SEcTION III, 1916 [145] TRANS. R.S.C. 
Contact Resistance in Oil. 
By H. E. REILeEy, M.Sc., and VioLET HENRY, M.Sc. 
Presented by Pror. H. T. BARNEs, F.R.S.C. 
(Read May Meeting, 1916). 
Contact resistance may be defined as the electrical resistance 
of the junction of two conductors of similar or dissimilar metals or 
alloys. There have appeared several papers dealing particularly 
with the effect of pressure on the contact resistance when applied to 
the contact surface. If two electric conductors are arranged in a 
circuit in such a way that pressure may be applied at the junction of 
the two conductors, the electrical resistance at the contact point will 
unquestionably depend upon the pressure applied to the conductors. 
In none of these papers are given data for the values of minimum 
pressure necessary to produce a low resistance contact, where a cur- 
rent is conducted from one piece of metal or alloy to a similar or 
dissimilar metal or alloy as the case may be. 
In a paper by Streintz and Wesley! are given the results of re- 
searches on the resistance between two plane circular plates of brass. 
The diameters of these plates were 2-6, 1-97, 1-77 and 1-0 cms. 
respectively. It was found that the conductivity from one plate 
to the other across the junction was proportional to the applied 
pressure, and also to the diameter of the plate used. There are 
included in this- paper several pressure resistance curves. The 
pressures applied ranged approximately, from 50 to 8,500 grms. 
The resistances were found to have values between 29 and 521 mic- 
rohms. These investigators also studied the effects produced by 
media other than air upon the contacts. Their results show that 
when brass plates were immersed in oil the contact resistance was 
considerably less than in air; or in other words the same pressure 
would produce better contact in oil than in air. This fact is also 
borne out by results obtained by William Browning? Two brass 
circular plates 1-54 sq. cms: in area were used and it was found that 
the conductivity of the contact varied almost directly as the mechani- 
cal pressure between the contacts up to a certain value of the pressure. 
If oil was present, the conductivity was greatly increased. 
1 Physikalisch Zeitschrift 489, 1913. 
2 Journal of Instit. of Elec. Eng. Vol. 37, p. 372, 1906. 
