﻿Manchester Memoirs, Vol xlix. (1905), No. 10 



X. On the Temperature Co-efficient of Electrical 

 Resistivity of Carbon at Low Temperatures. 



15 Y 



H. MORRIS-AlREY, M.Sc, 



AND 



E. D. Spencer. 



Received and Read March 21st, 1903. 



The alteration of electrical resistivity with temperature 

 has been, in the case of most metals, very carefully 

 studied, the general result being that the resistance of 

 metals increases with rise of temperature. Dewar and 

 Fleming* who have made the principal measurements at 

 low temperatures find that the resistance of metals 

 continues to decrease as the temperature falls, and they 

 estimate that at the absolute zero, the resistance either 

 vanishes entirely, or possesses an exceedingly small value. 



A remarkable contrast to this behaviour occurs in 

 the case of carbon. In the pure crystalline state 

 (diamond) and in clean charcoal, carbon is practically an 

 electrical insulator, but in the graphitic state or in the 

 form of a coke, it conducts moderately well, its resistance, 

 however, decreasing as the temperature rises. It has 

 been pointed out by Beetzf that this anomalous behaviour 

 of carbon is the same as that of many conductors {e.g., 

 iron filings,) when tested in the form of a loose powder 

 and subjected to slight pressures. The conductivity of 

 such a mass, apart from the nature of its material, 

 depends solely on the number and extent of the contact 

 surfaces. On decreasing the temperature, the individual 

 particles become smaller, thus destroying some points 



*Phil. Mag, 1893, 3 6 > P- 2 7 J - 

 \Pogg. Ann. 3, i860, p. 629. 



April 17th, 1905. 



