5. In an electrical discharge device an envelope, a lamentary conductor constituting the sole source of the discharge within said envelope having an electrical conniection at each end lthereof, an electron emitting coating having an emissivity in excess of that from thoriumAoxide on said conductor, and an ionizable gas surrounding said conductor, the breakdown potential of said gas per unit length of said conductor -being less than the potential drop along said unit length necessary to raise said conductor to electron emitting temperature.

6. In an electron discharge device an envelope, a iilamentary conductor constituting the sole source of the discharge within said envelope, an electron emitting coating having an emissivity in excess of that from thorium oxide on said conductor, and an ionizable gas surrounding said conductor, the pressure of said gas being sutiltemperature.

7. In an electric lamp an envelope, a readily ionizable gaseous medium within said envelope,

means to lower the normal breakdown potential of said medium along a restricted path of lesser diameter than said envelope, said means consisting in a mass of electron emitting material having an emissivity in excess of that `from thorium oxide, and means to energize the emitting material, said emitting and energizing means constituting the sole source of energy discharge in said envelope.

8. In an electric lamp an envelope, a lilamentary conductor constituting the sole source oi.' the discharge within said envelope and wound in the form of a helix and having an electrical connection at each end thereof, a coating of electron emitting material having an emissivity in excess of that from thorium oxide on said conductor, and an ionizable gas within said envelope and surrounding said conductor, the 'breakdown potential of said gas per unit length of said helix being less than the potential along such unit length of helix necessary to raise said conductor to electron emitting temperature.

9. In an electric lamp an envelope, a illamentary conductor constituting the sole source of the discharge in the form of a helix, a coating of electron emitting refractory material having an emissivityin excess of that from thorium oxide on said helix, and a gas comprising a mixture of neon, argon, and a metal vapor within said envelope and having such a pressure that the ionization of said gas when said conductor is heated will be restricted to the vicinity of said electron emitting material.

10. In an electric lamp an envelope, a closely wound coil of resistance wire in said envelope, a coating of electron emitting material having an emissivity in excess of that from thorium oxide on the surface of said coil, and an ionizable gas consisting of a. mixture Aof neon and argon surroundingsaid coil and having a pressure of substantially 200 mm. of mercury, said coated coil forming the sole illuminating element of the lamp.

11. In an electrical discharge device the combination of an envelope, a conductor constituting the sole source of the discharge mounted therein, particles of an alkaline earth metal oxide in intimate contact with said conductor, and a gas of the argon group and mercury vapor or mixtures thereof surrounding said conductor.

12. In an electrical discharge device the combination of an envelope, an electron emitting conductor constituting theA sole source of the discharge having an electron emissivity in excess of thorium oxide mounted within said envelope, and an inert ionizable gas of the argon group surrounding said conductor.

13. In an electrical discharge device the combination of an envelope, a conductor constituting the sole source of the discharge mounted within the envelope, barium oxide on the surface of said conductor, and a gas of the argon group within said envelope.

14. In anelectrical discharge device the combination of an envelope, a conductor constituting the sole source of the discharge mounted within said envelope', a coating of an alkaline earth metal oxide on said conductor, and a gas of the argon group within said envelope.

15. In an electric lamp the combination of an envelope, an inert ionizable gas of the argon group and mercury or mixtures thereof within said envelope, a conductor constituting the sole source of the discharge formed of coiled tungsten metal mounted within the envelope and surrounded by said gas, and an alkaline earth metal oxide coating on said conductor.

16. In an electrical discharge device the combination of an envelope, a coiled refractory metal conductor constituting the sole source of the discharge mounted therein, strontium oxide on the surface of said conductor and an atmosphere of argon and neon gases Within said envelope.

17. In an electrical discharge device the combination of an envelope, a coiled refractory metal conductor constituting the sole source of the discharge mounted therein, particles of calcium oxide on the surface of said conductor, and an atmosphere of argon, neon and metal vapor within said envelope.

18. A process for forming and maintaining a luminous gas discharge in the vicinity of a wire coated with electron emitting material and immersed in an inert ionizable gas which comprises passing an electric current through said wire and raising the potential across the Wire to the point where the potential per unit length along the wire 'is in excess of the ionization potential of the ionized gases adjacent the wire.

19. A process for forming and maintaining a luminous gas discharge in the vicnity of a wire coated with electron emitting material which coated wire constitutes the sole source of the discharge and immersed in an inert ionizable gas which comprises passing an electric current through said wire and raising the potential across the Wire to the point where the potential per unit length along the wire is in excess of the ionization potential of the ionized gases adjacent the wire.

CHESTER H. BRASELTON.

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