Experimental Electrical Testing BY STUDENTS Compiled chiefly from data furnished by SCIENCE TEACHERS AND STUDENTS IN UNIVERSITIES, COLLEGE PREPARATORY SCHOOLS, AND HIGH SCHOOLS For the Science Teacher WESTON ELECTRICAL INSTRUMENT CO. NEWARK N. J. EXPERIMENTAL ELECTRICAL TESTING A COMPILATION, INCLUDING PRACTICAL ELECTRICAL MEASUREMENTS ACTUALLY PERFORMED BY STUDENTS MONOGRAPH B-4 APRIL, 1914. ISSUED FOR SCIENCE TEACHERS IN EDUCATIONAL INSTITUTIONS " Everybody needs to know something about the working of electrical machinery, optical instruments, ships, automobiles, and all those labor- saving devices, such as vacuum cleaners, fireless cookers, pressure cookers and electric irons, which are found in many American homes. We have, therefore, drawn as much of our illustrative material as possible from the common devices in modern life. We see no reason why this should detract in the least from the educational value of the study of physics, for one can learn to think straight just as well by thinking about an electrical generator, as by thinking about a Geissler tube." From ",P.ratical Physios."; BLACK & DAVIS. WESTON ELECTKICAL INSTRUMENT CO. NEWARK, N. J. COPYRIGHT. 1914 BY WESTON ELECTRICAL INSTRUMENT CO. CONTENTS SUBJECTS. PAGE Argument ...................................................... 5 (jeneral Laboratory Work ........................................ 7 Resistance Measurements .......................... .............. 11 A Complex Lamp Bank .......................................... 13 Testing Fuses ................................................... 17 Induction ...................................................... 22 The Photometer ................................................. 28 Incandescent Lamp Testing ...................................... 32 Electroplating .................................................. 34 The Use of the Electric Heater in Efficiency Tests .................. 38 The Electrolytic Current Rectifier ................................. 53 The Weston Direct-current Movable Coil System .................... 65 The Weston Alternating- and Direct-current " Soft Iron " System ..... 68 Co-operators ................................................... 70 An Appeal ..................................................... 78 EXPERIMENTS. / 1. Resistance of a Conductor by the Substitution Method .......... 11 2. Comparative Resistance of Various Conductors .................. 13 3. Constructing and Testing a Lamp Bank Rheostat ............... 13 4. Test of Fuses ............................................... 17 5. The Fusing Effect of an Electric Current ........................ 19 6. Currents Induced by Magnetism ............................. 24 7. Currents Induced by Electro-Magnetism ....................... 26 8. An Exercise in Photometry ................................... 28 9. Practical Incandescent Lamp Testing ........................... 32 10. Electroplating with Copper ................................... 35 11. The Electro-Chemical Equivalent of a Metal .................... 36 12. The Electric Disk Stove or Hot Plate .......................... 41 13. Cost of Operating and Efficiency of an Electric Flat-iron ........ 43 14. Boiling an Egg by Means of Electricity ........................ 46 15. The Immersion Heater ....................................... 49 16. Making Cocoa and Candy with the Aid of Electricity .......... 49 17. Testing a Nodon Valve with Dry Cells ......................... 55 18. Testing a Nodon with a Direct-current Service Line ............. 56 19. Testing a Nodon Valve with Alternating Current .............. 57 20. Efficiency Test of a Nodon Valve ............................ 58 21. Efficiency Test with Two Nodon Valves in Series .............. 59 22. Puncturing the Insulating Wall of a Nodon Valve .............. 59 23. Efficiency Test of a Commercial Electrolytic Rectifier .......... 62 3 ARGUMENT THE Weston Monographs were prepared with the definite object in view of attempting to co-operate with and assist science teachers in high schools and collegiate preparatory schools throughout this country. Their context is exclusively on electrical subjects; and each deals with a particular theme. For instance B-l dwells upon the manifest advantages of training students engaged in laboratory work by means of stand- ard apparatus, such as they will encounter in practical work after graduation. It also calls attention to the fact that it is inconsistent as well as unwise to attempt to perform modern pro- gressive laboratory work by means of antiquated and obsolete apparatus. It shows what should be done. B-2 contains a series of simple yet exceedingly instructive experiments, and presents suggestions that should be of great value in the preparation or amplification of an electrical course. It tells what could be done. B-3 briefly describes several standard high grade and thoroughly reliable instruments, economical in price and par- ticularly adaptable to high-school work. In this Monograph B-4, we have compiled interesting and important data which will indicate some of the experiments which are actually being performed in progressive High Schools in these United States. We accomplished this by reproducing the actual work of students without revision or alteration, together with sketches, data-sheets, reports and instructors' comments, as well as apparatus actually used. We desire to explain as briefly as possible how B-4 has been produced. Early in the Fall of 1913, we issued a letter to over 7000 science teachers on our list, in which we directed attention to 5 6 ARGUMENT the Monographs we had already issued, and requested sugges- tions relating to experiments in electrical measurements which they would like to see embodied in future Monographs. We were immediately deluged with replies, and as soon as it was feasible we began preparing data relating to the experiments most in demand. We then conceived the idea of asking science teachers to furnish us with these experiments, instead of preparing them ourselves; and wrote to a number of those who were fortunate enough to possess a modern equipment, inviting them to con- tribute some specified exercises. In this manner we hoped to fulfill the requests of science teachers by publishing the work of other science teachers. The experiments offered are reproduced verbatim; but we have in some instances either simplified or elaborated connec- tion diagrams. Otherwise the authority for the execution of the work is vested in the contributor cited. Necessarily there was much repetition, and it obviously became practicable to print only a few of the contributions we received; but we desire to gratefully acknowledge the assistance of those teachers whose work is not incorporated in this Monograph. Their tests were of great value to us, and in many cases it was exceedingly difficult to make a choice. Entirely aside from their intrinsic pedagogical value, the majority of these experiments have a significance which cannot fail to arrest the attention of the progressive instructor. They prove conclusively that the trend of physics teaching is toward the practical application of fundamental principles. They indicate also that laboratory work requiring the use of instruments of precision may be successfully performed by young students of either sex. In conclusion we desire to direct special attention to the Nodon Valve and Rectifier experiments; because they are not only of the greatest interest pedagogically, but since they also possess utilitarian properties, in that they indicate how a teacher who has only alternating current service available, may easily and cheaply transform to direct current; and thereby open up a greater realm of electrical experiments specially suited to the High School Laboratory. WESTON ELECTRICAL INSTRUMENT COMPANY. GENERAL LABORATORY WORK IN preparing the minds of beginners in experimental electrical work, and in directing their attention to the ethical as well as the material considerations involved, it would be to their advan- tage to hear the following comments, which are adapted from an introduction to a loose leaf manual in Electrical Measurements. We are indebted to their author, Prof. James Theron Rood, Ph.D., of Lafayette College, for permission to use them. I. PREPARATION FOR LABORATORY WORK A well-trained experimenter, in any department of science, may at once be known by his ability to make clear, concise state- ments of the laws and phenomena of that department in which he is especially interested. An electrical laboratory is a place designed to help men to acquire such characteristics, but it is of value to any man only in proportion as he approaches his work therein with the proper spirit, imbued with the desire to do and learn. The first requis- ite is to come to the laboratory knowing fully what you are to do, and how you are to do it. Read in advance the direction sheets for the given experiments, look up the references, be prepared to get the most out of your performance of the given experiment. If you do not come so prepared, you are almost sure to become confused as to what must be done and as to the order which must be followed. Required observations are likely to be omitted, time may be wasted on useless readings, interest- ing and valuable phenomena may escape your attention or be wrongly interpreted, and you may finish with a confused instead of a clear conception of the method and the value of the test. Make yourself master of the experiment, in the preparation for it, in the performance of it, and in the writing of the report 7 8 GENERAL LABORATORY WORK about it. The students who must continually run to an instruc- tor for direction and advice can never rise very far. II. PERFORMING THE EXPERIMENT No general advice or directions can be given which will cover each and every experiment. Each test brings its own peculiar- ities, its own difficulties; but there are invariably certain things which mark the trained and careful experimenter. Some of these are given in what follows: III. APPARATUS All apparatus used in testing should be most carefully handled. What company would retain an employee who mis- used its instruments or machines? Accidents may happen to even the most careful experi- menters, but whenever they do occur, they should be reported at once. Placing the injured instrument back in its place without reporting its injury is the work of a sneak. Such action may result in the apparatus remaining unrepaired until a time when a co-worker, needing the apparatus for immediate use, discovers that it is injured and that it may have to be sent away for repairs. He is thus kept back in his work when, had the injury been known, suitable repairs might have been made before the apparatus was again needed. IV. DIAGRAMS Before beginning any experiment, make a clear diagram of the proper arrangement of all circuits to be used, with all connections, instruments, resistors, switches, cut-outs, etc., shown by the conventional symbols. Use heavy lines for indicating conductors carrying large currents, such as electric power service wires, bus-bars, feeders for motors, etc., and light lines for potential circuits, such as leads to the e.m.f. terminals of wattmeters, voltmeters, etc. Submit this diagram to the instructor for his criticism and approval. Then connect up according^ to this diagram. Make no changes in it without the approval^of the teacher. GENERAL LABORATORY WORK V. INSTRUMENTS Almost without exception, all makes of ammeters have un- insulated, metal binding-posts, while voltmeters have posts encased in insulation. The two kinds of meters can thus be at once told apart. Milli voltmeters are frequently used as ammeters by connecting shunts in the line, the potential drop across these shunts being proportional to the current; the read- ings of the meter when its leads are placed across the terminals of the shunt will be proportional to the current flowing, and may be read directly in amperes. When so used the values of the scale divisions of the meter will depend upon the partic- ular shunt used as well as upon the meter leads. Each milli- voltmeter must always be used both with its own shunt and its own leads. The shunt is always connected in the line and the milli voltmeter across the shunt. Remember, ammeters go in the line, voltmeters go across the line. Never lay instruments on the floor or on a chair. Always put them on a table and then pass the wires through holes in the edge of the table or else so fasten them that there can be no chance of an instrument being pulled down onto the floor. If any instrument has a zero error reading, allow for it in your readings, or have it reset by means of its zero adjusting device. NEVER OPEN OR CLOSE A CIRCUIT AT ANY AMMETER BINDING POST. Trace out the polarity of any D.C. circuit before connecting in an instrument. Be sure that the current flows through the instrument in the right direction. If it does not, OPEN THE CIRCUIT BEFORE REVERSING ANY AMMETER LEADS. REVERSE VOLTMETER LEADS AT THE CIRCUIT END, NOT AT THE METER. Read all meters to one-tenth of the smallest division. Look for any parallax when making a reading. VI. ORDERLINESS During the performance of all tests, see that all instruments, switches, lines, etc., are kept in an orderly condition and not allowed to become a confused maze. After finishing an experi- ment, see that all instruments, rheostats, lamps and other pieces of apparatus are replaced in their proper places in their cases. Coil up and put away all lengths of wire. Put everything 10 GENERAL LABORATORY WORK back in its place and leave the apj I 3 as weO as all the tables, etc., free from all \\ires and in perfect order ready for the next users. When finished, replace covers on all motors or dynamos used. Next to success in the performance, orderliness in the handling of laboratory apparatus is the most important thing to be learned in a laboratory. Your care in this respect will be considered in determining your term grade. VH. REPORTS To be able to write a satisfactory report of an investigation is an art and accomplishment that should be the desire and pride of every engineer, in even* walk of science. It is the keystone of all science. In its essence, an engineer's report is a why. a what, a how. a this and a therefore. A good engineer must have knowledge, judgment and common sense. The laboratory, rightly used, is the best place for the development of such powers, and should be valued as such. Let your laboratory motto be: WORK -OBSERVE THINK EXPERIMENTAL ELECTRICAL TESTING EXPERIMENT NO. 1 RESISTANCE MEASUREMENTS The following experiments were selected from a number kindly contributed by Mr. William F. Evans, Instructor in Physics, Girls' High School, Brooklyn, N. Y. They are copied from the laboratory note-book of the girl who did the work. A modification of these methods is used in shop practice for a preliminary measurement of resistance wires in course of manufacture. To eliminate errors due to a variation in cur- rent, the wire and the rheostat are both connected with one pole of the cell, and a double-throw switch is used, so that the at may be adjusted until the same deflection Is obtained when current is passed through either circuit in rapid succession. Reference, " Laboratory Exercises." Fuller and Brownlee, page 270. Resistance of a Conductor by the Substitution Method Apparatus. Weston ammeter: dry cell; rheostat, 50 cm., No. 30 German silver wire; and leads. (1) Connect up the cell, the ammeter and the unknown resistance in series, being sure that all contacts are dean and all connections tight. See Fig. 1. (2) Substitute the resistance box (with all plugs removed) for the unknown resistance and then decrease the resistance of the circuit until the current is the same as before. See Fig. 2. (3) What then is the resistance of the 50 cm. No. 30 G - 11 12 EXPERIMENTAL ELECTRICAL TESTING STUDENT'S REPORT (1) I connected up as in diagram the cell, the ammeter, and the unknown resistance (50 cm. No. 30 German silver wire), FIG. 1. RESISTANCE MEASUREMENTS. (Reproduced from Student's Sketch.) Evans' Method. Instrument Used is a Model 280, Weston Ammeter. Range 5 Amperes. being sure that all contacts were clean and all connections tight. 6 amperes. (2) I substituted the resistance box for the unknown resist- ance with all plugs out, and reduced the resistance of the cir- C FIG. 2. RESISTANCE MEASUREMENTS. (Reproduced from Student's Sketch.) Evans' Method. Instrument Used is a Model 280, Weston Ammeter. Range 5 Amperes. cuit by putting in plugs until the reading of the ammeter was the same as before 1.8 ohms. COMPARATIVE RESISTANCES OF CONDUCTORS 13 (3) The resistance then of 50 cm. of No. 30 G. S. wire is 1.8 ohms, because the reading was the same when the resist- ance box was connected as when the German silver wire was connected. EXPERIMENT NO. 2 COMPARATIVE RESISTANCES OF CONDUCTORS Apparatus. As in preceding experiment; together with other wires of various sizes. OBSERVATIONS Length of Conductor. Area of Cross-section . Amp. Ohms. (1) Varying Lengths (1) 50 cm. G. S. wire (2) 100 cm. G. S. wire (3) 150 cm. G. S. wire .05 sq.mm. .05 sq.mm. .05 sq.mm. .60 .32 .20 1.8 3.4 .6 (2) Varying Areas . . . (1) 50 cm. G. S. wire (2) 50 cm. G. S. wire (3) 50 cm. G. S. wire .05 sq.mm. . 10 sq.mm. . 15 sq.mm. .60 1.04 1.34 1.8 .8 .5 (3) Varying material . (1) 50 cm. G. S. wire (2) 50 cm. brass wire (3) 50 cm. copper wire .05 sq.mm. .05 sq.mm. .05 sq.mm. .65 2.28 3.70 1.9 .3 .1 Description. I connected up the German silver wire as in preceding experiment. Then I substituted the resistance box as in preceding experiment. First I used 50 cm., then 100, last 150 cm. of German silver wire. Next I used wire with .05 sq. mm. cross section; then 10 sq.mm., finally, 15 sq.mm. After this I used 50 cm. of brass and 50 cm. of copper wire in place of the German silver wire. March 21, 1913. EXPERIMENT NO. 3 CONSTRUCTING AND TESTING A LAMP BANK RHEOSTAT In commercial work, adjustable rheostats are extensively used; in fact they are indispensable when current from service lines is employed for experimental purposes. For precision tests in laboratories, rheostats that are non- 14 EXPERIMENTAL ELECTRICAL TESTING inductive and which have a negligible temperature coefficient are preferable and often necessary, but in general commercial testing adjustable lamp bank rheostats are most in demand for current regulation, or for building up a load. The rheostat described in this experiment should appeal to the science teacher because it. is simple in construction and yet permits a wide range of adjustment owing to the ingenuity of its designer. This rheostat was designed by Charles P. Rockwell, and constructed by him with the assistance of Gordon R. Milne, Barringer High School students, Newark, N. J. The tests made with it are their joint work. FUSES FIG. 3. A Complex Lamp Bank. Following is their own description: This board was designed to allow any number of lamps, up to twelve, to be connected in multiple, series, or multiple series. An oak board was obtained from the school shop. Accord- ing to plan, a Perkins 25 amp. double-pole single-throw switch and a fuse block were placed at the extreme right, four Perkins single throw, single-pole switches were placed next to these, two for ingoing and two for returning current. Two other Perkins switches placed next allowed current to cross over to different banks of lamps. Twelve sockets w T ere screwed at equal dis- tances from each other. TESTING A LAMP BANK EHEOSTAT 15 The small cut-out switches were made by bending copper strips into jaws for receiving copper strips as blades. Holes were bored to receive jaws which were sealed in place with seal- ing wax. Connections were made and lamps were screwed in as shown in Fig. 3. APPARATUS AND MATERIALS REQUIRED 195 WATTS < -OCh OO 00 OO- 128 WATTS 256 WATTS 1 Weston voltmeter. 1 W^eston ammeter. 1 portable testing set. 1 oak board 18X40 ins. 1 Perkins knife switch, 25 amp., double pole, single throw. ^[6 Perkins knife switches, 25 amp., single pole, single throw. Sheet copper for mak- ing 27 switches (jaws and blades) which may be replaced with single-throw switches. 1 Edison double-plug cut-out. 12 Bryant porcelain receptacles, keyless. 12 carbon filament 32 C.P. lamps. 2 fuses, mica cap, 15 amp. 15 ft. No. 14 (B. & S. gauge) bare copper wire. DIRECTIONS FOR OPE- RATING AND TESTING FIG. 4. Trumbull single-pole, 122 WATTS ooo ooo ooo 162 >WATTS FIG. 5. IV, V, VI, VII, VIII. T, U y V, W, X. NOTE. All switches not specified closed must be open. For all lamps in multiple: Close III, C, D, E, F, G, H, K, L, M, N, 0, P, S, 16 EXPERIMENTAL ELECTRICAL TESTING For all lamps in series. Close III, VI, IX. A, F, I, K, Q, V, W, P, G. FOR MULTIPLE SERIES GROUPING Three groups in series, each group containing four lamps in multiple. Close all except IV, if, VII, VIII, IX. Two groups in series, each group containing four lamps in multiple. Close all except III, V, VII, VIII, IX. -oooo- oooo 57 WATTS FIG. 6. ARRANGEMENT Multiple Watts. No. of Lamps. Series Watts. MULTIPLE SERIES. See Fig. 4 Watts. Groups of No. in Mult. 124 248 368 485 585 695 845 955 1080 1197 1310 1420 1 2 3 4 5 6 7 8 9 10 11 12 125 60 37.5 27 20 15 12.5 10 8 7 6 5 2 in series 2 in series 2 in series 2 in mult. 3 in mult. 4 in mult. 128 195 256 MULTIPLE SERI 3 in series 3 in series 3 in series ES. See Fig. 5 2 in mult. 3 in mult. 4 in mult. 80 122 162 MULTIPLE SERI 4 in series 4 in series 4 in series ES. See Fig. 6 2 in mult. 2 in mult. 3 in mult. 57 60 85 WATTS PER LAMP IN ABOVE ORDER 1st COLUMN Lamp No 1 2 3 4 5 I 6 1 7 . 8 [ 9 i 10 i 11 ,2 Watts 124 124 120 120 100 110 150 1 110 135 i 118 1 113 1 110 TEST OF FUSES RESISTANCE PER LAMP 17 Lamp No. 1 2 3 4 5 6 7 8 9 10 11 12 Res Hot 112 112.2 116 116 139.2 126.3 124.2 126.3 118.8 118.0 123.2 126.3 Res Cold 225 230 240 230 235 235 230 245 225 242 235 240 R (hot) was when filaments were incandescent. V 2 Formula used R ~= or R 118 2 W ' R (cold) was when lamps were at room temperature (22 C.). Results were obtained by measurement with a portable testing set. EXPERIMENT NO. 4 TEST OF FUSES' From Lafayette College, Department of Electrical Engineering, Labora- tory Direction Sheets. Available through the courtesy of the author, Professor J. T. Rood. References: Barr, Direct Cur. Elec. Eng., p. 479; Swenson and Franken- field, Vol. I, p. 342; Standard Handbook for Elec. Engs., p. 585; Foster's Handbook, pp. 217, 1275. Purpose. Every electric circuit should be provided with some form of apparatus designed to prevent the flow of any excessive current which might start a fire or burn out any appa- ratus. The insurance companies require that all lighting and motor circuits shall be so fused or protected that the current- carrying wire shall never be overheated. Such protective devices are called cut-outs. They may be pu tinto two classes, fuses and circuit breakers. Fuses, according to their arrangement, may be divided into three classes, open, expulsion and enclosed. Circuit breakers are somewhat more convenient, but are much more costly and occupy more space. They are better for cir- cuits carrying large current, or where the circuit is liable to be opened or overloaded frequently, since they are more sure of opening the circuit. Construction. Fuses are merely strips of metal of such shape and material as will fuse or " blow " before any excess current can flow for any length of time. The I. R. losses in the 18 EXPERIMENTAL ELECTRICAL TESTING metal due to the current passing causes the strip to become heated. If the heat is generated faster than it can be radiated, the fuse material melts and the circuit is thus opened, provided the arc does not hold between the terminals of the fuse block on account of the metallic vapor which may be left in the air between them. This limits the amount of current which a given fuse can safely break, unless there is provided some means of expelling the hot vapor (expulsion fuses), or of condensing it (enclosed fuses). In this last the vapor is supposed to be immediately condensed in the spaces between the granules of the non-inflammable, non-conducting material which fill the tubes. On account of the variation of the alloy in the different parts of the fuse wire, as well as on account of the effect of air currents, open fuses cannot be depended upon to always blow at the same current with the same length and diameter of fuse wire. For open fuses alloys of lead, antimony and bismuth are mostly used. Enclosed fuses are mostly of zinc. For large fuses copper is sometimes used, but it is liable to hold the arc through its vapor. Object. The object of this experiment is to test some commercial fuse wire and to determine the relation (a) between length and the fusing current (6) between diameters for this last, all diameters of wires tested should be of the same make) , (c) to investigate the construction and action of some types of enclosed fuses. Apparatus. Various diameters of fuse wires, fuse block with adjustable terminals, adjustable resistor, Weston ammeter and inch scale, also line switch. Part I. Set the terminals of the fuse block 1J inches apart in the clear and insert a length of fuse wire. Connect the fuse block in series with the ammeter, adjustable resistor and switch; and connect the whole across the D.C. supply circuit. See that the resistance is set to allow only a small current to flow, close the switch and slowly increase the current until the fuse blows. Repeat with the same size of wire for fuse lengths of 2, 2J, 3, and 3J inches. Repeat this series for all the dif- ferent diameters of wire given you. Record make of wire, rated capacity, and blowing current. Calculate and record the per- centage ratio between the rated capacity and the blowing cur- rent. Note carefully the construction of each. THE FUSING EFFECT OF AN ELECTRIC CURRENT 19 Report. Describe what you did. Plot curves showing (a) relation between length and fusing current for wires tested, (6) relation between diameter and fusing current for a given length of fuse. The form of curve for this last is usually: *-(//)*, where d = diameter of wire ; / = fusing current, and a = constant depending on the composition of the wire. Give good sketches of the construction of the enclosed fuses tested and give description of the details of each. Questions, (a) Do you think the size or mass of the ter- minals of the fuse block can affect the value of the fusing current? (b) If, so, how? (c) Would this effect be proportional for all lengths of the fuse wire? Why? Why should the current in every case be increased slowly? Why should the enclosed fuses be given a preliminary heating before being blown? EXPERIMENT NO. 5 THE FUSING EFFECT OF AN ELECTRIC CURRENT The following experiment on fuses was supplied by Mr. Milton M. Flanders of the Bliss Electrical School, Takoma Park, Washington, D. C. It is so clean-cut and practical that comments are superfluous. Sketch is a reproduction of the one sent in by the students performing the test. TEST NO. A-400 HEAT A study of the fusing effect of an electrical current. OBJECT OF TEST To determine the current and time required to melt fuses under 'various conditions. 20 EXPERIMENTAL ELECTRICAL TESTING APPARATUS REQUIRED 1 ammeter (0-100) 1 rheostat 1 stop watch 1 thermometer Various fuses 1 circuit breaker 1 switch Connecting wires CONDUCT OF TEST I. Preparation. Set up the apparatus as per diagram, con- necting to a source of low potential and high current, as a stor- CIRCUIT BREAKER AMMETER FIG. 7. STUDY OF THE FUSING EFFECT OF AN ELECTRICAL CURRENT. (Reproduced from Students' Sketch.) Flanders' Method. Instrument Used was a Model 1, Weston Ammeter. Range 100 Amperes. NOTE. For all ordinary laboratory work, fuses that will " blow " at 1 to 20 amperes will suffice, and an ammeter of lower range than the above will be preferable. age battery. Close switch S and after inspection by instructor, admit current and correct polarity of ammeter if necessary. See Fig. 7. II. Operation, (a) Admit current to 200 per cent rating of fuse under test, holding this constant by means of the rheo- stat R. Open switch 'S and simultaneously start stop-watch. Note the exact time required for the fuse to open the circuit. Repeat at least three times. (6) Repeat above with different fuses, as directed. (c) Repeat above on increasing current, the rate of increase being 1 ampere per minute, and tabulate results. THE FUSING EFFECT OF AN ELECTRIC CURRENT 21 (d) Repeat operation (a) with the fuse wire in contact with some foreign insulating substance. (e) Repeat operation (a), first raising temperature of fuse 50 C., by means of a heating chamber. III. Calculation. Tabulate all results as indicated below: Fuse. Wire. Length. Deg. C. Rating. Amps. Time. Note. Link Shawmut 1.625 17.8 6 12 10 11 11 Avg.l0.66+ REPORT ON TEST No. A-400 Instrument used: Weston Model 1, Ammeter No. 5378. Centigrade Ther- mometer No. 3. DATA OPERATION (a) Type. Wire. Length. Ins. Temp. Deg. C. Rating, Amps. Amps. Time, Sec. Remarks. Daum Damn Shawmut Shawmut 1.625 1.625 22 22 6 6 12 12 8.6 7.2 Average Time Daum Shawmut 1.625 22 6 12 10.0 8.93+ sec. OPERATION (6) Type. Wire. Length. Ins. Temp. Deg. C. Rating, Amps. Amps. Time, Sec. Remarks. Link Link Shawmut Shawmut 1.625 1.625 17.8 17.8 6 6 12 12 10 11 Average Time Link Shawmut 1.625 17.8 6 12 11 10.66+sec. OPERATION (c) Type. Wire. Length, Ins. Temp. Deg. C. Rating, Amps. Amps. Time. Sec. Remarks. Daum Shawmut 1.625 21 6 12 12 min. 4 sec. Daum Shawmut 1.625 21 6 10 9 min. 20 sec. Daum Shawmut 1.625 21 6 10 9 min. 12 sec. 22 EXPERIMENTAL ELECTRICAL TESTING OPERATION (l The amount of any metal which a current of one ampere will deposit in one second is called the electro-equivalent of the metal. For one metal this amount is always the same. Con- sequently this is a very accurate way to measure electricity. (Current strength.) " (signed) L. O. GREENE." March 6, 1913. Instructors' appended comments: " The method of dealing with the varying current should have been explained. " In which direction does the metal in a plating solution always travel? Upon which electrode is it deposited? " Copper plating is of great commercial importance because iron and steel are always plated with copper before giving them a finishing coat of nickel. COMPILER'S NOTE. EXPERIMENT NO. 11 THE ELECTRO-CHEMICAL EQUIVALENT OF A METAL Substantially the same experiment as the foregoing is given herewith. It was contributed by Mr. Arthur H. Killen, In- structor in Physics, Flushing High School, Flushing, New York. This experiment was performed and the report written by one of the senior students.* It was accompanied by a very creditable sketch which we reproduce. (See Fig. 12.) Experiment. To find the electro-chemical equivalent of a metal. Object. To find the electro-chemical equivalent of copper. Apparatus. Two strips of copper, a copper sulphate solu- tion plating bath, a Daniell cell, a Weston ammeter, wire, wire connectors. * Mr. Killen informs us that the student's age was 18 years. THE ELECTEO-CHEMICAL EQUIVALENT OF A METAL 37 Work Done. I carefully weighed a strip of copper which was to be plated. I connected, in series, the Daniell cell, the Weston ammeter and the two strips of copper (the one care- fully weighed) and another which had been placed in the copper sulphate solution electroplating bath. At intervals of one min- ute, I took readings of the Weston ammeter during forty minutes and averaged them to find the amperage or current strength during the forty minutes. I then removed the strip on which SULPHURIC ACID SOLUTION COPPER ON WHICH PLATE IS TO BE DEPOSITED DANIELL CELL COPPER FROM WHICH PLATE IS TO BE TAKEN COPPER SULPHATE SOLUTION ELECTRO PLATING BATH FIG. 12. THE ELECTROCHEMICAL EQUIVALENT OF A METAL TEST. (Repro- duced from Student's Sketch.) Killen's Method. Instrument Used was a Model 1, Weston Standard Ammeter. Range 2 Amperes. the copper was deposited from the electroplating bath and care- fully rinsed and dried it. I then reweighed it. OBSERVATIONS : Weight of strip to be plated 22 . 952 grams Weight of strip to be plated after forty minutes. 23 . 532 grams Amount deposited in forty minutes 58 gram Average amperage or current strength 73 ampere Amount deposited by .73 ampere in one hour . . 87 gram Amount deposited by 1 ampere in one hour. ... 1 . 191 grams Amount deposited by 1 ampere in one second. . .0003308 gram Conclusions. The electro-chemical equivalent of copper is .0003308 gram, that is .0003308 gram of copper is deposited by one ampere in one second. 38 EXPERIMENTAL ELECTRICAL TESTING MATHEMATICAL WORK 1st weight of object to be plated ...... 22 . 952 grams by .73 amp. Weight of object to be plated after forty minutes .................. 23 . 532 grams by .73 amp. Weight of deposit at end of 40 minutes . . .58 gram by .73 amp. .58 ^ = .0145, wt. deposited in one minute by .73 ampere. .0145X60 = .87, wt. deposited in one hour by .73 ampere. 87 : =^ = 1.191+wt. deposited by one ampere in one hour. ./ o 1 191 .00033083, wt. deposited by one ampere in one second. Sylvanus Thompson gives .0003281 as the electro-chemical- equivalent of copper. (Signed) HENRY GREENBERG, (A. H. K., Instructor.) THE USE OF THE ELECTRIC HEATER IN EFFICIENCY TESTS.* By ERNEST REVELEY SMITH, Syracuse North High School. We are living in an age of commercialism. The relation of output to input is the great factor which determines our investments whether large or small. What is so general about us cannot fail to enter our laboratories. The toys that have been used so long as equipment are rapidly disappearing, their purposes well served. In their places are coming the newer commercial appliances, the experimental uses of which commend themselves instantly to the boy or girl as something worth while. Among the commercial offerings to the Physics laboratory, few have greater possibilities than the various types of electric heaters. The very fact that the electric stoves, flatirons, immer- sion heaters, etc., are taking their places among the things of our every day life makes the use of them in the laboratory both interesting and profitable. * Reprinted from School Science and Mathematics, Vol. 13, 1913. Avail- able through the courtesy of the author. COMPILER'S NOTE. THE ELECTRIC HEATER IN EFFICIENCY TESTS 39 Also they are the most adaptable of ^any of the laboratory equipment for work along efficiency lines, since all that is neces- sary for performing the experiment, besides the heater itself and the sources of current, is common equipment found in every laboratory. Generally we use an electric stove, with a voltmeter and an ammeter of suitable ranges, a flat bottom aluminum sauce pan, a watch and a thermometer. The ammeter is connected in series with the stove and the voltmeter shunted across its terminals, see Fig. 13. (A watt- meter may be used in place of these instruments.) While the kettle, and the kettle with the water are being weighed, the cur- rent is turned on through the stove, so that it may come up to VOLTMETER AMMETER TO D.C. LINE FIG. 13. INSTRUMENTS SHOWN ARE WESTON MODEL No. 1, VOLTMETER AND AMMETER. Alternating Current Apparatus may be Substituted. the normal working temperature. In this way very little heat is absorbed by the stove itself during the actual tests. The temperature of the known weight of water is now taken and the kettle placed on the stove just as the stop watch is started. Voltmeter and ammeter readings are taken every min- ute and their average readings used, since there is usually con- siderable variation in the potential of city currents. At the end of a given time (ten minutes), the temperature of the water is read after stirring, and the current is cut off. From the average current and fall of potential through the stove, its resistance is computed. The heat developed in the stove is computed from the well-known formula, calories = 0.24C 2 J^. The water equivalent of the kettle is found from 40 EXPERIMENTAL ELECTRICAL TESTING its mass and specific heat. Then the heat absorbed is the mass of the water including the water equivalent of the kettle, multi- plied by the change in temperature. The efficiency is now obtained by dividing the calories absorbed by the calories devel- oped. The efficiency tests that have been made in our school for the past three years have given results varying from 45 to 50 per cent with one stove and from 65 to 70 per cent with another. This experiment may be varied in several details. The apparent efficiency will be raised from 10 per cent to 15 per cent by using a large amount of water in place of 400 or 500 grams. Covering the kettle will usually raise the results by 3 per cent or 4 per cent. Again enclosing the kettle and stove in an asbestos jacket will give a result some 5 per cent to 10 per cent higher. This jacket is easily made from asbestos sheeting. Another variation brings into use the heat of vaporization. The experi- ment is continued until part of the water has boiled away. The kettle and contents are then weighed. The heat absorbed is equal to the sum of the heat necessary to bring all the water to the boiling point and that required to vaporize the water lost by boiling. This method will give results slightly higher than the first. The immersion heater (see Fig. 14) gives much higher re- sults than the stove. Our tests have shown an efficiency vary- ing from 90 per cent to 98 per cent. The heater is tested in the FIG. 14. THE IMMERSION HEATER, same way as the stove. For general use about a laboratory this device is very satisfactory as it will heat water more quickly than gas and may be used with any kind of a dish. The flatiron makes an excellent stove. In fact, many manu- facturers furnish a stand to hold it inverted as well as a dish shaped to fit its working surface. Its efficiency is not as high as the immersion heater or stove, ranging from 40 per cent to 60 percent, depending largely upon the shape of the kettle. THE ELECTRIC DISK STOVE OE HOT PLATE 41 In laboratories having electricity but no stove, an incandescent bulb may be used for efficiency tests. If the experiment is per- formed first with a covered opaque calorimeter, and then with a glass jar, the relative amounts of energy given off as heat and light may also be determined. In any of the above experiments the cost of electricity may be easily computed. If the pupil has found, earlier in his work, the cost of using a gas stove or burner for a similar length of time, he now has data for an interesting comparison. Usually I divide the class into several squads of five or six for these experiments. While one squad is performing this experi- ment, the other members of the class are working on an experiment for which we have individual apparatus. One pupil from each squad weighs the kettle and water, another reads the thermometer, another has charge of the wiring, while others read the voltmeter and ammeter or hold the watch. This insures the constant attention of each member of the squad since he has something to do which is definite and vitally important to the experiment. Of course, the entire experiment may be performed by two pupils, if desirable, or made a class exercise, letting several pupils make the readings for the class. Which- ever way it is done, it furnishes one of the most instructive as well as popular experiments in our laboratory. EXPERIMENT No. 12 THE ELECTRIC DISK STOVE OR HOT PLATE * Contributed by Mr. H. C. PHILIPPI, Head of Science Department, State Normal School, Bellingham, Washington. Object. To determine the efficiency of an electric disk stove or hot plate. Apparatus. Electric disk stove; Weston voltmeter; Weston ammeter; two-quart copper tea-kettle; thermometer; balance and weights; watch. See Fig. 15. * Contributor states: "The results are those actually obtained by members of my class." COMPILER'S NOTE. 42 EXPERIMENTAL ELECTRICAL TESTING For convenience in making connections the plug and flexible cord are removed from the stove, the stove mounted upon a board and its terminals permanently attached to binding posts in the board. The connections are, of course, those of any electrical power test. Before making the test which is to A. C. LINE FIG. 15. EFFICIENCY TEST OF AN ELECTRIC DISK STOVE OR HOT PLATE. (Reproduced from Students' Sketch.) Philippi's Method. Instruments used were Model 155 Weston A. C. Ammeter, range 10 amperes, and Model 155 Weston A. C. Voltmeter, range 150 volts. These instruments may also be used with direct current. become a matter of record, it is well to make a preliminary test to get the stove into a steady thermal state. With the two- quart kettle, it will be found convenient to use about four pounds of water and allow current from 110-volt lighting mains to pass for about ten minutes. If the current runs much above five or six amperes, the time must be shortened. COST OF OPERATING AN ELECTRIC FLAT IRON 43 RESULTS OBTAINED BY STUDENTS Trial (1). Trial (2). Trial (3). Weight of water used 4.4 lb. 4.41b. 4.41b. Weight of tea-kettle 1 lb 1 Olb. l.Olb. Water equivalent of tea-kettle aDDr 1 lb. 1 lb. 0.1 lb. Initial temperature Fahrenheit Final temperature 66.2 129.2 59.0 123.8 59.9 123.8 Rise in temperature. ,. Average voltage applied Average current in amp 63.0 107.0 4 95 63.8 107.0 4 95 62.9 107.0 4.95 Time current ran. . . 10 min. 10 min. 10 min. Heat gained (B.T.U.) Power input (watts) 283.5 530 287.1 530 283.0 530 Energy input (watt-sec.) (Joules) Heat equivalent of this energy 1055 watt-sec. = 1 B.T.U... . Efficiency of stove and kettle . Average efficiency Cost per hr. to operate this stove at lOc. per kw. hr 318,000 301. 4 B.T.U. 94.0% 94.4% 5.3c. 318,000 95.2% 318,000 93.9% EXPERIMENT No. 13 COST OF OPERATING AND EFFICIENCY OF AN ELECTRIC FLAT IRON Contributed by Mr. F. H. BEALS, Barringer High School, Newark, N.J. Object. To determine (1) Cost of ironing roller towels. (2) Efficiency of an electric flatiron. Apparatus. Electric flatiron weighing 5.8 pounds rated as weighing 6 pounds and using 110 volts and 4.2 amperes, ironing board 38"X14J", having no padding but covered with a roller towel stretched over the surface, dampened towels, Weston wattmeter (150 volts and 5 amperes), fuse blocks and connections, balance, scales and weights. See Figs. 16 and 17. Performed by ELIZABETH ARCULARIUS. Assisted by RUTH A. HUSK and KATHARINE VAN ALEN. MANIPULATION Directions. Sprinkle towels in preparation for ironing. Con- nect up iron and wattmeter as shown in diagram, Fig. 17. Let the current run 2J minutes to heat the iron. Iron rapidly so 44 EXPERIMENTAL ELECTRICAL TESTING as to waste as little heat as possible. To find the number of calories required to evaporate water, allow 80 calories per gram to heat from room temperature to temperature of evaporation, and 536 calories to evaporate water. Let A represent output in calories = loss of weight X (536 +80). To find heating power of current, let B represent input in calories = watts X sec. X. 24. To find efficiency use A + B. *To find cost allow 10 cents per K.W. hr. Cost = watts -f- 1000 Xhr.XlOc. FIG. 17. BEALS' WATTMETER METHOD. (Reproduced from Connection Chart.) Instrument used was a Model 16 Weston Wattmeter No. 2- A. Ranges 5 Amperes and 75 and 150 volts. Method. General Principle: After the towels were damp- ened and weighed, the ironing was commenced. The wattmeter was read at regular intervals and recorded. When the towels were ironed they were weighed again. The length of time taken for ironing was also noted. The average number of watts was found, and the loss of weight in grams due to evaporation was determined. Throughout the experiments readings were taken as recorded below. CASE I. A wet towel was used. In finding the efficiency no allowance was made for evaporation or absorption. COST OF OPERATING AN ELECTRIC FLAT IRON 45 CASE II. Conditions the same as in Case I. CASE III. Five towels were dampened the evening before as for ordinary ironing. In finding the efficiency no allowance was made for evaporation or absorption. CASE IV. A very damp towel was used. In finding the efficiency allowances were made: (1) For evaporation, due to the heat of the room, that would have taken place in the 8J minutes without ironing. (2) For absorption of moisture by towel covering board. (3) For evaporation (while airing 4 minutes) due to heat of towel, above room temperature. No allowance was made for heating the iron. The temper- ature of the room was 22 C. It may be of interest to know that the relative humidity for the day was 55 per cent, but this was not used. DATA AND CALCULATIONS No allowances for correction Case. I II ill Condition of towel Weight wet. . 1 wet 413 g. 1 very wet 421 2 g. 5 slightly wet 1255 4 g. Weight ironed 273 . 5 g. 268 3 g. 1180.6 g. Loss of weight 139 5 g 152 9 g 74 8 g. Watts average 531 5 541 3 535 Time taken for ironing .... Efficiency 13.5 min. 80 1% 15.0 min. 80 6% 8.5 min. 70% Cost of ironing towels $.012 $.013 $0.007 Allowance for corrections Case. IV Condition of towel 1 very damp Time to heat iron 1.5 min. Watts average : . . 531 . Weight wet 382 .9 g. Weight ironed 234 . 4 g. Loss of weight by ironing 148 . 5 g. Time actually consumed in ironing 10.0 min. Weight of towel covering board (before ironing) 233 . 9 g. Weight of towel covering board (after ironing) 247 . 6 g. Increase in weight of towel covering board 13 . 7 g. Weight of towel immediately after ironing 234 . 4 g. Weight of towel dampened to same degree as one ironed 382 .9 g. Weight of same towel hanging 8| min. in ah* 366.6 g. Loss of weight in this second towel 15 . 3 g. Efficiency 88.5% Cost of ironing one very damp towel t $0 . 007 46 EXPERIMENTAL ELECTRICAL TESTING Efficiency. Case I. 139.5 X (536 +80) 85932 531 X 13.5 X60X.24 103226.4 M ^/0' Case II. 152.9 X (536 +80) * 94186.4 541.3X15X60X.24 116920.8 5U ' D/0 ' Case III. 74.8 X (536+80) 46076.8 ^ 535X8.5X60X.24 65484 /0 * Case IV. (148.5 -13.7- 15.3) (536+78) = 73373 531 X 10 X 60 X. 24 76464 yb ' u/0< Conclusion. It seems to me that the reason why the efficiency is lower in Case III is because the amount of moisture to be evaporated is not so great in this case as in the others. Cer- tainly the cost of ironing depends upon the quantity of water used in sprinkling. The cost of ironing five towels moistened as in ordinary ironing was found to be 0.7 cent. Computations were checked by George Y. Sosnow. EXPERIMENT NO. 14 BOILING AN EGG BY MEANS OF ELECTRICITY Contributed by Mr. ERNEST R. SMITH, Vice-Principal of the Syracuse North High School, Syracuse, N. Y. Object. To find the cost of boiling an egg by means of electricity, and incidentally to determine the efficiency of the stove. Apparatus. Small disc stove, Model 155 Weston Voltmeter; Model 155 Weston ammeter; aluminum kettle; thermometer; BOILING AN EGG BY MEANS OF ELECTRICITY 47 platform balance and weights; eggs; watch and source of A.G. current. HUBBEL PLUG 10 AMP. FUSE FIG. 18. BEALS' A. C. VOLTMETER AND AMMETER METHOD. (Repro- duced from Connection Chart.) Instruments used were Model 156 Weston A. C. Voltmeter, range 150 Volts and Model 156 Weston Ammeter, range 10 amperes. Results. Weight of kettle Weight of kettle and cold water Temperature of cold water Weight of kettle and contents after boiling egg for (3) min Temperature of boiling water for day Temperature change of water Fall of potential through stove Current through stove Resistance of stove ( R =-^ j Heat developed in stove in 20 minutes = .24 C 2 #* = .24X(5.31) 2 X21.09X20X60 Water equivalent of kettle (MXS) 215.4 grams 1222. 6 grams 23.8 C. 1151 grams 99.45C. 75.65C. 112 volts 5.31 amps. 21.09 ohms 171,336 cal. 47 . 4 grams 48 EXPERIMENTAL ELECTRICAL TESTING Heat absorbed by water in coming to the boil- ing point, 1054.6X75.65 ................ 79,780.5 cal. Heat used in boiling away 71.6 grams of water 71.6X537 ............................ 38,449.2 cal. Total heat absorbed by water .............. 118229.7 cal. , . Output 118229.7 Efficiency of stove = = +. . . . 112X5 31 Kilowatt-hours of work - y^ Xf ....... .198 kwt. hr. luuu Cost of operating stove to boil egg for 3 min- utes at 8j per kwt.hr .................. 1.6 cts.* (Signed) DELPHINE BE QUILLARD. Dec. 8, 1913. Manipulations. The small electric stove was connected to the A.C. main and an ammeter put in series with it and a voltmeter shunted across its terminals. I found the weight of the kettle empty, and filled two-thirds full of cold water. After taking the temperature of the water, the kettle was placed on the stove and the current turned on. Readings of the volt- meter and of the ammeter were taken every minute. When the water began to boil the egg was put in and the boiling con- tinued for three minutes. The kettle and hot water were weighed again. From the barometer reading, the temperature of boiling water for the day was determined. The computations as indicated in the tabulation were made. The cost of boiling the egg was found to be 1.6 cents and the efficiency of the stove 69 per cent. * Several eggs might have been cooked at a very slight increase over the above cost for one, as the dish and quantity of water were sufficiently large. INSTRUCTOR'S NOTE. THE IMMERSION HEATER 49 EXPERIMENT NO. 15 THE IMMERSION HEATER The experiment was repeated, using a smaller dish and an immersion heater. See Fig. 14. Results : Weight of dish 145 . 2 grams Weight of dish and cold water 455 . grams Temperature of cold water 23 . 8 C. Weight of kettle and contents after boiling egg 3 minutes (4.5 minutes) 425 . grams Temperature of boiling water for day 99.45 C. Temperature change of water 75.65 C. Fall of potential through heater 111.0 volts Current through heater 6 . 06 amps. Resistance of heater 18.31 ohms Heat developed in 4J minutes = .24 X(6.06) 2 X 18.31X4.5X60 43,505. leal. Heat absorbed by water in coming to boiling pt. 24,533 . 3 cal. Heat used in boiling away 30 gms. of water. . . 16,110.0 cal. Total heat absorbed 40,643 . 3 cal. Efficiency of heater 93 . 4% 111X6.06, 4.5 Work done by heater - ., -- X-^: .05 kwt. hr. 10UU bU Cost of boiling egg at 8ff per kwt. hr 0.4 ct. (Signed) DELPHINE BE QUILLARD. December 8, 1913. See Fig. 15 (Philippics arrangement) for suitable diagram of connections containing instruments used. COMPILER'S NOTE. EXPERIMENT NO. 16 MAKING COCOA AND CANDY WITH THE AID OF ELECTRICITY Contributed by F. H. REALS Object. To find the cost of making Cocoa and Candy (Fondant) and of boiling water on the electrical disk stove; also determining the efficiency of the stove. 50 EXPERIMENTAL ELECTRICAL TESTING Apparatus. Weston Voltmeter and Ammeter, Disk Stove, Double Boiler, Thermometer, Graduate. See Fig. 18. Performed by Helen Burnett and Marion Butler. Making Cocoa, Experiment A. Making Fondant Candy, Experiment B. Boiling Water, Experiment C. Case I Case I Ingredients IngVedients Cocoa, 8 level tea- spoonfuls. Sugar, 6 level tea- Sugar, 1 cup (2 oz.) J Water, f cup, (96 c.c.) Cream of tartar, ^ 1000 c.c. of water in the lower part of the double boiler, and upon spoonfuls. Cold water, 2 cups teaspoonful. the disk-stove. Bring to boiling point, (500 c.c.). Method recording time taken Cold milk, 2 cups Mix sugar, cream of to perform experiment. (500 c.c.). tartar, and water to- Method Pour the ^ cold milk and water into the metal boiler on the disk- stove. Make the elec- trical connections as shown on the sketch; record time and turn on current. Mix the cocoa and sugar well together in a bowl; add cup of cold water and stir to make a thin paste. Pour some of the hot gether in lower part of double boiler. Place on the disc-stove, having had the current on 2 min. to allow for heat- ing. Record time. Stir mixture until sugar is completely dissolved, boil uncovered until a drop of the mixture dropped from the end of a spoon spins a thread, or until it forms a thick, jelly-like consistency when dropped into cold TTTQf Of Case II Place 250 c.c. of water in the lower part of the double boiler, and 500 c.c. of water in the upper part. Place both parts on the disk-stove, together and heat. Record time taken to heat water in upper boiler and obtain other necessary data. mixture into the bowl and wash out all the cocoa into the boiler. Bring to a boil and boil three min. WdtCl Turn off current, first recording time. Pour the mixture upon a iwell-greased marble slab or a flat platter. When f~^QCO TT sufficiently cool so that V^d/bC 1J. the mixture does not Ingredients adhere to the finger Cocoa, 3 level table- when touched in the spoons. center, beat with wooden Sugar, 3 level table- spoon until the mix- spoons. ture becomes too hard Water, 2 cups (500 to beat, then knead c.c). with the hands. When Milk, 2 cups, (500 c.c.) it becomes sufficiently M +V> cooled, roll into small ivietnoa balls for bonbons. Mix cocoa, sugar, and water thoroughly. Bring milk to boiling point; add first mix- ture and bring all to scalding point. (About 80 C.) MAKING COCOA AND CANDY 51 Outer Parts of' Double Boiler. Both Parts of B. B. Cocoa, Experiment A. Candy, Experi- ment B. Water, Experiment C. Time required to heat plate Volts (average) 2 min. Case I 114.5 3.6 412.2 630 g. 0.1 63.0 g. (2c.)500c.c. (2c.)500c.c. 2 min. Case II 119.0 3.8 452.2 630 g. 0.1 63. Og. (2c.) 500 c.c. (2c.)500c.c. 100 C., 79 C. 25 C. 15 C. 14.5 min. $.0109 2 min. 2 min. Case I 117 3.7 432.9 630 g. 0.1 63. Og. 1000 c.c. 96 C. 25 C. 15 min. $.0108 2 min. Case II 117 3.7 432.9 630 g. 0.1 63.0 g. 750 c.c. 95 C. 25 C. 32 min. $0 . 023 26% 29% 115 3.7 425 . 5 630 g. 0.1 63. Og. 96 c.c. 2i''c! 15.5 min $.0116 Amperes (average) Watts-volts amperes Weight of boiler Water equivalent of boiler (approx.) Water equivalent of boiler (approx.) Quantity of water used Quantity of milk used Tern, of water alone after 8 min. . . . Tem. (cocoa and water) when finished Tem water before heating 92 C. 26 C. 15.5 C. 24 min. $.016 Tem. milk before heating Total time taken to make Cost to make 100 ) c.c. of cocoa. . . . Cost to make 235 g. of candv Cost to boil 1000 c.c. of water in Cost to heat 250 c.c. of water in the lower boiler, and 500 c.c. of water in the upper boiler, i.e., cost of both Practical efficiency (water) Theoretical efficiency (water and dish) 72% 81% 76% 81% Conclusion. It is evident that the electric disk stove is not nearly as efficient when both parts of the doubler boiler are used as when the single dish is used. And also that the real efficiency calculated for actual heating of water is less than efficiency reckoned on the basis of amount of metal and water used. Practical efficiency = Weight of water X change in temp. No. watts X No. seconds X. 24 Theoretical efficiency = (weight of water +.1 wt. of boiler) change in tem. No. wattsXNo. seconds X. 24 In calculating efficiency we considered two cases. (1) Practical efficiency, when we took into consideration only the heating of the water actually used and (2) theoretical effi- ciency, when we considered the heat absorbed by both the water and the dish. 52 EXPERIMENTAL ELECTRICAL TESTING The cost of making 2 quarts of cocoa was about 2.7 cents; for making over J pound of candy, 1.16 cents. INSTRUCTOR'S NOTE. The second year of science for girls at Barringer High School differs from the course for boys, one- fifth of the girls' year being devoted to cooking. The work in electricity for girls is correlated with this branch of domestic science. All the electrical experiments, except Case II above, were performed in the physical laboratory; the second method of making cocoa seemed to the Cooking Department more satisfactory. There can be no doubt that the exercises in electrical heating and cooking have touched the daily life and experience of the girls who have done them. They are incomparably superior to the old, conventional experiments of the physical laboratory, so far as the girls are concerned. It may be of interest to observe that the above method of measuring efficiency by the amount of water evaporated has been used at the Barringer High School to obtain the efficiencies of an electric toaster and an electric stove, and conversely to obtain the latent heat of vaporization. The highest efficiencies were obtained when there was con- tact, as in the case of the electric flat iron, and the lowest when the heating was chiefly by radiation, as in the electric toaster. Domestic electrical contrivances are not of course primarily designed to serve as a means of affording physical quantities which may be readily determined with scientific exactness; but rather to permit useful work to be performed with expedi- tion, convenience and minimum cost. Hence individual results obtained from different sources may disagree, without, however, detracting from their educational value. Lack of space compelled us to defer the publication of several additional exercises on domestic electrical apparatus. Upon request we will mail copies of the following : Cost of Frying on the Disk and Oblong Stoves. Cost of Operating an Electric Toaster. COMPILER'S NOTE. AN ELECTROLYTIC CURRENT RECTIFIER . 53 AN ELECTROLYTIC CURRENT RECTIFIER (Prepared by the Compiler) In the following pages we devote considerable space to a description of an apparatus known as a Nodon Valve or Electro- lytic Current Rectifier. We were extremely surprised at being unable to find a single High School text-book which gave even a cursory reference to this subject; and although we do not manufacture apparatus of this type, we are publishing the results of our experiments. We do so because there are many schools which are limited to alternating current line service, the character of which nec- essarily is not adapted to the performance of many experiments requiring direct current, which should form part of a High School course. In addition apart from its practical value as a means of transforming alternating current into pulsating direct current, the apparatus merits the careful consideration of all science teachers because it may be easily and cheaply constructed; and forms the basis of an experiment that should be included in every laboratory schedule. That there is a pressing demand for some such device is testified to by the numerous inquiries we have received for information pertaining to a simple form of rectifier; and it is a great pleasure to present the results of our investigations. While our work is not exhaustive, it furnishes ample material for exercises, and when practicable we should be glad to receive reports from instructors w r ho decide to include the rectifier as part of their laboratory equipment. Students are certain to become interested in a method of converting " a.c." into " d.c.," and especially will this be the case when it is explained how often some type of converter is used in practical work, when it becomes necessary for instance, to charge an automobile storage battery at once, and no " d.c." is available. The Nodon valve form of rectifier has been selected for description, because it is extremely simple in construction, and a " valve " can be made in a few minutes at a trifling cost. 54 EXPERIMENTAL ELECTRICAL TESTING It cannot be ranked as an efficient form of rectifier, and no such claim is made for it; but fortunately great efficiency in transformation is not a matter of vital importance in school laboratories, the main desideratum being to obtain direct cur- rent service when required. Although also somewhat erratic in its behavior, in that the pulsating direct current it furnishes is not always steady, it would be difficult to find a single piece of apparatus which is more interesting and instructive than a Nodon Valve, when used in connection with accurate measuring instruments. THE NODON VALVE Small Nodon Valves are inexpensive and are very easily made. All that is required is a jar containing a plate or rod of aluminum partly immersed in a saturated solution of bicarbonate of soda, and an inactive conductor. Sheet aluminum yg- inch thick costs less than $1.00 per square foot at retail. If it is too tough or brittle to bend easily, aluminum can be softened by holding over a Bunsen flame. In order to obtain good results it is of great importance that the aluminum employed is practically pure. Much of the commer- cial aluminum used in manufacturing condensers, etc., is adul- terated with zinc. We found that such material gave low efficiency, in some cases even causing the pointer of the direct-current instrument to vibrate to an extent likely to damage the movement. For experimental purposes, several of these valves were con- structed at the Weston laboratories. They consisted of glass jars 6 inches in diameter and 7 inches in height, containing plates of aluminum and lead. The lead plates were 10 by 2J inches in area, and yg- inch in thickness. The aluminum plates were 1 inch by 10 inches, also of yg- inch thickness. It was found that the dimensions of the electrodes, jars, etc., were of no special consequence, and that equally good results were obtained when lead, iron or carbon were used for' the inactive pole. AN ELECTROLYTIC CURRENT RECTIFIER 55 EXPERIMENT NO. 17 TESTING A NODON VALVE WITH DRY CELLS When the aluminum pole of one of these valves was con- nected with the carbon pole of a battery of two dry cells, and a voltmeter was included in the circuit, the latter indicated 1-f- volts. See Fig. 19 (e.m.f. of cells was app. 2.8 volts). The pointer rapidly dropped to nearly zero, finally becoming station- ary at 0.11 volt. When the test was repeated with a milli- ammeter, the initial current was 0.40 ampere, which finally dropped to 0.0015 ampere, where it remained. J D.C. VOLTMETER DRY CELLS FIG. 19. TESTING A NODON VALVE WITH DRY CELLS. The initial current is of course affected by resistance of instru- ment and leads, the dimensions of the valve, etc. The Action of a Nodon Valve The reason why a Nodon valve permits a flow of current practically in only one direction is substantially as follows: When a direct current is passed through a solution made of bicarbonate of soda, ammonium phosphate or any similar alkali, by means of two pieces of immersed iron, lead or carbon, it will be found that gas bubbles form on the plates, and will rise freely to the surface. If alternating current be used instead, almost no gas is formed. In either case the liquid acts as a resistor, which can be shown by connecting an ammeter in series and changing the distance between the plates. The temperature of the solution is raised by the passage of the current. When, as stated in Experiment No. 17, a strip of aluminum takes the place of one of these lead or carbon plates, it will be 56 EXPERIMENTAL ELECTRICAL TESTING found that the current will still flow freely when the circuit is completed with the (+) plus pole of the battery connected with the lead or carbon. But, if the + pole is connected with the aluminum, the initial current rapidly diminishes. This is partly due to the fact that gas bubbles form on *he aluminum plate, and rise to the surface of the liquid as they are crowded off by others. These gases are oxygen and hydrogen. In this respect, the action of the valve resembles that of an ordinary simple cell consisting for instance, of plates of zinc and copper, dipped in an acid solution. But there is another and more complex action taking place. Substantially, the aluminum is attacked by these gases, which combine with it to some extent, and form upon its surface a non-conducting layer of hydroxide of aluminum. If the alum- inum plate could be completely covered with this hydroxide, it would practically become a non-conductor, and almost all elec- trical transmission would cease. The fact is, however, that when a direct current is used as stated, some current continues to flow from the aluminum to the lead, " seeping " through the hydroxide layer (so to speak). When alternating current is used instead (with a single valve) the latter may be said to open and close successively for each cycle so that one-half of each alternating current wave is checked, the other half passing through and having a pulsating direct effect. The valve, however, is not perfect in its action, and may be said to " leak." EXPERIMENT NO. 18 TESTING A NODON VALVE WITH A DIRECT CURRENT SERVICE LINE When one of these valves was connected with a source of direct current (110 volts) in series with a lamp bank and an ammeter, the following results were obtained at the instant the circuit was closed. Plus (+) to lead pole, 1.95 amperes. Plus (+) to aluminum pole, 1.10 amperes. When the circuit had remained closed for thirty seconds with + to aluminum, the current was reduced to 0.15 ampere, and at the end of two minutes the total current flowing as indicated by a direct current milliammeter was 0.020 ampere. AN ELECTROLYTIC CURRENT RECTIFIER 57 EXPERIMENT NO. 19 TESTING A NODON VALVE WITH ALTERNATING CURRENT When alternating current is used in connection with a Nodon Valve, it is assumed as already explained, that pulsating direct current is obtained, since current is not supposed to flow from the aluminum to the lead. While this is not strictly the case, there is enough interference to produce a current which is sufficiently direct to be measurable by means of a direct current movable coil permanent magnet ammeter or voltmeter. But such an instrument will respond only to the direct cur- rent pulsations, and since a Nodon Valve will by no means rectify A.C.AM METER TOA.C.LINE FIG. 20. TESTING A NODON VALVE WITH ALTERNATING CURRENT. Instruments required are a Model 280 Weston Ammeter, range 5 amperes, and a Weston Model 155 A.C. Ammeter, range 5 amperes. the current entirely, the results obtained when the so-called direct current is tested with accurate instruments will seem perplexing and apparently paradoxical. For instance, when both an alternating and a direct current ammeter were connected in series with a Nodon Valve, a lamp bank and a source of 110-volt alternating current (see Fig. 20), the following results were obtained : Time in Minutes. A C Line 110 Volts. 1 2 3 4 5 10 D. C. Instr 0.05 0.50 0.61 0.65 0.67 0.67 0.69 ampere A. C. Instr 1.80 1.30 1.25 1.23 1.23 1.24 1 . 25 amperes 58 EXPERIMENTAL ELECTRICAL TESTING EXPERIMENT NO. 20 EFFICIENCY TEST OF A NODON VALVE In order to further investigate this matter, instruments were added to the circuit until the general arrangement was as shown on Fig. 21. The apparatus consisted of a Weston Standard Wattmeter connected with the A.C. line, directly indicating the power consumed. The instruments used for measuring the direct current were one Model 280 Voltmeter and one Model D.C. AMMETER A.C.AMMETER FIG. 21. EFFICIENCY TEST OF A NODON VALVE. 280 Ammeter, which indicate with direct current only; one Model 155 Voltmeter and one Model 155 Ammeter. The Model 155 instruments are of the " soft-iron " type and are operative with either direct or alternating current. Following are the results obtained : WATTS ON A. C. LINE 150.0 Line Voltage, 110 A. C. Volts. Amp. Watts. Direct current instruments 36 5 9 32.8 + Alternating current instruments 64 1 65 105 6 AN ELECTROLYTIC CURRENT RECTIFIER 59 EXPERIMENT NO. 21 EFFICIENCY TEST WITH TWO NODON VALVES IN SERIES Two valves were then employed in series (lead to aluminum) but there was no important difference in efficiency, as shown by the following data: WATTS ON A.C. LINE 138 Volts. Amp. Watts. Direct current instruments . . . 27 5 0.94 28.85 Alternating current instruments 46.5 1.55 72.07 EXPERIMENT NO. 22 PUNCTURING THE INSULATING WALL OF A NODON VALVE We have already found by Experiment No. 20 that a direct current and an alternating current ammeter connected in series with each other and operated through a Nodon valve will not give corresponding indications. The reason for this is fully explained in due course. But meanwhile, an interesting little experiment (original, we believe) may be easily performed, which consists in " punch- ing a hole in the insulating wall." All that is required for this operation is an alternating current outfit as shown on Fig. 20 and a piece of stiff iron wire, one end of which is bent at right angles to form a hook about 2 inches long. The end of this hook should have a sharp point. If the aluminum plate is touched below the surface of the liquid with this iron point, the direct-current ammeter instantly drops to nearly zero, and the total current increases, as indicated by the alternating current ammeter and the improved luminosit}^ of the lamp. See Fig. 22. If about eight lamps (16 c.p.) are connected in multiple for a load instead of only one, so that the current will be about 60 EXPERIMENTAL ELECTRICAL TESTING three amperes, the point of the hook will adhere to the aluminum to some extent, as if it were fused in by the action of the current. , Bubbles rise freely from the hook while in contact with the aluminum, indicating that the aluminum hydroxide will not adhere to the iron; and hence, since the point of the hook has been forced through the layer, it conducts current from the aluminum through the liquid to the lead, changing the apparatus into a simple liquid resistor. Only one valve should be used to get the best effect in this test. Construction and Arrangement of the Electrolytic Currrent Rectifier It is obvious that the only effect produced by one or more Nodon valves in series, is to impede the flow of an alternating current in one direction. The resultant direct current cannot have an efficiency greater than 50 per cent of the total alter- nating current, and is actually only about 25 per cent or less. It is possible, however, to obtain greater efficiency by arranging four valves in the form of a parallelogram and connecting the alternating current in such a manner that both halves of the current will be utilized to pro- duce a direct current. One of these rectifiers was purchased for experimental pur- poses and tested in the Weston laboratories. It consisted of four porcelain jars, each about 5J inches in diameter and 11 inches in height, provided with an insulated top and binding posts. Each jar contained a rod of aluminum and two plates of lead, the latter being connected together. The solution used was bicarbonate of soda. The general design was such that a large percentage of the alternating current was converted into direct current. FIG. 22. PUNCTURING THE INSU- LATING WALL OF A NODON VALVE. AN ELECTROLYTIC CURRENT RECTIFIER 61 The Theoretical Operation of the Electrolytic Current Rectifiers The current from an A.C. source enters at a, See Fig. 23> is checked at k, but may flow through the lead plate b to c to d, is again checked at i, but may flow through the instrument (or load) to e, continue through / and g and out to h, constituting half a cycle. The other half operates through h, is checked at A.C. LINE D.C. VOLTMETER A.C. LINE ic'j. 23. THE ELECTROLYTIC CURRENT RECTIFIER. g, but follows j and i to d, is checked at c and flows through the instrument to e, etc. A rather surprising feature of these rectifiers is that the direct-current voltage of the apparatus when the voltmeter is connected as shown on Fig. 23 is sometimes 20 per cent higher than the A.C. line voltage. This is only the case, however, when the direct current used is negligibly small. 62 EXPEEIMENTAL ELECTRICAL TESTING EXPERIMENT NO. 23 EFFICIENCY TESTS OF A COMMERCIAL ELECTROLYTIC CURRENT RECTIFIER In order to obtain some data in relation to efficiency, a test was made having a continuous Tun of two hours. See Fig. 24. Following are the results obtained: A.C. LINE, VOLTAGE 110 Pulsating Direct Current. Watts on A.C. Line. Tern, of Solution. Efficiency. Volts. Amp. Watts. Time. 320 85.0 1.70 144.5 23 C. 45.1% 380 87.0 1.72 149.6 1 hr. 32 C. 39.4% 450 85.0 1.70 144.5 2 hrs. 42 C. 32.1% FIG. 24. EFFICIENCY TEST OF AN ELECTROLYTIC CURRENT RECTIFIER. When the apparatus was connected directly with the A.C. line and no direct current was drawn, 45 watts were consumed. When nothing but a high resistance voltmeter was connected with the direct-current binding posts, it indicated 133 volts. Alternating-current voltmeters and ammeters were also used in making this test. Their indications taken simulta- AN ELECTROLYTIC CURRENT RECTIFIER 63 neously with the direct current observations averaged 1 1 per cent higher. Some experimenters state they have obtained greater effi- ciency by introducing a transformer in the circuit so as to reduce the voltage to 55 or below. Following is the result of a test made under such conditions: A.C. VOLTAGE 55 Pulsating Direct Current. Watts on A.C. Line. Tern, of Solution. Efficiency. Volts. Amp. Watts. Hours. 88.0 25.1 1.27 31.88 25. 2 C. 36.2% 80.0 22.0 1.10 24.20 1 28. OC. 30.2% 76.0 20.1 1.05 21.10 2 30. OC. 27.7% NOTE. It should be distinctly understood that it is not claimed that either of the results obtained is conclusive. On the contrary, it is quite probable that increased efficiency maybe obtained. It is also likely that some modifications of the apparatus including a water jacket or some other contrivance for keeping the temperature from rising unduly would have advantages. Caution. It is safest to include a lamp bank or some other resistor in the line when the rectifier is first used or after it has been idle for even a short time. There is often a current surge of 20 or more amperes when the circuit is first closed. This is due to the fact that the hydroxide has not had time to form. This surge also causes a strong pulsating current to develop at times, and unless fuses are put in both lines, damage may be done to apparatus in circuit. These rectifiers may be used to charge small storage batter- ies, but care should be taken to connect an ammeter in circuit together with a rheostat or bank of lamps, in order to regulate the current. The top part of the jars as well as the cover to which the elements are fastened should be dipped in hot paraffin before setting up, so as to prevent the solution from creeping. The liquid should occasionally be renewed, since it seems to deteriorate. 64 EXPERIMENTAL ELECTRICAL TESTING Instrument Indications in Connection with a Rectifier The reason for the difference between the indications of the direct and alternating current Weston instruments when used to measure the output of an electrolytic rectifier, is explained in an article by Albert Nodon, in Vol. I, of the Transactions of the International Electrical Congpess, St. Louis, 1904, entitled " Electrolytic Rectifiers An Experimental Research," page 510. This experimental research includes charts showing the wave form of the rectified current as obtained by means of the ondograph or oscillograph. If this rectified current is measured by a Weston alternating current ammeter, the result is that the instrument readings represent the effective current, which will be the square root of the mean square of the instantaneous values. Whereas, if a direct-current ammeter is used, its indications depend upon the arithmetic mean value of the instantaneous values of the pulsating current. If the transformation were perfect the difference between the indication of the two types of instruments would.be 11 per cent. The fact is, however, that the transformation is not perfect. The results obtained with a single valve prove this, and even when four valves are arranged in parallelogram form, there is a loss due to leakage as well as to resistance. This can be directly proven by measuring the pulsating current by means of an induction meter which will not indicate with direct current. It can be simultaneously shown that the direct-current instru- ment responds only to the direct-current pulsations; the alternat- ing current instrument gives the combined affect of direct and alternating current; and the induction meter indicates only the alternating current (or leakage), its indications being approxi- mately the difference between the other indications. In charging storage cells and in running direct-current motors as well as in the electro-disposition of metals, the above state- ments should be taken into consideration, since it is obvious that the only effective current for such work obtained from rectifiers of this type will be due to the direct-current pulsations. An article entitled " The Chemistry of the Electrolytic Current Rectifier," by Donald McNicol, will be found in the August, 1913, number of the " Electrician and Mechanic." WESTON DIRECT CURRENT MOVABLE COIL SYSTEM 65 THE WESTON DIRECT CURRENT MOVABLE COIL SYSTEM (Prepared by the Compiler) This system consists primarily of a coil which can rotate freely in a strong magnetic field produced by means of a per- manent magnet. When a current is flowing through it, this coil acquires magnetic properties and tends to assume a position which will reduce the distance between its poles and the oppo- sitely magnetized poles of the permanent magnet. Springs which also serve as current conductors tend to oppose the move- ment of the coil.* The Milliammeter An instrument which consists only of a coil, a magnet, a core and an elastic metallic conductor for controlling the movement of the coil, in short a " system " as described above, is in its simplest form a milliammeter. All Weston direct-current mov- able-coil systems are fundamentally uncalibrated milliammeters, although they may differ in size, in the strength of their magnetic fields, in the number of turns of wire in their movable coils, and in mechanical details. This is the case because all systems of this type are operated by means of a small current; and the extent of the deflection produced depends upon the strength of this current. The Millivoltmeter The system as described, is also an uncalibrated potential indicator of millivoltmeter, because a definite electromotive force is needed to overcome the resistance of the movable coil and force a current through it. If, therefore, we consider the system in its simplest form as consisting only of a movable coil, a core, a magnet, and a pair of springs directly connected to a * See also Monograph B-2. 66 EXPERIMENTAL ELECTRICAL TESTING pair of binding posts by means of leads of negligible resistance, then it follows that, for any deflection of the moiable coil at a fixed temperature the current will always be the same for that deflection. And since the resistance of the movable coil and springs will always be the same at a fixed temperature, it also follows that under the given conditions the electro-motive force required to overcome the resistance of the movable coil, etc., and produce any desired current, will always be the same unless extra resist- ance is added to the circuit. The Movable Coil Constant The movable coil constant is the component of current and e.m.f. pertaining to a particular system, that is to say, a system of a certain type or class; and under all normal conditions such constants are fixed and unchangeable. For instance, if the current required to obtain a full scale deflection is .01 ampere, and (r) the resistance of the movement is 6 ohms, then the e.m.f., required will be E = Ir, in this instance being 6 X. 01 = .06 volt, and the power required to produce a full-scale deflection will be .01 X .06 = .0006 watt. To extend the range of such an instrument for voltage meas- urements, it will be necessary to add a resistor to the circuit, and the resistance of such a resistor in ohms per volt is found E by the formula R=r. For instance, to obtain a 1-volt range, the added resistance in this instance will be: # = -rrr-6=9 Necessarily, to make a 100-volt instrument of the movement, a total resistance of 10,000 ohms will be required, and all other ranges will have a directly proportionate resistance. WESTON DIRECT CURRENT MOVABLE COIL SYSTEM 67 The Ammeter* In attempting to use the movement already referred to for current measurements, it will be apparent immediately that no current greater than .010 ampere should be passed through it. If therefore a larger current than this is to measured, some contrivance must be attached which will permit a larger cur- rent to flow, and yet limit the quantity flowing through the move- ment. This is most easily accomplished by means of a divided or shunted circuit. For instance, if a resistor is constructed of insulated wire having the same resistance as the movement, and is connected directly with the binding posts of the instrument, and the binding posts are then connected with a source of current, it may be deduced that such a current will split; and since the resistor has the same resistance as the movable coil, the current will split evenly, half of it going through the movement and half through the resistor. But, the movement will only respond to the current flowing through it, and not to the current flowing through the resistor. Since these currents are alike, it follows that the pointer will indicate half of the total current flowing. In other words, the ampere range of the instrument has been doubled. To determine how to still further extend the ampere range of the instrument it is only necessary to refer to the laws relat- ing to divided circuits. The current flowing through two parts of a divided circuit will be directly proportional to the resist- ances of these circuits. If, for instance, the shunt coil measured .06 ohm and the movement 6 ohms, then the current would be as .06 is to 6, that is, the current through the shunt would be 100 times as great as that passing through the movement. For it must not be forgotten that the voltage, at the binding posts is the same for the movement as it is for the shunt coil, and that * For data relating to Weston movable systems, see also " Elements of Electricity," Timbie, Chap. XIV.; "Physics," Mann and Twiss, page 169; " Practical Physics/'' Black and Davis, page 284; " Laboratory Manual," Black and Davis, page 64; " High School Physics," Carhart and Chute, page 371; "A High School Course in Physics," Gorton, page 405; "Elec- trical Instruments and Testing," Schneider and Hargrave, Chap. 4, and " Lessons in Practical Electricity," Swoope, Lesson 18. 68 EXPERIMENTAL ELECTRICAL TESTING consequently the less the resistance of the shunt the greater will be the current flowing through it. A point could therefore be reached where the shunt would have so low a resistance that it would carry practically all of the current, and not enough would flow through the movement to make it operative. Such a shunt would be described in practice ^s not having enough " drop," meaning that the potential difference between its extremes would be insufficient for the purpose for which it was intended. In practical work the shunts are usually constructed to have a standard drop of 50 or 100 millivolts. The resistance of the system is increased by adding non-inductive zero temperature coefficient material in series, so as to increase the e.m.f. required to produce a full scale deflection to 50 or 100 millivolts or some other value, according to the type of instrument, and the drop of the shunt. THE WESTON ALTERNATING AND DIRECT- CURRENT "SOFT IRON" SYSTEM (Prepared by the Compiler.) The direct-current movable-coil system described in the pre- ceding article is inoperative with alternating current, because its field as produced by a permanent magnet has fixed polarity. Consequently when an alternating current is passed through the movement, the polarity of the movable coil is thereby con- tinually reversed, and the movement oscillates instead of being deflected. The effect of an alternating current when applied to a direct-current movement can be plainly seen by the vibra- tion of the pointer,* but of course there is no continuous motion in one direction by means of which an alternating current could be measured. The movable element of the Weston soft-iron system con- sists of a small curved piece of iron fastened to a light pivoted shaft. This shaft is also provided with a truss form of pointer made of thin aluminum tubing, to which is attached a balance cross and a small vane. The shaft moves in jeweled bearings. * Experiments of this kind if protracted, neither improve the sharpness of the pivots nor lengthen the life of the pointer of a d.c. instrument. FIG. 25. PHANTOM VIEW OF WESTON MODELS 151, 155, 156, 159, 160. Moving Parts of "Soft Iron " Voltmeters. FIG. 26. PHANTOM VIEW OF WESTON MODELS 151, 155, 156, 159, 160 Moving Parts of " Soft Iron " Ammeters. THE WESTON "SOFT-IRON" SYSTEM 69 Near this movable element and concentric with it is a small curved tongue of soft iron which is rigidly held by a suitable support. (See Figs. 25 and 26.) Surrounding these is a field coil, made up either of a large number of turns of insulated wire when the instrument is to be used for the measurement e.m.f. or else of one or more turns of heavy conducting material, when designed for the measurement of current. Principle of Operation. When a direct current is passed through the field, the movable element and the fixed tongue of iron become magnetized by induction; but since they are within the field coil, their juxtaposed ends will have like polar- ities. Consequently these poles will repel each other. The only resultant motion possible is the rotation of the movable element. When alternating current is used, the polarity of the field coil will be alternately North and South, the number of reversals depending upon the frequency. The polarities of the movable and fixed iron parts of the system will also reverse correspondingly, but although the jux- taposed parts will have constantly reversing polarities, they will have like polarities in relation to each other, and therefore will necessarily repel each other continuously, thereby imparting a rapid series of impulses to the movable element, causing a deflec- tion in one direction only. This deflection is opposed and therefore controlled by the action of a delicate spiral spring; hence the extent of the rota- tion depends upon the strength of the current flowing through the solenoid. The peculiar shapes as well as the relative positions of the iron parts are patented features which are the outcome of much theoretical work and numerous experiments. As a result, the instrument is almost entirely free from hysteresis or lag; that is to say, the magnetization, demagnetization, and remagneti- zation of the iron, will be practically perfect. If the instrument is designed for current measurements, it is so arranged that all of the current passes through the sole- noid or field coil. This is also the case when intended for the measurement of e.m.f., but an adjusted resistor lies in series with the solenoid. The resistance of the instrument is thereby 70 EXPERIMENTAL ELECTRICAL TESTING increased, and the quantity of current which may flow is regu- lated. Precisely as in direct current movable coil instruments, the amount of current which will flow, depends upon the e.m.f. of the circuit across which the instrument is connected. The vane or damper moves in a fan-shaped pocket which is shown in Fig. 26 with the cove^ removed. When this vane is enclosed it damps the movement of the system without mechanical friction. That is to say, the vane does not touch any part of the receptacle but moves through confined air. The scales of these instruments are open and fairly uniform throughout four-fifths of the total range of deflection. CO-OPERATORS We extend our hearty thanks to all physics instructors who have assisted in the preparation of this monograph, either by their encouraging approval of our previous efforts, or by their suggestions and direct contributions. Among many others, we are especially indebted to the science teachers whose names we append, with occasional extracts from their communications: AMES, C. G., Instructor in Physics, High School, Berkeley, Cal. " I would be glad if you can spare me two extra copies of monograph B-2 for class use." ANDREWS, A. P., Instructor, Department of Physics, Min- neapolis, Minn. " There can be no possible question as to the service you are rendering schools. Personally, I expect to profit by it." BAER, C. E., Department of Science, The Lincoln High School, Seattle, Washington. " Please send all Monographs or other literature descriptive of such of your instruments as may practically be used in our modern high schools. I am on a committee of Seattle Physics teachers, appointed to outline a revised course in electricity from beginning to end, and need your co-opera- tion." CO-OPERATORS 71 BARBER, FRED D., Illinois State Normal University, Normal; 111. BARRETT, J. T., Department of Physics, Lawrenceville School, Lawrenceville, N. J. " Personally I was glad to see you entering a field where Tin Students' Instruments had been the only low-priced supplies available." BEALS, FREDERICK H., Department of Physics, Barringer High School, Newark, N. J. Formerly Prof, of Physics, Occi- dental College, Los Angeles, Cal. " I hope you will continue the good work of issuing monographs contain- ing experiments of practical value, experiments from the commercial testing laboratories and from workshops, exercises more nearly touching daily experience and commercial life than have hitherto been customary in school; real problems of the work-a-day, experiments which have living reality in the school laboratory." BLACK, PROF. N. HENRY, A.M. Science Master, Roxbury Latin School, Boston, Mass. " I have yours of the 20th inst., and am much interested in your efforts to give the schools a really good electrical measuring instrument, and at the same time to suggest how they may be used to get nearer to the real practical electrical problems. You may be interested to know that last year when I was getting out the Laboratory Manual to go with the text-book, your voltmeter and ammeter was the only form of electrical direct-reading instru- ment, which I felt enough confidence in to illustrate. (See Fig. 38 of Lab. Man.). Go ahead with this good work." BOYNTON, W. P., Professor of Physics, University of Oregon, Eugene, Oregon. "Your monographs are of interest to me personally, and also of value, as I am called on to advise present and prospective teachers in physics in the High Schools of this State." BURGIN, BRYAN 0., Department of Science, Albany High School, Albany, N. Y. BURNS, ELMER E., Instructor in Physics, Joseph Medill High School, Chicago, 111. " I have read the monograph carefully and do not see any way how it could be improved." CADY, W. G., Professor in Physics, Wesley an University, Middletown, Conn. " The idea of issuing these monographs is a good one." 72 EXPERIMENTAL ELECTRICAL TESTING CLARK, M. G., Superintendent of Public Schools, Sioux City, Iowa. " I am just in receipt of ' Elementary Electrical Testing/ and wish to take this opportunity to congratulate you upon the work which you have done in bringing practical problems of industrial life directly to the school. If industrial plants in general would take this same attitude, it would present, to the schools a challenge which they couid not ignore. " To what extent and in what way could I secure more copies of this monograph? " COLTON, GEO., Professor of Physics, Hiram College, Hiram, Ohio. " I appreciate the monographs which your company is sending out and can make use of some things in them in the laboratory work of my students." DOWD, MR. J. E., Classical High School, Worcester, Mass. " I will state that your monograph proved of great service and value to me, as much of the electrical apparatus we have is of your make, and the topics dwelt upon offered much information about them." DRAPER, JASON T., Master in Science, High School, Holyoke, Mass. " I plan to equip my laboratory at once with whatever is needed to carry out all that is outlined in your Monographs in Elementary Testing." EASTMAN, EARL, Science Department, High School, Atlantic City, N. J. " I find your monograph B-2 very helpful." ECKERT, ALBERT C., Eastern High School, Bay City, Mich. " Your monographs have proven a help to me. I have adopted several of the experiments you describe in my laboratory course." EDWARDS, RAY L., Professor Physics Department, Park College, Parkville, Mo. " I was very glad to receive the monographs B-l, B-2 and B-3." EGGEN, H. O., Instructor in Physics, Santa Ana High School, Santa Ana, Cal. " Your monographs will be helpful to me both in selecting instruments and in selecting experiments." EVANS, WM. F., Girls' High School, Brooklyn, N. Y. FEE, LEWIS H., Head of Science Department, Everett High School, Everett, Wash. CO-OPERATORS 73 FISCHER, H. F., Professor University of California, Berkeley, Cal. FOERSTE, AUGUST F., Instructor in Physics, Steele High School, Dayton, Ohio. FLANDERS, M. M., Bliss Electrical School, Takoma Park, Washington, D. C. " I would like any technical data you will furnish in regard to principle of operation of your soft-iron instruments." Fox, JOHN E., Western State Normal School, Kalamazoo, Mich. " I think your plan an excellent one and shall be glad to suggest some materials for future monographs which will be of interest to physics teachers." GARDINER, F., Headmaster of the Yeates School, Lancaster, Pa. " I should like to see experiments in efficiency tests, on the small trans- former, electric cooking utensils and current capacity test on commercial fuses." GLENN, EARL R., Department of Physics, Froebel School, Gary, Ind. " I have read the literature you sent with great interest and profit. Science instructors owe much to the company you represent." GORTON, F. R., Professor of Physics, Michigan State Normal College, Ypsilanti, Mich. " Your communication regarding the publication of B-4 compilation of laboratory exercises is at hand. I think the subject matter excellent, but feel that the experimental part is too full in some points and deficient in others. I shall be glad to see the publication." GRAHAM, PROF. W. P., College of Applied Science, Syracuse University, Syracuse, N. Y. GRIFFIN, CHAS. E., Head of Science Department, San Bernardino High School, San Bernardino, Cal. " I think at the present time the greatest need in the teaching of elec- tricity in our high schools is an apparatus for the demonstration of alter- nating current phenomena. Your plan of co-operation appeals to me as being especially desirable." 74 EXPERIMENTAL ELECTRICAL TESTING HAMMOND, H. E., Physics Department, Kalamazoo Public Schools, Kalamazoo, Mich. " I believe your company is doing a good work in putting out these monographs, and I think that there ought to be a response in a business way, or Weston instruments do what they are intended to do." HATHAWAY, F. R., Physics Director, Classical High School, Salem, Mass. " I received the two monographs and hope to take advantage of the suggestions contained therein, in teaching electricity this coming winter." HEDRICK, WM. A., Instructor in Physics, McKinley Manual Training School, Washington, D. C. " I like the monographs very much and their aid has persuaded one of the teachers to try the drop of potential along a wire, that I was not able to do before. We will take great pleasure in calling the attention of the physics Teachers' Ass'n to your instructive monographs." HULL, PROF. G. F., Wilder Laboratory, Dartmouth College, Hanover, N. H. " You are doing a great service to scientific teachers in sending out this literature." INGVALSON, EDWARD, Instructor in Physics, Lanesboro Public Schools, Lanesboro, Minn. " There is certainly need of reform as far as Lab. measuring apparatus is concerned, and I believe you are doing much good in circulating such literature as your monographs. The toy apparatus we have is a farce. Most science teachers know this but are handicapped in improving conditions." KELBER, C. M., Department of Physics and Chemistry, Petersburgh High School, Petersburgh, 111. " Perhaps some science teachers would find it suggestive if you were to describe a method for making efficiency tests of commercial electric heating units such as disk stove, percolator, etc. I have found such exercises very conducive to interest in my class work." KILLEN, A. H., Instructor in Physics, Flushing High School, Flushing, N. Y. LYON, LESLIE W., Department of Physical Science, Burling- ton High School, Burlington, Iowa. " I would particularly like to have discussed the measurement of electric power in such experiments as determining the efficiency of electric lights, electric iron, heating plates, etc." CO-OPERATORS 75 MARBLE, MILTON M., Department of Physics, New Haven High School, New Haven, Conn. " Please send with instruments, 25 copies of Monograph B-2 for students' use, and oblige." MARVELL, SUMNER E., New Bedford High School, New Bedford, Mass. " I found your monographs helpful in the physics work of the school. I have always felt that a closer contact between our teaching and commercial apparatus would be of great assistance to us." MCKENZIE, MONROE R., Professor of Physics, Parsons Col- lege, Fairneld, Iowa. MOORE, PROF. J. C., Master in Science, Worcester Academy, Worcester, Mass. " I wish to say that the monographs, especially B-2 and B-3, are excep- tionally useful to science teachers. We hope that you will continue to issue them and suggest practical work in electrical measurement. You will doubt- less be interested to know that they have stimulated us to equip a labora- tory for electrical work, separate from our regular physics laboratory." MOORE, J. COLIN, Instructor in Electricity, Lake High Manual Training School, Chicago, 111. " I shall be glad to make some suggestions for experiments which may be of use to others." NYE, ARTHUR W., Department of Electrical Engineering University of Southern California, Los Angeles, Cal. " I received the monographs early in the summer and was favorably impressed with them. I hope that you will continue their publication and that you will also publish some dealing with high-grade electrical instruments. There seems to be a lack of printed material about really high grade practical engineering electrical measurements." PACE, Miss LILLIAN, Central High School, Washington, D. C. " I have always thought that something of the sort sent out by makers of instruments which we use would be most acceptable and am glad you have entered in this work. It will give me pleasure to co-operate with you and make suggestions." PEET, J. C., Department of Electricity and Chemistry, Technical High School, Harrisburg, Pa. " Your experiment on the Heating Effect of current is especially good. I should like to see you add one on Chemical Effect, using the copper volt- 76 EXPERIMENTAL ELECTRICAL TESTING meter to standardize an ammeter. Keep up the good work started in these monographs." PHILIPPI, H. C., Department of Physics, State Normal School, Bellingham, Wash. " I should be glad to have you discuss in future monographs any practical electrical measurements suitable for high-school work or for the first two years of college physics." POND, ETHEL C., Physics Teacher, Sycamore High School, Sycamore, 111. " I consider publications such as yours the most valuable help a physics teacher can receive, and I wish to express my appreciation." POORE, CHAS. D., The Northern Normal and Industrial School, Aberdeen, South Dakota. " I remember on getting your monographs, of at once being struck with the need of just such things in perfecting my electrical course." RANDALL, J. A., Pratt Institute, Brooklyn, N. Y. RATCLIFF, R. F., Department of Physics and Chemistry, Central Normal School, Danville, Ind. " Monograph B-2 is very valuable to us, especially, in that it gives sample experiments from the practical electrician's point of view. This is a phase of the work we wish to develop." REED, HAROLD B., East High School, Cleveland, Ohio. " Have read the monographs with the greatest interest. They are a real contribution. Shall try out several of these experiments this year. Shall be glad to do anything possible to help along a good cause." RIAL, DAVID, Instructor in Physics, State Normal School, Mansfield, Pa. ROOD, JAMES T., Professor of Physics and Engineering, Lafayette College, Easton, Pa. " Your idea that these monographs shall have so much intrinsic merit that they will be carefully kept in file as matter of value, is, I think, most admirable. Prosit! " ROTHERMEL, JOHN J., Physics Laboratory, Eastern High School, Washington, D. C. " I hope to be able to take some work on efficiency tests of small trans- formers, and probably also in electric cooking utensils. I should be very glad to have about half a dozen copies of Monograph B-2 and B-3 that I could use with one of my classes in their electrical experiments this year." CO-OPERATORS:, J ;' 0^:''-::: A 77 SMITH, ERNEST REVELEY, Instructor in Physics, Syracuse High School, Syracuse, N. Y. TURNER, GEO. M., Hasten Park High School, Buffalo, N. Y. " Our work with the triple-range voltmeters and double-range ammeters Model 280 proved very satisfactory. No instrument was abused by any pupil either by accident or intent. It is our purpose to extend their use during the course in electrical work of the present school year. TWINING, H. L., Head of Physics and Electrical Engineering, Los Angeles High School, Los Angeles, Cal. " You are making a move in the right direction in developing instruments of accuracy for high schools. I am writing a text on elementary electricity covering the first year's work and also a manual to accompany it. In it I am going to feature your instruments and recommend their use. I do this because they are the best that the world has to offer." Twiss, G. R., Professor of Physics, Ohio State University, Columbus, Ohio. " Replying to your letter of January 21st, which has been overlooked because of the pressure of semester examinations, I would say that I am very much interested in your enterprise looking to the publication of mono- graphs on experiments that can be made with standard commercial instru- ments, and that have direct commercial and industrial bearings. I think that if wide publicity is given to such experiments, the movement cannot fail to be productive of much good to the pupils of the high schools. I should be glad to receive all the pamphlets of this character that you have issued up to date, and to be placed on your mailing list for other material of similar interest that you may issue from time to time." VAWTER, C. E., Professor of Physics, Virginia Polytechnic Institute, Blacksburgh, Va. " I have four of your minature instruments and I consider them the greatest find that I have made for my electrical work in a long time. I shall get more." WATJCHOPE, PROF. J. A., Department of Physics, Mechanics Arts High School, St. Paul, Minn. " I sincerely hope you will continue the publication of the monographs, as the suggestions are helpful to me and I am sure must be to many other teachers. This is excellent work that you are doing." WEBSTER, EVANS, Head of Physics Department, English High School, City of Lynn, Mass. " What we need most in our elementary laboratories is a galvanometer in portable form for use with the slide wire bridge, and which can be used 78 EXPERIMENTAL ELECTRICAL TESTING without a shunt box, costing not over six or seven dollars. The galvanom- eters usually found (made by . . . ) are the most exasperating pieces of apparatus to put in the hands of students that I know of." WOOD, LYNN H., Professor Department of Physical Science, Union College, College Point View, Neb. " We have received your monographs B-l, B-2 and B-3. We appreciate them very much. For a long time the w*ork in electricity in our science department has been altogether too theoretical, and we welcome any changes that will tend to make the work more practical. We are adopting many of the experiments which you give in these monographs." WYLIE, R. M., Professor of Physics, Marshall College, Hunt- ington, W. Va. " Most high schools buy their equipment as you know, to fit their partic- ular course. If the laboratory manuals which are put out by the book companies to accompany such texts as Milliken & Gale, Carhart & Chute, Gorton, or Hoadley's new book, only contained cuts of your minature instruments and precise directions for their use in the experiments in elec- tricity, you would find many schools trying yours and using them." AN APPEAL If our monographs are of service to the reader, if we have succeeded in bringing him in touch with the earnest efforts of others, then, from a utilitarian stand- point, it would seem that the most suitable return any physics instructor can make, will be to recipro- cate with new material or helpful suggestions, through the medium of our publications. THIS BOOK IS DUE ON THE LAST BATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE D*TE DUE. THE PENALTY WILL INCREASE TO SO CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY 1933 USE OCT2 196 OT 8 196) LD 21- UNIVERSITY OF CALIFORNIA LIBRARY