Experiments have been carried out at temperatures of 263° C and higher between oxygen adsorbed as atoms on the silver catalyst, and ethylene, ethylene oxide and acetaldehyde. The course of reaction was followed by measuring the change in pressure, and analyses of the products were made by micro-fractionation of the gases at low temperatures. In the reaction of ethylene with an oxygen-covered catalyst, the absence of an induction period in the pressure-time curve showed that oxidation of ethylene to carbon dioxide and water by a route not through ethylene oxide is possible. The reaction of acetaldehyde with the oxygenated catalyst was too fast to measure. The reactions of ethylene oxide were found to be complex, and reaction occurred both with the oxygenated and the clean catalyst. On a clean catalyst, ethylene oxide was simultaneously isomerized to acetaldehyde and converted back to ethylene and adsorbed oxygen; the acetaldehyde and adsorbed oxygen then reacted to form carbon dioxide and water. Both ethylene oxide and acetaldehyde, but not ethylene, were adsorbed with decomposition to form a non-volatile layer on the catalyst. This was composed of carbon, hydrogen and possibly oxygen, combined in indefinite and varying proportions. The kinetics of the reaction between ethylene and the adsorbed oxygen layer were measured. Throughout the course of any one reaction, the rate of oxidation to carbon dioxide was proportional to the square of the concentration of adsorbed oxygen, but the velocity constant depended on the initial concentration. The apparent energy of activation was 10 kcal. It is thought that when ethylene reacts with a single adsorbed oxygen atom, ethylene oxide is produced, and that with a pair of adsorbed oxygen atoms, intermediates such as formaldehyde are produced which react rapidly to form carbon dioxide and water.