Section III., 1914 [125] Trans. R.S.C. 



Contact Resistances of Metals and Alloys. 



By H. E. Reilley, M.Sc. 



Demonstrator of Physics, McGill University 



(Presented by Dr. H. T. Barnes, F.R.S.) 



(Read May 28, 1914). 



In 1910 two Japanese scientists, Kimura and Yamamoto, pub- 

 lished in the Coll. Sci. and Engin. Mem. Kyoto 2. 4. a paper on the 

 unilateral conductivity of minerals in contact. These experimenters 

 showed that the power of rectification diminishes with increasing 

 pressure, which phenomenon was found to be most marked in the 

 case of copper pyrites, of covelline and of bornite. In 1913 Mr. A. L. 

 Clark, as a result of extensive research on carbon contacts, observed 

 that the resistance for loose contacts increased with time. These 

 with several other papers giving similar results contain the only avail- 

 able data on the subject of contact resistances. Hence the following 

 experimental work has been undertaken to investigate first, the re- 

 lation between the pressure and resistance of various contacts of 

 metals and alloys. Such data will be of interest, for instance, in the 

 construction of delicate relays. A second phase of the subject con- 

 sidered is the effect on the pressure-resistance ratio of conductors 

 due to careful cleaning of the surfaces of the substances forming 

 electrical contact. 



(a) Method of procedure. 



In general the method of attacking these questions was, as out- 

 lined by Dr. H. T, Barnes, to make an adjustable contact of the alloy 

 or metal under investigation and to connect this contact as a shunt 

 with a very sensitive Broca galvanometer using in the experiment a 

 current of lxlO- 5 amperes. Fig. 1 shows the arrangement of the 

 apparatus : — 



B is a storage battery having an E. M. F. of about 2 volts. 



M is a megohm consisting of resistance coils of 100,000, 200,000, 

 300,000 and 400,000 ohms. 



G is a Broca galvanometer, No. 4703. A scale and a reflected 

 spot of light were employed to indicate the current passing through 

 the galvanometer. 



