Part 17 (2/2)

_277. Battery Jars._ For small cells, use gla.s.s tumblers. Ordinary gla.s.s fruit jars are good. Even earthen bowls may be used, and for large cells--if you have nothing better--you can use small earthen crocks or jars.

278. Gla.s.s Bottles can be cut off so that they will make excellent jars.

If you have thin bottles, you can cut them with strong cord. Tie one end of the cord, which should be 5 or 6 feet long, to a door k.n.o.b or to a solid post. Tie the other end around your body. Make one complete turn of the cord around the bottle where you wish to cut it; draw the cord tight by stepping back, and with both hands draw the bottle back and forth vigorously many times, so that the cord will rub it hard and make it very hot. Do not let the cord move lengthwise upon the bottle. This will make a circle around the bottle that is very hot. Immediately plunge the bottle into cold water, the colder the better. Use ice-water, if you have it. If you produce heat enough, the bottle should crack all the way around very neatly. File off any sharp corners and edges with a wet file.

279. A hot iron can be used with success to cut off a bottle. File a deep groove first, hold the red-hot iron first on one side of file mark and then on the other to start the crack. You can lead the crack wherever you wish by keeping the iron about 1/8 in. ahead of it.

280. A small gas-flame will be much better than a hot iron, and you may easily use it, if you have gla.s.s tubing, rubber tubing, etc., in your shop. Draw out the gla.s.s so that the gas will burn in a fine needle-like flame about 1 in. long. Keep the point of the flame about 1/4 in. ahead of the crack. The gla.s.s tube should be held in a rubber tube connected with the gas pipe.

CHAPTER XXI.

TOOLS AND MATERIALS.

_281. Your Workshop._ If possible, keep all your work, tools and apparatus in one room, and lock the door when you leave.

The work-bench may be made of an old kitchen table, or of a strong, large box. The tool chest may be made of any clean box about the size of a soap box. Shelves can be made by setting soap or starch boxes on their sides, one above the other.

_282. The tools_ needed are generally mentioned in the proper places, under the directions for construction. It is better to buy your tools as required, than to buy too many at once, some of which you may not need.

If you have absolutely no tools, not even a saw or hammer, you will be obliged to buy or borrow, although a great deal can be done with a good knife. Do not be satisfied with rough-looking pieces of apparatus.

There are a few important tools needed for this work. While subst.i.tutes can be found for most of them, the boy who has access to a wood-working bench and tools will be able to do better and more rapid work than the boy who has no such tools.

283. List of tools. The following tools are needed, if rapid, accurate work is desired:

(1.) Lead pencil. (2.) A rule, divided into sixteenths for measuring. A straight foot rule will do,--cost one cent. (3.) Steel point for scratching lines on tin and copper. A stout needle-point is just the thing. (4.) An awl for making holes in wood; one that is a little less than 1/8 in. in diameter is best. (See App. 25.) (5.) A try-square with a 6 in. blade, so that you can mark out your apparatus with square corners. You can use a square-cornered box or piece of pasteboard, if you have no try-square. (6.) Chisels are very useful, but you can do wonders with a good sharp knife. (7.) Screw-driver. Do not use a good knife-blade for a screw-driver. (8.) A saw, one with teeth that are not too coa.r.s.e is to be preferred. (9.) A plane is extremely useful to make your wood-work smooth and neat; but a great deal can be done with the sharp edges of broken gla.s.s, followed by a good rubbing with fine sand-paper. (10.) A brace and a set of bits may be needed in 2 or 3 cases, but nearly all of the holes can be made as in App. 25. (11.) Punches for sheet-tin, etc., will save much time. (See App. 26, 27.) For small holes in binding-posts, etc., use a flat-ended punch, 1/8 in. in diameter. You should have one 1/4 or 5/16 in. in diameter, if you make your yokes, armatures, etc., as in Chapter VIII. A blacksmith will help you out with this. (12.) A center-punch or sharp-pointed punch for making dents in metal. A sharp-pointed wire nail will do for tin and copper. (13.) Files for metal. (14.) Some sort of a vice or clamp. (See App. 79, 80.) (15.) Shears for cutting sheet-tin, etc. A pair of old shears will do. (16.) An anvil or piece of old iron that may be used to hammer on to flatten tin, etc. An old flat-iron makes a good anvil.

(17.) Hammer.

The small hollow handle tool sets are very handy, and they contain small chisels, awls, screw-driver, etc. These sets cost from 50 cents up.

_284. Materials._ For wood you will find the sides and ends of clean soap or starch boxes about the right thickness; they are fairly smooth to begin with. For thin wood use cigar boxes. The pieces from old boxes should be removed with care, and saved in one place, which may be called your lumber yard. All nails should be removed with a claw-hammer. Look out for nails when using a saw, plane or other edged tool. (See -- 297.) The edges of bases, etc., may be bevelled as shown in Fig. 95. This is not necessary, but it adds greatly to the appearance.

285. Screw-Eyes. Bra.s.s screw-eyes, with copper burs, make excellent binding-posts. (App. 45, 46.) Those that are 3/8 in. in diameter inside the circle are about right. These are about 1-1/4 in. long in all, with a 1/2 in. thread.

286. Copper Burs, such as are used with rivets, are very handy. The size that is 1/2 in. in diameter, with a 1/8 in. hole, is good.

[Ill.u.s.tration: Fig. 125.]

287. Copper Wire. This can be bought at an electrician's. The only trouble, however, in buying small quant.i.ties is that you may have to pay a large price in proportion. If you get it on 1/2 lb. spools you can handle it much better (see App. 23) than you can if you have it in a tangle. It is well to have 1/2 lb. of No. 24 or 25 for electro-magnets, current-detectors, etc., etc. 1/2 lb. of No. 30 will not be too much, if you make induction coils. If you handle your wire carefully, single cotton-covered will do. Double cotton-covered is better than single, but it costs more. Be careful not to injure the covering. (See below for splicing wire.) Look out for broken wire.

288. Splicing Wire. Fig. 125. Do not simply touch two wires together and imagine that you have a good connection; a mere twist is not sufficient. Clean the ends of old wire thoroughly with a file or knife-blade, and join them as shown in Fig. 125.

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