US872936A - Tungsten electric incandescent lamp. - Google Patents

Description

I PATENTED DEC. s, 1907.

-, J; A. flE ANYl TUN'GSTEN ELECTRIC 'INGANDESGENT LAMP.

LPPLICIATIOI FILED 11K. 19, 1:905- A I'IED STATES JQHN ALLEN HE ANY,'OF YORKfPENNSYLVANIA.

TUNGSTEN ELECTRIC INGAKDES CE NT LAMP.

To all whom it may concern:

Be it known that I, JOHN ALLEN HEANY,

a citizenof the United States, residing at York, in the county of York, State of Pennsylvania, have invented certain new and use- -ful Improvements in Tungsten Electric Incandescent Lamps, of which the following is -a full and clear description and'which 'will enable thoseskilled in the art to fully under stand the same. ,In an application filed by me December the use of certain very. refractorypure for filaments andelectrodes together with *Fcertain new processes for manufacturing them. Such substances as tungsten, titanium, zirconium, molybdenum, osmium, silicon, andboron or mixtures of the same, are disclosed in this prior application. I-have 'y'found' that. .one" of the most suitable sub- 'Stancestherein named for use as an incandescent filament is a very pure dense and homogeneous body ofminute diameter (being almost hair-like and consisting exclusivel of metallic tungsten- This filament 1s placed in the bulb in which a vacuum is created. "I have discovered that such a filament will stand a much higher temperature in such a vacuum than any carbon filament or a filament consisting of a carbid of tungsten for-instance or carbids of similar refractory metals, or in fact than any other kind of a filament which has heretofore been known.

has been impossible to obtain the necessary resistance, because pure tungsten has ahigh .Jspecific conductivity. The reasons for; these statements are well known in the art and re: quire no extended discussion in the present specification.

f the pure state or admixed with a small-percentage of a-suitable substance to increase the resistance without materiall "reducing I the efiiciency, and .to mount-sue filaments in an electric-lamp in such'a manner that they can be used as practically and perfectly as the ordinary carbon filament.

Specification of Letters Patent. Application filed January 19. 1906. Serial No. 241.782.

29, 1904, Serial No. 238769, I. havedisclosed 'metals, metalloids, or mixtures ofthe same Before my invention it has not been pos-l sible to form a tungsten filament which had su'ch a minute cross-sectional area-andwas of such sufiicient length and'strength so that iti My invention consists in forminga strong but very fine vfilamentof-tungsten either in Patented 16a. 3, 1907.

" of a substance or substances having-a second enlarged detail views of t e same.

support suchfilament for use in the lamp. My said application No. 238769 of- Decem eiiicientthan the ordinary carbon filament,

aments can be made commerciallyin large quantities, and at arreduoed cost and which will also be of superior quality and I- have,

more or less -to the details of construction of thelamp and the means for supporting the filament in the lamp.

a great technical difference between successful which is brittle,althougli elastic, encold, and a tantalum filament; whichis ductile cold. It is,therefore, impossible to-wind a tungsten filament back and forth on a spider, as is done in the tantalum lain The tan:

. talum lamp has a continuous ament-sup;

ported by insulating sup orting-- means,

.w'hereas my lamp hasa pur'ality of indie.

ducting supports, which, however, are of such current carrying capacity that they remain practically cold".

In the accompanying drawings} I. have. shown a tnngstenfilament' in an incandes- 1 cent lamp and refe ito said drawings, Figure 1 is an elevationalviewgpartly in section, of said lamp, -and Fi 2, 3, 4, and 5 are To make a tungsten filament. successfully, .certainprecautions' are necessary as wellas 1;

certain new and-useful'means are 'require'dto also, devised certain new features relating y mounting a fragile tungsten filament,"

and'which can be permanently bent whenvidual filaments connected in series by con-.

In the process for making tun ten filament. disclosed in my application 0. 238769 thefollowing steps are requisite: Tungsten I am aware that it is old-to form'aglower l which has been obtained. in a fine powder 55 class conductivity, that is of substances which. when cold are non-conductors, Y but which .when heated {become conductive. This forms no part of my present invention. v

her 29, 1904, discloses the .process for mak ing a tungsten filament which ism'uch more in almost exclusive use-toda-y, and in fact it 1 i f re, have devised a process by. which said It; will be readily understood tliatthere is and in a very high degree of purity is intimately mixed, with. a small percentagefof. arafiin and made into a plastic mass. It

is then squirtedthrough a small die under 5 pressure into filamentary shape, The filament thus obtained may .withdue care be handled and 'is' then; placed in an oven,

",wheredts temperature is graduallyvraised to nearly'fthelo'xidation point-of tungsten.

.10 During SuChheatingthe paraffin is driven out as, vapor and is 'dissipated, asean be easily proven by an analysis of the filament,

wlzichgwill bef foun-dto be, pure tungsten,

. or it"can-be easily proven. by. the fact that if thelunip'of parafi'inwhich isrto be used is placed .,,on a glass, such as a watch glass, and is similarly heated it will vanish leaving no trace behind1,'on the glass. the ,fi lament above described apparently au slightlyfritsthegvery tungsten particles togethcryand-when cooled the'filamentcan bemountedgin -anincandescent lamp in the samelinannerasj-is the ordinary carbon filamen-t but; requires. of' course both care and s1 (l6 j.- :l7l1 breakage is: considerable.

(so mounted.- and' the bulb has the iihla ment' and jthe -filament shrinks o greatly both in crQSSQSectiOnand in length, owing to ithe f; ct that the particles become sintered into-a dense mass and it is-necessaryto hang'a s mallinert weight in the loop of thefilament to "giv'e it the proper shape, the

weight being afterwards" removed.- The.

mostrjs'erious defect, however, is thatthe shrinkage is uneven-,and two .filamentsrna difier'as to lengtlrand specific resistance, 1f

, the'small articles of-the powderlsquirted b 40 into the 'fi aments is ofvarying degreesof' tungsten-filaments can be worked at high efii'ciencies and since such filaments have a high specific conductivity]; have found it necessary, .not only to mount a plurality of such filaments (sha ed like a hair-pin) in series within the b b, but also to make the' filaments of.. extremely small cross-section 111 order that the lamp containing these tungsten filaments inay be operated upon ordinary commercial voltages as for example,

110 volts.

.terial, order that t: e material ofg the die will not he abraded and cause contamination, 55". and becauseit is-extremely diihcult-to bore as the diainondqor salpphire or similar .ma'

The heating ofxhaustd; af ,xmrmt I of electricity director :alternating is sent through material, it isvalmo'st impossible te'form a very fine filament in this manner, the very finest opening which can'be bored at the present time being too large for my urpose'. I, therefore, "have employed suitab e tungsten" com ounds, which can be readily squirted t oughthe rather small openings of the dies abovereferred to, and thereafter .such 'a compound filament is-reduced to.

the proper openingin a die ofsuoh hard metallic tungsten in such a way that the.

the filament will shrink'greatly'hoth in length the filament will shri still further but under certain conditions this further shrinkage filament. of hair-like cross section, wreadily retaining its shape inusage.

If the filament has uneven or weak spots, it maybe flashed in vapor of tun sten oxy chlorid'and hydrogen whereby the hydro- .gen reduces the chlorin compound "and metallic tungsten is deposited u on the weak spots or places'ina manner ana ogous to the mannerin which-ordinary carbon filaments are flashed, a-hydro-carbon. But I' find that 'it is I not necessary. tovresort to this physical nature or texture and scatters and to throw away defective filaments'although reduced to a minimum by ,my'new processes. I havesmce substltut very fine 'p11re' tungsten powder with such an alloy when the. low melting alloy is melted and have squirted such a mixture resembling ordinary fuse wire. *The wire when cold is bent into the form required and on being heated by the passage of electric particles readily sintered together shrinking greatly'during the 0 eration. I have found n such instances't at it is im ossible to drive out the last trace of sucii analloy binder, and the filan'lent' so produced frequently blackens'the bulb, when-used. I have used 'camplior, starch, sugar and sulfur. as a i from the carlmnized'b'imler would reduce v such oxid, but carlmnhas sucha particular The filaments must be squirted through a,

die of very hard material, suchfor instanceaflinlty for tungsten oven at a low tempera- :ture, sayred heat,- that' I have found it necessary to keep such impurities out of the mass from the start, so that they need; not

reduced; .mfetalli-c particles willi -a'dhereiaizlidz and cross-section.v When is afterwards" smtered inx the bulb-bi the' electric current, n

opera'tiomas it is very tedious and since the ClGPOSlh of tungsten seems to be of a different the number of. such defective filaments .is-

ed :for the paraffin binder various low melting alloys which can e, procured commercially and I mix the I 'when' in a'warm massinto awire, somewhat .be thereafter redfoved, and so that no trace of the same was left behlnddurin-gremoval is but slight and the result will be auniform ssi 'discolors thebulbj during use. It is cheaper current through the wlre' in a vacuum, the, 5 alloy metal 1s boiled out and the tungsten .120' binder, adding a theoretical amount of tungsten oxld so..tha'tcarbon such a trace being sufii cient toor greatly impair the final. roduct.

I have obtained exce entresults by the use of yellow tungsten oxid with a water or paraflin binder, and I have also used the bluev and brown oxid and the sulfid similarly, each being reduced at a-low heatin hydrogen Tungstenoxids, if heated in ammonia, orm nitrids, which can be easily decomposed topure tungsten, the ammonia assists the heat in removing the parafiin binder before the oxid is hot enough .to form the nitrid. v

It is Well known that the United States Patent to de Lodyguine No; 575002 of January 12, 1897, disc oses the process for. coating a fine carbon or platinum filament with tungsten by heating the filament by an electric current in the the volatile chlorin com ound of tungsten. I have obs'ervedthat the eposit thus formed is partly oxid of tungsten, and that the carbon combines with the tungsten in any event to form the carbid by such a process, 25.-even if carried out underdifierent degrees 'of pressure and temperature. The deposit is also of such a physical nature and texture that it will fly off and discolorthe bulb if it is attempted to use the lamp. Where a plati-' num-fillet is usedthe platinum alloys with the tun sten and forms a compound, which is readiy fusible at a comparatively low It is, therefore, obvious that temperature. in my earl attempts to manufacturefilament in w ich a' carbonizable binder was used with the fine tungsten powder, that the result would be much more suitable for use as a fillet u on which to deposit tungsten than the carbon fillet of de Lod guine, since the final result or product woul not contain nearly so muchcarbon even traces of which such as I have discovered are deposited from the small amount of vaporized h dro-carbon from thepil in the mechanical e aust ump, are often sufiicient to form a low carbi when the pure tun sten filament is bein worked free'from occ uded gases when high heated during exhaustion. Such 'acarbi invariably blackens the bulb. I have tested such a carbid and not tungsten of carbon alone, and this shows the necessity for; keeping the carbon out entirely from the start to the finish "of the process. I'have tried to decarbonize such tungsten carbid filaments -by methods used analogously with other carbidand have found, that a little carbon invariably remains and this little is suflicientto reatly lower the efliciencyof the lamp. 'A ll sue methods were discarded for that method in which the fine tungsten powder was made into a paste with a parafiin binder since they were unreliable and too complicated.- As

hereinbefore stated the metal paste method 68v does not produce a.filament. of sufliciently presence of hydrogen and" deposit and have found it'to be tungsten,

sinall cross section althou the filament is much sma 4 mg tungsten upon a carbon taming carbon.

amin tungstates can be made intoa mass same .with a little water without the aid of any other bindingmeans whatever and that such a squirted thread can" be readily handled and wound upon forms, braided, coiled, &c., or such a mass ma be formed into minute'hollow tubes or s eetsand in each case can be readily reduced in hydrogen by gentlyheating and that if, after the reduction is complete, the temperature is raised .the metal particles frit into a dense, pure tungsten body which will shrinkonly' slightly or not at all. even-u to its *melting point. This fact I .deem o articular importance as it does away with t e subsequent costly sintering operation'and furthermore the unreduced threads. canbe looped and supported upon an inert rod,such as-a tungcoated with tungsten, while the freeends are hanging vertically in a vertical reduction furnace and that the metal filaments greatly shrink both-in cross-section (a very valuable strong and coherent and do not kink or tangle with each other and 1118 be readily sepasup ort in the bulb. Furthermore, avery 'smal percentage of thorium added to the more readily, A little metallic zinc, aluminium or vmagnesium may be added to aid the oxygen of the tungstates to form their oxids which ma be-volatilized out in the case of zinc oxi or may remain within to miniuni and -magnesium, oxids. -On the other hand I may adda very'little boron or lowering the melting the amount added-s ould not be enough to form the well known borids or'silicids, all of which are of low fusingpoints. In case a discovered that the carbon from the pump will form the carbid of silicon whichis very refractory andzof ve high resistance and will thus pr'event the ormation of the undosirable tungsten c'arbid, although in some cases a little free silioonima be left over. In'fcase a little rare earth oxi is mixed with the tungsten oxid or tungstates and formed and reduced in h drogenj the tungsten remaining 'rare earth oxide which should thus increase the resistance. The reduction h it is pure and ler than that re t I have discovered that the ammonium and sten rod orfa magnesia or alumina-Jodin reduction, these metals combiningfwith- :increase the resistance,-as incase of alusilicon to increase/the resistance without point very much, but

compound only wil be reduced and the sulting from the impure method of deposit 5 core or core con-- which can be 'squirtedjby merely mixing the very feature) and in length, although they remain rated. and mounted directly upon the finalf tungst'atewill cause it to shrink and sinterlittle silicon is added to the tungsten-I have I sliould take pl'ae abundance or reducing and the reduction tube exhausted thereafter gas, such as hydrogen or carbon monoxid 1 or water gas and'the gas can be afterwan'ls passed 'throu' h" drying bottles, and used I 5 again especiatly fas hydrogen is rather ex. P81151178. L i

In ordelgto prepare niy squirtable mass of tungstateand water I may start with a coinmerci'al-tungstie oxid 0 which is more or 10 less pure, butI-'=prefer+tg start 'with' the mi nerals-wolfrainite or'scheelit'e. The former is fused with'sodiurn carbonate and reduced to a sodium-tungstate Whichistreated with a strong mineral acid to formtungstie oxid (W0 which is a yellow powder. If the ore The tungstie oxid is mixed with pure water conducted into. the liquid. VVhenno more tungstic acid. will dissolve the solution is 'filt'ered until clear. This solution is evaporated on water-bath until-one half 1(.ll'l.il-lIlS and allowed to cool. By this-time cr \fstals will be formed around the edge of the dish which should be Washed quickly with pure ice water, the liquid is to be thrown away as it contains most ofthe impurities. The salt i thus produced is now oxidized in hot dilute nitric acid to "which a little hydrochloric acid Lisf'added from time to time until the material has become rich orz'i-nge in color and granular when it is allowed to settle and the acid and a water oured oil. The tungstic acid. is now washer. with piiredistilled water and allowed to resettle and. rewashed until the water which is poured ofi' will not turn blue litmus paper red.' -*The tungstic' acid'i s driedon a squirted as above described and looped-over ing cutwith a pair of scissors so that a large tically, and are thus air drie'd for a few hours.

They are then placed in a ,verti'e al' magnesia, or alumina tube the insidejof which. is care'" fully lined with metallic tungsten andwex ternal heat applied by a powerful gas or eleetrie heating n'ieans while the reducing gas,

preferably hydrogen, is passed through. Theheatis low at first until complete reduction takesplace, after which it isincreased so as i .to sinter the metallkz filamcnts as much as 65 possible. The reducing gasinay-be shut ofl' scheelite is used it may be treated direct with.

a mineral acid to produce the tungstic oxid. Q

and heated 'and stirred while ammonia gas is water'bathf andweighed. This 'crystalliza up with a little "water-and can be easily ,a tungsten rod, the lower ends of the loop be number of hair pin shapedthrea'dshang Yer-- P 2 0f resilient arin's' v ing 'ofthese filaments in the incandescent 'Aygain when the lampisnetin use; an when soc etcor base 7, andjeitherfone orboth of" 1 may be platinum i ablyhair-pin shape but a rease operated; The filaments a: iserieszbyme'ans a: short len t so w ire '14, the apex of each the gla'ssstem 9:, and these by means of a suitable pump, if desired, and may then-be highly-heated when upon cool ing the filaments will be found dense and strong, They will hang in substantially" straight loops-and willresemble polished platinu m, under the microscope.- I They will i not stick to "one -another,-"under this treat- 1 ment although they have been renderedery jdense, and they are uniform as to shape, size 75 and. conductivity. Thisfeature -I deem of particl'ilar i1nporta1'i'ce, in the commercial;

production of a tungsten'lamp. The mountlainpintroduces new features and preean tions which are notmet within the ordin tryv 2 carbon lamps;v "Tungsten filan ents' for e'x-f -i ample, when operating at one'wattjpe P: or less, are somewhat plastiezanil' unles. supk 2 ported will sagaanil'bendoi'it'bl'." shape, :espo' cially lf-whllG'lfl-lnp-'iS subjectto gfifibgationl F it israther fragile'a'sf .7 t section anrlj-veiyibri Furtherm eith'e filaments often slirinlfslightlj after mounted upon ithe' iinal lsi'ip'port u must be provided hich shrinking without su'b'eeting' to undue sitrainjandE-W filament in the desiredp eircuiting. absorb the shocks or vibr-t n'ientsduring;- shipmI1t.- i H I have shown-in- Fig; 1"aeiindbulbiti, aLlthough of course any" shape .ofihu'l'bf desired I ma "be used, and provided with a suit'able aments t on-vir'ithk'liit'shorti shown three tungsten filaments 3 r' iref I number may be *"employed r'lepending the length and diameter of their the ivoltage upon which the nnected in.

Vi ha-P i I e nbedcledin res may 'be' 1 made of the same jniaterial he wires-{12, 1 5 but areof su'llicicntly lar 'e di ineterltolra a a. .4 main 'pi.-act1cally cold during the passage of f the electric cl'lrrent therethrough'.

. At the lower end of the support 'l'O' arearl sucbsuppbr l lfil be abl tq c itana' 1 1 is to. be

ma of fine -s pi'ral'springs of suitable a metal suchas platinum, iron, mckel,'copper,'

, 't anta um orveven carbon, and these springs are of such good heat conductivity that they .remain cool during'the'operation'of the lam They ma be of sufii'cient diameterv 1301151118411.

"thus ego and may be weakenedby being flattened neantheend' where they are fused into the glasssupport 10, or they may be of 10. very fine wire with a bead-oftungsten or other good heat conducting material applied at the-sp0t.where the filaments and springs V contact." I

. I have shown a series of intermediate supports 1.6 which may encircle 011601 both legs of each hair-pin filament looselylto-prevent vibration, and these supports may be made of metal wire or of a metallic oxid, preferably covered with tungsten, or they may consist fthem to bend during the oper'ationo the lanip.

Themounting of the hair-pin: lfilament upon the stem is as follows:"lhe"tungsten entirely of tungsten, as it is not necessa? for tube are very dense,ydue to the high heating during the latter part of this operation, but the legs are substantially parallel as shown in Fig. 2. Each filament'is slipped through the 0 loose intermediate support 16, if'sucha sup-' port be employed and the free ends are engaged by the short connecting wires which have been previously bent into a small hook at their ends as shown in Fig. 4. v 4 This small hook can now be fused into an inclosing' bead by suitable electrodes in hydrogen or other inert gas, but-Iprefe'r to form the short wire I into'asmall eye, .as shown in Fig. 5,-and to pass the end oi" the filament therein loosely I40 and'to apply'a paste ofyery fine tungsten,

'whichcan ibe readily prepared by reducing ammonium" tungst ate in hydrogen, and -a little water,-the.paste-being'shown at 17 Fig.v Y 5. Or a-carbomzable binder may be added- '45 to the fine tungsten in which case the carbid maybe formed; but as this joint is not subiected to a very high heat, this is not a drawack. In any case, however, a loop ofeach' hair-pinfilament is in engagement with one of the -convolutio nsof the spiral spri 15 preferably near the free end there ci as shown in Fig. 2. A little paste may be added where the spring and filament touch to pie-. vent overheating if desired, and the stem is placedina. 'warm" oven/to dry the paste sho'wnat v1-7, The water will be driven out and the eye 18 is then squeezed a pair of red hotjpincers whichcauses the eye to sink into the paste which is rendered. semi-plastic by the heat and upon coolin'gafirm dense joint is formed which will not contaminatethe filament and which Will-b8 cool when the lam' is iiioperation; The filament is not oxi 'zed bythis treatment even when it is" fit carried'nn intheopen air such amanner oi."

. 25 filaments 'as they .come from the reduction .making the connection above descrl edis m my opmion offgrea industrial ortancei The lampisnow p 'a'cedion thefpum the legs'of each hair-pin filament being su sta'nf ftially parallel asshown in Fig. 2 and'itis to '70 be noted that :the filaments are just astheyf. come from the reduction-tube and have not: been subjected to a subseguent shrinking op-,

.eration inia vacuifinor inert-environment, which 11 hGretOfOIGPIjOVQd-tO be both errapensive and tedious; 5, I When thela'mp is eithausted' the. current is sent throughthe series of filaments and eachone shrinks slightly so that a re s,

thereof slightly converge). toward the loop thereof asfshown inFigt-3 before; the spring is put underperceptible tension. Each fila- -ment can thus shrink independentlyaccording 'exactly"to,fth e necessary or' requisite amount andjsiter it' has; been soshruiik to approximately itsfi'na l position as shown in;

Fig, 3, it is sup orted nl-this'jdesir'ed POSi-e tion -and canst1 cxpand nr contract slightly by reason ";of "the -'-,resiliency, of; the spring.

withoutsubjecting the-"filament'tdadan er'-,901

.Ous strain? In 1 fact thd'spring 3' will -'-'o mntake ,a permanent bend if 'tliefilament"conthe reduction tube, but after such a perma-,; nent bend the spring will oon'acting as y fore, namely,- keep the amenti the de sired, position andipe 'init slight ,Iekpansion and contraction of the filament'dunng use;

-tracts strongly due to imperfect'shrinkage' in a s In addition-the springs;absoi bshockswhieh 1 T 1 might be otherwise da figerous "to: thfbrittlei -filament When itiis cold 11$ f instahcefin 'shipmenta In my Patent N j I i I F1906, which is avdivisionef inyaapplication -ff N o. 239769 .filed December 29,1.1904,;I ,liave 105,:

disclosed and claimed the use"offa.- filament formed from the alloy'oft tehand-another refractory metal, toget er with theta;

process for making it, and in my PatentNo;

84254 6 of January 29, 1, 907','whichis also ai division of said app 'cat1on No{ 2 387769: 1,; have disclosed and claimed'a pure titanium-"I filament and the recess of making it. another v di'visiona application; No; 344068 1 filed November '19, 1906, :I have claimedca .new process for making refractory, metallic filaments, and infanotheriiivisional applica- Ition No, 332786 filed August 31 1.906,,1 have claimed a tungsten filament, having certain newcharactens-tics, and which last named 1 2! application is nowm'vclved in an interference.

have retained certain claims to noveliprocesses" for making refractory metallic filaments of higlh efiiciency.

be certain ncvel'features oi the incan-. I

' descent filaments and the process of making the same andal'slo-eertain novel'features for mounting and connectingthem to the lead-in I wires as set forth the'present'application 180 In the original. Case No.',238769 I:

have claimedin divisional applications, Ap'ril 11-8, 1906, Serial 'Nos. 312392; 312393, and 312394; a 4 -.-H av1 ng thus described the nature and ob-' 5 je'ct" pf'my invention what I' desire to claimi. and secu hyLe'tters Patent-z; 1. ,The cjo'mbinationof a lurality of fine hair-pin shapedfilaments of ense but fragile refracto metallic material connected in 10 series an a su port for said filaments within aryacuunrbul with suitable current con necting wires forsaid series of filaments, said support comprising a plurality of spiral sfirmgs, each of which engages a filament at t 0100 thereof, and'ana ditional steadying means ocatedbetween said springs and the other end oi each filament. 2. A high voltage incandescent electric lamp comprising filaments formed-into-a co herent mass and consistin sten mounted in a plurality "of hair-pin shaped units'in series and supported by a fine spiral spring at the loops of each hair-pin and by suitable connections at the other end 251 and having also an additional steadying means. p

;3.- A mount for refractory metallic filaments. Comprising a stem with suitable leadwires and a supportmounted upon said 20 stern and comprising a plurality of short oon 6 s7s,'e'semostly of tungd'uctors toconn'ect a plurality ofjfine hair 1 V pmiilaments in series at one end thereof, a

the other end thereof toengage each hair-pin filament and. additional intermediate steady ing means'for the filaments.

pThe -method of mounting. refractory metallic filaments which are dense, but whichare-subjeet to slight, longitudinal contraction after'b'eing mountedon the su port 40 in the .bulband during useiof the amp, which com rises the connectingof a; lurality of fine air-pin filaments in-series y the aid of intermediate 'sho'rtyconductors of greater currentcarrying ca "acity and in connecting bo'th' terminals -0 the series of filamentswith suitable lead-in wires, the short conductors and lead-in. wires acting as supports for the endof the hairin filaments opposite the-loops thereof, an in provide .ing a plurality of resilientsupports which are insulated from each other and o'ne-. ,of which engages eachihair-pin filamentatthe loop thereof, andthen heating said filaments so as to contract eachslightly therebyrcausing the straight lengths thereof to converge slightly towards the loops thereof and therebysirnultaneously causing each resilient support to be placed undenslightand individualtension as the individual shrinkage of encll' 6o filament requires.- I: I I- Q I OH AWEN ANK; Witnessesz'g ff ILLLOWEm.

' 1 lur'ality of fine-resilient spiral supports at

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