3065.     SCHENCK, R., AND STENKHOFF, R.  [Decomposition of Iron Carbide by Acids.]  Ztschr. anorg. Chem., vol. 161, 1927, pp. 287-303; Chem. Abs., vol. 21, 1927, p. 2091.

        Cementite (C, 6.69; Fe, 98.25; Si, 0.04; SO₄, 0.08%) prepared in the usual way and freed from ferrite and pearlite was treated separately with 600 cc. H₂SO₄ (I) (1/30, 1/3, 5 N) benzenesulfonic acid (II) (0.5, 1 N) and AcOH (III) (1, 3 N) in the presence of 0-220 gm. of the corresponding ferrous salts.  Determinations using 0.2 gm. cementite were conducted for 3 weeks at 60°.  The amount of free C precipitated increases with the increase in concentration of ferrous ion and the decrease in strength of acid.  The decrease or even failure in the formation of hydrocarbon is the result of the impossibility to attain the thermodynamically possible maximum yield owing to low reaction velocity; the depression of H-ion concentration by anions and the simultaneous ennobling of the Fe owing to ferrous ions.  According to the mass law these phenomena should supplement each other.  The results for the strong acid (II) are not in accord, but this probably is due to absorption of the acid by the C, thus indicating in the analysis an erroneously high value for C.  The results are given in tables and graphs.