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To the bath of molten metal thus obtained spiegeleisen or ferro-manganese is added to supply the required carbon and to otherwise act as in the Bessemer converter.

If steel was wanted a small amount of carbon, usually in the form of spiegeleisen, was introduced into the converter before the process was complete.

A small amount is used for spiegeleisen, and the rest as a flux.

Manganese itself has a value for steel-making; or, rather, for the making of spiegeleisen and ferro-manganese, which are used in the Bessemer and Siemens processes.

When all the carbon is removed, then exactly enough carbon is added by introducing molten spiegeleisen to produce steel of any desired temper with the utmost certainty.