Insulating Properties of Indiar libber. 511 



The readings obtained are plotted in fig. 8 (p. 513). The 

 index of " t " is *594 for the first experiment and *572 for the 

 second ; the index being apparently not greatly affected by 

 the charging volts. On March 28th and 30th, a series of five 

 experiments were made in which the temperature remained 

 practically constant, the pressure only varied about 1 per cent, 

 and the time of charge varied from 5 to 120 minutes. In 

 order to correct for the small variation in pressure, the dis- 

 charge current was assumed proportional to the charging 



volts, and the values of log ^ were plotted to log " £/' where 



c = current of discharge, E = charging volts, "t" = time 

 reckoned from commencement of discharge. This is shown 

 in fig. 4, and it will be seen that the points from the five 

 experiments lie on five straight lines passing through the 

 point 



log | = -9-000, log t= 1-010. 



The points therefore lie on the straight lines 



log | + 9-000= -.*;(log t- 1-010 ); 



and the values of the discharge current are given by the 

 equation 



- H— r. 



\10-9b7 



., =10x10" 



Jcj 



The values of the exponent x were found to give a straight 

 line when log (#— "415) was plotted to log T, and the equa- 

 tion for x was found to be 



:;;'7 



x — -415=4-055 T"' ; 



where T = time of charge in seconds (see fig. b'). From these 

 two equations, by substituting the time of charge and the 

 charging volts for each particular experiment, the five curves 

 in fig. 5 have been drawn, and the points actually obtained 

 closely follow these curves. In Table III. the readings of 

 the current for three discharges are given, the charging 

 pressure being 101 volts and the temperature constant. The 

 current is given by the equation 



"'(V'-Y 



where tf--43 = 6-22T-- 500 . 



~= 11-01 x 10" 

 hi 



