Page:Proceedings of the Royal Society of London Vol 69.djvu/502

482 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

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