482 



Prof. W. F. Barrett. On the Increase of Electrical 



tivity of the added element ; e.g., the metal aluminium is a far better 

 conductor than nickel, and yet alloyed with iron it decreases the 

 conductivity of iron far more than nickel. Silicon and aluminium 

 alloys of iron are extremely soft, and we should expect them to be 

 better conductors than the hard tungsten steels, and far better than the 



a 4 6 8 10 la 14 16 18 20 Z2. ZA 26 28 30 52 

 Percentages of Added EiemenC. 



FIG. 1. Specific Electric Eesistance of Alloys of Iron. 



manganese steels, which are very hard, but the reverse is the case. 

 Owing to their extreme softness, the alloys of silicon and aluminium 

 with iron have an enormously high magnetic permeability, which will 

 be referred to in the sequel. 



The resistance of iron containing O'l and - 3 per cent, of carbon and 

 other impurity is shown by the horizontal dotted lines in fig. 1. From 

 these data the increase of resistance produced by alloying iron with a 

 given percentage of any of the elements named can be determined by 



