KOTES
1196
slight overcorrection. Results for KOH alone, K$04 are nearly the KOH 3- KC1, and KOH same within experimental error. The discrepancy for KdFe(CN)a is decreased but not entirely eliminated. This discrepancy, as given by Fig. 1, is greater than it actually is because formation of the triple ion (K(+)sFe(CN)62- mas not considered. There is evidence for the formation of this ion16 but no quantitative datum is available. Further, other effects, and particularly the influence of ionic size, could be invoked to explain the remaining small departure from theory. This matter will not be taken up here, though it is being studied a t present in thie Laboratory. Ionic association of the reactant, K I 0 3 ( K = -0.25 for formation16 of K+IO3-), a!so should be considered since the faradaic current is the sum of the currentsfor thereduction of I03-andK+I03-. These two parallel electrode processes undoubtedly have different exchange densities. Further, the kinetics of dissociation of K+Io3- complicates matters. Double layer corrections for this type of process have been discussed semi-quantitatively, lo,l7 and theoretical analyses have been worked out. 18,19 This effect is probably minor here because of the TTeak association between K+ and IO8-. In conclusion, correction for ionic association of the supporting electrolyte and/or ionic reactants appears to be in order in the correlation between double layer structure and electrode kinetics. However, one would do well to remember the words of caution of Robinson and Stokesz0when usinx equilibrium constants for ionic association. Acknowledgment.-This investigation was supported by the Office of Naval Research.
+
(16) 8. R. Cohen, Thesis, Cornel1 University, Ithaca, N. Y., 1956, p. 34. (16) Cf.ref. 12, p. 124. (17) L. Gieret, ref. 11, pp. 109-138. (18) H.Matsuda, J . Phy8. Chem., 64, 336 (1960). (19) H. Hurwitz, Z.Elektrochem., 66, 178 (1H61). (20) R. A. Robinson and R. H. Stokes, "Electrolyte Solutions," 2nd edition, Academio Press, Inc., New York, N. Y.,1969,pp. 421-423.
Vol. 6G 130 120
110 100 90 80
70 60
i 0
10
30 40 50 60 70 Mole yo 1,3,5-trinitrobenzene. Figure 1. 20
1
j
80 90 100
melting point of 121.4' and the 2,4,6-trinitrotoluene had a melting point of 78.8'. I n addition, supercooling difficulties may have occurred. Shinomiya and Asahina obtained their data by the thaw-melt technique. Their results are in fair agreement with those obtained here except in the region of 30-50 mole % 1,3,5-trinitrobenzene. In this region considerable scatter in their data points occurs. These authors make no mention of compound formation. The present study mas made with an apparatus3 which permitted a step-wise heating approach to the liquids point. Solid-liquid equilibrium a t each thermal step was assured by demonstrating constancy of the light transmission of the sample a t each thermal step.
The 2,4,6-trinitrotoluene was recrystallized from benEene and ethyl alcohol. Following recrystallization i t was fused and allowed to freez; under a vacuum twice. The melting point was then 80.9 The 1,3,5-trinitrobenzene was recrystallized from ethyl alcohol, washed with ethyl alcohol, and air-dried. Before use, it was fused and allowed to freeze under avacuum twice. The melting point was then 123.6". Six-gram samples of the required compositions were melted and stirred thoroughly. The temperature of the THE SYSTEM %?,4,6-TRI.IiITROTOLT!ESE- sample then was allowed to fall until a small amount of solid was formed. The temperature of the sample then was raised 1,3,6-TRIXITROBENZENE stepwise holding the sample at each temperature until the light transmission of the sample became constant. In this BY LOHRA. BURKARDT manner the temperature was raised t o the point at which a Chemistry Daiston, U. S. Naval Ordnince Test Stataon, Chzno Lake, few crystals were in equilibrium with the liquid. The temCalzfornza perature then was raised in small increments until these Recezred A'otember 21, 1961 crystals disappeared, the last temperature being taken ae the The system 2,4,6-trinitrotoluene-1,3,5-trinitro- liquidus temperature. Eutectic melting points were obtained by heating the benzene has been investigated by Efremovl and completely solid sample through the eutectic melting point by Shinomiya and Asahina.2 Efremov's results are with a 0.1" temperature gradient between the bath and in considerable variance with those reported by sample. With a small enough temperature gradient, a flat Shinomiya and hsahina and those found in the is obtained at the eutectic melting point.
present investigation. Efremov's data indicate a simple system with a eutectic at 5G.1Oj, 2,4,6-trinitrotoluene which melts a t 48.3'. The lower values reported by Efremov may stem from impure starting components. The 1,3,5-trinitrobenaene had a (1) N.
N. Efremov, Lenangrad. Polztekhnzchesku znstztut rmenz
M . I . Kalzwna, 28, 217 (1919). (2) C . Shinomiya and T. Asahina, J . Chem. (1936).
Soc J a p a n , 67, 732
.
The system forms a weak equimolar compound with an incongruent melting point of 61.5' at 47 mole yo 1,3,btrinitrobenxene. The eutectic n4xture contains 39 mole yo 1,3,5-trinitrobenzene and melts at 59.4'. Data for the system are shown graphically in Fig. 1. ( 3 ) L. A. Burkardt, W. S. LfcEnan, and €I. W.Pitman, Reu. Scz. Instr. 2'7 693 (1956).
