Resistivity caused by Alloying Iron vrith Various Elements. 4* 1 



estimating the conductivity, the results obtained can only be regarded 

 as a more or less close approximation to the true value.* 



A more formidable difficulty is the impossibility of obtaining such a 

 collection of alloys free from the admixture of disturbing impurities. 

 Slight variations in the amount of these impurities, especially in the 

 amount of carbon present, produce in the low percentages a profound 

 effect on the conductivity and also on other physical properties of these 

 alloys. However, in most of the specimens Mr. Hadfield has succeeded 

 in reducing these impurities to a lower amount than any other large 

 collection of alloys yet made. Carbon, manganese, and silicon were 

 the impurities most commonly present, and the sum of these in the 

 specimens selected was, as a rule, under 1 per cent. 



There were sixty-eight specimens of these alloys having various per- 

 centages of a single element added to iron ; these were as follows (the 

 element with which the iron is alloyed being named in the first 

 column) : 



Manganese. ... 18 specimens ranging from $ to 1HJ per cent, of Mn. 



Carbon 13 ^ . H ,- C. 



Nickel 12 i 31 Ni. 



Tungsten 4 1 15 W. 



Chromium.... 3 2 9 Cr. 



Copper 3 H 3 Cu. 



Aluminium... 3 I 2k Al. 



Silicon 2 2i 5| Si. 



In addition to these there were fifty-two other specimens having 

 two or more of the above elements alloyed to iron in various pro- 

 portions. 



In every case, with the doubtful exception of copper,! a decrease in 

 conductivity was found to result from alloying iron with another 

 metal, even when that element, as in the case of aluminium, had itself 

 a conductivity far higher than that of the iron. From the conduc- 

 tivities of the specimens, their specific resistances were calculated ; 

 these were plotted against the percentages of the added element. A 

 series of fairly smooth curves were thus obtained for each alloy. These 

 curves are shown in fig. 1. It will be noticed that the addition of 

 silicon or aluminium to iron produces the greatest increase in electric 

 resistance and tungsten the least, and that a remarkable change in the 

 electric resistivity of nickel steels occurs at high percentages. There is 

 obviously no connection between these curves and the electric conduc- 



* It was satisfactory, however, to find that in a dozen or more specimens which 

 were drawn into wire, and the specific resistances of which were measured in the 

 ordinary way, the results obtained corroborated the values found from the rod*. 



t The specimens of copper-iron alloy were very few, and the results masked by 

 the varying impurities they contained; very little alteration of the conductivity 

 appeared to be produced by the addition of copper to iron. 



