ACTIVATION" OF ELECTRICAL CONTACTS BY ORGANIC VAPORS 807 



periments upon activation in vapor of the organic compound fluorene.^ 

 According to the observations, the critical rate of operation was found 

 to be proportional to the partial pressure of fiuorene rather than to its 

 square as in (2). This is a discrepancy which must be overlooked in our 

 present state of knowledge. To test (2) for fiuorene at 20°C, we require 

 values of D, the diffusion coefficient of fiuorene in air, p, the partial 

 pressure of fiuorene at 20°C, and m, the number of adsorbed fiuorene 

 molecules per cm- of surface. The value of D == 0.067 cm-/sec. was ob- 

 tained from a linear relation between ID and (molecular weight)^''-, 

 which holds quite well for a number of organic compounds. The value 

 p — 0.0-1 mm Hg is the geometrical mean between 0.23 and 0.007 mm Hg, 

 respectively the vapor pressures of napthalene and anthracene at 20°C. 

 We have estimated m = 3.3 X 10^"* molecules/cm-, which is related to 

 the corresponding number for benzene, 7 X 10^^ in the inverse ratio 

 of the molecular weights. ^^ These numerical values give from (2) 



n = 0.75 operation/second 



as the critical rate that vnW just permit one monolayer in the time the 

 contacts are separated. The observed critical rate for activation at 20°C 

 from Fig. 2 of Reference 8 is 3. The agreement is pretty good when the 

 crudeness of the model is considered. 



6.3 Sputtering and Burning in a Glow Discharge 



If both arcs and glow discharges occur when electrical contacts are 

 operated in an atmosphere containing an activating organic vapor, the 

 activation of the contacts resulting from the arcs is inhibited by the 

 occurrence of the glow discharges.* This effect is sometimes very bene- 

 ficial in extending the life of telephone relay contacts. In fact a very 

 simple protective network, consisting only of an inductance of the order 

 of 10"^ henry placed very close to one of the contacts, has been devised 

 which, under some conditions, will increase the contact life by a factor 

 of about 10. 



Quantitative measurements have been made of this inhibiting action 

 of a glow discharge, and from them it has been concluded that the effect 

 is attributable to sputtering and burning of carbon in the discharge. In 

 making these measurements, a pair of contacts was operated in an at- 

 mosphere containing limonene vapor in such a way that arcs and glow 

 discharges occurred alternately in controlled fashion. A charged capaci- 

 tor was discharged in an arc at each closure. By the use of an auxiliary 

 synchronized relay in series with one of the contacts, the circuit was 



* It should be pointed out incidentally that a glow discharge in air can also 

 activate silver electrodes. It produces silver nitrite on their surfaces, ^^ and silver 

 electrodes with a layer of nitrite are fully active until the layer is burned off. 



