220 



O. U. VONWILLER. 



THE CONDUCTION OF ELECTRICITY IN 

 MOLYBDENITE. 



By Associate-Professor O. U. Vonwiller, b.Sc. 



[Read before the Royal Society of N.S. Wales, December 7, 1921] 



Summary. — When a current flows from copper to molyb- 

 denite to copper the main part of the resistance consists 

 usually of the two contact resistances. The relation of 

 these to the size and direction of the current is investigated. 

 The resistivity of the material is found to be independent 

 of the direction and magnitude of the current. Observa- 

 tions made with any but small currents are irregular on 

 account of temperature changes produced by the passage 

 of the current. 



Readings at various temperatures ranging up to 200° C. 

 show effects resembling those obtained at room temperature. 

 The contact resistances decrease greatly on rise of tem- 

 perature, but no constant relation holds between contact 

 resistance and temperature. The resistance, apart from 

 contact resistances, decreases with rise of temperature, but 

 efforts to obtain a value for the temperature coefficient of 

 resistivity or conductivity were not successful, probably 

 because mechanical changes were caused by the heating. 



For a circuit containing two copper-molybdenite junctions 

 at temperatures differing by one degree the e.m.f. is found 

 to be 560 micro-volts, the current flowing from copper to 

 molybdenite at the hot junction. 



In 1913 the writer read before this Society a paper on 

 the rectifying property in silicon and selenium, 1 in which 

 it was shown that in the former material the conductivity 



1 This Journal, Vol. xlvii, 129, (19 13). 



