520 



Mr. A. W. Ashton on the 



in Table X. Only one condenser showed any great de- 

 terioration, viz. C, which after 270 hours continually broke 

 down. 



Table X. — Results of Alternating Press 



ure Experiments. 



Condenser. 



Treatment. 



of edges 



whether 



shellacked 



or not. 



Total No. 



of 

 Hours on 

 alternating 

 pressure. 



Total No. 



of 



Faults 



occurring. 



Remarks. 



A. 

 B. 

 0. 

 D. 



E. 



Shellacked 



Shellacked 



Not 

 shellacked 



Not 

 shellacked 



Not 

 shellacked 



1200 



1230 



270 



1300 



7200 



1 

 

 7 

 3 

 10 



No discharge observed 

 at edges of tinfoil. 



No discharge observed 

 at edges of tinfoil. 



Considerable discharge 

 from edges of tinfoil. 



Discharge observed 

 from edges. 



Discharge observed 

 from edges. 



15. The experiments were continued in London, the con- 

 densers at first being joined up to a transformer in the 

 Charing Cross substation of the London Electric Supply 

 Corporation ? to which Company I am indebted for the gra- 

 tuitous use of their alternating pressure. During the third 

 year the condensers were subjected to alternating pressure 

 at the Northern Polytechnic Institute. The pressure used in 

 each case was 2600 volts (R.M.S.), but the frequency in 

 the former case was 100 and in the latter case 50. 



Three condensers, F, G, and H ; were made from No. 1 

 rubber. The resistance of each condenser was measured 

 before putting on the transformer : they were then submitted 

 to the action of 2600 alternating volts, being only taken off 

 at intervals to measure their resistances. The results 

 obtained are given in Table XL, from which it will be seen 

 that the resistance of these condensers continually increased. 

 The total number of faults occurring in these condensers was 

 three ; and as far as could be ascertained the treatment 

 appeared to have no effect on the rubber, with the exception 

 that it became somewhat harder and less elastic. Three 

 condensers , called K, L, and M, were made of No. 2, i. e. 

 pure Para rubber. The resistance of all three condensers 



