Alloys of Ferro-Manganese and Copper, 473 



ard was 0*770 ohms; and its temperature- coefficient was about 

 •000010 per degree Centigrade. 



The test piece, enclosed in a U-shaped tube of glass, was 



placed in an oil hath and alternately heated to 100° (land 



cooled to 20°. The reference standard was kept at the room 



temperature. Its changes of resistance were regarded as 



iigible. 



The application of the method jnst described, to a number 

 of ferro-manganese-copper alloys, brought to light a remarka- 

 ble and very troublesome property of this class of metals. It 

 was found that they decreased in resistance each time that they 

 were subjected to a change of temperature, even through the 

 Bmall range made use of in the attempt to determine their 

 temperature-coefficients. The character of these changes can 

 best be illustrated by quoting a series of measurements to 

 which one of the alloys was subjected. An alloy containing 

 80*82 per cent of copper and 19*12 per cent of ferro-man- 

 ganese, had been hard drawn in the process of obtaining a 

 strip suitable for measurement. Its specific resistance at 20°, 

 referred to pure copper as unity, was 30-38. It was repeatedly 

 heated to 100° and cooled to 20° with the following result : 



Table I. 



Efect of repeated heating and cooling upon the resistance of Alloy No. 6, 



(hard drawn). 



Observation. Temperature. Specific resistance. Relative resistance. 



1 20° 30-380 1-0000 



2 100 30-186 -99331 



3 20 30 163 -99287 



4 100 30-151 -99255 



5 20 30-138 -99202 



6 100 30-121 99180 



7 20 30-118 -99134 



8 100 30-118 -99134 



9 20 30-105 -99093 



10 100 30.099 -99072 



11 20 30-092 -99051 



12 100 30-101 -99092 



13 20 30079 -99007 



14 100 30-104 -99092 



15 20 30072 -98985 



We have, in the case of this alloy, a substance which in- 

 creases in conductivity each time it is heated and cooled 

 through the small range of 80°, the change in resistance dimin- 

 ishing in amount with each operation, but still perceptible at 

 the end of the seventh cycle. At the same time a positive 

 temperature-coefficient is being developed, which continues to 

 increase as the heating and cooling process is repeated. 



After being heated to 100° seven times, with the result 

 shown in Table I, the alloy was raised to a red heat. Its tern- 



