Resistance of Metals and Alloys. 



287 



R*. 



^ 



pt. 



pt. 



Remarks. 



1-6810 

 14346 



205-0 

 141-1 



2926-9 

 2497-7 



201-7 1 

 139-9 ; 



Taken in melted paraffin. 



1-2726 



97-95 



2215-8 



980 ^ 





1-1262 



5995 



1960-9 



60-50 | 

 18-70 y 





0-9659 



18-30 



1681-8 



Taken in paraffin oil. 



0-9658 



18-25 



1681-6 



18-65 1 

 16-80J 





0-9594 



16-45 



1670-5 





0-8982 



0-55 



15639 



0-55 



Taken in melting ice. 



0-7452 





1297-5 



- 39-4 





0-5883 





1024-3 



- 81-9 



Taken in C0 2 and ether. 



0-1658 



... 



288-7 



-197-1 { 



Taken in liquid oxygen boil- 

 ing at 761 millim. 



The longer coil was then employed to obtain resistance 

 ratios at lower temperatures reached by the use of liquid 

 oxygen boiling under reduced pressures. The measurements 

 being as follows : — 



1 i 



-Rt. t°. Pt. 



pt. 



Remarks. 



1-1687 

 0-6391 

 0-6341 

 0-5692 



| 



288-7 

 161-3 

 1600 

 143-6 



-197-1 

 -219-2 

 -219-3 

 -223-2 



Taken in liquid oxygen boil- 

 ing under pressures down 

 to 14 millim. of mercury. 



Volume-specific resistance at 0° C. . =1561. 

 Mean temperature-coefficient between 



0° and 100° C ='00428. 



It will be noticed that this pure copper has a very large 

 temperature-coefficient, and that its temperature-coefficient is 

 greater between 0° C. and 100° C. than that of silver. This 

 superiority is maintained at lower temperatures, and, as a 

 consequence, the copper resistance line crosses the silver line. 

 Although silver is a better conductor than copper at zero 

 Centigrade and at higher temperatures, yet at a temperature 

 of 200° below zero Centigrade copper is the better conductor, 

 and the cooled pure copper has the highest conductivity of 

 any metal we have obtained. On comparing the specific re- 

 sistance of the copper at + 201-7 pt with that at —223*2 pt, 

 it will be seen that at the lowest temperature the copper has 

 only 4 # 8 per cent, of the resistance it has at the highest. Hence 

 we have destroyed 95 per cent, of its resistance. At the 

 lowest temperature yet reached the copper has less than one 

 tenth of its specific resistance at zero Centigrade. 



