Nov., 1960 effect on the rate of solution of hydrogen in Pd by the electrical contact of Pt with Pd in acid solution. A palladium wire 10.5 cm. long and 0.38 cm. in diameter was mounted in a Teflon cell filled with 2 N H2S04 solution. All purification, electrode preparation and measurement procedures were identical to those found in the literature.lq3 Both the resistance of the wire and the potential against a Pt/H2 electrode in the same solution were recorded as a function of time while the Pd wire absorbed hydrogen from the acid solution. The solution is stirred with hydrogen flowing a t a rate of 230 10 cc./min. Zero time is taken when the hydrogen flow is first started and all potentials are measured against a Pt/H2 electrode in the same solution. The A-curves in Fig. 1 are plots of the data taken on the wire described above. The filled symbols are the potential-time points and the open symbols are the resistance-time points. The symbols represent points taken directly from the meters while the smooth curves were obtained from the recorder chart. After these data were collected, the wire was removed from the cell and annealed a t red heat in a flame for five minutes to remove the dissolved hydrogen. A piece of platinum gauze about 0.5 in area was spotwelded to the center of the palladium wire. After this wire had been mounted in the cell, the same procedures which had been used in obtaining the data for the Acurves were repeated. The B-curves in Fig. 1 are a plot of these data. The C-curves were obtained in the same way except that a platinum gauze 7 cm. long and 3 mm. wide was spot-welded a t about 10 points along the center of the Pd wire. From Fig. 1 it is seen that, as the contact with platinum is increased, the length of the 50-mv. plateau is shortened and the steady-state value is lowered for the potential-time curves. The length of the a-Pd-plateau' on the resistance-time curves is reduced and the slopes of these curves are increased as contact with platinum is increased. This may be explained by an increased rate of solution of hydrogen due to local cell action at the points of contact with platinum as suggested before.2 The reason why the points on the resistancetime curve in the case of the C-curve are lower than what might be expected may be traced to the parallel resistance of the platinum gauze. These data support the contention that conditions of high purity with regard to electrode materials, cell construction materials, solutions and gases are of the utmost importance4 in investigations of this kind. It is suggested that these data show why a 50 mv. plateau was not observed2 and why Frumkin and co-workers6 seem to have more active electrodes than Hoare and Schuldiner since the criterion for surface activity may be taken as the rate a t which a Pd/H2 electrode reaches the equilibrium value of zero volt os. Pt/H2 or the rate a t which palladium dissolves hydrogen. An interesting feature of the potential-time curves in Fig. 1 is the increase in the amount of initial overshoot of the plateau value with increas-
NOTES
1781
*
(5)
Private communication: A. Fedorova and A. Frumkin, Zhur. U.S.S.R.,t o be publlshed.
F i z . Khrm.
Fig. 1.-Potential us. time (filled symbols) and relative resistance, R/Ro, us. time (open symbols) curves for Pd wires in HI-stirred 2 N H2804 solution. Smooth potential-time curves are taken from recorder chart but broken resistancetime curves were not recorded. T = 24 i lo, H ~ f l o w= 230 i 10 cc./min. A curves for pure Pd wire; B curves for same Pd wire with one contact to P t ; C curves same Pd wire with about ten contacts to Pt (eee text). The insets show curves on expanded time scale.
ing rate of the solution of hydrogen due to contact with platinum. These data may provide supporting evidence for the existence of a supersaturated a-Pd-H phase.a (6) R. J. Ratchford and G. W. Castellan, THISJOURNAL, 61. 1123 (1958).
MECHANISM OF THE ISOTHERMAL DECOMPOSITION OF POTASSIUM PERCHLORATE' BY KURTH. STERN^ AND MARIJONBUFALINI Department of Chemistry, University of Arkansas, Fayetleville, Arkansas Received June 1.9, 1960
Recently considerable evidence has been presenteds that both the liquid and solid phase decomposition of KCIOl proceeds according to the mechanism
+ + +
KC104 +KClOs '/202 KCIOa --3 KC1 s/z02 KClOa +a/&C104 '/41Calvin, PrenticeHall, Inc., New York, N. P.,1952, p. 87. (4) L. G. Van Uitert. C. G. Haas, W. C. Femdlius and 8 .E. Do~glt%, J . Am. Chmr. Sbc., 7 6 , 459 (1983).
