Magnetic Permeability of various Alloys of Iron. 



81 



It will be noticed that the conductivity of 1447 B in the unannealed state is much 

 lower than 12871 in Series A, tliougli both have nearly the same percentage of 

 nickel. This is doubtless owing to the high carbon in the former specimen. 

 So also the last specimen of Series A, 1449 A, with 3 1-4 per cent, of nickel 

 (which might have been included in Series B), doubtless owes its remarkably 

 low conductivity, in part, to the 0'7 per cent, of carbon which is added to the 

 nickel. It may be that a carbide of nickel is formed in these cases, which, 

 diffused throughout the steel, would produce a very high electric resistance. 

 The specimen 1449 E owes its high resistance in part to the presence of 

 manganese ; it is really a nickel manganese steel, and as such is given again 

 later in Group 12, p. 89. 



The alloy 1449 A was a ductile and beautiful material, and easily drawn 

 into wire. A thin wire of this alloy was, therefore, made and submitted to 

 further examination. Its electric resistance was carefully measured by the usual 

 method, and the specific resistance found to have the large value of 86 microhms 

 per c.c. at 15° C. This corresponds with the estimated specific resistance 

 from the conductivity of a rod of the same material. The temperature co- 

 efficient of this remarkable alloy was also determined, and found to be 0*09 

 per cent, for 1°C. 



Enormous as is the resistance of this alloy, it is exceeded by another 

 specimen which has more manganese and less nickel added to the iron ; it is, 

 therefore, a cheaper material, and has an equally good temperature coefficient. 

 This specimen, marked 1414 B, contained 25 per cent, of nickel and 5 per cent, 

 of manganese. It is, therefore, a nickel manganese steel, and will be referred 

 to later on with others of the same class in Group 12. 



Tungsten Steels. 

 We next pass on to tlie alloys of tungsten and ii-on. 



Group 4. — Tungsten Steels. 



