336 On the Electrical Resistance of Pure Metals fyc. 



temperature. It is not improbable that we may find for such 

 bodies a maximum electrical resistance at the lowest attainable 

 temperatures, and that it may prove to be the case that pure 

 non-metals approach a maximum specific electrical resistance 

 and pure metals a minimum specific electrical resistance in 

 proportion as the absolute zero of temperature is approached. 

 In any case it is a matter of considerable interest to complete 

 the examination of the change of conductivity with diminished 

 temperature for all the metals in a state of the greatest 

 chemical purity. MM. Cailletet and Bouty expressed the 

 results of their experiments on the electrical resistance of 

 metals between zero Centigrade and —100° G. by giving the 

 value of the mean coefficient of resistance-change as fol- 

 lows : — If R* is the electrical resistance of the metal at f C, 

 and E its resistance at 0° C, then we may write 



R*=E (l±af). 



When t is in the neighbourhood of —100° C, a has the 

 following values, stated below, for the different metals. 

 We give in one column the results of the experiments of 

 MM. Cailletet and Bouty, and in the other coefficients for the 

 same temperature range calculated from a part of our results 

 in Table 1. 



Table IY. 



Metal. 



a = mean coefficient of resistance-change 

 between 0° and -100° O. 



Cailletet and 

 Bouty. 



Dewar and 



Fleming. 



Silver 



•00385 

 •00388 

 •00423 

 •00490 

 •00340 

 •00424 

 •00390 

 •00407 



•00384 

 •00390 

 •00410 

 •00531 

 •00354 

 •00509 



•00500 







Iron 



Platinum 



Tin 







Nickel 





From these values of the coefficients it is seen that nickel 

 and iron have pre-eminence in respect of rate of fall of resist- 

 ance with temperature. At ordinary temperatures pure iron 

 has a specific electrical resistance of about seven times that of 



