Revolving Disk I^terr i^ter 



By using a half brass., half bakelite disk and staggering 

 the brushes (fig, 19) j it was possible to attain an on-frac- 

 tion of Ool^l (off "Inaction, Oo8U8)o The on-fraction was 

 measured as the length of the disk circumference corresponding 

 to the '"on" position as determined with an open^closed circuit 

 indicator (ohmmeter),, divided hy the total disK circiimferenceo 



For each of five specimens, two replicate trials (revers- 

 ing the polarity of the electrodes between trials) were made 

 at an average current of lo5 amps (Experiment A), and again 

 at an average current of 2 anps (Experiment B) with a frequency 

 in each case of 1^,8 ropoS„ (table 11), At 1,5 ampsp 8 out of 

 10 trials vrere positive. At 2 amps, all 10 trials were posi- 

 tive <= It may be seen by comparison of the results in table 11 

 and table 12 ^ tliat by reducing the on-fraction from Oo25 to 

 Ool^lj the current for positive response has been reduced frcm 

 U to 2 anpSj vathi a corresponding reduction in current density 

 from O0OO2U to 0,0012 amps/cm^o 



It was impossible to further reduce the on-fraction 

 because of the thickness of the brusheso Moreover, even with 

 a relatively weak average current of 2 amps.^ there was consi- 

 derable arcing at the make and breaks wluch tended to bum 

 the bakelite and corrode the brass portion of the dLsko Fur- 

 ther experiments with the disk-type interrupter were not 

 undertaken. 



Plunging-electr o de Int errup ter 



To attain finer adjustment of the "on-off" ratio and in 

 the hope of reducing the g)ark at *-he make and break, a new 

 interrupter was designed (figo 20) <, This consisted essentially 

 of a revolvi.ng wheel, an eccentrically connected rods and an 

 electrode which iips momentarily into a glass jar containing 

 oil floating on mercuryo The jar sits on a platform which 

 may be raised or lowered, Ihus permitting fine adjustment of 

 the duration of contacto The wheel was driven at approximately 



15 ToPoSo 



The apparatus was not satisfactory. It vibrated consi- 

 derably, causing mechanical and electrical connections to 

 break, and more serious, causing irregular waves on the sur- 

 face of the mercury. Despite the use of transformer oil, and 

 later of pure mineral oil^ arcing occurred at the make and 

 break. Ihis gradually burned the tip of the electrode, chang- 

 ing the on-fraction. The oil and mercury soon tended to form 

 an "emulsion", which further changed the on-fraction and 

 caused arcing at the surface, 



75 



