3581.     VON WAUGENHEIM, F., AND WINKELMANN, -----.  [Production of Pure Carbon at Low Temperature.]  Thesis, Cologne, 1924; Ges. Abhandl. Kenntnis Kohle, vol. 8, 1929, p. 235.

        Formation of C on a reduced Fe catalyst proceeds only to a definite point, beyond which the activity of the catalyst virtually ceases.  The limit was established by a reduction in concentration of the Fe to about 1%.  The breakdown in the catalyst activity at a definite reduction of the Fe was believed to be due to the formation of a solid solution of a higher carbide and C, from which the catalytically active Fe₃C could not be regenerated.