Part 18 (1/2)

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 a.s.sortment from 1/2 in. long up to 1-1/2 in.

295. Screws. It is better to use bra.s.s 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. Sh.e.l.lac. Your wood-work will be much improved by using sh.e.l.lac 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 sh.e.l.lac bottle tightly corked. A small tin can or a teacup is best to hold the sh.e.l.lac when using it.

THINGS A BOY SHOULD KNOW ABOUT ELECTRICITY.

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

The book contains 180 pages, and 260 ill.u.s.trations; it measures 5 7-1/2 in., and is bound in cloth.

Seventh Edition Price, postpaid, $1.00

CONTENTS: Chapter I. About Frictional Electricity.--II. About Magnets and Magnetism.--III. How Electricity is Generated by the Voltaic Cell.--IV. Various Voltaic Cells.--V. About Push-b.u.t.tons, Switches and Binding-Posts.--VI. Units and Apparatus for Electrical Measurements.--VII. Chemical Effects of the Electric Current.--VIII. How Electroplating and Electrotyping are Done.--IX.

The Storage Battery and How it Works.--X. How Electricity is Generated by Heat.--XI. Magnetic Effects of the Electric Current.--XII. How Electricity is Generated by Induction.--XIII.

How the Induction Coil Works.--XIV. The Electric Telegraph, and How it Sends Messages.--XV. The Electric Bell and Some of its Uses.--XVI. The Telephone, and How it Transmits Speech.--XVII. How Electricity is Generated by Dynamos.--XVIII. How the Electric Current is Transformed.--XIX. How Electric Currents are Distributed for Use.--XX. How Heat is Produced by the Electric Current.--XXI.

How Light is Produced by the Incandescent Lamp.--XXII. How Light is Produced by the Arc Lamp.--XXIII. X-Rays, and How the Bones of the Human Body are Photographed.--XXIV. The Electric Motor and How it Does Work.--XXV. Electric Cars, Boats and Automobiles.--XXVI. A Word About Central Stations.--XXVII. Miscellaneous Uses of Electricity.

This book explains, in simple, straightforward language, many things about electricity; things in which the American boy is intensely interested; things he wants to know; things he should know.

It is free from technical language and rhetorical frills, but it tells how things work, and why they work.

It is brimful of ill.u.s.trations--the best that can be had--ill.u.s.trations that are taken directly from apparatus and machinery, and that show what they are intended to show.

This book does not contain experiments, or tell how to make apparatus; our other books do that. After explaining the simple principles of electricity, it shows how these principles are used and combined to make electricity do every-day work.