ACTIVATIOX OF ELECTRICAL CONTACTS BY ORGAXIC VAPORS 805 



temperature is found to ])e of the order of ;)00°C, rather than ()00°C. 

 The correct order of magnitude gives support to the general ideas behind 

 the theory. 



According to this very simple model, activation takes place most 

 promptly for arcs of 100 ergs energy, and for such arcs the net carbon 

 formed per arc corresponds to the benzene molecules adsorbed on the 

 area 2-kR{^, which is obtained from Ecj. (1) by setting R = A = Ri . 

 In vacuum at the same energy, the carbon formed per arc would come 

 from benzene on the area 4x7?!-. Thus for 100 erg arcs activation will 

 occur almost as quickly in air as in vacuum, but for arcs of greater energy, 

 much more slowly than in vacuum. Qualitative observation has con- 

 firmed this general conclusion. 



That this picture is, however, over simplified in a fundamental man- 

 ner is clear from the effect of electrode contours upon ease of activation. 

 For flat electrodes, activation is very much more prompt when the sur- 

 faces make good contact over a large area than when misalignment re- 

 sults in contact on a rather small area. Furthermore, flat contacts can 

 often be activated very promptly under conditions for which crossed 

 wires cannot be activated at all. (Reference 8, page 335). In a ciualitative 

 way this is understood, but the inhibiting effect of restricted areas is not 

 amenable to quantitative consideration. This effect makes quite clear 

 that the model of an annular ring about an arc is too idealized to be of 

 much quantitative value. 



One might expect tliat the burning off of carbon would be greatly 

 influenced by atmospheric conditions, and thus the ease of activation 

 would depend upon such conditions. This is indeed found to be the case 

 in experiments in which the air contains water as well as the activating 

 vapor. In unpublished experiments F. E. Haworth determined the num- 

 ber of operations required to activate contacts under a particular set of 

 standard conditions for a wide range of relative humidity. In the range 

 from 10 to 88 per cent relative humidity, the number of operations to 

 make contacts fully active increased exponentially from 1.4 X 10^ to 

 1.0 X 10^, and at relative humidities of 95, 98 and 100 per cent, activa- 

 tion was not attained at all. Furthermore the process of activation could 

 be reversed by water vapor, and contacts that had been made fully active 

 in dry air containing an organic vapor were made completely inactive 

 by continued operation in the same vapor after the addition of water. 

 The effect of water in these experiments may have been due to covering 

 the surfaces so thoroughly with water molecules that the activating 

 vapor could not be adsorbed, or to burning carbon by the water gas reac- 

 tion, C -f- H2O -^ CO -j- H2 . The exponential relationship between num- 



