extrapolated the concentration to zero flow rate. Because this is no longer considered sound practice (17,19), the result is suspect. Domange (4) calculated the data for reaction 2 by the same method; however, on re-examination of the data the authors find an apparent "plateau region" at flow rates of approximately 10 ml. per minute. Recalculation of the data that apply in this region leads to the value given in the table. The data of Hood and Woyski (8) for reaction 3 were obtained in a plateau region, and the equilibrium was approached from both directions; nevertheless, the present authors' calculation of the heats of reaction by the third-law method shows a small but distinct trend. For these calculations, free energy functions for the gases were taken from the JANAF Tables (12) and those for solids, except NiF2, from Kelley's compilation (15). The free energy functions for NiF2 were calculated from the extraploated low-temperature heat capacity data according to Catalano and Stout (3). The auxiliary AHf°v alues used for calculating Aff/&>8(NiF2) are (in kilocalories per mole): NiCl2, -73.04 (2); H20, -57.8 (24); and HC1, -22.1 (24).
CONCLUSIONFor the reasons given above, the authors believe that the earlier values of AHfi9e(NiF2) based on equilibria data are suspect and that their value, based on the direct combustion of nickel in fluorine, is preferable. In spite of the difficulties of burning nickel in fluorine and incomplete combustions, the precision obtained is acceptable.Recent solid-state e.m.f. measurements (Lofgren, N. L.,Mclver, E. J., U. K. Atomic Energy Establishment, Rept.AERE-R-5169, 1966) on the cell Mg, MgF2|CaF2|NiF2, Ni, in combination with the value AHfim (MgF2, c) = -268.7 kcal. per mole ( 22), yielded «the values AH. fi9e(NiF2,c) = -156.7 =or -157^6 kcal. per mole, respectively, depending on whither the calculations were made by the seconder third-law methods. The latter values are in excellent agreement with the value reported.LITERATURE CITED
