Experiments by Hadfield quoted by Campbell show that "after making allowances for the variations in other elements, it will be found that the aluminium has little effect upon the tensile strength, while it does not materially injure the ductility until a content of 2 per cent, is reached."

1 F. W. Harbord, " The Metallurgy of Steel," 1904.

Experiments by the latter author, however, appear to lead to the following conclusions: -

"(1) The addition of one-half of 1 per cent, of aluminium increases the tensile strength between 3000 and 8000 lbs. per square inch, exalts the elastic limit to about the same proportion, and injures very materially the elongation and contraction of area. The effect both upon strength and ductility is more marked in the case of low than in high steels.

"(2) The addition of another half of 1 per cent, does not have much effect upon the ultimate strength or the elastic limit, but it still further decreases the ductility of the metal."