134 



REPORT — 1894. 



The fall in resistance is small, and for the period of nearly five years 

 does not amount to more than ^ per cent. 



I have, for the sake of comparison, made a measurement of the resist- 

 ance of a specimen of annealed copper wire sent me by the same firm, and 

 for this the resistance value is identical with that obtained at a previous 

 date : — 



This, on the whole, is what one would expect. In the case of wires of 

 other material the change would probably be greater, as the difference in 

 resistance between annealed and hard-drawn copper wires is less than that 

 for wires of other materials. 



In my previous communication a method ' of annealing was described 

 which gave satisfactory results. The wire was packed in asbestos and fine 

 carbon in a copper vessel and heated for twenty-four hours. The follow- 

 ing results amongst others were obtained : — • 



Matthiessen's values are 

 1550 



1516 



34 



Messrs. Swan and Rhodin give for the values of the specific resist- 

 ance : — 



Hard-drawn 18° AnnpnleJ 18° Difference 



1720 16S0 40 



I have recently been annealing copper wires by heating them in 

 boiling paraffin (220°) ; and after slow cooling the wires seem to be 

 completely annealed : — 



Hard-drawn 18° 

 1526 



Annealed 18° 

 1486 



Difference 

 40 



A wire sent me as annealed gave the result : — 



Annealed 18°, 1488 



This wire was then hardened, and, reannealed as above described. 



Annealed 18°, 1489 



gave the value: — 



> B.A. Report, 1890, p. 126. 



