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. [Illustration: FIG. 185.—Apparatus for Electrolysis Experiment.] Water is composed of oxygen and hydrogen and so bubbles of oxygen and hydrogen gas will rise from the liquid. Figure 185 illustrates a very simple arrangement for decomposing acidulated water into oxygen and hydrogen gases. It consists of a bottle with the bottom broken out, and provided with a cork fitted snugly into the neck. Two glass tubes pass through the cork. A small piece of platinum wire is sealed into the inside end of each glass tube. The platinum wires are connected to copper wires leading out of the lower ends of the tubes. If the bottle is inverted and filled with a dilute solution of sulphuric acid, the current from two or three dry cells will decompose the water. The battery should be connected to the wires running through the glass tubes. Bubbles of gas will rise from the platinum wires. Oxygen gas will rise from the positive wire or electrode and hydrogen gas from the negative electrode.