1504 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1953 



about 800 ergs. This was followed by a rapid transition into metal loss 

 instead of a bridge. This loss increased with increase in energy. 



DISSIMILAR CONTACTS 



EFFECT OF POLARITY ON ARC CHARACTERISTICS 



An experiment was carried out to find the contributions of the anode 

 and cathode in determining the characteristics of the arc. Use was made 

 of the fact that carbon contacts are unique in having low minimum arcing 

 current and high arc voltage compared to most metals; see Table I. 

 Furthermore, carbon contacts always gave a constant field strength line 

 for arc initiation at small separations even when they were cleaned by 

 the heavy arcing process. Tests were carried out with a variety of con- 

 tact metals against carbon. All the results obtained were qualitatively 

 the same. For illustration only the experiments with palladium-carbon 

 contacts are reported here. 



Test specimens were carefully prepared in the following fashion. Pal- 

 ladium to palladium contacts, mounted on the cantilever bar set-up, 

 were cleaned by the heavy arcing process. One contact was removed and 

 replaced by a carbon contact with its surface polished and freed from 



HEIGHT OF BRIDGE OR LOSS IN ANGSTROMS 



O -1- - o 



o o o o 



o o o o 



Fig, 9 — Bridge formation during the arc. 



