98 Barrett, Brown & Hadfield — On the Electrical Conductivity and 



Conclusions. 

 A complete summary and discussion of our results will be given in a 

 subsequent paper, when our experiments, wliich are still in progress, are more 

 complete. Exact results can only be obtained from a series of specimens where 

 the impurities are eitlier absent, or small and constant in amount ; and also 

 where the specimens are in the form of wires or rods turned to a uniform 

 diameter throughout their length, the physical state and prior heat-treatment of 

 each specimen being alike. Although it is difficult to obtain all these conditions, 

 we hope, by a proper selection from a large number of analysed specimens, 

 wliich have been carefully annealed and turned down to a uniform cross- 

 section, eventually to approach more nearly to an ideal series. So far, how- 

 ever, our results have shown that : — 



(1) In all cases a larger, and in some of the alloys a very much larger, 

 increase in electric resistance is produced by the first additions of the added 

 element than for similar amounts added after the alloy is rich in that particular 

 element. 



(2) The increase in the electric resistance of iron produced by alloying 

 it with an equal percentage of different elements varies through a wide 

 range, according to the nature of the added element ; but this increase of 

 resistivity does not appear to be connected with the specific resistance of the 

 added metal. 



(3) Taking the specific electric resistance of mild steel, or of iron containing 

 approximately the same amount of impurities as are present in the alloys we have 

 tested, to be about 15 microhms per c.c. at the temperature of the air, then the 

 addition of corresponding amounts (say 3 per cent.) of the following metals 

 raises the resistance in the case of annealed alloys of iron and 



3 per cent of Tungsten to about 17, or an increase of 2 microhms. 



,, Nickel ,, 21, ,, ,, 6 ,, 



,, Chromium ,, 24, ,, ,, 9 ,, 



,, Manganese ,, 30, ,, ,, 15 ,, 



„ Silicon ,, 45, ,, ,, 30 ,, 



,, Aluminium ,, 48, ,, ,, 33 ,, 



With a corresponding alloy of iron and copper, no increase but probably a 

 slight decrease in resistance is produced. No carbon steels containing a corre- 

 sponding percentage of carbon have been tested ; but for very small additions, 

 of under one per cent., the increase of resistance produced in pure iron by the 

 presence of carbon appears to be greater than that caused by the addition of a 

 correisponding amount of any other element. 



