THE PHENOMENA OF ELECTROSTATICS. 



233 



very high temperature so that electrons (negative ions) are emitted 

 in great numbers. The result is that the current continues to 

 flow between the carbon tips. The column of hot vapor between 

 the carbon tips is called an electric 

 arc, and the intense heating of the 

 two carbon tips is due to their bom- 

 bardment by the ions which move 

 across the arc and carry the electric 

 current. The electric arc may be 

 easily maintained between a hot neg- 

 ative carbon (cathode) and a rapidly 

 rotating disk (a cold anode), but not 

 between a cold cathode and a hot 

 anode. This shows that the emis- 

 sion of negative ions (electrons) . by 

 the hot carbon is essential to the 

 formation of the electric arc. The 

 appearance of the arc between car- 

 bon electrodes is shown in Fig. 

 164.* 



Fig 1 64. 



133. Chemical effect of the dis- 

 charge through gases. The discharge of electricity through 

 gases is accomplished by the ionization of the gas as above ex- 

 plained. This ionization means not only the breaking down of 

 the molecules of a compound gas but also the separation of elec- 

 trons from the individual atoms of the constituents of the com- 

 pound gas. The ionization of mixed gases promotes chemical 

 combination. Thus, the nitrogen and oxygen of the air combine 

 slowly under the action of the electric spark. 



When oxygen (or air) is ionized, the recombination of the 

 oxygen ions results in the production of ozone. Thus the 



* The properties of the electric arc are discussed in great detail in a paper by C. 

 P. Steinmetz, Trans. International Electrical Congress, Vol. II, pages 710-730, St. 

 Louis, 1904 ; in a paper by W. R. Whitney, Trans. American Electrochemical 

 Society, Vol. 7, pages 291-299, 1905 ; and in J. J. Thomson's Conduction of Elec- 

 tricity Through Gases, pages 604-620. 



