How Two Boys Made Their Own Electrical Apparatus Part 2

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 gla.s.s 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 gla.s.s, 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 gla.s.s 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 1/2 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 1/2 pint can be made into a convenient measuring gla.s.s 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 b.u.t.ter 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 b.u.t.ter 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.

[Ill.u.s.tration: 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 1/4 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 1-1/2 in. long and just large enough to push through the hole. The tin may be simply rolled up. If you have gla.s.s 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 7/8 in. thick for a 1/4 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.

[Ill.u.s.tration: 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.

_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.

[Ill.u.s.tration: Fig. 13.]

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.