bars, AA, Fig. 1.

Cut six pieces, 17-1/2 in. long and punch holes to fit and rivet
onto the remaining holes in cross bars, AA, Fig. 1. Clean it up
and give it a coat of black Japan or dead black.

** Trap for Small Animals [82]

This is a box trap with glass sides and back, the panes of glass
being held in place by brads placed on both sides. The animal does
not fear to enter the box, because he can see through it: when he
enters, however, and touches the bait the lid is released and,
dropping, shuts him in. This is one of the easiest traps to build
and is usually successful.

[Illustration: Trap]

** Homemade Grenet Battery [83]

Procure an ordinary carbon-zinc, sal-ammoniac battery and remove
the zinc rod. If the battery has been used before, it is better to
soak the carbon cylinder for a few hours to remove any remaining
crystals of sal-ammoniac from its pores.

The truncated, conical zinc required is known as a fuller's zinc
and can be bought at any electrical supply dealer's, or, it may be
cast in a sand mold from scrap zinc or the worn-out zinc rods from
sal-ammoniac batteries. It should be cast on the end of a piece of
No. 14 copper wire. Amalgamation is not necessary for the zinc one
buys, but if one casts his own zinc, it is necessary to amalgamate
it or coat it with mercury. This may be done as follows:

Dip a piece of rag in a diluted solution of sulphuric acid (water
16 parts, acid 1 part); rub the zinc well, at the same time
allowing a few drops of mercury to fall on a spot attacked by the
acid. The mercury will adhere, and if the rubbing is continued so
as to spread the mercury, it will cover the entire surface of the
zinc, giving it a bright, silvery appearance.

Next procure what is known as a wire connector. This is a piece of
copper tube about 1-1/2 in. long having two thumb screws, one on
each end on opposite sides (Fig. 2). The upper screw is to connect
the battery wire, the lower one to raise and lower the zinc. The
battery is now complete, and the solution (Fig. 1) must be
prepared. Proceed as follows:

In 32 oz. of water dissolve 4 oz. potassium bichromate. When the
bichromate has all dissolved, add slowly, stirring constantly, 4
oz. sulphuric acid. Do not add the acid too quickly or the heat
generated may break the vessel containing the solution. Then pour
the solution into the battery jar, until it is within 3 in. of the
top. Thread the wire holding the zinc through the po