** How to Make a Bunsen Cell [206]

This kind of a cell produces a high e.m.f. owing to the low internal resistance.  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 pieces found in a scrap pile that usually occupies a fence corner on almost every farm.  The cylinder consists of

[Illustration:  Complete Homemade Gasoline Engine]