US2600390A

US2600390A - Low-capacity vapor-electric device

Info

Publication number: US2600390A
Application number: US201783A
Authority: US
Inventors: John L Boyer
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1950-12-20
Filing date: 1950-12-20
Publication date: 1952-06-17
Anticipated expiration: 1969-06-17
Also published as: BE507928A; FR1050514A

Description

June 17, 1952 J. L.. BOYER 2,600,390

LOW-CAPACITY VAPOR-ELECTRIC DEVICE Filed Dec. 20, 1950 Fig.|.

lNvENToR John L Boyer.

ATTORNEY Patented June 17, 1952 nLOW-('JAPACI'IJY VAPOR-ELECTRIC DEVICE John L. Boyer, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation oflennsylvania Application December 20, 1950, Serial No.`201,783

Claims. 1

My invention relates to vapor-electric devices or tubes, and particularlyto low-arc-drop hotcathode arc-discharge devices using a Vaporizable discharge-metal selected from the group consisting of cesium, rubidium and potassium. Such of temperatures on both the anode and the cathode, thus making it diicult to have an economical design for small tubes of this class.

An object of my present invention is to providel "l l5 tubes have to be operated with a narrow range a tube of the stated class, which does not require any complicated temperature-control. In the accomplishment of this object, I provide, among other things, a cooling-means which includes a fusible material having a melting-point at approximately the desired temperature to which said cooling-means is to hold its associated internal portion of the device.

My invention is an improvement over a vaporelectric device which is described and claimed in a copending application of August P. Colaiaco and myself, Serial No. 144,354, led February 15, 1950. As pointed out in this copending application, the three metals, cesium, rubidium and potassium, form a more or less distinctive class by themselves, which may be described as the alkali metals having four, five and six shells in their atomic structure, or the stable alkali metals having more than three shells. The entire group of alkali metals consists of six elements, of which the rst two and the last are readily distinguishable from the other three, with which my invention is particularly concerned.

The two lightest alkali metals, lithium (Li) and sodium (Na) are separated, in some periodic tables, from the heavier light metals of thealkali-metal group (IA), as being distinctive because of their electron-grouping. The physical and chemical characteristics of these two lightest alkali-metals are also distinctively different from the group comprising cesium, rubidium and potassium. Sodium has a minimum breakdown voltage which comes at too low a pressure-distance product pd for my purposes; and it is also too active, chemically.. Lithium has a vapor-pressure which is much too low for my purposes, as this low vapor-pressure requires too high a temperature to obtain a practically usable Vvapor-pressure which is high enough to give a su'iciently high current-density to be practical for my purposes.

The sixth and heaviest alkali metal, No. 87 in the periodic table, was formerly called virginium, but has now been proved to be an element which is called francium (Fa), an unstable 2. atomic-pile product which is very radio-active, and which has an extremely short half-life of only a few minutes, so that is is unsuitable for my purposes. W

It is also an object of my invention to provide a new tube-design in which the Ycesium or other i discharge-metal is condensed on the cold end of the cathode, as distinguished from being condensed elsewhere, as on the anode, as in certain previous designs. This condensation-place of the discharge-metal is determined by making the cold end of the cathode the coolest partof the tube. This has the double advantage of getting the discharge-metal pool at the cathode-potential, in a place which makesit impossiblekto have positive-ion bombardment during the inverse voltage-periods, thus guarding against electronemission from this pool and consequent arcbacks during said inverse voltage-periods. The discharge-metal pool, at the cold end of the cathode, is also at a spot at which the temperature is not materially affected by the intensity of the arc, and hence not materially affected by the load-current, as 'in previous tube-designs in which the discharge-metal pool was at or near a part of the anode.

My invention consists in the combinations,

systems, structures, parts, and methods of de- Y The form of embodiment `of my invention, as

shown in Fig. 1,Ycomp`rises an evacuatedV enclosure-meansincluding an anode-portion 5 of the enclosure-means', a Ycathode-portion 6 of the enclosure-means, and an insulator-to-rnetal sealing-means s between said anoderand cathode portions. There is also enclosed, within the 'enclosure-means, a quantity of a discharge-metal selected from the group comprising cesium, rubidium and potassium.

The cathode-portion 6 of the-enclosure-means includes a re-entrant metal tube-portion i6, whichextends into the enclosure-means. This cathode-tube I6 has aclosed inner end l1. .'The

inner endof the cathode-tube lcarriesperipheral metal fins I8, extending cut radially therefrom, like a plurality of washers, for providing an extended cathode-surface which constitutes the active arc-terminating surface of the cathode.

The cathode-tube l and its fins iB are preferably made of nickel, or atleast the exposed surfaces of these parts, which are exposed to the vapors within the device, are preferably made of nickel. The rest of the cathode-portion E, and all of the anode-portion 5, may be made of either iron (including steel) or nickel.

The active part of the cathode, namely the cathode-tube portion carrying the ns t8, has to be heated to a suitable emitting-temperature during the operation of the device. When cesium is the discharge-metal, this cathode emittingtemperature is around '700 C. or '750 C., or even somewhat higher; when rubidium is at the emitting-temperature, the active cathode-portion should be maintained at a temperature of about 700 or 720 C. to say 800 C.; and when potassium is the discharge-metal, the active cathode-temperature should be perhaps about 800 C'. to 900 C.

To heat the active emitting-surface of the cathode, I provide a, cathode-heater IS, which is disposed within the cathode-tube l5, the heater being preferably concentrated at the finned end of the cathode-tube, and being supplied with a sufficient amount of electrical energy to maintain the desired temperature. The heater I9 may be supplied with electrical heating-energy through a terminal-lead 20 which extends through an insulating seal 2l in the base 22 of the cathodeportion 6.

In vapor-electric devices of the class described, it is necessary to maintain some internal portion of the device at a temperature which is cooler than any other internal portion of the device during the operation of the device, so as to provide a condensation-surface on which Vapor of the discharge-metal condenses. The temperature of this condensation-surface determines the operating vapor-pressure of the discharge-metal, and hence it is necessary to provide a condensation-temperature which is Within certain suitable temperature-ranges, being about 220 C. for cesium, 240 C. for rubidium, or 280 C. for potassium, these temperatures being merely illustrative. All other internal portions, both metals and insulators, of the device (other than said condensation-surface) have to be maintained at temperatures which are higher than the condensation-temperature, in order to prevent unwanted condensation.

In vapor-electric devices of the described class, it is also necessary to variably cool the anode. The play of the arc on the anode tends to heat the anode to temperatures which, is unchecked, would be hot enough to make the anode emit like a cathode, thus spoiling the operativeness of the tube. This anode-heating is a variable quantity, depending upon the intensity of the arc, and hence upon the amount of loadcurrent which is being carried by the vapor-electric device. It is usually desirable to keep the anode at a fairly uniform low temperature, in order to keep well under the electron-emitting or backfiring-temperature of the anode.

In those discharge-tubes in which the condensation-surface is the anode, or a part of the anode. as will be described in connection with Fig. 3, the anode-temperature may be the condensation-temperature. In those types of tube in which the condensation-surface is provided at some part of the tube other than the anode, as Will be described in connection with Fig. l, it is necessary to hold the anode to some temperature which is higher than the condensation-temperature. When cesium is the discharge-metal, for example, in Fig. 1, the anode-temperature mfy be 232D C., or somewhere between 230 and 30 C.

In Fig. 1, I show a preferred form of embodiment of my device, in which a non-linear coolingmeans is provided for the anode-portion 5, for automatically providing approximately the amount of cooling which is necessary to hold the anode at a fairly steady temperature. This non-linear anode-cooling means, for the tube which is shown in Figs. 1 and 2, is characterized by having a fusible material 25, which has a melting-point at approximately the desired temperature to which said cooling-means holds its associated internal portion of the device, in this case the anode-portion 5. When no portion of the anode-surface is the condensation-surface, as in the tube illustrated in Fig. l, and when cesium is the discharge-metal, the fusible material 25 may be tin, which melts at 232 C., or it may be some metal alloy, or even an insulating compound, which has a melting-point between, say 230 and 300 C.

In the preferred form of construction of the fusible-material cooling-means, provision is made for the natural thermally induced circulation of the fusible material 25 after it has melted. To this end, I preferably design the device so that the heat-radiating enclosure-portion of the device, which is to be cooled, stands upright or in a vertical position, as is the case of the tubular side-walls of the anode-portion 5 of the device. Spaeed from the outer surface of this heat-radiating enclosure-portion (such as the tubular anode-surface 5) I provide an upstanding heat-barrier 30, which is suitable heat-insulating solid. When the heat-radiating enclosure-portion, such as 5, is tubular or cylindrical, the heat-barrier 30 is also tubular or cylindrical,

, being mounted on suitable pins or feet 3i.

Spaced from the other side of the heat-barrier 30, I provide an upstanding heat-radiating cooling-plate 35, which, if the heat-barrier is cylindrical, would also be cylindrical. The heatradiating cooling-plate 35 radiates or conducts heat directly to the ambient atmosphere, either wth or Without the aid of heat-radiating fins 3 The space between the heat-radiating enclosure-portion, such as the anode-portion 5, and the cooling-plate 35, is lled with the fusible material 25. For holding the fusible material 25 when it is melted, I provide a suitable container-means, such as is provided by top and bottom flanges 31 and 38 of the cooling-plate 35. The top and bottom ends of the heat-barrier 30 are spaced from the top and

bottom portions

37 and 38 of this container-means, so that the molten fusible material 25 can circulate over the top of the heat-barrier 30 and under the bottom of the heat-barrier; or other suitable disposition and arrangement of the barrier is made so that such a circulation will be possible.

In the operation of the fusible-material cooling-means just described, the presence of the heat-barrier 30 prevents the conduction or radiation of very much heat from the anode-portion 5 of the evacuated container, as long as the fusible material 25 remains in its solid state, in which it does not circulate. As soon as the egeooct anode-surface reaches?v the I melting-point of the fusblematerial (T, however, the anode begins to'inelt the `fusi/ble material, and the latent heat of vfusion ofthe fusible material holds the anode to substantially the melting-point of this material', until substantially all of the fusible material is melted. When this happens, the fusible material begins to circulate, with a naturalcirface of the anode 5 tothe inner surface of the cocling-plate may be assisted, if desirable, by providing heat-transfer fins di) on the outer Sur- Y face of the anode 5, and other heat-transfer ns I on the inner surface of the cooling-plate 35.

YIn the preferred illustrative form 0f construction of a vapor-electric device, as shown in Fig.

l,VIV I preferably make use of a special cathodeconstruction in which thev active emitting inner end of the Cathode-tube I6 isheated'` (by the heater I9), and in which suitable means are provided for'externally cooling the outer, or enclosure-entering, end of the cathode-tube I6. The cathode-tube I8 is made long enough (and the tube-Walls are thin enough) so that the bottom end, or enclosure-entering end, of this cathode-tube i6, or of the attached external cathode-parts, is the coolest part of the device,

whereby the `discharge metal condenses thereon. Usually, as illustrated, the natural heatradiation from the exposed cathode-surfaces vMi Vto the ambient atmosphere, without any coolingi'lns or external blowing-means, suices to keep the attached end of the cathode-tube I6 at a uniform temperature which is just about right. Sometimes, it may be necessary to add a certain amount of heat-insulation d?, for keeping the cathode-portion E of the evacuated container from getting too cool, and this heat-insulation may be thickened, as indicated at lid, at places Where the internal tube-parts are to be kept at still hotter, or non-condensation, temperatures, as in the vicinity ofthe insulator-part S.

It will thus be observed that I have provided, in Fig, 1, a basic design in which the dischargemetal condenses on a surface which is. not subject to variable amounts of heating in response 'to variable load-currents carried by the device.

rIhe cool bottom or outer endofthe cathodetube I6V is admirably suited for this purpose,

because the hot inner end of this cathode ltube necessarily operates at a fairlyconstant emittingtemperature, vand the cool bottom or outer .end of this tube is sulciently farremovedfrom vthe arcrso that itis not materially affected bythe intensity of the arc, which is anothervvay of saying that it is not materially affected bythe amount of load-current Which is being carried by the device. Inl a small, inexpensive` dischargetube, therefore, Without complicated automatic temperature-controlling means, it iseasy, .to d esign the tube so that the cool end of the,` cathodetube I6 operates at a fairly constant temperature, independent of load-conditions. Y In Fig. 1, I have chosen this cool-endYcathode;-temperature fasY the coolest temperature of the devi c e or "the temperature at which condensation takes place, and at Which the vapor-pressurefwithi the hdeviceis controlled. f f A Since vthis coolingl or condensing-place for the alkali-metal pool (which maybe only a-few drops) is at the cold-end@ofthev cathode;v this alkali-metal pool isat the cathode-potential, and henceY it -cannot have any positive-ion-bombardment Which-if it were present, would initiate electron-emission and cause faults during the tube-operation.. The collection Yof the alkalimetal-pool at the cold end of the cathode is further advantageous over previous vconstrui'ztions in which this pool vhas been collected at or near the `lower end of the anode of the device, because the lower end of the cathode is inherently much the better place, since its temperature `is not aiectedby the intensity 'of 'the varc, and hence it is notaf'fected bythe load-current of the device. l f

In accordance with the preferred form of embodiment of` my invention, as shown in Fig. 1,

VI combine, withv this cathode-tube construction having the .condensation-surface `at itsV lower or outer end, a fusible-material cooling-means for automatically taking .care of the Wide range of cooling-rates which are necessary to Vtake care of the anode-cooling, under variable load-conditions. 1 v

yI- thus provide-*a small, ,compact vapor-discharge tube which has noexternal moving parts, either for artificially circulatinga cooling-medium or for cooperating with thermally responsive devices. 1 As previously intimated, however, my present Yinvention is notlimited, in its use, to the preferred construction which is shown in/Fig. l, as thefusible-material cooling-means is of generalbapplication to vany device having an internally heated partwhich is subject to a Wide vrange of internal zheating, under-various operating-conditions of thejdevice. Inparticular, in vapor-electric; tubesgusin'g a discharge-metal of cesium,-rubidium or potassium,` it is frequently desirable torapply my 'fusible-material: coolingmeans lto the anode-portion of the evacuated enclosure, Whether or. not said anode-portion constitutes a condensation-surface for the dischargemetal. My fusible-material cooling-means is also-of, generalapplication to the maintenance vof the condensation-temperature,.Within narrowly prescribed limits, regardless of 4Whether the condensation-surface is a part of th'e anodeportion of the tube, orthe cathode-portion of the tube,` or some other separate portion of the tube. `j I have accordingly shown, in Fig. 3, an alternative formof embodiment of my invention, in ayvapor-electric, device in `which the anode-portion 55 is held at such aternperature that at least `apart of this anode portion 5'5 is the coolest part of the device, so as to .provide the condensationsurface. I'n Fig. 3,lthis anode-portion 55 is pro- Lvided with a fusible-material cooling-means 65, having a ineltin'g-poiritat about the desired condensation-temperature.which controls the vaporpressure of the tube. The other parts`f'`the f .tubeVin Fig. 3, may bemore or less similar to the construction which has `already been described .for Fig. l, except that theproportions are dif- I claim'as my invention: j

1. A vapor-electric device having an evacuated enclosure-means including an anode-portion of the enclosure-means, a cathode-portion of the enclosure-means, and an insulator-to-metal sealing-means between said anode and cathode portions, a quantity of a discharge-metal selected from the group comprising cesium, rubidium and potassium, a heating-means for heating the active emitting-portion of the cathode, a coolest-surface cooling-means for cooling some internal portionof the device to a temperature which is cooler than any other internal portion of the device during the operation of the device, whereby to provide a condensationsurface for the discharge-metalr and to control the operating vapor-pressure of the dischargemetal, and a non-condensing-surface coolingmeans for cooling some other internal 'portion of the device to a somewhat warmer temperature during the operation of the device, whereby to prevent the condensation of said discharge-metal on said other internal portion; characterized by at least one of said cooling-means including a fusible material having a melting-point at approximately the desired temperature to which said cooling-means holds its associated internal portion of the device. n

2. The invention is defined in claim 1, characterized by said fusible-material cooling-means comprising the combination; with an upstanding heat-conducting enclosure-portion of the device, adjacent to the place which is to be internally cooled, of an upstanding heat-barrier spaced from the outer surface of said heat-conducting enclosure-portion, an upstanding heat-conducting cooling-plate spaced from the other side of said heat-barrier, said fusible material being disposed on both sides of said barrier and filling the space between said heat-conducting enclosure-portion and said cooling-plate, and a container-means for said fusible material when it is melted, the disposition and arrangement of the barrier and container-means being such that molten fusible material can circulate over the top of the barrier and under the bottom of the barrier.

3. A vapor-electric device having an evacuated enclosure-means including an anode-portion of the enclosure-means, a cathode-portion of the enclosure-means, and an insulator-to-metal sealing-means between said anode and cathode portions, a quantity of a discharge-metal selected from the group comprising cesium, rubidium and potassium, a heating-means for heating the active emitting-portion of the cathode, and an anode-cooling means including a fusible material having a melting-point at approximately the desired temperature to which said cooling-means holds said anode-portion of the enclosuremeans.

4. The invention as defined in claim 3, characterized by said anode-cooling means comprising the combination, with an upstanding wall of said anode-portion, of an upstanding heatbarrier spaced from the outer surface of said upstanding wall, an upstanding heat-conducting cooling-plate spaced from the other side of said heat-barrier, said fusible material being disposed on both sides of said barrier and filling the space between said upstanding wall and said cooling-plate, and a container-means for said fusible material when it is melted,` the disposition and arrangement of the barrier and containermeans being such that molten fusible material 8 can circulate over the top of the barrier and under the bottom of the barrier.

5. A vapor-electric device having an evacuated enclosure-means including an anode-portion of the enclosure-means, a cathode-portion of the enclosure-means, and an insulator-to-metal sealing-means between said anode and cathode portions, a quantity of a discharge-metal selected from the group comprising cesium` rubidium and potassium, a heating-means for heating the active emitting-portion of the cathode, a coolest-surface cooling-means for cooling some internal portion of the device, other than said anode-portion, to a temperature which is cooler than any other internal portion of the device during the operation of the device, whereby to provide a condensation-surface for the discharge-metal and to control the operating vapor-pressure of the discharge-metal, and a non-condensing-surface cooling-means for cooling said anode-portion to a somewhat warmer temperature during the operation of the device, whereby to prevent the condensation of said discharge-metal on said other internal portion; characterized by at least one of said coolingmeans including a fusible material having a melting-point at approximately the desired temperature to which said cooling-means holds its associated internal portion of the device.

6. The invention as dened in claim 5, characterized by said fusible-material cooling-means comprising the combination, with an upstanding heat-radiating enclosure-portion of the device, adjacent to the place which is to be internally cooled, of an upstanding heat-barrier spaced from the outer surface of said heat-conducting enclosure-portion, an upstanding heatconducting cooling-plate spaced from the other side of said heat-barrier, said fusible material being disposed on both sides of said barrier and filling the space between said heat-conducting enclosure-portion and said cooling-plate, and a container-means for said fusible material when it is melted, the disposition and arrangement of the barrier and container-means being such that molten fusible material can circulate over the top of the barrier and under the bottom of the barrier.

7. A vapor-electric device having an evacuated enclosure-means including an anode-portion of the enclosure-means, a cathode-portion of the enclosure-means, and an insulator-to-metal sealing-means between said anode and cathode portions, a quantity of a discharge-metal selected from the group comprising cesium, rubidium and potassium, a heating-means for heating the active emitting-portion of the cathode, and a coolest-surface cooling-means for cooling said anodeportion to a temperature which is cooler than any other linternal portion of the device during the operation of the device, whereby to provide a condensation-surface for the discharge-metal and to control the operating vapor-pressure of the discharge-metal; characterized by said cooling-means including a fusible material having a melting-point at approximately the desired temperature to which said cooling-means holds said anode-portion of the enclosure-means.

i8. The invention as defined in claim 7, characterized by said anode-cooling means comprising the combination, with an upstanding wall of said anode-portion, of an upstanding heat-barrier spaced from the outer surface 4of said upstanding wall, an upstanding heat-conducting coolingg plate spaced from the other side of said heatbarrier, said fusible material being disposed on both sides of said barrier and filling the space between said upstanding wall and said coolingplate, and a container-means for said fusible material when it is melted, the disposition and arrangement of the barrier and container-means being such that molten fusible material can circulate over the top of the barrier and under the bottom of the barrier.

9. A vapor-electric device comprising an enclosure-means, an anode, a cathode, and a quantity of a discharge-metal within said device, said discharge-metal being selected from the group consisting of cesium, rubidium and potassium; said cathode including a re-entrant metal tubeportion extending into said enclosure-means, said cathode-tube having a closed inner end, metal ns carried by said cathode-tube near said closed inner end, a cathode-heater disposed within said cathode tube, said cathode-heater being concentrated at the finned end of the cathode-tube, and means for cooling the enclosure-entering end of the cathode-tube, said cathode-tube being long enough so that its enclosure-entering end is the coolest part of the device, whereby the dischargemetal condenses thereon.

10. A vapor-electric device comprising an enclosure-means, an anode-portion of the en-A closure-means, a cathode, and a quantity of a discharge-metal within said device, said discharge-metal being selected from the group consisting of cesium, rubidium and potassium; said cathode including a re-entrant metal tube-portion extending into said enclosure-means, said cathode-tube having a closed inner end, metal ns carried by said cathode-tube near said closed inner end, a cathode-heater disposed within said cathode tube, said cathode-heater being concentrated at the nned end of the cathode-tube, and means for cooling the enclosure-entering end of the cathode-tube, said cathode-tube being long enough so that its enclosure-entering end is the coolest part of the device, whereby the dischargemetal condenses thereon; and an anode-cooling means including a fusible material having a melting-point at approximately the desired temperature to which said cooling-means holds said anode-portion of the enclosing-means.

11. The invention as defined in claim 10, characterized by said anode-cooling means comprising the combination, with an upstanding wall of said anode-portion, of an upstanding heat-barrier spaced from the outer surface of said upstanding wall, an upstanding heat-radiating cooling-plate spaced from the other side of said heat-barrier, said fusible material being disposed on both sides of said barrier and filling the space between said upstanding wall and said cooling-plate, and a container-means for said fusible material when it is melted, the disposition and arrangement of the barrier and container-means being such that molten fusible material can circulate over the top of the barrier and under the bottom of the barrier.

l2. A device having an internally heated part, an upstanding heat-radiating portion of the device for cooling said internally heated part, said heat-radiating portion having an upstanding outer surface, an upstanding heat-barrier spaced from the outer surface of said heat-radiating portion, an upstanding heat-radiating coolingplate spaced from the other side of said heatbarrier, fusible material disposed on both sides of said barrier and iilling the space between said heat-radiating portion and said cooling-plate, and a container-means for said fusible material when it is melted, the disposition and arrangement of the barrier and container-means being such that molten fusible material can circulate over the top of the barrier and under the bottom of the barrier, said fusible material having a melting-pointl at approximately the desired temperature to which said heat-conducting portion is to be held.

13. A vapor-electric device comprising an enclosure-means, an anode, a cathode, and a quantity of a discharge-metal within said device, said discharge-metal being selected from the group consisting of cesium, rubidium and potassium; said cathode including a metal tube-portion extending interiorly into said enclosure-means, a portion of said cathode-tube carrying metal fins at a region within the interior of the enclosuremeans, means for heating the inside of the cathode-tube at the iinned portion thereof, and means for cooling the cathode-tube in a region Where it enters the enclosure-means, said cathode-tube being long enough so that said cooled enclosureentering region is the coolest part of the device, whereby the discharge-metal condenses thereon.

14. A vapor-electric device comprising an enclosure-means, an anode-portion of the enclosure-means, a cathode, and a quantity of a discharge-metal within said device, said dischargemetal being selected from the group consisting of cesium, rubidiurn and potassium; said cathode including a metal tube-portion extending interiorly into said enclosure-means, a portion of said cathode-tube carrying metal ns at a region within the interior of the enclosure-means, means for heating the inside of the cathode-tube ai; the finned portion thereof, and means for cooling the cathode-tube in a region where it enters the enclosure-means, said cathode-tube being long enough so that said cooled enclosure-entering region is the coolest part of the device, whereby the discharge-metal condenses thereon; and an anode-cooling means including a fusible material having a melting-point at approximately the desired temperature to which said cooling-means holds said anode-portion of the enclosing-means.

l5- The invention as defined in claim 14, characterized by said anode-cooling means comprising the combination, with an upstanding wall of said anode-portion, of an upstanding heatbarrier spaced from the outer surface of said upstanding wall, an upstanding heat-radiating cooling-plate spaced from the other side of said heatbarrier, said fusible material being disposed on both sides of said barrier and filling the space between said upstanding wall and said coolingplate, and a container-means for said fusible material when it is melted, the disposition and arrangement of the barrier and container-means being such that molten fusible material can circulate over the top of the barrier and under the bottom of the barrier.

JOHN L. BOYER.

No references cited.