ACTIVATION OF ELECTRICAL CONTACTS BY ORGANIC VAPORS 781 



carbon, and upon metal surfaces on which carbon particles have been 

 dusted. The results of these tests have supplemented measurements upon 

 active noble metal contacts and have led to a great increase in our knowl- 

 edge of activation. In fact they open the way to a fairly thorough under- 

 standing of the subject. 



2.1 Striking Field 



Five different experiments have been carried out, which were designed 

 to discover the reason for the low striking field at active contacts. Al- 

 though the results of these experiments do not establish the reason for 

 the low striking field in any definitive fashion, they do lead to an ex- 

 planation which seems entirely satisfying. 



The simplest of these experiments has already been reported at the 

 end of Section 1.1. It is the observation that the striking field at active 

 contacts is much the same at different striking voltages, of course below 

 air breakdown only. 



In another experiment, not heretofore published, W. S. Boyle and 

 P. Kisliuk produced active spots at various points along a palladium 

 wire. The wire, which lay on the axis of a glass cylinder, was made active 

 at these selected points by repeated short arcs in an atmosphere 

 containing limonene vapor. The other electrode was operated by an elec- 

 tromagnet outside the cylinder, with the magnet arranged so that the 

 electrode could be placed at any location along the wire or withdrawn 

 completely at anytime. After activating a number of points, as determined 

 by continuous oscilloscopic observation, the cylinder was exhausted and 

 field emission currents were drawn from the wire to the cylinder. From 

 observation of a fluorescent coating on the inside of the cylinder, it was 

 found that the positions along the wire, which gave the largest currents, 

 were quite unrelated to the active spots. From this experiment, one can 

 conclude that the work function of active spots along the wire was not 

 lower than the work function of other parts of the wire, and also that 

 there was no significant enhancement of field emission at these spots 

 because of roughness. Thus, the activation of contacts by organic vapors 

 is not due to enhanced field emission currents because of lowering of the 

 work function or because of greater surface roughness. 



In a third experiment by F. E. Haworth,^ measurements were made 

 of the electrode separations at which an arc strikes between a palladium 

 electrode and a smooth palladium surface upon which carbon particles 

 had been deposited. For this experiment, solid carbon particles of fairly 

 uniform size were obtained by blowing air at a low controlled rate 



