﻿326* Dr. P. E. Shaw on the Disruptive Voltage of Thin 



The " knee " occurs at 300 volts, the horizontal part ex- 

 tending to 8//,, i. e. well to the right of the plotting shown. 

 After Sfi the gradient is very small. Air has greater strength 

 than any liquid for small distances ; but the liquid curve in 

 all cases crosses the air curve for discharge lengths varying 

 between 2^/jl and 6/ju. That is, for any greater distances 

 the liquids have much greater strength than air. 



The order of strength for the higher voltages used is 

 roughly: — 



Hexane, heptane, armacell, pen tane, octane, Sterling varnish, 

 cod-liver oil, linseed oil, fusel oil, ohmaline, castor oil, tur- 

 pentine, olive oil, rape oil. Paraffin and transformer oil are 

 both weak. Eesin oil gave very irregular results, not showing, 

 as might be expected, great strength. 



Notes and Precautions. 



1. The voltmeter was carefully standardized. 



2. The loud-speaking telephone in the discharge circuit 

 was shunted with non-inductive resistance of a few ohms. 

 Some experimenters in previous researches have kept the 

 discharge surfaces shunted with a voltmeter, so that the 

 discharge is shown by the fall of the voltmeter-pointer. This 

 seems faulty; for when discharge commences, it will be at 

 once violently retarded by an inductive rush from the volt- 

 meter. In the present work the shunted telephone of low 

 resistance indicates discharge, the voltmeter being then cut 

 out and no inductive resistance left in circuit. 



3. The members of the homologous series are very volatile ; 

 the method employed is to cause drops of them to fall slowly 

 on the discharge surfaces, a fresh drop arriving before the 

 last has evaporated. 



4. The discharge is of the nature of a volcanic eruption, 

 the cathode loses material and a distinct pit or crater forms 

 there, while fine dust is scattered on both electrodes. The 

 surfaces approach, but do not always meet on discharge. To 

 avoid dust the surfaces are wiped after each discharge. 



5. The discharge surfaces should be treated with care 

 whilst the zero is being obtained. u Make " and " break " 

 should be made as little as possible, and the zero should not 

 be much overrun. The highly polished surfaces, even of the 

 very hard iridio-platinum, are easily damaged for discharge 

 work. 



6. If a contact is " wheezy," it is rejected at once ; this 

 indicates bad polish, and always produces electrolysis or 

 premature discharge. 



