It is a good plan to use two telephone receivers mounted on a head band so that both ears can be used and the hands left free to manipulate the switch. If a set of telephone receivers wound to a high resistance for wireless telegraph purposes is used it will greatly increase the range of the outfit.
Six to eight first class dry cells will be required to form the battery. A push button is placed in series with the transmitter so that the battery current will be consumed only when the button is pressed. This makes it necessary to push the button when sending a message. When the lever of the two point switch rests on the contact A the circuit is completed for transmitting. When the lever rests on B the telephone receivers are connected to the coil and the apparatus is ready for receiving a message.
If the apparatus is used only for demonstrating purposes, a camera tripod will be found very convenient for supporting the coils. The transmitter and switch can be fastened to the top of the tripod and the batteries placed in a box on the ground. It is absolutely necessary that the coils be perfectly parallel to each other when messages are being transmitted back and forth. It is well to start with the coils comparatively close to each other, say ten or twelve feet at first, and then gradually increase the distance.
Coils approximately four feet in diameter and containing about seventy-five turns of wire will transmit and receive messages about one hundred and fifty feet. The range can be increased slightly by using more batteries. If too much battery is used, however, the telephone transmitter will become very hot and is liable to burn out.
It is impossible, of course, to "call up" over a set of wireless phones such as these. If you succeed in getting your set to work satisfactorily with your chum across the street and wish to talk to him it will be necessary for you to arrange some predetermined time.
In order to operate your phone place the switch lever on the contact A. Hold your finger tightly against the push button so that the circuit is completed and talk slowly and distinctly into the transmitter. The transmitter will operate the best when the mouthpiece points on a level with your mouth. The lips should be about one inch away from the mouthpiece. Speak in a low even tone. The switch at your friend’s station should be resting on B. When you finish speaking throw your switch to B and listen in your telephone receivers. The operator at the other station should throw his switch to A and push the button. He may then talk to you.
CHAPTER XIX. MISCELLANEOUS EXPERIMENTS AND APPARATUS.
ELECTROLYSIS.
Liquid which will conduct a current of electricity is called an *electrolyte*. All electrolytes are compounds, that is, they consist of more than one substance. When an electric current passes through a liquid it decomposes it. This process of decomposition is called *electrolysis*.
Pure water is not a conductor of electricity. If sulphuric acid is added to water, the mixture become an electrolyte and will conduct. If an electric current is passed through water containing sulphuric acid, it will decompose the water.