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How Two Boys Made
Their Own Electrical
Apparatus

Containing Complete Directions for
Making All Kinds of Simple Apparatus
for the Study of Elementary Electricity
BY
THOMAS M. ST. JOHN, Met. E.
Author of "Fun With Magnetism," "Fun With Electricity,"
"The Study of Elementary Electricity and Magnetism
by Experiment," "Things A Boy Should Know
About Electricity," etc.

EIGHTH EDITION

THOMAS M. ST. JOHN
CASCADE RANCH

COPYRIGHT, 1898,
BY THOMAS M. ST. JOHN

How Two Boys Made Their Own Electrical Apparatus.

TABLE OF CONTENTS.

A WORD TO BOYS.

The author is well aware that the average boy has but few tools, and he has kept this fact constantly in mind. It is a very easy matter for a skilled mechanic to make, with proper tools, very fine-looking pieces of apparatus. It is not easy to make good apparatus with few tools and a limited amount of skill, unless you follow simple methods.

By following the methods given, any boy of average ability can make the apparatus herein described.

Most of the illustrations have been made directly from apparatus constructed by young boys.

It is impossible to describe the different pieces of apparatus in any special or logical order. It is taken for granted that you have some book of simple experiments and explanations to serve as a guide for the order, and to give you an idea of just the apparatus needed for the special experiments.

It would be foolish to start in and make all the apparatus described, without being able to intelligently use it in your experiments. Take up a systematic course of simple experiments, and make your own apparatus, as needed.

Before making any particular piece of apparatus, read what is said about the other pieces of the same general nature. This will often be a great help, and it may suggest improvements that you would like to have.

In case your apparatus does not work as expected, read the directions again, and see if you have followed them. Wrong connections, poor connections, short circuits, broken wire, etc., will make trouble. With a little patience and care you will be able to locate and correct any troubles that may come up in such simple apparatus.

Thomas M. St. John.

How Two Boys Made Their Own Electrical Apparatus

CHAPTER I.

CELLS AND BATTERIES.

APPARATUS 1.

1. Carbon-Zinc Cell. Fig. 1. If you have some rubber bands you can quickly make a cell out of rods of zinc and carbon. The rods are kept apart by putting a band, B, around each end of both rods. The bare wires are pinched under the upper bands. The whole is then bound together by means of the bands, A, and placed in a tumbler of fluid, as given in [App. 15]. This method does not make first-class connections between the wire and rods. ([See § 3.])

Fig. 1.

APPARATUS 2.

Fig. 2.

2. Carbon-Zinc Cell. Fig. 2. In case you want to make your cell out of carbon and zinc rods, and do not have any means of making holes for them in the wood, as in [App. 3] and [4], you will find this method useful. Cut grooves, G, into one side of the wood, A, which should be about 4½ × 1 × ½ in. The grooves should be quite deep, and so placed that the rods will be about ¼ in. apart. A strip of tin, T, ½ in. wide, should be bent around each rod. The screw, S, put through the two thicknesses of tin will hold the rod in place. Another screw, X, acts as a binding-post. The zinc rod only is shown in Fig. 2. The carbon rod is arranged in the same way. Use the fluid of [App. 15].

3. Note. When the bichromate solution of [App. 15] is used for cells, the strong current is given, among other reasons, because the zinc is rapidly eaten up. This action goes on even when the circuit is broken, so always remove and wash the zinc as soon as you have finished.

APPARATUS 3.

4. Carbon-Zinc Cell. Fig. 3. The wooden cross-piece, A, is 4½ × 1 × ½ in. The carbon and zinc rods, C and Z, are 4 in. long × ½ in. in diameter. The holes are bored, if you have a brace and bit, so that they are ¾ in. apart, center to center. This makes the rods ¼ in. apart. To make connections between the rods and outside wires, cut a shallow slot at the front side of each hole, so that you can put a narrow strip of tin or copper, B, in the hole by the side of each rod. Setscrews, S, screwed in the side of A, will hold the rods in place, and at the same time press the strips, B, against them. Connections can easily be made between wire and B by using a spring binding-post, D, or by fastening the wire direct to the strips, as shown in [App. 4].

Fig. 3.

Use the battery fluid given in [App. 15], and use a tumbler for the battery jar. This cell will run small, well-made motors, induction coils, etc. ([See § 3].)

APPARATUS 4.

5. Carbon-Zinc Cell. Fig. 4. The general construction of this cell is the same as that of [App. 3]. There are 2 carbons, C, each 4 × ½ in. The holes for these are bored in A 1¼ in. apart, center to center. The zinc rod, Z, is a regular battery zinc, 6 × ⅜ in., and has a binding-post, Y, of its own. The rods, C, are held in A, and connections are made as explained in [App. 3].

Fig. 4.

The wire, X, is fastened direct to the strips, B, as shown. When ready to use this cell, be sure that the wire connecting the carbons does not touch Z. (Why?) The other wire is connected to Y. The wooden piece is 4½ × 1 × ½ in. Use the battery fluid of [App. 15] in a tumbler. This cell will run small motors, and is good for induction coils, etc. ([See § 3].)

APPARATUS 5.

Fig. 5.

6. Experimental Cell. Fig. 5. Cut a strip each of copper, C, and zinc, Z. (See list of materials.) They should be about 2 in. wide and 4 in. long. Punch a hole through each, one side of the center, for screws, E. The wooden cross-piece, A, should be 4½ × 1 × ⅞ in. The battery-plates, or elements, should be screwed to this, taking care that the screws, E, do not touch each other. If the holes are made in the position shown in Fig. 5, the screws can be arranged some distance apart.

The wires leading from the cell may be fastened under the screws with copper burs, or spring binding-posts ([App. 42]) can be slipped on the top of the plates.

The solution to be used will depend upon what the cell is to do. For simple experiments use the dilute acid ([App. 14]). If for small motors, use the formula given in [App. 15]. The zinc should be well amalgamated. ([App. 20].)

APPARATUS 6.

Fig. 6.

7. Experimental Cell. Fig. 6. In some experiments a comparison is made between cells with large plates and cells with small ones. This form will be convenient to use where narrow plates are desired. Those shown are 4 × ½ in. They are screwed to the cross-piece, which is 4½ × 1 × ⅞ in. Do not let the screws touch each other. The wires are fastened under the screw-heads.

APPARATUS 7.

Fig. 7.

8. Experimental Two-fluid Cell. Fig. 7. This cell has a zinc strip, Z, and copper cylinder, C, for the "elements." The porous cup, P C, is fully described in [App. 11]. Z is 5 × 1 in., and should be well amalgamated ([App. 20]). (Study reasons for amalgamation.) A zinc rod, like that shown in Fig. 4, may be used instead of the strip. The copper cylinder, C, nearly surrounds P C, and is made from a piece of thin sheet-copper, 6 × 2 in. The narrow strip, or leader, A, is 5 × ½ in. To fasten it to C, punch two small holes in C and A, put short lengths of stout copper wire through the holes, and hammer them down so that they will act as rivets, R. C can be hung centrally in the tumbler by bending A as shown. Y and X are spring binding-posts ([App. 42]). The battery wires can be fastened directly to Z and A, as suggested in Fig. 4.

9. Setting up the Cell. Arrange as in Fig. 7, but remove Z from P C. Pour some of the acid solution of [App. 14] into P C until it stands about 2½ in. deep, and at once pour the copper solution of [App. 16] in the tumbler, on the outside of P C, until it stands at the same height as the liquid in P C. As soon as the liquids have soaked into P C, you can put Z in place, when the cell will be ready for use. Remove and wash Z, when you have finished, and if you wish to use this cell occasionally, remove the liquids and wash P C thoroughly in water. When dry it will be as good as new. The acid rapidly acts upon Z, so it is better to remove Z if you wish to leave the experimenting even for a few minutes only.

Put a few crystals of copper sulphate (blue vitriol) in the tumbler under the copper, to keep the copper solution saturated. (See text-book for the chemical action in this two-fluid cell.)

APPARATUS 8.

Fig. 8.

10. Two-fluid Battery. Fig. 8. When two or more cells are joined together the combination is called a battery. Fig. 8 shows two experimental cells joined in series. (Study methods of joining cells.) For convenience, and to keep them from being easily overturned, a frame has been made for them. The base, B, is 8 × 4 × ⅞ in. To the back of this is nailed the upright board, A, 8 × 4½ × ½ in. On the top of A are 3 binding-posts, 1, 2, 3, which consist of metal strips 1¼ × ½ in. At the lower ends are screws which are connected with the cells, as shown. Spring binders can be easily slipped on and off the upper ends of the strips, so that one or two cells can be used at will. Bent strips, C, are nailed to B, to hold the tumblers firmly in place. This framework is not necessary, of course, to the proper working of the battery, but with it you are much less liable to upset the cells.

APPARATUS 9.

11. Gravity Cell. Fig. 9. In the two-fluid cell of [App. 7] the fluids were kept apart by the porous cup. The gravity cell is really a two-fluid cell in which the two liquids are kept separate by the joint action of the current and the force of gravity. This cell is used for telegraph lines and for other closed-circuit work.

12. Construction. The zinc and copper, Z and C, Fig. 9, can be purchased about as cheaply as you can make them. There are many forms of the zincs, the one shown being called the crow-foot shape. The copper may be star-shaped, or as shown. If you wish to make C, use thin sheet-copper. Brush copper, 1¾ in. wide, is excellent for the purpose. Use a piece 12 or 15 in. long, and fasten to one end of it a copper wire, W, which must be covered with paraffined paper, or with rubber or glass tubing, where it passes up through the zinc sulphate solution and near Z. The glass jar, J, may be made from a large glass bottle. (See index for battery jars.)

13. To Set Up the Cell. (A) Place C upon the bottom of J, with W in the position shown. (B) Put in enough copper sulphate crystals to cover the bottom of J, but do not try to entirely cover C. At the start ½ lb. will be enough. (C) Pour in clean water until J is half full. (D) In another vessel dissolve 1 or 2 oz. of zinc sulphate in enough water to complete filling, J. (E) Hang Z in place (Fig. 9). Z must never touch C. They should be about 3 in. apart. A wire is attached to Z by the screw, S, and the hole, H. (F) Pour the zinc sulphate solution into J until it is within an inch of the top. It should cover Z.

Fig. 9.

(G) Connect the wires leading from Z and C to your sounder and key. (See diagram.) The cell will be weak at first, and it may not be able to run your sounder. If this is the case, "short-circuit" it by allowing the current to run around and around through the sounder and key, the switch being closed. You may also "short-circuit" the cell by joining the two wires together. This will, in a few hours, make the dividing line between the blue and white quite distinct, when the cell will be stronger. If you have a short line only, the battery may be short-circuited through your sounder or other coils of wire for 5 or 6 hours a day, without working it too much. It may be necessary to draw off some of the clear zinc sulphate, replacing it with clear water, if the blue line gets too low. Add water occasionally to make up for evaporation.

14. Regulating. The two solutions are kept apart by gravity, as the copper sulphate is heavier than the zinc sulphate. The dividing line between the blue and white solutions is fairly clear when the battery works well, and it should be about half way between C and Z, or about at J, Fig. 9. Never allow the blue to get as high as Z, as this indicates that the cell is not worked enough. The dividing line can be lowered by allowing it to run a buzzer or bell for a few hours, or by simply short-circuiting it. If the blue gets much below J it indicates that you are working the cell too hard, or that you need more copper sulphate. The harder the cell works, the more zinc sulphate is formed, and the lower the dividing line becomes.

15. Gravity Batteries of two more cells are needed when used on telegraph lines. You will need 1 cell to each sounder; that is, for a short line in the house with two sounders, use 2 cells. If you use a few hundred feet of wire running to a friend's house, use 3 cells. They must be joined in series; that is, the copper of one to the zinc of the other. (See diagram of complete telegraph line.) Do not use ground connections for short lines and home-made sounders; use a return wire. Do not use different kinds of cells upon the same line.

APPARATUS 10.

16. Storage Battery. To show the principle of storage batteries it is only necessary to use two plates of lead dipped in the battery fluid of [App. 14]. The cell may be made as in [App. 5], Fig. 5, the only difference being that both plates are of sheet-lead. It will be an advantage to make the plates rough by hammering against them a coarse file. (See explanations and experiments with this form of cell in text-book.)

APPARATUS 11.

Fig. 10.

17. Porous Cups for Two-fluid Cells. Fig. 10. Very good porous cups can be made from ordinary blotting-papers, the average ones measuring 9½ × 4 in. White ones should be used, so that you will not be bothered with the color coming out. Soak the edge along one end of the blotter in paraffine (Index) for about ¼ in. When this is cold, roll the blotter into the form of a cylinder that is a little over 1 in. inside diameter, and have the paraffined end on the outside. This will make 2 thicknesses of paper all around, and a little to spare. Rub a hot nail over the paraffine to melt it, and stick the end to the cylinder. By putting on a little more paraffine along the edge where the end laps over, a good solid cylinder can be made. The cylinder should be strengthened still more by dipping each end into melted paraffine for about ⅛ in. The dark stripes around the ends and down the front of the cylinder (Fig. 10) are to represent the paraffine. Cut out a bottom about ¼ in. larger all around than the cylinder. This may be paraffined to make it stiff. It should be fastened to the cylinder with paraffine. Paraffine is not acted upon or softened by water or acid, as is the case with glue.

APPARATUS 12.

18. Porous Cups for Two-fluid Cells. Instead of the blotters of [App. 11], you can use short lengths of mailing-tubes, which are used to protect pictures, etc., when sent by mail. If you find that the particular tube tends to unwind when soaked, you can use a little paraffine along the edges of the spiral, as suggested in [App. 11]. Bottoms can be made for the cups as before.

APPARATUS 13.

19. Porous Cups for Two-fluid Cells. Ordinary unglazed earthen flower-pots make good cups. The hole in the bottom should be closed with a cork, or by fastening a piece of pasteboard over the hole with paraffine. The pasteboard may be fastened to the under side of the bottom more easily than to the upper side.

20. Note. It is a good idea to soak the top edge of porous cups for about ¼ in. in paraffine to keep the solutions from crawling up by capillary attraction. If the solutions constantly evaporate from the soaked tops of the cups, they not only waste but they get the whole thing covered with crystals.

CHAPTER II.

BATTERY FLUIDS AND SOLUTIONS.

21. Sulphuric Acid. This acid must be handled with great care, as it (the concentrated) is very strong, and will burn the hands, eat holes in clothing, carpets, etc.; it will even char wood. Do not let any of it drop anywhere accidentally. If you wish to pour concentrated acid into a bottle, place the bottle to be filled upon a plate, and wipe all drops of acid from the outside of it afterward. The concentrated acid should be kept in tightly-corked bottles, as it absorbs moisture from the air very rapidly. Ordinary corks should be paraffined if they are to be used in acid bottles, or they will be soon eaten up.

22. Mixing. When sulphuric acid and water are mixed, considerable heat is produced. Never pour water into the acid, as the heat would be produced so rapidly that the vessel containing the mixture might break. Always pour the acid into the water, and thoroughly stir the mixture at the same time. Earthen vessels do not break when heated as easily as glass ones. The mixing may be done in ordinary glass fruit-jars, if care be taken to pour the acid slowly into the water. The jars should be set in some larger dish, or in the sink, before adding the acid. If they get too hot, allow them to cool a little before proceeding with the mixing. As the acid is much heavier than water, it will immediately sink to the bottom of the jar, unless constantly stirred.

23. There are different grades of acid upon the market. For battery purposes you do not need the chemically pure (C P) acid. The ordinary "commercial acid" is all right, even though it is a little dark in color. You can get this at any drug-store. Get 5 or 10 cents' worth at a time.

APPARATUS 14.

24. Battery Fluid for Simple Cells. For the simple cell ([App. 5]), when it is to be used for experiments with detectors or in the study of polarization, etc., a very dilute acid is best. Mix 1 fluid ounce of commercial acid with 1 pint of water. This will make 17 fluid ounces ([See App. 19]), and your mixture will be one-seventeenth acid. Make up a pint or quart bottle of this at a time, and label it with the date:

Dilute sulphuric acid.
1 part acid, 16 parts water.
Apparatus 14.

25. Note. Do not fail to paste a label on all bottles as soon as you have put anything into them. Give the date, contents, and any other information that will help you to reproduce the mixture again. Do not write on them any abbreviations or other things that you will soon forget.

APPARATUS 15.

26. Battery Fluid; Bichromate Solution. For running small motors, shocking coils, etc., this solution will be found good when used with the zinc and carbon elements given in [App. 3] and [4]. The bichromate destroys the hydrogen bubbles which help to polarize cells so rapidly when the plain dilute acid ([App. 14]) is used. (Study polarization.) The zinc used in this fluid must be well amalgamated ([App. 20]).

Directions. With 1 quart of cold water placed in a glass or earthen dish, slowly mix 4 fluid ounces of commercial sulphuric acid. [Read § 22] carefully. When this gets about cold, add 4 ounces of bichromate of potash. Powdered bichromate will dissolve more quickly than the lump. Keep this fluid in corked bottles, labelled, with date:

Bichromate Battery Fluid.
Apparatus 15.

27. Always take the zinc from this fluid as soon as you have finished experimenting, or even if you have no use for the cell for a few minutes. The zinc and fluid are rapidly destroyed in bichromate cells even when the circuit is open. Always wash the carbon and zinc as soon as you take them from the fluid.

APPARATUS 16.

28. Battery Fluid. For 2–fluid cells ([App. 7]), a saturated solution of copper sulphate (blue vitriol) is needed. Place some of the crystals in a glass jar, with water, stir them around, and add the sulphate as long as it is dissolved. A few extra crystals should be left in the stock bottle so that the solution will always be saturated.

APPARATUS 17.

29. Vinegar Battery Fluid. For a few of the experiments with detectors, etc., good strong vinegar does well as the exciting fluid. This may be used with the copper and zinc or carbon and zinc elements. The amount of current given with vinegar and [App. 4] or [5] is sufficient to show many of the simpler experiments.

APPARATUS 18.

30. Battery Fluid. Strong brine, made by dissolving ordinary salt in water, will produce quite a little current with [App. 4] or [5]. The presence of the current is easily shown with the astatic detectors.

APPARATUS 19.

31. Measures for Water, Acids, etc. If you do not own a graduated glass, such as druggists use for measuring liquids, the following plan will be found useful. In the mixing of battery fluids, etc., while it is not necessary to be absolutely exact, it is necessary to know approximately what you are doing.

An ordinary glass pint fruit jar may be taken as the standard. This holds 16 fluid ounces, or 2 ordinary teacupfuls. A teacupful may then be taken as ½ pint, or 8 fluid ounces. You can probably find a small bottle that will hold 1 or 2 oz., and you can easily tell how much it holds by filling it and counting the number of times it is contained in the pint can.

A slim bottle holding ½ pint can be made into a convenient measuring glass by scratching lines on it with the sharp edge of a hard file. The lines should be placed, of course, so that they will show how much liquid you must put into it to make 1 oz., 2 oz., etc. Instead of the file marks, a narrow strip of paper may be pasted upon the bottle, and the divisions shown by lines drawn upon the paper.

APPARATUS 20.

32. To Amalgamate Battery Plates. To keep the zinc plates or rods in cells from being eaten or dissolved when the circuit is opened, they should be amalgamated; that is, they should have a coating of mercury. The local currents (see text-book) aid in rapidly destroying the zinc, unless it is amalgamated. Do not amalgamate copper plates—merely the zinc ones.

33. Place a few drops of mercury in a butter dish. Dip the zinc into the solution of [App. 14], then lay it upon a flat board. This is necessary with thin sheet-zinc, as it becomes very brittle when coated with mercury, and will not stand hard rubbing. If you also dip a very narrow piece of tin into the dilute sulphuric acid, you can use this as a spoon and lift one drop of mercury at a time from the butter dish to the zinc. By tapping the tin upon the zinc, the mercury will leave the tin. Put the mercury only where the zinc will be under the solutions in the cell, then rub the drops around with a small cloth that has been dipped in the acid. The zinc will become very bright and silvery, due to the mercury. Do not get too much mercury on it, just enough to give it a thin coat, as it will make the thin zinc so brittle that it will very easily break. Amalgamate both sides of the zinc.

CHAPTER III.

MISCELLANEOUS APPARATUS AND METHODS OF CONSTRUCTION.

APPARATUS 21.

34. For Annealing and Hardening Steel. (See text-book for reasons why some parts of electrical apparatus should be made of hard steel, while other parts should be made of soft iron.)

35. To anneal or soften spring steel so that you can bend it without breaking it, heat it in a candle, gas, or alcohol flame until it is red-hot; allow the steel to cool in the air slowly.

36. To harden steel, heat as before, then suddenly plunge the red-hot piece into cold water. This will make the steel very hard and brittle.

Small pieces may be held by pinching them between two pieces of wood. Needles and wires may be stuck in a cork, which will serve as a handle. (See text-book.)

APPARATUS 22.

Fig. 11.

37. Alcohol Lamp. Fig. 11. An alcohol lamp is very useful in many experiments, and it is better than a candle for annealing or hardening steel needles when making small magnets ([App. 21]). You can make a good lamp by using a small bottle with a wide opening. A vaseline bottle or even an ink bottle will do. Make a hole about ¼ in. in diameter through the cork with a small round file, or burn it through with a hot nail. Make a cylinder of tin about 1½ in. long and just large enough to push through the hole. The tin may be simply rolled up. If you have glass tubing, use a short length of that instead of the tin. For the wick, roll up some flannel cloth. This should not fit the inside of the tin tube too tightly. The alcohol should be put into the lamp when you want to use it, and that left should be put back into the supply-bottle when you have finished, as alcohol evaporates very rapidly. The flame of this lamp is light-blue in color, and very hot.

Caution. Do not have your supply-bottle of alcohol near the lamp when you light the latter, or near any other flame. The vapor of alcohol is explosive.

APPARATUS 23.

38. Spool Holder for Wire. Fig. 12. When winding magnets it is necessary to have the spool of wire so arranged that it will take care of itself and not interfere with the winding. If you have a brace and bit, bore a hole in a base ⅞ in. thick for a ¼ in. dowel. The dowel should fit the hole tight. The spools of wire purchased can then be placed upon the dowel, where they will unwind evenly. The base may be nailed or clamped to a table.

Fig. 12.

APPARATUS 24.

39. Spool Holder for Wire. If you have no brace and bit to make [App. 23], nail a spool to a wooden base, place a short length of dowel in the spool, and use this combination as a spool holder. Make the dowel fit the spool by winding paper around it.

APPARATUS 25.

40. To Make Holes in Wood. If you have a brace and a set of bits, or even a small hand-drill, it will be an easy matter to bore holes in wood. An awl should be used to make holes for screws, such as those used in making binding-posts, etc., as the wood is very liable to split if a screw is forced into it without a previously-made hole.

Red-hot nails, needles, etc., are easily made to burn holes of desired diameters. They may be heated in a gas flame or by means of the alcohol lamp ([App. 22]). Flat pieces of hot steel will burn narrow slots, and small, square holes may be made with hot nails.

APPARATUS 26.

Fig. 13.

41. To Make Holes in Sheet-Metal. Fig. 13. Holes may be punched in sheet-tin, copper, zinc, etc., in the following manner: Set a block of hard wood, W, on end; that is, place it so that you will pound directly against the end of the grain. Lay the metal, T, to be punched, upon this, and use a flat-ended punch. A sharp blow upon a good punch with a hammer will make a fairly clean hole; that is, it will cut out a piece of metal, and push it down into the wood. A sharp-pointed punch will merely push the metal aside, and leave a very ragged edge to the hole. A punch may be made of a nail by filing its end flat.

APPARATUS 27.

42. To Punch Holes through Thick Yokes, etc. As soon as 5 or 6 layers are to be punched at one operation, the process becomes a little more difficult than that given in [App. 26]. If you have an anvil, you can place the yoke over one of the round holes in it, and punch the tin right down into the hole, the ragged edges being afterward filed off. Hold the yoke as in [App. 79] or [80] for filing. As you will probably have no anvil, lay an old nut from a bolt upon the end of the block of wood ([App. 26]), place the metal to be punched over the hole, and imagine that you have an anvil. Very good results may be obtained by this method. The size of nut used will depend upon the size of hole wanted.

APPARATUS 28.

43. To Straighten Wires. It is often necessary to have short lengths of wires straight, where they are to be made into bundles, etc. To straighten them, lay one or two at a time upon a perfectly flat surface, place a flat piece of board upon them, then roll them back and forth between the two. The upper board should be pressed down upon the wires while rolling them. If properly done, the wires can be quickly made as straight as needles.

44. Push-Buttons. Nearly every house has use for one or more push-buttons. The simple act of pressing your finger upon a movable button, or knob, may ring a bell a mile away, or do some other equally wonderful thing.

APPARATUS 29.

45. Push-Button. Fig. 14. This is made quickly, and may be easily fastened to the window or door-casing. One wire is joined to A and the other to C. B is a strip of tin or other metal, about ⅝ in. wide and 2 in. long. It is bent so that it will not touch A unless it is pressed down. This may be placed anywhere, in an electric-bell circuit or other open circuit, where it is desired to let the current pass for a moment only at a time.

Fig. 14.

APPARATUS 30.

46. Push-Button. Fig. 15 and Fig. 16. By placing [App. 29] in a box, we can make something that looks a little more like a real push-button. Fig. 15 shows a plan with the box-cover removed, and Fig. 16 shows a view of the inside of it, a part of the box being cut away. C, Fig. 15, is a wooden pill-box 1 in. high and 1¾ in. in diameter. Make a ¼ in. hole in the cover of C for the "button," G, which is a short piece of ¼ in. dowel. This rests upon a single thickness of tin, D, which is cut into a strip ⅜ in. wide and about 1¼ in. long. In the bottom of C are two holes just large enough to allow the screws E and F to pass through. The wires, A and B, pass from the binding-posts, X and Y, through small holes burned through the sides of the box, and are fastened under the screw-heads. The whole box is screwed to the wooden base, which is 3 × 4 × ⅞ in., by the screws, E and F. D should have enough spring in it to raise itself and G when the pressure of the finger is removed. The circuit will be closed only when you press the button.

APPARATUS 31.

47. Push-Button. Figs. 17, 18, 19. Fig. 17 shows a top view or plan of the apparatus. Fig. 18 is a sectional view; that is, we suppose that the button has been cut into two parts along its length and through the center line. Fig. 19 is an enlarged detail drawing of the underside of the spool, C. The same part is marked by the same letter in all of the figures.

Saw an ordinary spool, C, into two parts. One-half of C will serve as the outside case for the button. The part to be pressed with the finger is a short length of ¼ in. dowel. To keep this from falling out of the hole in C, a short piece of wire nail, N, has been put through a small hole in its lower end. A slot, F, has been burned or cut into the underside of C, so that N can pass up and down in it when D is raised and lowered. The rod, D, rests upon A, one of the contacts. This is a straight piece of tin, cut as shown in Fig. 17, the narrow part being ¼ in. wide and 1¼ in. long. The wide part is ¾ in. wide and 1 in. long. The other contact, B, is the same size as A. A deep groove, a little over ¼ in. wide, is cut into the base so that the narrow part of B can be bent down below the end of A. The base shown is 4 × 2½ × ⅞ in. The spool, C, is fastened to the base by 2 screws or wire nails put up through the base, their positions being shown by the dots at E, Fig. 17. X and Y, Fig. 18, are 2 screw binding-posts. It is evident that the current cannot pass from X to Y, unless the button, D, be pressed down so that the end of A will touch B.

APPARATUS 32.

48. Sifter for Iron Filings. Fig. 20. In making magnetic figures with iron filings, it is an advantage to have the particles of iron fairly small and uniform in size. A simple sifter may be made by pricking holes in the bottom of a pasteboard pill-box with a pin. The sifter may be put away with the filings in it, provided you turn it upside down.

Fig. 20.

APPARATUS 33.

49. Sifter for Iron Filings. Fig. 21. Punch small holes in the cover of a tin box with a small wire nail. If you have occasion to use sifters for other purposes, the different sizes can be made by using larger and smaller nails to punch the different tin covers. But one size of nail should be used for one sifter.

Fig. 21.

APPARATUS 34.

50. Sifters may be made by pricking holes in an envelope. A sifter with very small holes can be made of a piece of muslin cloth. This can be used in the form of a little bag, or a piece of it can be pasted over the open bottom of a pill-box.

APPARATUS 35.

51. To Cut Wires, Nails, etc. If you have no wire-cutters, or large shears, you can cut large or small wires by hammering them against the sharp edge of another hammer, an anvil, or a piece of iron. Do not let the hammer itself hit upon the edge of the anvil. The above process will make a V-shaped dent on one side of even large wires, or nails, when they may be broken by bending back and forth.

CHAPTER IV.

SWITCHES AND CUT-OUTS.

52. Switches, Cut-Outs. Where apparatus is to be used frequently, such as for telephone and telegraph lines, it pays to make your switches, etc., carefully. The use of these switches, etc., will be shown in the proper place. Their construction only will be given here.

APPARATUS 36.

Fig. 22.

53. Cut-Out. Fig. 22. Details. X, Y, and Z represent 3 binding-posts like [App. 42]. These are fastened to a wooden base that is about 3 × 5 × ¾. The ends of the wires shown come from and go to the other pieces of apparatus. Q shows a stout wire or strip of 2 or 3 thicknesses of tin. Suppose we have an apparatus, as, for example, an electric bell, which we want to have ring when someone at a distance desires to call us. If we use a telephone or telegraph instrument we shall want to cut the bell out of the circuit as soon as we hear the call and are ready to talk. Suppose the current comes to us through the wire, A, Fig. 22. It can pass by the wire, C, through the bell and back to X. If we wanted simply to have the bell ring, the current could pass directly from X into the earth, or over a return wire back to the push-button at our friend's house. If, however, we are to use some other instrument, by lifting the end of Q out of X and pushing it into Y, the bell will be cut out, and the current can pass on wherever we need it.

APPARATUS 37.

54. Cut-Out. Fig. 23. The main features of this are like those of [App. 36]. The three binding-posts are like [App. 46]. Instead of a band of metal to change connections, as Q in [App. 36], a stout copper wire is used. This can be easily changed from one of the upper binding-posts to the other, thereby throwing in or cutting out any piece of apparatus joined with the upper connectors.

APPARATUS 38.

55. Switch. Fig. 24. This simple switch has but one contact point, D, which is a screw-head. This switch may be used anywhere in the circuit by simply cutting the wire carrying the current, and joining the ends of the wire to the binding-posts X and Y. The metal strip, E, is made of 2 or 3 thicknesses of tin. It is ⅝ in. wide and about 5 in. long, and presses down upon D, when swung to the left, thus closing the circuit. The short metal strips shown are ⅝ × 1¼ in. The upper strip is joined to the end of E by a coiled copper wire, C W. (See [App. 50].) If the current enters by the wire, A, it will pass through C W, E, D and out at B. The strip E is pivoted at F by a small screw. The base may be 3 or 4 × 5 × ⅞ in.

APPARATUS 39.

56. Switch. Fig. 25. By increasing the number of contact points and the wires leading from them, a switch may be made to throw in one or more pieces of apparatus. This variety of switch is useful in connection with resistance coils (Index). By joining the ends of the coils with the points 1, 2, 3, etc., more or less resistance can be easily thrown in by simply swinging the lever, E, around to the left or right. The uses of this will be again referred to.

Fig. 25.

Details. The base of the one shown in Fig. 25 is 4 × 5 × ⅞ in. thick. The switch, E, is a band of 2 thicknesses of tin ⅝ in. wide. It is pivoted at F with a screw. To the end of E is fastened a copper wire, which leads to the upper binding-post, X ([App. 46]). The apparatus has 5 contact points, marked 1, 2, 3, etc. These consist of brass screws and copper washers. With F as a center draw the arc of a circle that has a radius of 4 in. Place the screws 1, 2, etc., along this arc, and about ⅝ in. apart, center to center; that is, the screws are all 4 in. from F, and are, therefore, in the form of a curve.

The last screw forms a part of the binding-post, Y. Suppose 4 pieces of apparatus, marked A, B, C, and D, be connected with 1, 2, etc., as shown. These may be, for example, coils of wire to be used as resistance coils. If the current enters at X, it will pass along at E and be ready to leave at Y, as soon as E touches one of the contact points. If E be placed upon 1, the current will be obliged to pass through all of the coils, A, B, etc., before it can get to Y. In this case the resistance will be greatest. If E be now moved on to 2, only A will be cut out, and the total resistance reduced. By placing E upon 4, but one coil, D, will be in the circuit. When E is upon 5 the current will pass through the switch with practically no resistance. This is the principle upon which current regulators work. (Study resistance in text-book.) When E is in the position shown in Fig. 25 no current can pass.

CHAPTER V.

BINDING-POSTS AND CONNECTORS.

57. Binding-Posts are used to make connections between two pieces of apparatus, between two or more wires, between a wire and any apparatus, etc., etc. They are used simply for convenience, so that the wires can be quickly fastened or unfastened to the apparatus. There are many ways of making them at home. The following forms will be found useful and practical. Although some that are given are really connectors instead of binding-posts, we shall give them the general name of binding-posts.

APPARATUS 40.

58. Binding-Post. About the simplest form is a screw, or a nail with a flat head. The bare wire may be placed under the head of the screw or nail before forcing it entirely into the wood. This will keep the end of the wire in place, and another wire may be joined electrically to the first by merely touching it to the screw-head, or by placing it under the screw-head.

APPARATUS 41.

Fig. 26.

59. Binding-Post. Fig. 26. This consists of a screw and a copper washer or "bur." The screw is a "round-headed brass" one, ⅝ in. long, number 5 or 7. The copper burs are No. 8, and fit nicely around the screws. By using 2 burs instead of 1, several wires may be easily joined together at one point. Scrape the covering from the ends of the wires, and place them between the burs.

APPARATUS 42.

60. Binding-Post. Fig. 27. A coiled spring serves very well as a connector. One end should be fastened to the apparatus, as shown, by clamping it under a screw-head. The other end of the coil should be pulled out a little, away from the other turns, so that you can stretch the spring in order to put the bare ends of wires between the turns. Any number of wires placed between these turns will be pinched and electrically connected. The coil should be about ½ in. long and less than ½ in. in diameter. You can make a coil by tightly wrapping stiff iron wire around a pencil. The steel wire springs taken from old window-shades are excellent for this purpose. They may be cut into lengths with tinner's shears.

APPARATUS 43.

61. Binding-Post. Fig. 28. Two copper or tin strips fastened at one end by a screw, the upper strip being bent a little at one end, make a connector that is useful for some purposes, where you want to make and break the connection frequently. The bare end of the wire which belongs to the apparatus is fastened under the screw-head. The outside wire, or wires, to be connected are pushed between the strips of metal. Another way is to fasten the outside wire to a strip of metal about ½ in. wide, and then push this between the strips shown in the figure. The strips shown should be about ¾ in. wide and 1¼ in. long.

APPARATUS 44.

62. Binding-Post. Fig. 29. A combination made between [App. 42] and [43] does well. Fasten a metal strip, ¾ in. × 1¼ in., to the apparatus by means of a screw. The apparatus wire should be fastened under the screw-head. A short length of spring may be pushed upon the upright part of the strip, as shown. Into this you can quickly fasten the outside wires.

APPARATUS 45.

63. Binding-Post. Fig. 30. This makes a very simple and practical binding-post for home-made apparatus. It consists of a screw-eye, preferably of brass. The circle or eye should be about ⅜ or ½ in. in diameter. The thread on such a screw-eye will be about ½ in. long. Two copper burs are used to pinch the wires.

APPARATUS 46.

64. Binding-Post. Fig. 31. This consists of a screw, screw-eye, bur and a metal strip, ¾ × 1¼ in. The apparatus wire should be fastened under the screw-head. Any outside wires which are to be joined to the apparatus should be clamped under the bur by turning the screw-eye. A small hole should be made in the wood before putting in the screw-eye. (See [App. 25].) Do not turn the screw-eye too hard, or you will spoil the thread made in the wood.

APPARATUS 47.

65. Binding-Post. Fig. 32. The size of the bolt used in this form of binding-post will depend somewhat upon the thickness of the base of the apparatus. In general, a ¾ or ⅞ in. base should be used where screws or screw-eyes are necessary. With this kind (Fig. 32) a thin base can be used. The head is shown counter-sunk into the bottom of the base. This is not necessary, provided at least 3 heads are placed far enough apart to form legs for the apparatus to stand on. Strips of wood may be nailed upon the underside of the base to make room for the heads in case they are not used as legs. The wires should be pinched between the nut and the copper bur shown. If the bolt is too large for a bur, an iron washer may be used. A washer may be made of tin, or two nuts may be used.

APPARATUS 48.

Fig. 33.

66. Binding-Post. Fig. 33. This is a suggestion for a combination of [App. 44] and [47]. It is useful in school apparatus. Wires may be permanently fastened on the right, under the nut, and a spring, as in [App. 44], may be slipped on the metal strip at the left, which is held under the head of the bolt.

APPARATUS 49.

67. Mercury Connector. A cup of mercury may be used as a connector. Make a small hole about ¼ in. in diameter and depth, in a piece of wood, and place 2 or 3 drops of mercury in this. The ends of wires dipped in this will be electrically connected.

APPARATUS 50.

Fig. 34.

68. Connector. Fig. 34. This shows how a wire may be fastened to one end of a short strip of tin. At the other end of the strip a slot is cut. This may straddle the body of a screw, or when left plain may be used to slip between the two metal strips shown in [App. 43].

APPARATUS 51.

69. Binding-Post. Fig. 35. The ends of two or more wires may be quickly joined electrically by placing them between the nuts of a short bolt. By using 3 nuts the bolt will more easily connect a large number of wires.

Fig. 35.

Make Additional Notes and Sketches Here.

CHAPTER VI.

PERMANENT MAGNETS.

70. Permanent Magnets may be made in many ways and from many different kinds of steel. The steel used for needles, watch and clock springs, files, cutting tools, etc., is generally of good quality, and it is already hard enough to retain magnetism. (See Retentivity in text-book.)

APPARATUS 52.

71. Bar Magnet. A straight magnet is called a bar magnet. Magnetize a sewing-needle. For some experiments a needle-magnet, as we may call it, is better than a large magnet.

APPARATUS 53.

72. Bar Magnet. A harness-needle, which is thicker and stronger than a sewing-needle, makes an excellent bar magnet.

APPARATUS 54.

73. Bar Magnet. For long slim magnets use a knitting-needle. Some knitting-pins, as they are sometimes called, break off short when bent, but most of them will bend considerably before breaking. These slim magnets are excellent for the study of Consequent Poles. (See text-book.)

APPARATUS 55.

74. Flexible Bar Magnets. It is often necessary to have flexible magnets so that they may be bent into different shapes. These may be made from watch or clock springs, as such steel, called spring steel, will straighten out again as soon as the pressure is removed from it. Corset steels, dress steels, hack-saw blades, etc., make good thin flexible bar magnets.

APPARATUS 56.

75. Strong Bar Magnets may be made from flat files. The handle end may be broken off so that the two ends of the file shall be nearly alike in size. These should be magnetized upon an electro-magnet.

APPARATUS 57.

76. Compound Bar Magnets are made by first magnetizing several thin pieces of steel, and then riveting them together so that their like poles shall be together, and pull together. To make a small compound bar magnet, magnetize several harness-needles, or even sewing-needles, and then bind them into a little bundle with all the N poles at the same end. Melted paraffine dropped in between them will hold them together. Rubber bands may be used also, or, if but one end is to be experimented with, the points may be stuck into a cork, and the heads used to do the lifting.

APPARATUS 58.

77. Small Horseshoe Magnets may be made from needles or from other pieces of steel used for bar magnets. They should be annealed ([App. 21]) at their centers at least, so that you can bend them into the desired shape. In the case of bright needles, like harness-needles, the part annealed will become blackened. If you heat the center only, and the ends remain bright for about ½ inch, you will not need to harden the needle again. It is an advantage to have the center of the magnet a little soft, as it is not then liable to break. The ends alone may be hardened by holding the bent portion away from the candle or gas flame, while heating the ends. The bent steel should be magnetized by drawing its ends across the poles of a horseshoe magnet.

APPARATUS 59.

78. Flexible Horseshoe Magnets may be made of thin spring steel. The distance between the poles can be regulated at will by bending the steel more or less. The poles may be held at any desired distance apart by thread or wire, which should be wound around the legs of the magnet a little above the poles. This will keep the steel from straightening out.

APPARATUS 60.

79. Horseshoe Magnet. Fig. 36 and 37. Magnetize two harness-needles, and stick them into a cork so that the poles shall be arranged as shown. The distance between the poles can be regulated to suit. This forms a very simple and efficient magnet, with the advantages of a real horseshoe magnet.

APPARATUS 61.

80. Armatures. All home-made magnets should be provided with armatures, or keepers. These are made of soft iron on the regular magnets, and tend to keep the magnet strong. (See text-book.) For the bar magnets described, a piece of sheet-tin, upon which to lay them, is all that is needed for an armature. The lines of force will pass through this. For the horseshoe magnets described, strips of tin, soft iron wires, or even a wire nail placed across the poles will greatly aid in keeping in the strength. The little magnets should not be dropped or jarred. (Study the theory of magnetism in text-book.)

CHAPTER VII.

MAGNETIC NEEDLES AND COMPASSES.

81. Magnetic Needles and Compasses consist chiefly of a short bar-magnet. When used to tell the directions, north, east, etc., the apparatus is generally called a compass. When we speak of the "needle," we really mean the compass-needle. The little magnet may be almost any piece of magnetized steel, provided it is arranged so that it can easily swing around. There are several ways of supporting the compass-needle. It may rest upon a pivot, it may be hung from a fine thread, or it may be floated upon water with the aid of a cork, etc.

82. Uses. We all know that compasses are used to point to the north and south, and we speak of the "points of the compass." This, of course, is the most important use of the compass, and it has been known for centuries. In the laboratory it is used to show or detect the presence of currents of electricity, and, in connection with coils of wire, it may show the relative strengths of two currents, etc. When used for such purposes it generally has special forms and sizes. ([See Galvanometers and Detectors.])

APPARATUS 62.

83. Compass. An oily sewing-needle will float upon the surface of water, when it is carefully let down to the water. A little butter may be rubbed upon the previously-magnetized needle to make it float better.