Alloys of Ferro-Mangane86 and Copper. 477 



the temper of the metal. A positive coefficient could be ob- 

 tained, however, in alloys containing more than twenty per 

 cent of ferro- manganese, only by thoroughly annealing the 

 specimen ; whereas in metals containing a larger proportion of 

 copper, either hardening or complete annealing developed a 

 positive coefficient. 



The marked influence of temper upon the conductivity of 

 these alloys, renders it difficult to determine the precise law of 

 the change in specific resistance with the composition. It 

 appears, however, from the results presented in Table V, that 

 the resistance increases nearly in direct proportion to the per- 

 centage of ferro-manganese. 



Mr. Blood's investigation also included two alloys which 

 contained nickel as well as ferro-manganese. The methods of 

 preparation and measurement were identical with those which 

 have already been described. The results, which are given 

 in Table VI, show exceedingly small negative coefficients in 

 the case of the hardened alloy. Annealing rendered the 

 coefficient of the alloy containing the smaller percentage of 

 nickel positive, and reduced the size of the coefficient of the 

 other specimen. 



Table VI. 



t Composition of the alloy. , , Temperature coefficients. » 



Copper. Ferro-manganese. Nickel. Alloy (hard). Alloy (annealed). 



78'28# 14-07£ 7-65# --000011 + -000007 



52-51^ 31-27^ 16-22^ --000039 -"000032 



The experiments described in this paper, show that the alloys 

 of ferro-manganese and copper, so far as their electrical be- 

 havior is concerned, must be considered as a distinct class. 

 Up to the time of Mr. Weston's discovery of their properties, 

 increase of conductivity with rise of temperature was sup- 

 posed to be confined to electrolytes, and to the single solid con- 

 ductor, carbon. Recent investigations have added sulphur to 

 the list, and it is evident that this set of alloys, at least, be- 

 longs there also. It is not improbable that the further study 

 of alloys containing metals of the iron group, will lead to the 

 discovery of other combinations, possessing the same interest- 

 ing and important characteristic. 



