98 Barrett, Brown & Haprretp—On the Electrical Conductivity and 
Conclusions. 
A complete summary and discussion of our results will be given in a 
subsequent paper, when our experiments, which are still in progress, are more 
complete. Exact results can only be obtained from a series of specimens where 
the impurities are either 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, 
which 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 e¢.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 ” 
RS Chromium 5 24, 43 . 9 es 
Manganese a 30, * is 15 a 
Ae Silicon = 45, 4 7" 30 Me 
¥ Aluminium i 48, e of 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 
corresponding amount of any other element. 
