Maynetic Permeabilit/j of various Alloys of Iron. 



89 



on the conductivity than the much smaller quantities of silicon added to the other 

 specimens. Compai'e also 1103 A and 1103 C, having nearly the same composi- 

 tion, except that the latter has 1'25 per cent, more silicon — an addition that 

 increases tlie electrical resistance 10-7 microlims for each 1 per cent, of added 

 silicon; vs^hereas, in 1103 A and 1102 A, having the same quantity of silicon, 

 the alloy 11 03 A, containing 2-25 per cent, more nickel than 1102 A, has 

 actually a higher conductivity. This is partly due to the fact that 1102 A. 

 has 0'41 per cent, more carbon in the alloy than 1103 A; and, as we have 

 seen (p. 80), small percentages of nickel do not injure the conductivity of poor 

 steels.* 



We now pass on to a veiy remarkable grouj), the nickel-manganese steels. It 

 was found that excellent alloys could be made with large percentages of both 

 these elements added to iron, and the result was a sei'ies of alloys, some of which 

 were found to have an extraordinary electrical resistance. 



Group 12. — Nickel-Manganese Steels. 



The conductivity of 1414 A is rather higher than 1109 D, though it contains 

 4-|- per cent, more nickel ; tested by the file, it was harder than 1109 D : this may 

 be due to a difference in thermal treatment, as the rod 1109 D was "water 

 toughened." 



Several of these specimens were drawn into wire, so that their sp. resistances 



* It is of course impossible to plot the relation between the conductivity and composition of these 

 compound alloys, in the form of curves such as are given in Class I., owing to the variation in each of the 

 two or more elements added to the steel. 



