s 4-1/2 x 1 x
1/2 in. The carbon and zinc rods, C and Z, are 4 in. long x 1/2 in. in
diameter. The holes are bored, if you have a brace and bit, so that they
are 3/4 in. apart, center to center. This makes the rods 1/4 in. apart.
To make connections between the rods and outside wires, cut a shallow
slot at the front side of each hole, so that you can put a narrow strip
of tin or copper, B, in the hole by the side of each rod. Setscrews, S,
screwed in the side of A, will hold the rods in place, and at the same
time press the strips, B, against them. Connections can easily be made
between wire and B by using a spring binding-post, D, or by fastening
the wire direct to the strips, as shown in App. 4.

[Illustration: Fig. 3.]

Use the battery fluid given in App. 15, and use a tumbler for the
battery jar. This cell will run small, well-made motors, induction
coils, etc. (See Sec. 3.)

APPARATUS 4.

_5. Carbon-Zinc Cell._ Fig. 4. The general construction of this cell is
the same as that of App. 3. There are 2 carbons, C, each 4 x 1/2 in. The
holes for these are bored in A 1-1/4 in. apart, center to center. The
zinc rod, Z, is a regular battery zinc, 6 x 3/8 in., and has a
binding-post, Y, of its own. The rods, C, are held in A, and connections
are made as explained in App. 3.

[Illustration: Fig. 4.]

The wire, X, is fastened direct to the strips, B, as shown. When ready
to use this cell, be sure that the wire connecting the carbons does not
touch Z. (Why?) The other wire is connected to Y. The wooden piece is
4-1/2 x 1 x 1/2 in. Use the battery fluid of App. 15 in a tumbler. This
cell will run small motors, and is good for induction coils, etc. (See
Sec. 3.)

APPARATUS 5.

[Illustration: Fig. 5.]

_6. Experimental Cell._ Fig. 5. Cut a strip each of copper, C, and zinc,
Z. (See list of materials.) They should be about 2 in. wide and 4 in.
long. Punch a hole through each, one side of the center, for screws, E.
The wooden cross-piece, A, should be 4-1/2 x 1 x 7/8 in. The
battery-plates, or elements, should be screwed to this, taking care that
the screws, E, do not touch each other. If the holes are made in the
position shown in Fig. 5, the screws can be arranged some distance
apart.

The wires leading from the cell may be fastened under the screws with
copper burs, or spring binding-posts (App. 42) can be slipped on the top
of the plates.

The solution to be used will depend upon what the cell is to do. For