US2147506A

US2147506A - Floating weight electric switch

Info

Publication number: US2147506A
Application number: US108986A
Authority: US
Inventors: Robert S Stoner
Original assignee: Brown Brockmeyer Co
Current assignee: Brown Brockmeyer Co
Priority date: 1936-11-03
Filing date: 1936-11-03
Publication date: 1939-02-14
Anticipated expiration: 1956-02-14

Description

Feb. 14, 1939. R, 5 STONER 2,147,506

FLOATING WEIGHT ELECTRIC SWTCH Filed Nov. 3, 1936 3 Sheets-Sheet 1 lull lIII

Feb. 14, 1939. R. ssToNER FLOATING WEIGHT ELECTRICA SWITCH Filed Nov. 3, 1936 3 Sheets-Sheet 2 lil n A (SEMI 7; (SUMQ WJ Feb. 14, 1939. R 5l STONER 2,147,506

FLOATING WEIGHT LECTRIC SWITCH Filed Nov. 3, 1936 3 Sheets-Sheet 3 JMW ROBERT 15mm-R, ,BY

@Ww SM www@ Patented Feb. 14, 1913s,?

Zdlidt maar otros Application November 3, 1936, Serlai No. 108,986

l t'lllims.

- having a weight oating upon a conducting liquid, the weight having associated therewith an armature which is adapted to be attracted by the magnetic forces produced by the energization of a coil, the uid displaced by the downward motion of the weight and armature being caused tcrise and engage a contact or electrode which is normally spaced apart from the liquid.

Another object is to provide a switch of the type described above, wherein the conducting liquid is of such a nature that it adheres to the electrode during the upward motion of the float and downward motion ci the fluid, thereby causing the breaking of the circuit to take place not between the viiuid and the electrode but between different parts of the iluid itself. In this manner the wear and pitting ci the electrode, which ordinarily takesv'place, are effectively reduced or prevented.'

Another object is to provide a noot-operated switch wherein the iluid consists of mercury having' other substances mixed therewith in such a manner as to form a mercury-like liquid, but

having the distinctive property of adhering to the electrode and of`being drawn out into a thin neck as the liquid surface moves laway from the electrode. This thin neck not only causes the breaking of the circuit to take place at a point away from the electrode, but also reduces the amount of current nowing across the neck at the instant of the break b'ecause oi the increase resistance of the small neck.

Another object is to provide an electric switch having a iloat operated by a coil in such a manner as to displace a liquid upwardly into engagement with an electrode, the liquid consisting principally of mercury and a foreign substance, such as a. metal resembling lead, and preferably forming an amalgam with the mercury.

Another object is to provide an electrode .for such a switch, the electrode being of such a configuration asto enhance the adhering action (Cl. E-i12) of the conducting liquid, thereby increasing the facility of forming the narrow neck between adjacent portions of the 1iquid;

Another object is to provide a neat-operated electrical switch of such a character as to have a snap action, thereby bringing about the breaking of the circuit in a much quicker period of time than in ordinary switches.

Another object is to provide a motor starting circuit for split phase motors employing a floatlo operated switch of such a character as to require a lesser amount of current to hold the switch in engagement than to close the switch in the rst place.

Another object is to provide a motor starting 1 circuit for c. split phasemotor, wherein the floatactuated switch is provided with a. plurality of windings so that a light-duty push button may vbe employed'in the circuit, one winding being used merely for closing the switch and the other 20 winding being used for holding the switch in its closed position; one winding being automatically cut out as the other winding is energized.

Another object is to provide a method of breaking electrical circuits consisting of passing the electrical circuit through a conducting liquid l having an electrode capable of being immersed therein, the liquid and electrode being of such al character that as they are moved apart from each other the liquid is drawn into a narrow 3 neck and subsequently separates, thereby first reducing the amount of current owing through the neck because of the increased resistance thereof, and finally severing the connection entirely.

In the drawings:

Figure 1 is a central vertical section through the switch of this inventin, showing the parts in the position of rest, with' the operating coil unenergized. 40

Figures 2 to 5, inclusive, are views similar to Figure 1,-but showing the successive stages of operationl of the switch.

Figure 6 is a side elevation ofthe switch shown in Figures 1 to 5, inclusive. 45

Figure '7 is a wiring diagram showing the switch of Figures 1 to 6, inclusive, employed in starting a split phase induction motor.

Figure' is a diagrammatic View of a mcdied switch having a plurality of windings, one Winding being employed for initially closing the switch and the other for holding the switchv in its closed position.

Figures 9 to 19, inclusive, are enlarged views, partly in section, of various types of electrodes u employed in the switch shown in Figures 1 -to 6, inclusive. l

Figure 20 is a central vertical section through a modified form of switch employing a spherical float.' l

Figure 21 is a central Vertical section through another modified form of switch employing a spherical float.

In general, the switch of this invention con` sists of a container having a conducting liquid therein, an electrode normally spaced apart from the liquid, a ioat resting on the liquid, and a coil adapted when energized to attract the float and thereby to cause the level of the liquid to rise and engage the electrode, thereby closing the circuit between the liquid and the electrode. In particular, the liquid employed consists principally of mercury with the addition of a foreign substance, such as lead, which causes the mercury to adhere to the electrode rather than to be separated instantly therefrom, as is the -case with pure mercury.

Hitherto,` in switches employing mercury, it 1 has been necessary to use evacuated tubes and exceedingly pure mercury in order to avoid leaving a skin-like layer of conducting foreign material between the electrode and the liquid in its receded position. 'Ihe tubes were evacuated or lled with an inert gas in order to prevent oxidation of the mercury and the subsequent formation of such a layer of foreign material. This eect of foreign matter in a mercury switch employing a glass tube short-circuited the tube and rendered it useless for further action. The present invention, however, deliberately utilizes mercury which is not only not pure, but in contrast, has a foreign substance or "substances added thereto to give it a different eect.

When the ordinary pure mercury engages the electrode of the ordinary switch the latter merely pushes the mercury aside, and when the level of the mercury recedes it drops instantly away from the electrode vwithout wetting it. In the present invention, however, the mercury mixture or amalgam adheres to the electrode and does not break away instantly. .In contrast, the break of the circuit occurs not between the mercury and the electrodel itself, as in switches hitherto made, but between diierentportions of the' mercury mixture at a point remote from the electrode itself. o 'I'his construction adds to the life of the electrode and' prevents wear and pitting.

A circuit is also provided wherein the switch' of this invention is employed in starting a split phase induction motor,` the switch having the characteristic of requiring a smalleramount of current to hold it in its closed position than toclose it in the rst place. 'I'he switch of this invention .also possesses a snap action, which breaks the circuit with' great rapidity when a breaking thereof, is desired.

Referring to the drawings in detail, Figure 1 shows one embodiment of the switch of this invention'as consisting of a lower casing portion Ill having a downwardly extending reduced portion II, theportions I0 and II being preferably 'of a non-magnetic material. The bottom of the portion II is closed by a plug I2, preferably of magnetic material, such as soft iron. The reduced portion IIis surrounded by a winding forming a coil I3, having an insulating layer Il thereover. 'I'he leads I5 and I6 of this winding are brought out, respectively, to ring-like portions I1 and I8 (Figure 6) which may be engaged by suitable clips, forming no part of the present invention,

and facilitating the rapid insertion or remal of the switch.

'I'he central portion of the switch includes a` cylindrical casing I9 of non-conducting material, surrounded by the ring-like portions I 'l and I8 and terminating in a cap 20 of conducting material, having a ring-like portion 2i for engagement by another clip, and an end portion Z2 having an aperture 23 for the reception of one end of an electrode 24. The inner end of the electrode 26 is preferably enlarged, or otherwise provided with a portion` 25 vprojecting therefrom to enhance the adhesion of the conducting material.

Arranged to reciprocate vertically within the casing portion I9 is a iioat 26 of annular form, and having an inner borg 21 within which is arranged one end of an armature 28 connected to the float by the arms 29. The ends of the oat are preferably streamlined, as at 36 and Si, so as to permit the passage of the uid with the least resistance. The armature 23 is of magnetic material adapted to be attracted by the plug I2 when the latter is magnetized through the energization of the coil I3. The arms 29 are likewise-preferably streamlined to enhance the passage of the fluid.

'I'he container, consisting of the portions` I9,

LIl and is, 1s pamauy nued with a uuid a2 of a foreign Vmaterial mixed therewith, such as lead in the proportion of one part of lead to six parts of mercury. These proportions, however, are not critical and other proportions and materials may likewise be used to give the mercury an adhering effect upon the electrode.

'I'he electrode itself may be made in a number of different forms, such as are shown in Figures 9 to 19, inclusive, in addition to the form shown in Figures 1 to 5, inclusive. In Figure 9 the electrode 33 consists of a cylindrical rod with a at end 34. In Figure 10 the electrode 35 has a rounded end 36. In Figure 11 the electrode 3l has a pointed end 38. Inv Figure 12 the electrode 39`has a cup-shaped concave end 40. In Figure 13 the electrode 4I has an enlarged head l2 with an annular depression 43 atthe back thereof. In Figure 14 the electrode 4I of Figure 13 has been provided with a roughened surface 44 upon the head 42. The electrode 45 shown in Figure 15 is provided with a solid enlarged head 46, with a roughened surface ll'I. The electrode i8 -of Figure 16 has been provided with an enlarged conical head`49, with or without annular ridges 50 on the shank thereof. 'I'he electrode of Figure 17, designated 5I, is provided with a reduced end portion 52, .with an `annular shoulder 53 separatingA the two portions of the electrode. 'I'he electrode 54 shown in Figure 18 consists of a head 55 having an annular groove 56 between it and It will be understood that the advantages of the invention are not limited to a liquid comprising a mixture of mercury and lead. Other metals, such as antimony, bismuth and tin have been iound suitable for mixture with the mercury. It is advisable, however, to employ for the electrode a material which will not amalgamate with the mercury, otherwise, the electrode itself will dissolve somewhat in the course of time. The present invention makes use of this mixture of other substances with the mercury in order that the resultant liquid will adhere to the electrode and be drawn out into a neck-like form when the electrode and liquid are caused to move away from each other.

It will be understood that the switch may be constructed without the iron plug I2 at the bottom thereof. The action would then be that of a solenoid I2 attracting the armature 28. The iron plug I2, however, intensifies and concentrates the magnetic action-of the winding I3.

Operation i I In the operation of the switch of this invention, the float 28 rests upon or near the surface of the liquid 32, depending upon the buoyant characteristics. Under such circumstances, if the liquid 32 consists of the mercury mixture described above, the surface of the liquid will be upwardly convex. When thewinding I3 is energized by closing the electrical circuit including it, the resulting magnetic field set up attracts the armature or plunger 28. The force of attraction is at first relatively weak, and increases in strength as the armature 28 moves downwardly in response to the magnetic attraction. This isl especially true when the iron plug I2 is used to concentrate the magnetic action of the winding I3. This characteristic causes the switch to have -a snap action so that the armature 28 is moving lvery rapidly as it approaches the downward limit of its motion. Meanwhile, the liquid displaced by the downward motion of the float 26 is forced upwardly past the spider arms 29, and through the bore 21 into engagement with the head 25 of the electrode 2l. This actionis shown in Figures 1 to 3, inclusive. Figure 1 shows the switch in its open position with the various parts at rest. Figure 2 shows the switch slightly after contact has been made between the electrode and the liquid. Figure 3 shows the switch after a full contact has been made. l

The motion of the mercury itself also gives a snap action, corresponding with the snap actionI of the armature 28 in moving downwardly into the winding I2. By this action the mercury is mechanically hurled up toward the top of the switch and into contact with the electrode by the downwardly accelerated plunge of the oat. By reason of the mixture of the mercury with one or more other substances, as explained above, the

ymercury adheres to the electrode rather than the electrode being merely pushed into an indentation in the surface of the mercury, as is the case when pure mercury is employed.

When the circuit is broken the float 2B rises and the level of the liquid correspondingly drops. As the liquid surface recedes from the electrode,

however', the adhesion of the liquid to the electrode causes the effect shown in Figure 4, whereby the liquid is drawn out into a neck-like form which becomes smaller and smaller as the liquid level falls. This nari-owing ofthe neck causes the electrical resistance thereof to be raised until only a small proportion of the current carried action because the two portions of the liquid,

literally explode apart from one another at the instant of the break. The gas within the switch,

lwhich may be either air or inert gas, together with the vaporization of the mercury by reason of the heat produced at the point ci break, cause this explosive effect which results, in a suppression of the arc. This eect still further reduces the danger of pitting the electrodes or of injuring the various materials in the switch.

Thusfthe actual break occurs not at the'surface of the electrode, but at a point slightly below it. The break occurs between different portions of the mercury, or other liquid, and not directly between the liquid and the electrode, as in ordinary mercury switches. This action greatly protects the surface of the electrode and reduces the serious pitting effect which occurs when pure mercury is used, as in ordinary switches.

As the level of the mercury recedes from its contact with the head of the electrode upon the deenergizationvof the winding I3, the mercury mixture or amalgam leaves the head 25 of the electrode with a rolling action, and a crystallization-like effect is observed. Upon analyzing the mercury mixture which is left upon the electrode head 25, it is found that the proportion of foreign substances to the mercury is much higher than in the main body of the liquid. This foreign substance becomes a granulated deposit upon the electrode and produces a much finer neck-like action, or a much finer thread of liquid as the surface thereof recedes from the electrode. Thus, assuming lead to be the mixing substance, if the ratio of lead to mercury is one to six elsewhere in the main body of the liquid, the ratio may be as much as one to one on the electrode. This important effect increases the efficiency of the switch without requiring a high mixture of 'foreign substance in the main body of the liquid iiirected to the same purpose of increasing the adhesion of the liquid.

Moreover, this thread-like or neck-like action which occurs when the circuit is broken, enables the switch to carry a much higher current than is possible with ordinary switches where pure mercury is used, and a direct break is made between the surface of the'mercury and the electrode surface. A switch of my invention may carry as muchas 50 to 100 amperes of current, an amount much greater than an ordinary switch of the same size and employing pure mercury can carry. The reason for this effect is as stated above. that the neck-like action greatly increases the resistance' across the switch and therefore reduces the current actually flowing to a mere fraction of that flowing when the switch is fully closed. The alloy or mercury mixture is drawn out into a form somewhat resembling a water spout. This separation of the point of break from the electrode itself enablesthe use of a cheapmetal for the electrode, as contrasted with the expensive tungsten or platinum necessary for use with ordinary mercury switches where the break. occurs directly at the surface `of the electrode. The break between different .portions of the amalgam or mercury mixture protects the electrode itself to such an extent that an ordinary soft iron screw used as an electrode has been successfully used to break the circuit of current of 50 to 100 amperes without serious pitting over a considerable period of time.

It will be observed, moreover, thatl the switch of the present invention may be operatedwithout evacuating the air as the latter does not create an adverse eect by its oxidation of the mercury. The question of impurities in the mercury is a serious problem in ordinary mercury switches, especially those employing glass tubes. As the mercury switch tilts, or lthe mercury otherwise moves, it tends to leave a trail of impurities between the electrode and the mercury surface, thereby shortcircuiting the switch. In the present invention, however, these impurities do not impede the action of the switch because the tube does not tilt, and a complete path of impurities is never made possible.

Furthermore, the action of the switch itself has a purifying eiect upon the mercury mixture so that a clean surface `is always presented to the electrode. In the action of the switch it is observed that although the mercurymixture surface 'is completely coatedv with impurities, in the position shown in Figure 1, by the time the mercury has risen to engage the electrode these impurities have moved aside like a curtain. and presented a brilliantly reecting mercury.l surface to the electrode. Moreover, the iioat 26 may be spaced with a considerable clearance between it and the side walls of the container I9 because the rising of the mercury itself into this space acts as a kind of lcushion-and spacing agent, prevventingv the sticking of the float to theside walls. This arises from the dlculty of passing'mercury throughlsmall apertures and is very useful when the switch is employed in connection with dinary metal, such as iron or aluminum is used,

the coating or oxide or other impurities which the metal may acquire, do not affect the switch adversely after a few closures thereof. It lhas beenfound that with this mercury mixture instead of pure mercury the mixture exerts an effect similar to tinning the electrode where it is impure or coated with rust and like substances at the start of the operation. Y

VIn addition to the foregoing qualities, this Vswitch possesses the additional feature of releasarcanos ing eld windings 6l to' 61,

Improued switch. :mit for splitv phase motor circuits Y' Y Y In Figure 7 there is shown a split phase motorcircuit having windings B0, 6I, 62 and 63 and splitphase 'or starting

windings

6d, 65, 66 and S1 arranged in staggered sequence between the windings 60 to 63,-inclusive. The windings 60 and 62, for example, are wound in an opposite direction from the windings 6I, and 53, whereas the windings 64 and G6 are wound in an opposite direction from the windings G and G7. The windings 60 to 83, inclusive, are led out to the lines 68 and SS, whereas the windings 64 to S1, inclusive, terminate in the li'nes 'le vand. il. The

lines l@ and S8 are connected to one another, as

at l2, and terminate in the connection plug 13.

From the opposite terminal of this plug the line Il-i5.. To this ring il is connected one lead of the coil or winding i3, the opposite end being connected to'the line 69. The line 'II is connected cury 32 and the electrode 24 between the lines 'i4 and 69, thereby energizing the starting

wind ings

64, 65, 66 and 61, as well as the windings 60, 6|, 62 and G3. `'Ihe motor then starts its rotation, and as it comes up to speed the reverse 14 runs to the lower ring I I of the mercury switch Y electro-motive force arising from opposing theA impressed current, causes the current in the switch winding I3 to drop steadily until ata certain deiinite speed approaching its full running speed (say 1500 R. P. M for a F150-R. P. M. motor), the current becomes insuflicient to hold the amature 28 against the buoyant effect of thel float 26 in the mercury mixture 32.

Due to the fact that a greater amount of current is required to close the switch than to re- V)lease and open it, a lag effect occurs in association with the main field and the starting eld.

The main. fleld'windlngs SII to El, inclusive, are usually of heavy wire with a relatively low re- -sistance andhigh reluctance, whereas the startinclusive, arranged 90 degrees in rotation therefrom, are of high resistance and low reluctance. As the current drawn by the 'motor drops as it -increases its speed past the critical point where it is insumcient to hold the mercury 'I5 in a closed posi-v tion, the switch 'I5 opens, removing the starting vwindings El to 61inclusive, from the circuit and leaving only the main eld windings 6 to p 63, inclusive. The iron plug I2 intensies the magnetic action and can be varied in size and magnetic characteristics in order to adjust the lag characteristics arising from-this effect. The

motor continues to rotate under the eil'ect of its main windings 68 to G3 alone until it is stopped by opening the main switch 16. A When the main switch 'I6 is again closed the main and starting field windings then draw' the full amount of amperage possible, and the mercury switch 'I5 is again closed. It'again remains closed until the motor speed reaches the critical point at which the current flowing through the coil I3 is insuflicient to hold down the armature 28, whereupon the switch again opens and the main nexos ,5

operate without the starting elds, in the manner heretofore described.

Multiple winding mercury switch circuit The mercury switch circuit shown in Figure 8 is especially adapted for starting split phase motors and enables the use of light-duty starting and stopping switches, such as ordinary push button `switches not particularly adapted to the passage of heavy current. For this purpose the .mercury switch 11 is provided with a winding 18 of light wire and a winding 19 of heavy wire. The light winding 18 serves as a switch-closing winding and the heavy winding 19 as a holding winding for `holding the switch in a closed position. The internal arrangement or the switch 11 is the same as that shown in Figures 1 to 5, inclusive, except that the iron plug I2, here designated 88, is insulated by the insulating lportion 8| from the remainder of the portion I Connected to this end plug 88, which serves as an additional terminal on the switch, is the line 82 forming the lead from one end of the heavy winding 19, the other lead 83A of which consists of one of the power lines, an auxillary line 84 from which leads to one terminal of the stopping push button switch 85. From the opposite terminal of the latter the line 88 runs to the lead 82 of the heavy winding or holding coil 19. From the line 88 the line 81 runs to one lead of the fine winding or closing coil 18, the opposite lead 88 of which is brought out to one terminal of the starting push button switch 89. From the opposite terminal of this switch the line 98 runs to join the line 9| interconnecting the windings of the motor 92 with the terminal 93 of the electrode'24. The remaining line 94 is the power line leading to the motor 92. A line switch 95 makes and breaks the circuit between the

lines

83 and 94 and the current mains 98 and 91, respectively.

In the operation' of the circuit shown in Figure 8, the general action of the switch is as described previously. When the starting push button switch 89 is closed the circuit is closed between the

lines

98 and 88, thereby energizing the iine wire closing coil 18 by way of the lines 81, 88, the stopping push button switch and the

lines

84 and 83. The energization of the closing coil 18 attracts the armature 28 and iloat 28,- and causes the mercury mixture 32 to riseand engage the electrode 24, closing thev circuit between the

terminals

93 and 88. When this occurs the current ilows from the line 91,` through the main switch 95, the line 94, the

motor 92, the line 9|, the terminal 93, the switch 11, the terminal 88, the line 82, the holding winding 19, the line 83 and the main switch to the line 98. This energizes the holding coilv 19 and causes it to hold the armature 28 and float 28 in their lower positions even when the push buttonswitch 89 is released by the operator.

The closing winding 18 -is therefore completely deenergized the instant the operator releases ,the starting switch 89. Even though the operator keep the starting switch 89 closed, however, the

winding 18 is not endangered by the flow of heavy current because it is shunted out by the connection between the

terminals

93 and 88 as soon as the switch closes. Consequently, the circuit shown in Figure 8 ds capable of employing very light-duty switches and no damage can result to the switches even if the operator keeps the push button switches closed for an appreciable period of time. The closing winding 18 is cut out automatically and instantly by the aotion of the holding winding 19 as soon as the switch closes. It the operator depresses the stopping button 85, however, the motor circuit is instantly broken as this action bridges the ter minals of the holding coil, the deenergization of which instantly releases the amature 28 and float 28. Accordingly, no damage can result to the windings even though the operator maintains the stopping switch 85 in a depressed position for an appreciable period of time.

Ball float switch The modified switch shown in Figures 20 and 21 employs aball V98 within a cup-like casing 99 having mercury or a similar conducting liquid |88 therein. The side of the casing 89 is `pierced by electrodes |8| and |82, insulated by the insulating portions |83 and |84 from the casing 98. Optionally the casing 99 may itself be made of insulating and non-conducting material. A plug |85 closes the bottom of the casing 99 and a winding |88 surrounds this casing, the leads |81 and |88 being connected to a suitable source of electrical energy, in the manner previously described in connection with the other forms of switches.

The iioat 98 consists of a ball which is o! iron or which has an iron core. If the ball is all of iron it is preferably coated with an insulating coating, such as synthetic resin, hard rubber, etc. When the winding |88 is energized the magnetic field thereby set up attracts the float 98, forcing it downwardly and causing the top surface |89 to rise to the point where it simultaneously immerses the electrodes |82 and |8|. This closes the circuit and causes the energizetion of the lines ||8 and leading from the electrodes |8| and |82. The use of the ball iloat 98 effectively prevents any sticking because it will roll up and down the inner walls of the casing 99.

The switch shown in Figure 21 is similar to that shown in Figure 20 except that the end plug ||2 replaces the terminal |82 and the terminal ||3 replaces the terminal |84. H4 is energized, in a manner similar to the winding |88, the iioat ||5 is forced downwardly into the mercury H8 within a cup ||1, causing the mercury to overow into the space adjacent the electrode H3. Accordingly, the circuit is closed between the line H8 connected to the plug |12 and the line ||9 leading from the electrode ||8.

Time delay' switch The switch shown in Figures l to 6,`inc1usive, can be employed as a time delay switch by causing the apertures between the armature 28 and the iioat 8| to be restricted in size so as to impede lthe free passage of uid therethrough. Under these circumstances, the/float and armature will not become operative to make or break the circuit instantly after the coil I3 has become energized or deenergized, because the opposition onered by the small apertures adjacent the arms 29 will exert a cushioning action by the mercury and retard the action of the switch. In this manner the switch is given a dash pot action which provides a time delay feature. It will be also observed that by reducing the clearance be- As the winding' coil I3 at the top of the switch, so as to make the rendering said liquid adherent to said electrode switch'a normally closed instead of a normally open switch like the switch in Figures 1 to'6, inclusive, the thus modiiied switch can be used as a time delay' overload protection switch for electrical circuits, especially where the mercury is made to pass through restricted orifices, as described above. Under these conditions the current normally owing through the switch coil would be insuicient to open this normally closed switch. When an overload of current passes ythrough the coils, however, it will actuate the armature and iloat in such a manner as to open the circuit between the mercury mixture and the electrode. It, however, the surge is oi' merely momentary duration so that the motor windings can carry it without damage, the dash pot action of the mercury in passing through the restricted apertures, such as those existing between the armature v28 and the float 3|, will interpose a time delay before the switch can become operative to open the motor circuit. This time delay is eilicient in preventing stoppages of the motor caused by momentary overloads whichthe motor windings can conveniently carry.

It will be understood that I desire to comprehend within this invention such modications as come within the scope of the claims and the invention.

. Having thus fully described my invention, what I claimas new and desire to secure by Letters Patent, is:

1. In combination. a container, a conducting liquid in said container, an electrode, means associated with said container for selectively creating a magnetic field, and iloat means responsive to thecreation of said magnetic field for displacing 'said liquid into engagement with said electrode, said liquid being adherent to said electrode to f\orm ank elongated portion between said electrode and said liquid in response to the separation o! said electrode and said liquid.

2. In combination, a containena conducting liquid in said container, an electrode, means associated with said container for selectively creating aV magnetic iield. and oat means responsive to the creation of said magnetic iield for displacing said liquid into engagement with said electrode, said liquid comprising a mixture of mercury and a material rendering said liquid adherent to said .electrode and attenuable into a slender column upon the separation of, said electrode and said liquid.

3. In combination, a container, a conducting liquid in said container, an electrode, means assocated with said container for selectively creating a magneticiield, and oat means responsive to the creation of said magnetic field for displacing said liquid into engagement with said electrode, said liquid comprising a mixture oi mercury and a material amalgamatable therewith and attenuable into a slender column upon the separation of said electrode and said liquid. 4..In combination, a container. a conducting i liquid in said container, an electrode, means as` sociated'with said container for selectively creating a magnetic eld, and float means responsive to the creation of said magnetic eld for displacing said liquid into engagement with said electrode, said liquid being adherent to said electrode and attenuable into a slender column upon the withdrawal thereof, said electrode being of material resistant to dissolubility by said liquid.

the liquid thereto.'

material resistant to amalgamation with saidmercury.

6. In combination, a container, a conducting liquid in said container, an electrode, means associated with said container for selectively creating and abolishing a magnetic eld, and iioat means responsive to the creation of said magnetic field for displacing said liquid into engagement with said electrode and responsive to the abolition of said magnetic field for attenuating said liqmd into a slender column attached to said electrode, said liquid comprising a mixture of mercury and a metal rendering said liquid adherent to said electrode upon the separation of said electrode and said liquid.

'7. In combination, a container, a mercury alloy in said container, an electrode, means adjacent said container for selectively'creating and abolishing a magnetic field, and float means re-v sponsive to the creation of said magnetic ileld for displacing said liquid into engagement with said electrode and responsive to the abolition of said magnetic iield for attenuating said mercury alloy into a slender column attached to said electrode, said mercury alloy comprising a mixture of mercury and lead.

8. In combination, a container, anelectrode, a conducting liquid in said container adherent to said electrode, means adjacent said container for means responsive to the creation of said magnetic ileld for moving said liquid and said electrode relatively to each other, said electrode having a roughened surface whereby to enhance the adhesion of the liquid thereto.

10. In combination, a container, an electrode,

a conducting liquid in said container adherent to said electrode, means adjacent said container for creating a magnetic field, and float-actuated means responsive to the creation of said magnetic ileld formoving said liquid and said lelectrode relatively to each other, said electrode having a projecting portion thereonwhereby to assist the adhesion of the liquid thereto. i

11. In combination, a containen'an electrode,l

a conducting liquid in said container adherent to said electrode, means adjacent said container for creating a magnetic neld, and :Heat-actuated means responsive to the creation of said lmagnetic ileld for moving said liquid andv said electrode relatively to each other, said electrode having an enlarged head whereby to assist the adhesion of 12. In combination, a container. an electrode.

' a conducting liquid in said container adherent to said electrode. means adiscent said container for creating a magnetic iield, and doet-achiaized means responsive to the creation o! said magnetic neld ior moving said liquid and said electrode relatively to each other. said electrode hav- ,ing a tip with a recess therebehind whereby to assist the Aadhesion oi the liquid thereto.

13.l In combination, a container, an electrode, a conducting liquid in said container adherent to said electrode. means adJacent said container for creating a magnetic field, naat-actuated means responsive to the creation o! said magnetic neld for moving said liquid and said' electrode relatively to each other, and means at the tip of said electrode ior increasing the adhesion of the liquid thereto.

14. In combination, a container, an electrode.

aconductingliquidinsaidcontaineradherent to said electrode. and means responsive to the withdrawal oi-said electrode from said liquid for Initially 101mm( l!! donated column' of liquid between laid electrode and the main`body oi said liquid and for iinaliy severing said elonaated l5. In combination, a container, an electrode,

v"amixtureoimercury and at leastone othersub-4 ROBERT B. B'IONIR.