474 E. L. Nichols — Electrical Resistance of the 



perature-coefficient was then redetermined with the result 

 shown in the following table : 



Table II. 

 Resistance and temperature coefficient of Alloy No. 8, {after annealing at a red heat\ 



Temperature. 



Specific resistance. 



Coefficient. 





(At 20°) 



(At 100°) 





20° 



28-418 







100 





28-610 



+ -000052 



20 



28-446 







100 





28-597 





20 



28-440 





+ -000052 



The effect of repeated annealing upon the resistance and 

 coefficient of these alloys, is still more strikingly exhibited in 

 the behavior of a specimen containing a larger proportion of 

 ferro-manganese. The alloy in question consisted of 70*65 

 parts of copper and 29*35 parts of ferro-maganese. After 

 being brought into a condition of stability, such that further 

 heating and cooling through a range of eighty degrees had 

 but little permanent effect upon its conductivity, it still 

 showed, when hard drawn, an appreciable negative coefficient. 

 It was then annealed three times at a red heat ; specific resis- 

 tance and coefficient being determined for the range 20° to 

 100°, after each annealing. The results are given in Table III. 



Table III. 

 Effect of repeated annealing upon Alloy No. 11. 



Condition, r- Specific resistance. > Coefficient. 



20° 100° 20° 



Rather hard 4610 45-99 46-09 -'000024 



Once annealed 4510 45*18 45-09 +'000021 



Twice annealed 44-07 44-33 44-06 + -000068 



Thrice annealed 42*76 43-58 42-74 +'000192 



This metal possessed very nearly indeed the composition for 

 which, in the patent specifications already referred to, the 

 remarkable property of decreasing resistance with rise of tem- 

 perature was claimed ; which claim is substantiated, so far as 

 the hard- drawn alloy is concerned. It will be seen that the 

 coefficient depends upon the temper of the metal, and that it 

 would projbably be an easy matter to bring the latter into such 

 a state that the change of resistance, which is, in all conditions 

 of the alloy, very much smaller than in any other of which 

 we have definite data, would be too small to be detected. 



It appears, moreover, that the conductivity of this alloy 

 was increased about 2 per cent by each successive annealing 

 at a red heat, and that even after being thus annealed three 

 times, it was subject to a further slight but measurable increase 

 of conductivity, amounting to at least *02 per cent, when sub- 

 sequently heated to 100° and cooled to 20°. 



