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 Sec.
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