THEORY OF THE ELECTRIC ARC 179 



While suggestions have thus been made as to the cause 

 of the ionization between the electrodes, not even a be- 

 ginning has been made toward a quantitative analysis of 

 the amount of the electric force. Not even in the mercury 

 arc do we know the absolute velocity of the ions, the poten- 

 tial difference for ionization by impact, the rate of recom- 

 bination, or the mean free path of the ions, and yet all of 

 these quantities must be known in order to give an ex- 

 planation of the magnitude of the electric force. 



Action in Arc not the Same as in an Electrolyte. It 

 should be clearly understood that the explanations here 

 offered are not in any way based on the idea that the cur- 

 rent in the arc is carried by particles driven off from the 

 electrodes. If the current were carried by particles the 

 spectrum of the vapor of the arc would be a continuous 

 spectrum instead of the line spectrum which is actually found. 



Neither is it possible that the current is carried by atoms 

 or molecules driven off from the electrodes as in electro- 

 lytes. It has been shown, for example, by Matthies 1 that 

 the current in the mercury arc is carried by electrons and 

 not by charged atoms. Both the pressure on the anode and 

 the behavior of the current flowing to an exploring electrode 

 placed in the vapor indicate this. 



The same thing is shown by the experiments performed 

 by Weedon. 2 He found that a copper cathode kept cool 

 by water does not lose 1/1500 of what it should lose, if 

 Faraday's law applied, and that the gain on the anode was 

 very slight. 



It has been thought by some that disintegration, such 

 as is produced by boiling or by oxidation, must occur at 



1 Ann. d. Phys., 37, 738; 1912. 



2 Paper presented at Amer. Electrochem. Soc., in 1904. 



