Having studied the powerful reducing condition inside the iron blast furnace, it is no surprise to us to know that any other element present in the ore and as easily reduced as iron will come out with it as it runs from the furnace. The well-known exception to this rule is that sulphur can be fluxed off with the slag, if the slag is maintained both highly fluid and rich in lime. But the reduction goes even further than this, for, in the presence of the metallic iron, elements, not reducible otherwise, are quickly absorbed and kept from reverting back to oxide.
Thus it results that all pig iron contains more or less of silicon, manganese, phosphorus, sulphur, and small quantities of any other reducible element originally present in the ore or in the charge - these may be chromium, copper, arsenic, titanium, vanadium, etc. The iron, of course, is saturated with carbon, nearly all of which will separate as graphite if it cools slowly enough, and otherwise will be in combination and make the iron white.
Now, the physical properties of the material made by remelting and recasting pig iron (then called cast iron) will depend largely on whether the carbon is graphitic or combined in the final casting. It will fit the use for which it is intended, only if it has the right amount of graphite and the right amount of combined carbon. The size of the graphite flakes also is important. Much manganese makes the iron hard; much phosphorus makes it brittle; much sulphur makes it quite unfitted for many purposes. But the effect of each of these constituents is not only directly but indirectly through simultaneous effect on the state of the carbon. Iron of something like the compositions shown in Table V will be made for the purposes indicated.* The limits are rather wide, and, for many purposes, the right composition will be obtained by mixing irons in varying proportions.