Magnetic Permeabiliti/ of various Alloys of Iron. 



91 



contains 4i per cent, more nickel than 1109D, and 1414 B has 6 per cent, more 

 nickel than 1414 A. Taking the sp. resistances of these in the form of wire 

 (being in similar condition), and comparing the increase in resistance for each 

 1 per cent, of nickel added to the alloy, we find a very similar result to that given 

 previously from the measurements in Group 3. On p. 80 we found that, in 

 alloys of iron containing from 1 to 11 per cent, of nickel, the average increase 

 of resistance for each 1 per cent, of added nickel was 1"6 microhms. From 

 Group 12 we see that in composite steels, containing from 19 to 25 per cent, 

 of nickel, the increase of resistance for each 1 per cent, of added nickel is 

 1*2 microhms, between these limits the same rate will be found on referring to 

 Group 3, p. 78. From Groups 3 and 12 we get the following : — 



This indicates a continuous reduction in conductivity produced by nickel, 

 when added to alloys of iron, even up to very large percentages, though, as 

 already stated, the effect of small quantities of nickel in steel is not nearly 

 so great as that of manganese, silicon, or aluminium. 



Having examined the conductivity of the nickel-manganese, or manganese- 

 nickel steels, we will now take a series of specimens where other elements 

 besides nickel are added to manganese steels. Here is a group of manganese 

 chi'omium steels. 



Group 13. — Manganese-Chromium Steels. 



the same result ; the substance has been submitted to prolonged and repeated heating and cooling for 

 upwards of three years, in most cases no sensible deterioration of the material has been noticed. For 

 some time past all the resistance coils in the electric installation of the Royal College of Science have 

 been replaced by reostene with a great saving of space and economy of material. Some specimens of 

 thin reostene wire have, however, undergone a molecular change and become brittle and useless. — W.F.B. 



TKANS. Kcji'. DUB. SOC, U.S. VOL. VII., I'AKT IV. P 



