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. Brass 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.

[Illustration: Fig. 125.]

287. Copper Wire. This can be bought at an electrician's. The only trouble, however, in buying small quantities 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.

289. Copper. Sheet-copper can be purchased at a tinsmith's or at a hardware store. Electricians usually have a thin variety of copper called brush copper, which makes good battery-plates, binding-posts, etc. You can cut this thin copper with an ordinary pair of shears.

290. Iron. For thin sheet-iron, nothing is better than sheet-tin. (See tin.) Hoop iron is thicker than tin, and makes good yokes, etc. In many cases, ordinary nails may be used where a magnetic substance is needed. Annealed iron wire is extremely soft. (See text-book for experiments with steel and iron.)

291. Steel. Old files, watch-springs, clock-springs, corset-steels, knitting-needles, harness-needles, hack-saw blades, sewing-needles, etc., are generally made of a good quality of steel.

292. Zinc, in the sheet form, can be bought at a hardware store. For a few cents you can get quite a large piece. Get the thick pieces for heavy battery-plates of an electrician. You do not need anything that is thicker than 1/8 in. The zinc rods are usually amalgamated.

293. Lead can be bought at a plumber's, tinsmith's, or hardware store. You may want some for a storage cell.

294. Nails. Wire nails are best for light work. Get an assortment from 1/2 in. long up to 1-1/2 in.

295. Screws. It is better to use brass screws around electrical apparatus. For the small work, for binding-posts, etc., use 5/8 No. 5. Another handy size is No. 7, from 3/4 to 1-1/4 in. long. The round-headed screws are best, unless you want to countersink them.

296. Tin. This is really thin sheet-iron, covered with tin. Save up tomato-cans, cracker-boxes, condensed-milk cans, etc. The cracker-boxes are just as good as sheet-tin, as the pieces are large and clean. You can remove the solder from cans by heating them in the kitchen fire. Knock out the bottoms with a poker when the solder gets soft. Clean the tin with sand-paper.

297. Carbons. You can get carbon rods or plates at an electrician's. If you have arc electric lights in your city, you will be able to pick up carbons; these, however, generally have a coating of copper, which must be eaten off with dilute nitric acid. This is a bother. You will find it cheaper to buy the 1/2 in. rods that are 12 in. long, and uncoated.

298. Shellac. Your wood-work will be much improved by using shellac upon it after you have thoroughly sand-papered it. You can get it, all prepared, at a paint store. Wood-alcohol is used to thin it if it gets too thick. Keep it in a wide-mouth bottle. Paint it on quickly and evenly with a brush, and do not go over it again when it is partly dry. Wait until it is thoroughly hard before putting on a second coat. It should be fairly thin to spread well. Clean your brush in wood-alcohol before putting it away, and keep the shellac bottle tightly corked. A small tin can or a teacup is best to hold the shellac when using it.

* * * * *

THINGS A BOY SHOULD KNOW ABOUT ELECTRICITY.

By THOMAS M. ST. JOHN, Met. E.

The book contains 180 pages, and 260 illustrations; it measures 5 × 7-1/2 in., and is bound in cloth.

Seventh Edition Price, postpaid, $1.00

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