Insulating Properties of Indiarubber, 



515 



10. The results of experiments made on the mica con- 

 denser are given in Table VI. and fig. 10. 



Table VI. — Readings of Discharge-Current from 

 Mica-Condenser. 



After 60 minutes' Charge. 



After 120 minutes' Charge. 



Time in Current in 



Time in 



Current in 



seconds. 



Amps. XlO - 8 - 



seconds. 



Amps. XlO 8 . 



35 



445 



38 



3-19 



45 



297 



48 



2-56 



55 



2-23 



58 



2-14 



67 



1-642 



68 



1-824 



75 



1-347 



76 



1-615 





95 



1-300 



Charging volts . . . 204. 



112 



T091 



Equation : — 



Charging volts ... 



97 4 



= 10'9xlO- ( V- 1,M . 



Equation : — 







^=11-48x10 



-7/ --98.'^ 



Two sets of readings of discharge current are given. The 

 first after one hour's charge at 200 volts, the second after 

 two hours' charge at 97 volts. In both cases the current 

 may be expressed as a power function of the time. The 

 exponent of u t" is —1*155 for 60 minutes' charge, and 

 — 0*98 for 120 minutes' charge. The readings of current 

 during the charging of the mica condenser are plotted in 

 fig. 10. It has, however, not been found possible to repre- 

 sent the charging current for mica by any equation of 

 form similar to those obtained from the okonite cable. In 

 Tables VII. & VII [. (p. 516) the readings obtained from the 

 paraffin-paper condenser are given. Both experiments were 

 made on June 26th, 1900 ; the condenser, however, being 

 heated after the first experiment and allowed to cool under 

 pressure as described in Section 4. The charging current in 

 each case is given by an equation similar in form to those 

 obtained for the okonite cable, and the readings of discharge 

 were also found to satisfy an equation of the form c=Kr I . 

 The value of x for 20 minutes' charge is '846 in the first 

 case, and *849 in the second. 



11. From the first experiments made on the pure rubber 

 to determine the variation in the resistance with different 

 pressures, it appeared that the current became constant after 

 one or two hours' electrification. If this is so, it is evident 



