390.     BRUNAUER, S., JEFFERSON, M. E., EMMETT, P. H., AND HENDRICKS, S. B.  Equilibria in the Iron-Nitrogen System.  Jour. Am. Chem. Soc., vol. 52, 1931, pp. 1778-1786; Chem. Abs., vol. 25, 1931, p. 3550.

        An atmospheric pressure the % NH₃ in a gaseous H₂-NH₃ mixture in equilibrium with an Fe-Fe₄ N mixture is 37±2 at 400° and 14.5±1 at 575°.  The % NH₃ in a similar equilibrium with Fe₄N-Fe₃N is 77±2 at 400°, 70±2 at 444°, and 57±1.5 at 500°.  The composition and lattice dimensions of the phases with an Fe:N ratio of 2:2.7 in equilibrium with various H₂-NH₃ mixtures is determined at 400° and 444°.  The dissociation pressure of Fe₃N is calculated as 3 X 10⁵ atm. at 450°.