Magnetic Permeability of various Alloys of Iron. UU 
These results are plotted in the accompanying curves, fig. 3. The specimens 
marked respectively 1879 B and 1323 C, owing to their low carbon, have a higher 
order of conductivity than their true place in the series, and the former causes the 
peculiar hump in the curve of Series A.* When the percentage of manganese in 
the alloy is high (say over 7 per cent.) the resistance is so great that the presence 
of 4 or even 1 per cent. more carbon makes little difference in the conductivity ; 
onic the last two specimens in Series A are plotted in the Series B curve. 
-annrealé splecump 
annealed ake tted |\curve 
il 
y 
i 
oS 
8 
Seee’. eee 
EOP 
— 
Shes 
EEC eee 
its 
eeecencepe CE ETAIED 
Fie, 3. 
As in the case of the carbon steels it will be noticed how very rapidly the 
conductivity falls for the first small additions of manganese, whereas after 
7 per cent. further additions appear to have comparatively little effect on the 
conductivity. The first two specimens in Series A show that an increase in 
the percentage of manganese from 4 to 1 per cent. causes an increase of 
sp. resistance at the rate of 1:82 microhms for every one-tenth per cent. of 
*The curves were engraved in all cases from the earlier determinations of the conductivity. The 
values shown in the tables for the conductivities of the annealed rods are more correct, the difference being 
due to the more exact method of finding the sectional area by means of displacement, as already 
explained in the footnote to p. 71. The specimens marked 89 and 84 have an anomalous conductivity 
in the annealed state; this result may be due to some change produced by the annealing process. The 
effect of heat treatment on the physical properties of manganese and nickel steels needs further 
investigation. 
N 2 
