US2495707A

US2495707A - Triboelectric metal identifier

Info

Publication number: US2495707A
Application number: US602378A
Authority: US
Inventors: Doschek Antony
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-06-29
Filing date: 1945-06-29
Publication date: 1950-01-31
Anticipated expiration: 1967-01-31

Description

LN MM W@ llli EL HQ@ A. DOSCHEK TRIBOELECTRIC METAL IDENTIFIER Filed June 29, 1945 Patented Jan.. 3l, 1950 UNITED STATES PATENT OFFICE TRIBOELECTRIC METAL IDENTIFIER Antony Doschek, Grafton, Pa.

Application June 29, 1945. Serial No. 602.378

l2 Claims. (Cl. F75-183) l This invention relates to the identification and sorting of metal pieces with relation to their chemical and metallurgical characteristics and particularly to procedure and apparatus for accomplishing such an ldentication and sorting. An object of the invention is to provide a new and improved procedure for identifying and sorting metal pieces which is more accurate and more convenient to apply than procedure heretoeffectively and rapidly employed in connection with a wide variety of metals and alloys and in connection with metal pieces of widely different shape and size and which will not mar the surface of such metal pieces or otherwise detrimentally affect the same.

These and other objects are attained by means of the procedure herein described and the apparatus here illustrated and described.

In the drawings,

Figure 1 is a wiring diagram illustrating equipment embodying my invention and capable of being employed in carrying forward procedure constituting an embodiment of my invention.`

Figure 2 illustrates a detail of the apparatus employed in carrying forward the procedure of my invention and which also diagrammatically illustrates the preferred type of relative movement between two conductors while the same are maintained in tribo-electric union.

Various procedures and mechanism for identifying and sorting metal pieces have been employed, with measured success. The broad and fundamental object of my invention is to provide a new procedure and a new `mechanism for identifying and sorting metal pieces which can be eilectively, rapidly and conveniently employed in determining the identity or non-identity of any two metal pieces and which is capable of almost universal application from the standpoint of the various known metals and alloys and also from the standpoint of the size, shape and location of the metal pieces subjected to the identifying and sorting procedure.

In accomplishing this and the other objects herein set forth, I have adapted the tribo-elec tric principle to the identiiication and selection of metals. This principle has long been known but, so far as I know, it has only been employed in connection with dielectrlcs and then as hardly more than a laboratory demonstration in the generation of static electricity by the rubbing together of two dissimilar dielectric materials. The tribo-electric phenomenon, as generally known, involves the generation of friction between two unlike materials in intimate contact and atleast one of which is a dielectric, and the production thereby of a static charge of electricityon the surface of the dielectric material involved.

I have discovered that this tribe-electric principle may be employed in determining the similarity or dissimilarity (chemical or metallurgical) in the compositions of two metallic pieces.` That is to say, I have discovered that, where two metallic pieces are subjected to the tribe-electric eect, they may be identified as either similar or dissimilar from the standpoint of their chemical and metallurgical characteristics. This discovery grows out of my prior discovery that, where two dissimilar metal pieces or specimens are placed in intimate contact with each other and rubbed together insuch a way as to generate friction, a discernible and readily measurable electric current is produced. On 'the other hand, if the specimens or pieces, placed in triboelectric union, are chemically and metallurgically similar, no electric current is generated.

By tribo-electric union, I means two specimens maintained in contact with each other and moved so as to generate friction while said pieces are located in, and their contact with each other completes, an electric circuit. I have found that a regular periodic or pulsatory movement best suits my purposes and that the relative movement 'as between the two specimens should preferably be such that the point of contact is continuously changing on each specimen. I have also discovered that the electro-motive force, generated by two dissimilar specimens in triboelectric union, is designated by the character and the degree of dissimilarity; that, within limits, the electro-motive force, generated by two dissimilar specimens in tribe-electric union, increases with the time duration of the union, the length or amplitude of the reciprocating or pulsatory movement of the two specimens relative to each other, the frequency of the pulsations and the degree of pressure by which the specimens are held in contact with each other.

My experiments also indicate that, while the electro-motive force, generated by the tribo-electric union, increases with the time of the union, the amplitude of the movement, the frequency of pulsation and the amount of pressure employed in holding the specimens in contact with each other, the rate of increase eventually falls 01T after a maximum potential has been reached. That is to say, my research discloses that the character and degree of dissimilarity between two specimens will determine the point at which maximum saturation is reached and the indication, therefore, is that, for every two dissimilar pieces of metal, there is a dem'te saturation point, from the standpoint of E. M. F. developed by a tribe-electric union, at which no further increase in E. M. F. will result and independently of a continued increase in the time of the union, the amplitude of the pulsatory movement, the frequency of the pulsations and/or the pressure involved in making the union.

In identifying and sorting metal pieces, I employ a specimen of known chemicaland metallurgical characteristics. This specimen is successively placed in tribo-electric union with the various pieces to be tested for the purpose of determining their identity or non-identity with the known specimen. By this means, various pieces of metal may be identified as either identical with or different from the known specimen. This procedure can be carried forward with other known specimens and, in this way, a number of pieces of metal may be grouped as being either identical with or non-identical with one or another of the various known specimens.

For convenience of application and also for the purpose of maintaining conditions substantially constant throughout each test, I preferably employ an electrically-actuated reciprocating tool, such for example as a filing tool, for reciprocating the known specimen. That is to say, the specimen of known chemical and metallurgical characteristics is secured into the chuck of the reciprocating tool and is made a part of a metallic circuit which includes an electro-responsive device, such as galvanometer, for measuring a value of such current as may be generated. The chucked specimen is then placed in contact with a piece of metal to be tested or identied and, in this way. the metallic or measuring circuit is completed. After making such adjustments in the circuit as may be necessary to balance out 0r off-set thermo electric effects and/or contact potentials, the electric tool is energized so that the contacting pieces are moved relatively to each other to thereby create a tribo-electric effect and generate a current in the metallic or measuring circuit.

With such an arrangement, the number of reciprocations per unit of time, of the known specimen, can be accurately controlled and the amplitude of those reciprocations can also be maintained constant. In addition, the pressure exerted by the chucked piece on the other piece of metal involved by the test may also be maintained substantially constant throughout the test. As will be disclosed throughout the further description, I also employed means for automatically timing the duration of each test, i. e., for

.automatically controlling the length of time during which the reciprocating tool is energized.

Figure 1 is a wiring diagram in which I have diagrammatically illustrated some of the instrumentalities included in apparatus embodying my invention. As there shown, a three-wire plug P is employed for connecting the apparatus to a source of alternating current. This plug includes a ground wire connection 6, which is shown as grounded and which is electrically connected to shields 1, 9 and I6 which are diagrammatically shown in dotted lines and will be further described. Leads II and I2 are shown as directly connected to the plug P and each includes a separate arm of a switch I3 and also a fuse I5. These power leads II and I2 are also directly connected to the terminals of the primary coil I5a of a transformer I5. The motoractuated reciprocating tool I6 is also electrically connected to the leads II and I2 by wire Il, switch or jack I6, wire I9, switch 20, wire 2l, wire 22, switch or jack 23, wire 26, wire 25, electrically-actuated switch or relay device 26 and wire 2l.

As illustrated, the transformer I5 is provided with two secondary windings |55 and I5c. The winding I5c is designed to develop 6.3 volts where the line voltage, delivered to the primary winding I5a is 110 volts. The secondary winding I5c is electrically connected to the filaments of a thyratron 2050) tube 36 and a diode rectifier (6X5/GT) tube 3l and also to the filament of a lamp bulb 32 for illuminating the galvanometer.

The secondary winding I5b is preferably designed to deliver volts under conditions such as above described in connection with the primary winding I5a. It is illustrated as forming a part of a well-known time relay circuit operating on the grid rectification principle. As shown, a multi-tap resistor 33 is shunted across the terminals of the winding I5b and one tap thereof is connected to one element of a capacitor 33 and also to the grid of the tube 30 through a resistor 35. The other element of the capacitor is also connected to the grid through a resistor 36 thus providing a drain-off circuit for the capacitor. The cathode of the tube 30 is connected to one terminal of the winding I5b through wires 3l and 38, electrically-actuated switch or relay 39 and wire 40. 'I'he wire 38 is connected to the other terminal of the winding I5b, thereby coinpleting a circuit when the switch or relay 39 is closed. A resistor 38 interrupts the wire 3B and, therefore. is included in the circuit when completed.

The plate of the tube 3U is connected to the energizing coil 4I of the normally closed relay 26 and through that coil to the wire 38. The screen grid of the thyratron is also connected to the wire 38 through a resistor 42. The energizing coil i3 of the relay 39 is connected to the lead II by Wire M and to lead I2 through wire 45, switch or jack 66, Wire 41, wire 2|, switch 20, switch or jack I8 and Wire I'I. The current to the filament of the lamp 32 is controlled by a normally closed relay [I8 the coil 49 of which is connected to the lead II by wire 50, wire 25, normally closedrelay 26 and wire 21. The other terminal of the coil '49 is connected to the lead I2 through wire 5I, wire 45, switch or jack 46, wire 4l, wire 2|, switch 26, Wire I9, switch or jack I8 and wire I1.

The test or measuring circuit is shown as including a galvanometer 52 which is in circuit with

clamps

53 and 54; Each clamp is in electrical contact with one of the two pieces (l0 and 1I) located in tribo-electric union and, starting with the clamp 53, the measuring circuit includes wire 53', switch or jack 55, wire 56, galvanometer 52, critical damping resistor B9, wire 5l, switch 5 or jack 5t, wire 59, the slide wire 60 of a slide wire potentiometer, the wire 6I and the clamp 54. The center tap of the slide wire 60 of the potentiometer is shown electrically connected to the cathode of the diode rectifier 3l by means of wire tt and switch or jack 64. The plate of the rectiner is connected to the slide arm 65 of the slide wire potentiometer by means of wire 58, switch or jack 5l, and wire 58.

The specimen of known characteristics is usually a small piece of metal and it is, therefore, convenient (although not necessary) to move it relatively to the piece to be tested or identified. For this reason, I have indicated the piece 'Ill as the reference specimen and the piece that is movable with relation to the piece to be tested, i. e., the piece III. It may also be assumed that the clamp 53 of Figure 1 represents the chuck of the reciprocating tool, that it is included in the measuring circuit and that it is operatively and also electrically coupled to the reference specimen lil. It may also -be assumed that the piece 'IIII to be tested is held stationary in a vise or is of such size that it remains stationary independently of the type andsextent of movement of, and the pressure applied by, the contacting piece llt. In any event, the piece to be tested is electrically connected into the measuring circuit and the clamp 54 is employed for that purpose. When the reference specimen l0, in electrical contact with the device 53, is placed in contact with the metallic part 'II to be tested and shown as engaged by the clamp 54, it is possible that the galvanometer 52 will indicate the presence of a current even before the pieces l and II are moved relatively to each other under conditions such as to create friction. Such a current How is undesirable and is caused chiefly by differences in the chemistry of the contacting parts throughout the measuring circuit, and possibly by some thermoelectric effect. The diode recter tl and the slide wire potentiometer ttl-tt are provided for the purpose of balancing out these undesired current ows. A movement of the arm t to one side of the center tap of the slide wire 60 will cause a positive bias to be impressed upon the circuit of the galvanometer. While movement of the arm 65 along the slide wire and on the other side of the center tap will impress a negative bias upon the galvanometer circuit. The extent of the bias thus imposed is determined by the position of the arm t5 around the slide wire. This results from the fact that when the filament of the diode rectifier tube 3i is heated, the cathode of that tube will emit electrons causing current to flow from the cathode to the plate of the tube (Edison eifect). It is for this reason that the cathode of the tube tl is connected to the center tap of the slide wire t@ and the position of the arm 65, around the slide wire t@ on one side or the other of the center tap, will determine whether or not negative or positive potential is imposed upon the galvanometer circuit and the intensity of that potential. I believe that such a use of the diode rectier is novel and I note that it provides a source of current for balancing out or off-setting undesired current ows in any circuit, such as the galvanometer or measuring circuit here disclosed.

In preparing for a tribo-electric test, care must be taken to provide clean surfaces on both pieces, involved by the test, so that a representative portion of the surface of each piece is in contact with the other piece during the union. Dielectric and 39 thus closing the circuit of conducting mill scale must be removed and other surface conditions not representative oi the core of each piece must be corrected. This is essential to accuracy of results. While the extent of the surfaces in contact with each other is not important, lt is, nevertheless, important that the contact between the surfaces be an intimate one throughout the duration of the test.

In initiating the test, the switch I3 is closed. This energizes the transformer I5 and, after the filaments of the tubes 30 and 3| are heated up, the apparatus is in readiness for a test. The reference piece 10. i. e., the piece of known chemical and metallurgical composition, is connected to the clamp 54 in such a way as to ensure a good electrical connection. The piece 'II to be compared with the piece 10 is then secured to the clamp 54 in such a way as to ensure a good electrical connection. Thus, it is apparent that each of the two pieces is included in the metallic circuit of which the galvanometer 52 forms a part. The cleaned surfaces 0f the two pieces 10 and 1I are then placed in intimate contact with each other thus closing the measuring circuit.

As previously indicated. the closing of this circuit may occasion a flow of undesired currents therein. After these currents are balanced out by adjusting the arm 65 of the slide wire potentiometer -65, the tribe-electric union between the contacting pieces 'I0 and'lI is completed by closing the switch 20. This causes the actuating motor ofthe reciprocating tool I 6 to operate and to reciprocate the reference specimen 10.

It will be understood that the clamp 53 not only represents means for electrically connecting the reference piece 10 to the wire 53' but also means for mechanically connecting it to the reciprocating part of the tool I6. Simultaneously with the completion of the tribu-electricunion between the pieces 1U and 1I, by the reciprocation of the piece 10, the relay 48 operates to open its normally closed contacts, thus opening the circuit supplying current to the galvanometer lamp 32, thus preventing illumination of the galvanometer indicating dial. The closing of the switch 20 also energizes the coil 43 and occasions a closing of the relay switch the thyratron tube 30. This tube will, therefore, become eiective after the negative bias, accumulated on the capacitor 34, has drained oif through the

resistors

35 and 36 to the point where the tube 30 will fire. Thus, it is apparent that the thyratron circuit acts as a time relay, the period of which will depend upon the extent of the charge accumulated on the capacitor 34. The firing of the tube 30 causes current to flow through the energizing coil 4I oi the normally closed relay switch 26 thereby actuating that relay to open the power circuit to the motor of the reciprocating tool I6. The opening of this circuit deenergizes the coil 49, thus closing the relay switch 48.

The closing of the switch 48 energizes the lamp 32, thus illuminating the calibrated scale mens 1li-1l, involved by the test, the period of the union, the intensity of the pressure occasioning the contact between the specimens, the frequency of the reciprocations of the piece 'l0 and4 the a-mplitude of the reciprocations. That is to say, the test will have been completed.

- If the galvanometer indicator discloses that the tribo-electric union did not occasion a current iiow during the test, a second test may be run during which the pressure between the two v\ieces and/or the time of the test is increased. If the galvanometer still discloses an absence of current flow, it can be assumed that the specimens 'l0- 1I involved by the test are identical from the standpoint of their chemical and metallurgical composition.

If current ow is observable at the completion of a test, this flow should increase proportionately as the time and/or press-ure is increased in order to constitute a valid indication of the chemical and/or metallurgical dissimilarity of the specimens. That is to say, if currentfiow is observable at the completion of a brief interval test but this current flow does not increase proportionately to an increase in testing time (other conditions being maintained substantially constant), then it can be assumed that the current flow is the result of some parasitic electrical effect which has occurred subsequent to the time of balancing the galvanometer circuit. Likewise, an increase in the contact pressure between the specimens in tribe-electric union should occasion a corresponding increase in current ow in the measuring circuit and a failure to obtain such an increase denotes an effect other than a triboelectric effect. For convenience of adjusting the period of each test, the resistor 33 will preferably be of such form that one or the other of its various taps may be readily connected to one element of the capacitor 34.

In Figure 1 of the drawings, the elliptical lines 9 and I0, which are shown electrically connected to the ground line 6, are employed for diagrammatically indicating that the metallic shields of the cables, connected with the various switches or jacks I0, 23, 46, G4, 58, 55 and 'l2 are all grounded.

As previously noted, I prefer to employ a type of relative movement, between two specimens, involved by a test, such that the point of contact, between the two specimens, moves with relation to each specimen. In Figure 2, I have illustrated an arrangement of apparatus and specimens which will accomplish such a result. As there shown, the special clamp 53 is intended to diagrammatically illustrate a form of clamp capable of being secured into the chuck of the reciprocating tool I6 and of being mechanically and electrically connected to one of the specimen pieces 10-1|. It will be noted that the clamp 53 is provided with a stem 14 which is bent at an angle of about 45 degrees. The portion of the stem remote from the clamp is intended to be secured into the chuck of the tool I6 and the tool i6, while operating, moves the clamp 53 back and forth in the direction of the arrows, shown associated with Figure 2. The piece 10, shown secured to the clamp 53, is then placed in contact with the other piece 1I, forming a part of the tribo-electric union. The contacting edges or surfaces of the piecesA extend at about 90 degrees to each other. Under such conditions, the reciprocations of the piece 10 will cause the point of contact between the pieces to travel along the line y-y on the piece 10 and :v -z' on the piece 1| and under conditions such that when the piece l0 is at one end of its stroke, the points y and a: will be in contact, whereas when the piece 10 is at the other-end of its stroke, the points :zz' and y will be in contact.

While I prefer this type of movement, it should be noted that the magnitude of the triboelectric effect is exactly the same independently of whether the point of contact between the two pieces moves with relation to one or both pieces. It, however, should be stated that a scoring of one piece or a work-hardening of the point of contact on one piece, where there is no scoring or work-hardening at the point of contact on the other piece, will occasion a marked tribo-electric effect even between two identical pieces. As to this, it should also be noted that unequal scoring of the surfaces of the two pieces involved by the tribe-electric union will occasion a marked effect even where the pieces are identical as to composition, whereas equal scoring of the two such pieces will occasion little or no effect.

It will, of course, be apparent that unequal scoring and spot work-hardening is minimized by so moving the pieces relative to each other that the point of contact is continuously changing on each piece. Conversely, a saw-like movement of one piece, with relation to the other, will contribute to unequal scoring and spot workhardening since, under such conditions, the point of contact remains substantially xed on one of the pieces. While a type of relative movement, which occasions a continuous movement of the point of contact on each piece, is highly desirable, I, nevertheless, prefer a rhythmic, cyclic type of relative movement of the pieces, i. e., a movement such as is obtained vunder conditions illustrated in Figure 2, wherein one piece is reciprocated under conditions such that the amplitude and the periodicity of the reciprocations are substantially constant.

I have discovered that all metals examined by me are either electrically positive or negative with respect to other specific metals. My experience, therefore, indicates that a tribo-electric series of all the various metals may be so arranged that metals heading the list are positive with respect to all metals later in the list. To illustrate, I note that as to the pure metals iron, copper and tungsten, iron is positive to both copper and tungsten, copper is positive to tungsten but negative to iron and tungsten is negative to both copper and iron. My experience also indicates that a similar electric series of alloys may be arranged. I refer first to ferrous alloys and note that S. A. E. 1020 (mild steel) is positive to both S. A. E. 416 (14% chromium steel) and S. A. E. 304 (18-8); that S. A. E. 416 is positive to S. A. E. 304 and that S. A. E. 304 is negative to both 1020 and 416. As a further example, I note that brass (major constituent copper, minor zinc) is positive to aluminum (major constituent aluminum, minor copper) and a high nickel alloy (containing about 60% Ni, about 14% Cr with remainder substantially all Fe); that the aluminum is positive to such alloy and the alloy is negative to both brass and aluminum.

While I have illustrated and described but one embodiment of the apparatus embodying my invention, it will be apparent that various changes, substitutions, omissions and additions may be made in the apparatus and that the procedural Steps, herein defined as part of my invention,

may be modied or varied without vdeparting from the spirit and scope o! my invention as defined by the appended claims.

What I claim is:

l. A method of comparing two pieces of metalr from the standpoint of their chemical and/or metallurgical composition, which consists in including each such piece in a metallic circuit, completing such circuit by placing such pieces in contact with each other, balancing out of such circuit such current iiow, if any, as takes place at the completing of said circuit, occasioning relative movement between said pieces while maintaining themin contact and in ascertaining the current flow, if any, in said circuit during such movement.

2. In an apparatus for determining the chemical and/or metallurgical identity or non-identity of two metal pieces, a measuring circuit, an electro-responsive device located in said circuit for indicating a value current flowing therein, means for connecting two contacting pieces into said circuit to close the same, with the pieces in series with each other and with said electroresponsive device, means for moving at least one such piece while maintaining the contact therebetween and while retaining said pieces in said circuit, and means for timing the operation of said piece moving means.

3. In an apparatus for determining the chemical and/or metallurgical identity of two metal pieces, a measuring circuit, an electro-responsive device included in said circuit, means for connecting two pieces to be compared into said circuit, so that placing said pieces in contact with each other closes said circuit with the pieces in series with each other and with said electroresponsive device, means for occasioning a flow of current through a portion of said circuit to odset such current flow, if any, as is occasioned by the closing of said circuit, a mechanism for moving at least one of said contacting pieces relatively to the other while both are retained in said circuit, and means for timing the operation of said mechanism.

4. In an apparatus for determining the chemical and/or metallurgical identity of two metal pieces, a measuring circuit, an electro-responsive device included in said circuit, means for connecting two pieces to be compared into said circuit, so that placing said pieces in contact with each other closes said circuit with the pieces in series with each other and with said electroresponsive device, means for occasioning a fiow of current through a portion of said circuit to offset such current flow, if any, as is occasioned by the closing of said circuit, an electrically actuated mechanism for moving at least one of said pieces relatively to the other while said pieces are retained in said circuit in contact with each other, and timing means energized simultaneously with the starting of said mechanism for timing the operation of said mechanism.

5. In an apparatus for determining the chemical and/or metallurgical identity of two metal pieces, a measuring circuit, an electro-responsive device included in said circuit, means for connecting two pieces to be compared into said circuit, so that placing said pieces in contact with each other closes said circuit with the pieces in series with each other and with said electroresponsive device, means including a diode rectiiier tube for passing current through a portion of said circuit to offset such current flow, if any, as is occasioned by the closing of said circuit, and

a mechanism for moving at least one of said pieces relatively to the other while said pieces are retained in circuit closing relationship.

6. Apparatus for determining the chemical and/or metallurgical identity or non-identity of two pieces of metal, which comprises a metallic circuit, an electro responsive device for indicating current flow within said circuit, means for connecting two pieces of metal to be tested into said circuit so that placing such pieces in contact with each other closes said circuit with said pieces located in series therein, means including a potentiometer and electronic vacuum-tube for occasioning a current ilow through at least a portion of said circuit to counterbalance such current iiow, if any, occasioned by the closing of said circuit and means for moving said pieces relatively to each other while retaining them in circuit closing contact.

7. In an apparatus for determining the chemical and/or metallurgical identity or non-identity of two metal pieces, a metallic circuit, an electro-responsive device located in said circuit for indicating a value of current flowing therein, means for connecting two metal pieces to be compared into said circuit so that placing said pieces in contact with each other closes said circuit with the pieces located in series with each other and with said electro-responsive device, means for occasioning a ow of current through at least a portion of said circuit to neutralize such current flow, if any, as is occasioned by the closing of said circuit, and means for moving at least one such piece so as to produce a rhythmic cyclic relative movement of said pieces while retaining them in circuit closing contact and while maintaining such neutralizing ow of current.

8. A method of determining the identity or non-identity of two metal pieces as to their chemical and/or metallurgical composition which consists in placing such pieces in frictional contact, occasioning relative movement between the pieces while maintaining such contact between them and determining the electrical potential occasioned by such movement while neutralizing such electrical potential occasioned by contact only of said pieces.

9. A method of determining the chemical and/or metallurgical identity of non-identityv of two pieces of metal, which consists in placing the two metal pieces in contact with each other, neutralizing such electrical potential as may be occasioned by the contact only of such pieces, then moving the pieces relatively to each other While maintaining such contact and determining the electrical potential generated by such movement while continuing to neutralize such potential as is generated by contact only of such pieces.

10. A method of determining the identity or non-identity of two metal pieces as to their chemical and/or metallurgical composition, which consists in placing such pieces in frictional contact, occasioning relative movement between such pieces while maintaining them in contact, timing the action of such relative motion and after a predetermined time determining the electrical out-put occasioned by such relative motion while neutralizing the effect of such electrical cut-put occasioned by contact only of such pieces.

11. A method of determining the chemical and/or metallurgical identity or non-identity of two pieces of metal, which consists in moving such pieces into frictional contact while they constitute a part of a metallic circuit, neutralizing the current flow, if any, within said circuit occasioned by the contact of such pieces. so moving such pieces relatively to each other that the point of contact therebetween moves relatively to both pieces, timing the period of such movement and indicating the current ow within such circuit at the end of a predetermined period of such movement while continuing to neutralize the current flow occasioned by contact of said pieces.

12. A method of determining the identity or non-identity of two pieces of metal from the standpoint of their chemical and/or metallurgical composition, which consists in including said pieces in a metallic circuit, placing such pieces in frictional contactwith each other and thereby closing such circuit, neutralizing such current flow, if any, as takes place Within said circuit at the closing thereof, moving said pieces relatively to each other for a determined interval while maintaining the conditions of contact and the type of such movement substantially constant, measuring the electrical potential, if any, occasoned by such movement during such interval and again moving such pieces relatively to each other while in contact with each other but under REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 759,096 Germakian May 3, 1904 1,502,330 Bernini July 22, 1924 1,922,792 Cain Aug. 15, 1933 2,003,024 West May 28, 1935 2,366,844 Doschek Jan. 9, 1945 OTHER REFERENCES Havenhill et al.: Journal of Applied Physics, vol. 15, Nov. 1944, pages 731-740.

National Bureau of Standards, Circular C438, issued June 10, 1942-, page 34.