The nature of gold surfaces, after heating in low pressures of oxygen, has been studied by several techniques. Effects due to impurities on the surface were observed ; there was no evidence of the presence of an oxide of gold. The results suggest that the impurities in the gold diffuse to the surface and form isolated, projecting, regions so that there is only partial coverage of the gold surface by impurities. Evidence is reported which suggests that the lack of agreement in the published work on the electrochemical behaviour of gold is due to impurity effects.

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Communications to the Editor Yol. 65 that were not exposed to oxygen. Therefore, the soluble platinum(IV)-alumina complex postulated by McHenry, et al., does not exist under reforming conditions, i.e., after reduction with hydrogen. Upon intentional oxygen exposure of the reduced catalyst, considerable amounts of platinum appeared as the soluble form. Because soluble platinum was obtained in the absence of alumina and in the absence of chloride, there is no evidence for a specific soluble platinum complex. A possible alternative for the species dissolved by HE may be metal upon which oxygen is chemisorbed. Both hydrogen3 and carbon monoxide2 chemisorption studies on reduced catalysts have been interpreted to indicate that the platinum is a very highly dispersed form. Thus, a large fraction of the platinum atoms is on the surface and available for chemisorption of oxygen. These particles, because of their small size, have exceptionally high surface energies. The very low value for soluble platinum in Experiment 9 shows that the chemisorbed oxygen is removed readily by hydrogen at room temperature. This is consistent with recent work by Chon, Fisher and Aston,6 which showed by a calorimetric technique that chemisorbed oxygen (or hydrogen) on platinum can be quantitatively titrated at room temperature with hydrogen (or oxygen).

The behaviour of hot gold filaments, in vacuum and in oxygen at pressures of a few microns of mercury, has been studied. Two main effects were observed-the disappearance of gaseous oxygen and a rate of evaporation of gold considerably greater in oxygen than in vacuum.The rate of disappearance of oxygen ( E ) depended on the purity of the gold, but the amount which disappeared was too large to be explained as oxidation of impurities in the metal. The disappearance is attributed to an impurity-catalyzed conversion of oxygen molecules from the ground to the metastable lAg state, the 0; attacking the walls of the reaction vessel. E decreased as the walls became protected by a film of evaporated gold. The enhanced rate of evaporation of gold in 0 2 is attributed to the removal of an inhibiting surface film of impurity. In N2, E was zero and there was no enhanced evaporation of gold.The activation of molecular oxygen is discussed in appendix 1 by D. M. Gilbey. Appendix 2 by D. Clark reports on the structure of the evaporated gold deposits.

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