Insulating Properties of Indiarubber. 521 



Table XI. — Experiments on Indiarubber under the 

 Action of Alternating Pressure. 



Con- 

 denser. 



Descrip- 

 tion of 

 Rubber. 



No. of 

 Hours on 



alternating 

 pressure. 



Effect of Alternating Pressure. 



Result of 



treating 



with Ozone 



for five 



minutes. 



Resistance. 



No. of 

 Faults. 



General 

 effect. 



F.I 



a.! 



From 

 No. 1 

 (Pure). 



3000 

 3000 



937 



Increased 



from 149 Q. 



to 14,000 Q. 



Increased 



from 

 1900 Q to 

 200,000 Q. 

 Increased 



from 

 167 Q to 

 19,000 Q. 





 2 



1 



No 

 discoloration. 



No 

 deterioration. 



Apparently 



not 



attacked. 



"1 



M. J 



From 

 No. 2 

 (Pure 

 Para). 



About 60. 



Always 

 very high. 



Faults 



always 



occurring. 



Great 



discoloration 



around 



edges. 



Violently 



attacked. 



Left in 



shreds. 



N. 



No. 3 

 (vulcan- 

 ized). 



About 60. 



Always 

 very high. 



Faults 



always 



occurring. 



Slight 

 discoloration. 



Slightly 

 attacked. 



was very high, being about 200,000 megohms. When 

 subjected to 2600 alternating volts, they all broke down 

 within three days, and a peculiar discoloration of the rubber 

 was noticed round the edges of the tinfoil and the outer 

 edges of the rubber. Some chemical action appeared to 

 have taken place, the rubber being discoloured, less trans- 

 parent, and slightly porous. The tinfoil was cut away from 

 the faults in each condenser, and on again connecting the 

 condensers to the transformer they broke down almost im- 

 mediately. The discoloration appeared to have advanced still 

 further from each edge, and also appeared round the edges 

 where the tinfoil was cut clear from former faults. The 

 condensers were then put on the transformer a third time 

 with a similar result ; no appreciable change in resistance 

 could be detected in condensers K, L, and M. A condenser, 

 N, made from vulcanized rubber No. 3, was also subjected to 

 2400 alternating volts. This rubber would not stand the 

 pressure very long but broke down twice within 21 hours, 

 the white surface being slightly discoloured round the edges 

 of the tinfoil. All the condensers showed pale lines of light 

 round the edges of the tinfoil when the pressure was 



