. Procure a glass jar such as used for a
gravity battery, or, if one of these cannot be had, get a glazed
vessel of similar construction. Take a piece of sheet zinc large
enough so that when it is rolled up in the shape of a cylinder it
will clear the edge of the jar by about 1/2 in. Solder a wire or
binding-post to the edge of the cylinder for a connection.

[Illustration: Cross Section and Completed Cell]

Secure a small unglazed vessel to fit inside of the zinc, or such
a receptacle as used in a sal ammoniac cell, and fill it with a
strong solution of nitric acid. Fill the outer jar with a solution
of 16 parts water and 5 parts sulphuric acid. The connections are
made from the zinc and carbon.

** Optical Illusion [206]

Can you tell which of these three figures is the tallest? Make a
guess, and then verify its correctness by measurement.

[Illustration: Who is tallest?]

** One Way to Cook Fish [206]

One of the best and easiest ways of cooking fish while out camping
is told by a correspondent of Forest and Stream. A fire is built
the size for the amount of food to be cooked and the wood allowed
to burn down to a glowing mass of coals and ashes. Wash and season
your fish well and then wrap them up in clean, fresh grass, leaves
or bark. Then, after scraping away the greater part of the coals,
put the fish among the ashes, cover up with the same, and heap the
glowing coals on top. The fish cooks quickly--15 or 20
minutes--according to their size.

If you eat fish or game cooked after this fashion you will agree
that it cannot be beaten by any method known to camp culinary
savants. Clay also answers the purpose of protecting. the fish or
game from the fire if no other material is at hand, and for
anything that requires more time for cooking it makes the best
covering. Wet paper will answer, especially for cooking fish.

** Hardening Copper [206]

A successful method of hardening copper is to add 1 lb. of alum
and 4 oz. arsenic to every 20 lb. of melted copper and stir for 10
minutes.

** Packing Cut from Felt Hats [206]

Felt from an old hat makes good packing for automobile
water-circulating pumps. Strips should be cut to fit snugly in the
stuffing box. When the follower is screwed down, it will expand
the felt and make a watertight joint.

** Homemade Gasoline Engine [206]

The material used in the construction of the gasoline engine, as
shown in the accompanying picture, was p