The chemical physics involved in the precipitation of free carbon from the alloys of the iron-carbon system

As a result of recent research it is held that the iron-carbon alloys must be considered as an iron-iron carbide system as indicated in the accompanying diagram; the author is satisfied that the double diagram based on the assumption of a metastable and a stable equilibrium is inaccurate, since, in the liquid or the solid state, that carbon which is in solution is contained in solution as carbide. The experiments to be described afford evidence that the carbide must separate out from the solution before free carbon can appear, and that it is only the structurally free carbide that can dissociate; free carbon will not separate from the solid solution.