198 Mr. S. Ratner on Polarization 



Recovery of a Polarized Bulb. 



3. A polarized bulb when left to itself gradually returns 

 to its normal condition. The rate of recovery may be 

 investigated by studying the resistance of the bulb at 

 definite intervals after a certain stage of polarization has 

 been reached and the discharge interrupted. One set of 

 experiments of this kind gave the following results : — A 

 degree of polarization was first produced where, with a 

 pressure of *042 mm., the necessary sparking potential was 

 equivalent to a spark length of 14 cm. After an interval 

 of 5 minutes the sparking potential as measured by the spark 

 length fell to 12 cm., and after intervals of 15, 30, 45, and 

 60 minutes the corresponding sparking potentials were 10, 7, 

 4*5, and 2*5 cm. Left overnight the bulb was found to 

 be completely depolarized, so that a p.d. of 1500 v. could 

 again produce a normal discharge. 



More accurate experiments in this direction were now 

 carried out under conditions where a comparatively small 

 potential difference could produce a discharge, and in this 

 case a battery of small accumulators could be used instead 

 of the induction-coil and the potential difference measured 

 with accuracy. The experiments are based on the fact that 

 if in a polarized bulb the pressure be slightly increased by 

 introducing gas from outside, the sparking potential falls 

 abruptly, whereas the resistance of the bulb still remains 

 considerable and manifests a gradual decrease with time, 

 characteristic of the resistance of a polarized bulb. If, now, 

 at definite intervals of time, different voltages taken from 

 the battery be put across the bulb and the currents pro- 

 duced by the discharge measured, the results may supply 

 definite data for the determination of the rate of recovery 

 of the bulb. Table I. shows the results of one set of these 

 experiments. In column t. the intervals of time in minutes 

 are given ; in columns C 3500, C 2500, and C 1500 the 

 current through the bulb in hundredths of a milliampere, 

 the p.d. applied being 3500, 2500, and 1500 v. respectively. 





Table I. 





t. 



C 3500. 



C 2500. 



C 150( 



1 



2 



— 



— 



5 



8 



3 



— 



10 



22 



14 



4 



20 



58 



34 



16 



40 



110 



78 



46 



60 



160 



105 



76 



120 



195 



130 



95 



240 



215 



160 



125 



