234 ELEMENTS OF ELECTRICITY AND MAGNETISM. 



peculiar odor which is given off by a Toepler-Holtz machine or a 

 Wimshurst machine is due to the ozone which is formed. The 

 action which takes place in the formation of ozone from oxygen 

 is as follows : Ordinary oxygen is bi-atomic, that is, it contains 

 two atoms of oxygen in the molecule. lonization causes the dis- 

 integration of these bi-atomic molecules forming mono-atomic 

 oxygen, and this mono-atomic oxygen recombines forming a 

 large proportion of bi-atomic oxygen again and a small propor- 

 tion of tri-atomic oxygen, or ozone. In the production of ozone 

 for commercial purposes a blast of air is driven between two 

 metal plates which are connected to a high voltage alternator. 

 The repeated reversals of the high electromotive force between 

 the plates ionizes the intervening air repeatedly, and the recom- 

 bination of the ions is accompanied by the formation of a certain 

 percentage of ozone, as above explained. In order to produce a 

 high degree of ionization throughout the entire region between 

 the two metal plates, it is necessary to place a thin plate of glass 

 between the metal plates so as to prevent the formation of a 

 single spark from plate to plate. The effect of this glass plate is 

 to cause a fine brush discharge to take place throughout the 

 entire region. Without the glass plate a single brilliant spark 

 passes through the air. With the glass plate, a diffused violet 

 luminosity is produced throughout the region between the metal 

 plates. 



134. Radio-activity.* The chemical elements uranium, tho- 

 rium, and radium and their compounds have the property of 

 making a surrounding gas an electrical conductor. Thus, one 

 ten-millionth of a gram of radium bromide which is left as a 

 residue upon a metal plate by evaporating a small quantity of a 

 dilute solution of radium bromide on the plate, causes a gold 

 leaf electroscope to be discharged in a few seconds when the 



*The student is referred to the following books for a full discussion of radio- 

 activity : Radioactivity, by E. Rutherford, Cambridge, 1905 (second edition); 

 Radioactivity, by Frederick Soddy, London, 1904 ; and Radioactive Transforma- 

 tions, by E. Rutherford, New York, 1906. 



