Magnetic Permeability of various Alloys of Iron. 



77 



These results are plotted in the accompanying curves, fig. 3. The specimens 

 marked respectively 1379 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 ^ or even 1 per cent, more carbon makes little difference in the conductivity ; 

 hence the last two specimens in Series A are plotted in the Series B curve. 



Per-ca^tcLgo of MarLyarve 

 FlQ. 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 | 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 eases from the earlier determinations of the conductivity. The 

 values shown in the talles 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 ab-eady 

 explained in the footnote to p. 71. The specimens marked 39 and 34 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. 



N2 



