THE ELECTRON THEORY. 289 



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

 two atoms of oxygen in the molecule. lonization causes the 

 disintegration of these bi-atomic molecules forming ions of mono- 

 atomic oxygen, and this mono-atomic oxygen recombines forming 

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

 portion 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 re- 

 combination 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 corona 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. 



147. 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 radium- 

 covered plate is held near to the metal plate of the electroscope. 

 Uranium and thorium have the same effect but the discharge 



* 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 Transformations 

 by E. Rutherford, New York, 1906. See also Rutherford's Radioactive Substances 

 and their Radiations t Cambridge, 1913. 



